ON Semiconductor · SD sensitivity SD-sen1 AM 1 MHz, the ANT input level such that the IF counter...

72602RM (OT) No. 6655-1/54

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Semiconductor Components Industries, LLC, 2011 January, 2011

LA1787M

Overview The LA1787M integrates all six blocks required in a car radio tuner on a single chip.

Functions • FM front end • FM IF • Noise canceller • Multiple • AM up-conversion • FM/AM switch • MRC

Features • Improved noise reduction methods — The FM front end provides excellent 3-signal characteristics equivalent to those of the LA1193M. — Superlative listenability due to improved medium and weak field noise canceller characteristics. — Improved separation characteristics — Anti-birdie filter — Improved AM and FM thermal characteristics — Excellent FM signal meter linearity — Modified N.C. circuit for improved noise rejection • Improved AM adjacent channel interference characteristics (40 kHz) • Double conversion AM tuner (up conversion) Reduces the number of external components required as compared to

earlier double conversion tuners, in particular, no crystal is required (when used in conjunction with the LC72144). • Sample-to-sample variation reduction circuit built into the FM IF circuit.

(Fixed resistors are used for the SD, keyed AGC, mute on adjustment, ATT, SNC, and HCC functions.) • Improved FM separation temperature characteristics • The LA1787 inherits the block arrangement of the LA1780M and supports pin-compatible designs. Package Dimensions unit : mm (typ) QIP64E(14X14)

Ordering number : ENN6655

Monolithic Linear IC

Single-Chip Tuner IC for Car Radios

14.017.2

1.0 1.0 1.6

0.150.35

0.1

15.6 0.8

0.8

3.0m

ax

1 16

17

32

3348

49

64

2.7

14.0

17.2

1.0

1.0

1.6

0.8

Mounted on a 40 x 80 x 1.3 mmglass epoxy printed circuit board

Independent IC

All

ow

able

pow

er d

issi

pat

ion,

Pd m

ax m

W

Ambient temperature, Ta C

RatingsParameter Symbol Conditions

min typ maxunit

[FM Characteristics] At the FM IF input

Current drain ICCO-FM No input, I40 + I45 + I54 + I59 + I60 + I61 60 94 110 mA

Demodulation output VO-FM 10.7 MHz, 100dBµ, 1 kHz, 100%mod, The pin 15 output 205 310 415 mVrms

Pin 31 demodulation output VO-FM31 10.7 MHz, 100dBµ, 1 kHz, 100%mod, The pin 31 output 190 295 380 mVrms

Channel balance CB The ratio between pins 15 and 16 at 10.7 MHz, 100 dBµ, 1 kHz –1 0 +1 dB

Total harmonic distortion THD-FM mono 10.7 MHz, 100 dBµ, 1 kHz, 100% mod, pin 15 0.3 1 %

Signal-to-noise ratio: IF S/N-FM IF 10.7 MHz, 100 dBµ, 1 kHz, 100% mod, pin 15 75 82 dB

AM suppression ratio: IF AMR IF 10.7 MHz, 100 dBµ, 1 kHz, fm = 1 kHz, 30% AM, pin 15 55 68 dB

Att-110.7 MHz, 100 dBµ, 1 kHz. The pin 15

5 10 15 dBattenuation when V33 goes from 0 to 2 V

Muting attenuation Att-210.7 MHz, 100 dBµ, 1 kHz. The pin 15

15 20 25 dBattenuation when V33 goes from 0 to 2 V*1

Att-310.7 MHz, 100 dBµ, 1 kHz. The pin 15

28 33 38 dBattenuation when V33 goes from 0 to 2 V*2

Separation Separation10.7 MHz, 100 dBµ, L+R = 90%, pilot = 10%. The pin 15 output

30 40 dBratio

Stereo on level ST-ON The pilot modulation such that V26 < 0.5 V 1.2 2.4 4.4 %

Stereo off level ST-OFF The pilot modulation such that V26 > 3.5 V 0.6 1.6 %

Main total harmonic distortion THD-Main L 10.7 MHz, 100 dBµ, L+R = 90%, pilot = 10%. The pin 15 signal 0.3 1.2 %

Pilot cancellation PCAN 10.7 MHz, 100 dBµ, pilot = 10%. 20 30 dB

The pin 15 signal/the pilot level leakage. DIN audio

SNC output attenuation AttSNC10.7 MHz, 100 dBµ, L-R = 90%, pilot = 10%.

1 5 9 dBV28 = 3 V → 0.6 V, pin 15

AttHCC-1 10.7 MHz, 100 dBµ, 10 kHz, L+R = 90%, pilot = 10%.0.5 4.5 8.5 dB

HCC output attenuationV29 = 3 V → 0.6 V, pin 15

AttHCC-2 10.7 MHz, 100 dBµ, 10 kHz, L+R = 90%, 6 10 14 dB

pilot = 10%. V29 = 3 V → 0.1 V, pin 15

Input limiting voltage Vi-lim 100 dBµ, 10.7 MHz, 30% modulation. The IF input such33 40 47 dBµ

that the input reference output goes down by 3 dB

Muting sensitivity Vi-mute The IF input level (unmodulated) when V33 = 2 V 27 35 43 dBµ

SD-sen1 FM The IF input level (unmodulated) (over 100 mV rms) 54 62 70 dBµ

SD sensitivity such that the IF counter buffer output goes on

SD-sen2 FM 54 62 70 dBµ

IF counter buffer output VIFBUFF-FM 10.7 MHz, 100 dBµ, unmodulated. The pin 23 output 130 200 270 mVrms

VSM FM-1 No input. The pin 24 DC output, unmodulated 0.0 0.1 0.3 V

Signal meter outputVSM FM-2 50 dBµ. The pin 24 DC output, unmodulated 0.4 1.0 1.5 V

VSM FM-3 70 dBµ. The pin 24 DC output, unmodulated 2.0 2.7 3.5 V

VSM FM-4 100 dBµ. The pin 24 DC output, unmodulated 4.7 5.5 6.2 V

Muting bandwidth BW-mute 100 dBµ. The bandwidth when V33 = 2 V, unmodulated 150 220 290 kHz

Mute drive output VMUTE-100 100 dBµ, 0 dBµ. The pin 33 DC output, unmodulated 0.00 0.03 0.20 V

Operating Characteristics at Ta = 25°C, VCC= 8.0V, in the specified test cricuit for the FM IF input

Continued on next page.

No. 6655-2/54

LA1787M

SpecificationsMaximum Ratings at Ta = 25°C

Operating Conditions at Ta = 25°C

Parameter Symbol Conditions Ratings Unit

Maximum supply voltageVCC1 max Pins 6, 40, and 61 9 V

VCC2 max Pins 7, 45, 54, 59, and 60 12 V

Allowable power dissipation Pd max Ta ≤ 55°C 950 mW

Operating temperature Topr –40 to +85 °C

Storage temperature Tstg –40 to +150 °C

Parameter Symbol Conditions Ratings Unit

Recommended supply voltageVCC Pins 6, 7, 40, 45, 54, 59, 60, and 61 8 V

VCCST IND Pin 26 5 V

Operating supply voltage range VCC op 7.5 to 9.0 V

RatingsParameter Symbol Conditions

min typ maxunit

[FM FE Mixer Input

N-AGC on input VN-AGC83 MHz, unmodulated.

81 88 95 dBµThe input such that the pin 2 voltage is 2.0 V or below

W-AGC on input VWAGC83 MHz, unmodulated. The input such that the pin 2

104 110 116 dBµvoltage is 2.0 V or below. (When the keyed AGC is set to 4.0 V.)

Conversion gain A.V 83 MHz, 80 dBµ, unmodulated. The FE CF output 19 30 48 mVrms

Oscillator buffer output VOSCBUFFFM No input 85 110 165 mVrms

[NC Block] NC input (pin 30)

Gate time τGATE1 f = 1 kHz, for a 1-µs, 100-mV p-o pulse 55 µs

Noise sensitivity SNThe level of a 1 = kHz, 1-µs pulse input that starts

40 mVp-onoise canceller operation. Measured at pin 30.

The pulse rejection effect provided by the noise canceller.

NC effect SN-NCFor a repeated 1-µs wide pulse, frequency = 10 kHz,

5150 mV p-o. The ratio of the FM mode pin 15 output referenced to the AM mode pin 15 output (effective value)

[Multipath Rejection Circuit] MRC input (pin 27)

MRC output VMRC V24 = 5 V 2.2 2.3 2.4 V

MRC operating level MRC-ONThe pin 32 input level at f = 70 kHz such that

10 15 20 mVrmspin 24 goes to 5 V and pin 27 goes to 2 V

[AM Characteristics] AM ANT input

Practical sensitivity S/N-30 1 MHz, 30 dBµ, fm = 1 kHz, 30% modulation, pin 15 20 dB

Detector output VO-AM 1 MHz, 74 dBµ, fm = 1 kHz, 30% modulation, pin 15 130 195 270 mVrms

Pin 31 detector output VO-AM31 1 MHz, 74 dBµ, fm = 1 kHz, 30% modulation, pin 31 110 175 230 mVms

AGC F.O.M. VAGC-FOM1 MHz, 74 dBµ, referenced to the output, the input amplitude

51 56 61 dBsuch that the output falls by 10 dB. Pin 15

Signal-to-noise ratio S/N-AM 1 MHz, 74 dBµ, fm = 1 kHz, 30% modulation 47 52 dB

Total harmonic distortion THD-AM 1 MHz, 74 dBµ, fm = 1 kHz, 80% modulation 0.3 1 %

Signal meter outputVSM AM-1 No input 0.0 0.2 0.5 V

VSM AM-2 1 MHz, 130 dBµ, unmodulated 4.8 6 7.3 V

Oscillator buffer output VOSCBUFF AM1 No input, the pin 15 output 185 230 mVrms

Wide band AGC sensitivityW-AGCsen1 1.4 MHz, the input when V46 = 0.7 V 92 98 104 dBµ

W-AGCsen2 1.4 MHz, the input when V46 = 0.7 V (seek mode) 83 89 95 dBµ

SD sensitivitySD-sen1 AM 1 MHz, the ANT input level such that the IF counter output turns on. 24 30 36 dBµ

SD-sen2 AM 1 MHz, the ANT input level such that the SD pin goes to the on state. 24 30 36 dBµ

IF buffer output VIFBUFF-AM 1 MHz, 74 dBµ, unmodulated. The pin 23 output 200 290 mVrms

No. 6655-3/54

LA1787M

Note: These measurements must be made using the either the IC-51-0644-824 or KS8277 IC socket (manufactured by Yamaichi Electronics).* 1. When the resistor between pin 58 and ground is 200 kΩ.* 2. When the resistor between pin 58 and ground is 30 kΩ.

Continued from preceding page.

Function List

FM Front End (Equivalent to the Sanyo LA1193)• Double input type double balanced mixer• Pin diode drive AGC output• MOSFET second gate drive AGC output• Keyed AGC adjustment pin• Differential IF amplifier• Wide band AGC sensitivity setting pin, and narrow

band AGC sensitivity setting pin• Local oscillator

FM IF• IF limiter amplifier• S-meter output (also used for AM) 6-stage pickup• Multipath detection pin (shared FM signal meter)• Quadrature detection• AF preamplifier• AGC output• Band muting• Weak input muting• Soft muting adjustment pin• Muting attenuation adjustment pin• IF counter buffer output (also used for AM)• SD (IF counter buffer on level) adjustment pin• SD output (active high) (also used for AM)

Noise Canceller• High-pass filter (first order)• Delay circuit based low-pass filter (fourth order)• Noise AGC• Pilot signal compensation circuit• Noise sensitivity setting pin• Function for disabling the noise canceller in AM

mode

Multiplex Functions• Adjustment-free VCO circuit• Level follower type pilot canceller circuit• HCC (high cut control)• Automatic stereo/mono switching• VCO oscillation stop function (AM mode)• Forced monaural• SNC (stereo noise controller)• Stereo display pin• Anti-birdie filter

AM• Double balanced mixer (1st, 2nd)• IF amplifier• Detection• RF AGC (narrow/wide)• Pin diode drive pin• IF AGC• Signal meter output (also used for FM)• Local oscillator circuits (first and second)• Local oscillator buffer output• IF counter buffer output (also used by the FM IF)• SD (IF counter buffer on level) adjustment pin• SD output (active high) (also used for AM)• Wide AGC• Detection output frequency characteristics

adjustment pin (low cut, high deemphasis)• AM stereo buffer

MRC (multipath noise rejection circuit)

AM/FM switching output (linked to the FM VCC)

No. 6655-4/54

LA1787M

Operating Characteristics and Symbols Used in the Test Circuit DiagramsSwitches (SW)Switch on = 1, SW off = 0There are two switches that use signal transfer.— SW2: switches between the mixer input and the IF input.— SW4: switches between noise canceler input and IF output + noise canceler input.

No. 6655-5/54

LA1787M

Types of SG used

PG1 (AC1) Used for noise canceler testing. A pulse generator and an AF oscillator are required.

AC2 Used for FM front end testing. Outputs an 83 MHz signal.

AC3 Used for FM IF, noise canceler, and MPX testing. Outputs a 10.7 MHz signal. Stereo modulation must be possible.

AC4 Used for AM testing. Outputs 1 MHz and 1.4 MHz signals.

AC5 Used with the MRC. Can also be used for AF and OSC.

Power supply

VCC 8 V

VCC1 5 V SD, stereo, seek/stop

VCC2 0.1 V / 0.7 V / 2 V / 4 V These levels Keyed AGC, Mute ATT

VCC3 0.1 V / 0.6 V / 2 V must be variable. HCC, SNC, SASC (MRC)

• Trimmers (variable resistors)

VR1 Separation adjustment

VR2 Pilot cancellation adjustment

• AC voltages

VA1 AM/FM OSC Buff Pin 4

VA2 First IF output Pin 53 → CF → pin 51 load level (10.7 MHz)

VA3 IF counter buffer Pin 23 (10.7 MHz/450 kHz)

VA4 MPX OUT Left ch Pin 15 (AF)

VA5 MPX OUT Right ch Pin 16 (AF)

Test Points• DC voltages

VD1 FM RF AGC voltage Pin 2

VD2 AM/FM SD, AM Tweet, FM stereo indicator Pin 26

VD3 AM/FM S-meter Pin 24

VD4 MRC output Pin 27

VD5 Mute drive output Pin 33

VD6 AM antenna damping voltage Pin 46

VD7 N.C. Gate time Pin 8

• Switches

Parameter ON OFF

SW1 AM/FM switching. The FE VCC is supplied to pin 62. FM AM

SW2 FM IF switching. Pin 51/FE output FE IF OUT (A) AC3 (B)

SW3 For conversion gain testing Conversion gain measurement (A) Other/purposes

SW4 For switching between noise canceler input and IF output + noise canceler. AC1 (A) Other/purposes

SW5 High-speed SD High-speed SD Other/purposes

SW6 SEEK/STOP (IF BUFF ON/OFF) STOP Seek (IF buffer output)

SW7 MUTE ATT 200 kΩ MUTE 200 kΩ OFF

SW8 MUTE ATT 30 kΩ MUTE 30 kΩ OFF

SW9 For pilot cancellation testing When pilot cancellation is used When pilot cancellation is not used

SW10 Mute off (pin 33) MUTE OFF MUTE ON

Pin No. Function Description Equivalent circuit

3 F.E.GND

7VCC

A L C

A13558

Pin Descriptions

No. 6655-6/54

LA1787M

1

ANT

1000pF

1000pF

100Ω

100Ω

300Ω

VCC 62 pin

RFAGC

A13555

+2

NAGCDET

WAGCDET

KEYEDAGC

ANTDAMPINGDRIVER

VCC

VCC

12kΩFET2nd GATE

A13556

4

VCC

25pF

20pF2kΩVT

A13557

An antenna damping current flows1 Antenna damping drive when the RF AGC voltage (pin 2)

reaches VCC – VD.

2 RF AGCUsed to control the FET second gate.

4 OSC Oscillator connection

AM first oscillator

7 AM OSCThis circuit can oscillator up to theSW band.An ALC circuit is included.


No. 6655-7/54

LA1787M


13 Pilot input Pin 13 is the PLL circuit input pin.

14 N.C, MPX, MRC, GNDGround for the N.C., MPX, andMRC circuits.

+

8 9

3kΩ

15kΩ3kΩ

3kΩ

1MΩ0.01µF

0.47µF

200Ω

A13559

13 12 11VCC

3.9kΩ0.01µF 6800pF

LPF

Differentialamp Gate

circuit

A13560

12 13

30kΩ

VCC

PLL

N.C

0.01µFA13561

After setting up the medium field (about 50 dBµ) sensitivity with the

8 Noise AGC sensitivity noise sensitivity setting pin (pin 8), 9 AGC adjustment set the weak field (about 20 to

30 dBµ) sensitivity with the AGC adjustment pin (pin 9)

11Memory circuit connection

Recording circuit used during 12 noise canceller operation.



No. 6655-8/54

LA1787M


15

3.3kΩ3.3kΩ

VCC

0.015µF 0.015µF

16

A13562

17 18

VCC

20kΩ

10kΩ

0.01µF 100kΩ

6.7kΩ

A13563

17 18

VCC

0.01µF

1.5kΩ

100kΩ

A13564

15 MPX output (left)Deemphasis

16 MPX output (right)50 µs: 0.015 µF75 µs: 0.022 µF

Adjustment is required since thepilot signal level varies with the

17 Pilot canceller signal output sample-to-sample variations inthe IF output level and otherparameters.

18 Pilot canceller signal outputPin 18 is the output pin for the pilot canceller signal.



No. 6655-9/54

LA1787M


20 VCO The oscillator frequency is 912 Hz.KBR-912F108 (Kyocera Corporation)CSB-912JF108 (Murata Mfg. Co., Ltd.)

19

5kΩDECODER

Compositesignal

30kΩ

4kΩ

0.047µF

A13565

20

CSB912JF108

VREF

10pF

A13566

+

+

+

21 22

15kΩ

15kΩ

19kΩ

VREF

A13567

Use a trimmer to adjust the

19Separation subdecoder input level.adjustment pin (The output level is not modified in

mono and main modes.)

21 PHASE COMP.22 PHASE COMP.



No. 6655-10/54

LA1787M


23

+–

+–

+–

4.9V50kΩ

150Ω

50F

1.3V

10kΩ

51kΩ

STOP

IFBUFF.

ForcedSD: 2.5V

SEEK5V

SD

SW

VCC

AM MUTE

IF counterbuffer

A13568

32

24

10kΩ

10kΩ

VCC

AM/FMSW

FMS-meter

AMS-meter

Outputs a 1-mAcurrent during AMreception

AM/FMSW

MRC

A13569

26

100kΩ

VDD

AM/FMSD

Stereoindicator

Seek/stopswitching

A13570



This pin functions both as the IF counter buffer (AC output) and asthe seek/stop switch pin.The voltage V23 switchesbetween the following threemodes.

23IF counter buffer seek/stop During FM reception:switching 5 V: Seek mode

2.5 V: Forced SD mode0 V: Reception mode

AM reception(two modes: 0 and 5 V)

5 V: Seek mode0 V: Reception mode

24 AM/FM signal meter Fixed-current drive signal meter output

In AM mode, pin 32 outputs a32 Dedicated FM signal meter 1-mA current. Thus the HCC

circuit is turned off.

The voltage V23 switches between three modes as follows. FM reception:5 V: The SD pin operates linked

to the IF counter buffer.

26 Stereo indicator for the SD pin2.5 V: Forced SD mode: operates

as the SD pin.0.7 V: Reception mode: stereo

indicatorAM reception: (two modes: 0 and 5 V)5 V: Operates as the seek SD pin.0 V: Reception mode. Not used.

No. 6655-11/54

LA1787M


+

27

2µA

100Ω

C2

VCC

VCC

Pin 28

A13571

28

VREF

A13572

+

32

1µF

29

VREF

A13573



The MRC detector time constant

27 MRC control voltage timeis determined by a 100 Ω resistor

constantand C2 when discharging and bythe 2-µA current and C2 whencharging.

28 SNC control inputThe sub-output is controlled by a0 to 1-V input.

The high band frequency output is controlled by a 0 to 1-V input.

It can also be controlled by the 29 HCC control input MRC output.

Use a resistor of at least 100 kΩwhen controlling with the pin 32FM S-meter signal.

No. 6655-12/54

LA1787M


31

30

+

VCC

VCC

10kΩ

FMdetectoroutput

AMdetector

Noisecanceller

1µF

50kΩ

4.2V

A13574

+

32

VCC

10kΩ

1kΩ

1µF

A13575

MRC input

+

33

HOLEDET

SOFTMUTE

Bandmuting

SEEKOFF

VCC

0.1µF

C1

50kΩ

10kΩ

50kΩ

MUTEAMP.

SD circuit

A13576



30 Noise canceller inputPin 30 is the noise canceller input. The input impedance is 50 kΩ.

Pin 31 is the AM and FM detectoroutputIn FM mode, this is a low-impedance output.

31 AM/FM detector output In AM mode, the output impedance is 10 kΩ.To improve the low band separation, use a couplingcapacitor of over 10 µF.

FM S-meter output block

32 IF S-meter output and MRCMRC AC input block

DC inputAdjust the external 1-kΩ resistor to attenuate the MRC AC input and control the circuit.

•The muting time constant is determined by an external RCcircuit as described below.Attack time: TA = 10 kΩ × C1Release time: TR = 50 kΩ × C1

•Noise convergence adjustment33 Mute drive output The noise convergence can be

adjusted when there is no inputsignal by inserting a resistorbetween pin 33 and ground.

•Muting off functionGround pin 33 through a 4-kΩresistor.

No. 6655-13/54

LA1787M


37 36 35 34

HOLEDET

Quadraturedetector

Bandmuting

IF limitter amplifier

A13577

0.1µF VREF R1

R2

VCC

VCC

C

390Ω

1kΩ

3pF

24

38

+– SD

Comparator

S-meter

R SD ADJ

130µA

A13578

24

39+–

KEYEDAGC

Comparator

S-meter

A13579

6.4kΩ

3.6kΩ

1.3V

50pF 150Ω

90µA

VCC

AM IF out



•The resistor R1 determines the width of the band muting function.Increasing the value of R1narrows the band.Reducing the value of R1 widensthe band.

34 AGC35 QD output •Null voltage36 QD input When tuned, the voltage between37 VREF pins 34 and 37, V34 – 37, will be 0 V.

The band muting function turnson when |V34 – 37| ≥ 0.7 V.

V37 = 4.9 V

A 130-µA current flows from pin

38 FM SD ADJ38 and, in conjunction with the external resistance R, determines the comparison voltage.

The keyed AGC operates when the voltage created by dividing thepin 24 S-meter output voltage bythe 6.4 and 3.6 kΩ resistors

39 Keyed AGC becomes lower than the voltageAM stereo buffer determined by the resistor

between pin 39 and ground.

This pin also is used as the AMstereo IF buffer pin.

No. 6655-14/54

LA1787M


41

A13580

+

2200pF

20kΩ

20kΩ

VCC

42

+–

DET

VCC

VCC

C

50kΩ

50kΩ

1kΩ

1kΩ

A13581

+

43

+

VCC

30kΩ

30kΩ

30kΩ

19kHz∠0°BIAS

1µF

A13582



The HCC frequency characteristics41 HCC capacitor are determined by the external

capacitor connected at this pin.

This pin is used to change thefrequency characteristics of the unneeded audio band under 100 Hz in AM mode to produce a clear audio signal.

Note: The LC capacitor must be connected between this pinand VCC (pin 40).

42 AM L.C. pin This is because the detector circuit operates referencedto VCC.

The cutoff frequency fC is determined by the followingformula.

fC = 1/2π× 50 kΩ × C

Inserting a 1-MΩ resistor between 43 Pilot detector pin 43 and VCC will force the IC

to mono mode.

No. 6655-15/54

LA1787M


45 IF output The IF amplifier load

+

42

DET

44

VCC

VCC

C2.2µF

0.022µF

50kΩ

50kΩ

240kΩ

G1

10Ω

SEEKON

IFAGC

A13583

45

DET

Pin 40 VCC

Pin 40 VCC

A13584

46

VCC

VCC

50pF

100Ω

20kΩ

ANT DAMPINGDRIVER

W.AGC AMP.

A13585



G1; Used for time constant switching during seeks.• Receptionτ = 2.2 µF × 300 kΩ

44 IF AGC • Seekτ = 2.2 µF × 10 Ω

The external capacitors are connected to VCC.This is because the IF amplifier operates referenced to VCC.

AM antenna damping I46 = 6 mA (maximum)46 drive output This is the antenna damping

Wide band AGC input current.

No. 6655-16/54

LA1787M


52 IF input The input impedance is 2 kΩ.

47

+–

VCC

30kΩ

R

140µA

Pin 24

MUTE

Inverter

A13586

+

48

+

57

+–

VCC

5.6V 10kΩ

Antennadamping

3.3µF

47µF

For AGC use

A13587

50

51

2.6V

10kΩ 10kΩ

0.022µF 330Ω

IF in

A13588

52

2kΩ

100Ω

A13589



FM muting on levelModify the value of the external

47adjustment

resistor to adjust the muting onlevel.

RF AGC rectification capacitorThe low frequency distortion isdetermined as follows: Increasing C48 and C57 improves

48 RF AGC bypass the distortion but makes the 57 RF AGC response slower.

Reducing C48 and C57aggravates the distortion but makes the response faster.

50 IF bypass51 FM IF input

Due to the high gain of the limiteramplifer, care must be taken whenchoosing the grounding point forthe limiter amplifer input capacitorto prevent oscillation.

No. 6655-17/54

LA1787M


53

56

IF OUT

IF IN

2.75V

300Ω

VCC

300Ω

A13590

54

49

OSC

Pin 40 VCC

Pin 40 VCC

330Ω

A13591

55

58

+–

W-AGC N-AGC62 pin

VCC

30pF

50pF

50µA

Signal meter

AM SD

C1

C2

MIXIN

MIXOUT

A13592



• Input and output pin or the firstIF amplifier

• Inverting amplifier

53 IF amplifier output V56 = 2 V56 IF amplifier input Input impedance: RIN = 330 Ω

V53 = 5.3 VOutput impedanceROUT = 330 Ω

The mixer coil connected to the

54 Mixer output: 130 µApin 54 mixer output must be

49 Mixer inputwired to VCC (pin 40).

The pin 49 mixer inputimpedance is 330 Ω

Pins 55 and 58 include built-inDC cut capacitors.The AGC on level is determinedby the values of the capacitorsC1 and C2.

55 W-AGC IN Pin 55 functions as the SDAM SD ADJ sensitivity adjustment pin in

AM mode.58 N-AGC IN

Muting attenuation The output current I55 is 50 µA,adjustment pin and V55 varies depending on the

value of the external resistor. The SD function operates bycomparing V55 with the S-metervoltage.

No. 6655-18/54

LA1787M


59

60

63

O S C

64

1ST.IF

30Ω

VCC

C1

C25pF

5pF

RF AMP

620Ω 620Ω

VCC

A13593

+

3

6 +–

FM.F.EAGC

AM/FMswitching circuit

SD VCC 510Ω

100kΩ3.3V

GNDA13594

8V

62

AM 1stMIX

to RFAmp.

10kΩ

2.1V

A13595

10

10kΩ

5.6V 20pF

33pF

X tal

to 2ndMIX

A13596


Double balanced mixerPins 59 and 60 are the mixer10.7-MHz output

59Mixer output Pins 63 and 64 are the mixer60

input.This is an emitter insertion typecircuit, and the amount of 63

Mixer input insertion is determined by the64capacitors C1 and C2.

Note:The lines for pins 63 and 64must be kept separated from the lines for pins 59 and 60.

Pin 6 functions both as the FM front end VCC and the AM/FMswitching circuit.

6 Front end VCC AM/FMswitching

1st MIXFirst mixer input

62INPUT

The input impedance is about10 kΩ.

Crystal oscillator circuit10 AM 2nd OSC The Kinseki, Ltd. HC-49/U-S and

a CL of 20 pF must be used.

V6 voltage Mode

When 8 V → FM

OPEN → AM

Block Diagram

No. 6655-19/54

LA1787M

12345678910111213141516

48474645444342414039383736353433

1718

1920

2122

2324

2526

2728

2930

3132

6463

6261

6059

5857

5655

5453

5251

5049

ANTD

BUFFAM1STOSC

AGC

AMPNOISE

PICANINPUT

TRIGGATE

COUNTER

AMP

HPF

FF19k<90k

LPF

SNC

MRC

FF19k<0

FF38k<0

FF

PHASECOMP

VCO

TRIGPILOTDET

P-CAN

SUBDEC

MATRIX

VCOSTOP

MAINHC

HCC

ANTD

HOLEDET

MUTEDRIVE

AMVSMAM SD

IF BUFF

FMVSM

IF limiteramplifier

FM SDDET

IFAGC

BUFF

L.C.

OSCBUFFOSC

DC-CDET

AFCCLAMP

Q.DETMUTEAMP

MIX

AM/FM

MIXRF AGCWB AGC

TWEET

BUFF

AM FMVREFSEEK

SW

SD/STIND

KEYEDAGC

IFREG

AM/FMSW

W.B.AGC

RF AGCAMPINPUT

+

+ –

+

+

+ +

++

+

++

+

+

+

+

+

+

AN

T D

OS

C

RF

AG

C

FE

GN

D

30kΩ

10kΩ

30kΩ

2kΩ

18pF

300p

F

6800pF0.01µF

0.01

5µF

0.01

5µF

0.01µF

0.22µF

0.47µF

1µF

1µF

1µF

AM HC

AM LEVEL 1µ

F

1µF

20kΩ

100kΩ

5.6kΩ

10kΩ

100k

Ω

8200pF

50kΩ

1kΩ

100kΩ

0.047µF

10.2

6MH

z

10pF5pF

25pF

20pF

18pF

1µF

0.02

2µF

0.02

2µF

0.02

2µF

0.01

µF

0.47

µF

1MΩ

+

AM

OS

C

MPXOUT

PI.CAN ADJ

SEP.ADJ

CSB912JF108

AM/FMS-METER

GND

5V

SNC

HCC

NC-IN

DET OUT

METER

FM

GN

D

NC

MP

X G

ND

N.C

.MP

XG

ND

MU

TE

DR

IVE

0.47

µF

0.47

µF

0.22

µF

0.02

2µF

2.2µ

F

3.3µ

F

1µF

11kΩ

IF7

100µ

F

2200

pF

AF

C IN

QD

OU

T

QD

IN

VR

EF

FM

SD

AD

J.

AM

LC

CH

CC

PIL

OT

DE

T

KE

YE

D A

GC10kΩ

10kΩ

30kΩ

240kΩ

6.8k

Ω

0.1µFRFAGC

GND

VCC

0.022µF

0.022µF

0.022µF

100µH

47µF

15pF

15pF

15pF

100µH

0.022µF30Ω

100k

Ω

1kΩ

510kΩ

20kΩ

2.7k

Ω

62pF

330Ω

FC18

ANTD

1MH

30MH

FM IF IN

FM IF OUT

AM IF IN

FE IF IN

0.02

2µF

220Ω

100Ω

AM MIX OUTFM WB AGCIN

AM SD ADJ

MUTE ATT

FEVCC

0.022µF

5pF

5pF

8pF

18pF

30Ω

30Ω

30kΩ

100k

Ω

180Ω 9p

F

39pF

100k

Ω

1000

pF

100k

Ω

100ΩGND

200kΩ

1000

pF

3SK

263

0.1µF

0.022µF

GND

1000pF

1000pF

30kΩ

22pF22pF

0.02

2µF

100k

Ω

VCC

VCC

100F

0.02

2µF

FMIF

AM

GND

FMIF

AM

NC

MPX

VCC

FM

/AM

VS

M

RIG

HT

CH

.

LEF

T C

H.

AM

/FM

OS

C B

UF

F

FM

GN

D

FM

/AM

VT

FM

AN

T IN

AM

RF

GN

D

AM

AN

T IN

AM

VC

C

SE

EK

→A

M/F

M S

DS

TO

P→

FM

ST

IND

.

0.022µFTO

AM

ST

ER

EO

(IF

OU

T)

ADJ

+

+

+

+

+

+

+

+

100k

Ω

100k

Ω

10kΩ

10kΩ

10kΩ

2.2kΩ

0.01

µF

3SK

583

1µF

22pF

22pF

7.2M

Hz

10µF

0.22µF

100p

F

100p

F

100p

F

100p

F

51kΩ

0.22µF

200k

Ω1k

Ω

68pF

2.2k

Ω4.

7kΩ

51kΩ

10µF

10µF

10µF

10µF

240k

Ω

240k

Ω

22kΩ

22kΩ

22kΩ

22kΩ

22kΩ

22kΩ

1kΩ

10kΩ

10kΩ

1kΩ

100k

Ω

100k

Ω1.

5kΩ

100µ

F

100µ

F

5.6V

9.1V

100p

F

CI

CL

DO

RD

S

AD

C

MU

TE

R O

N

SD

/MO

NO

ST

CE

LC86

7148

+B

12V

L

A13

597

R

VS

S

PDVD

D

FM

IN

CI

CL

DO

FM

/AM CE

AM

IN LC72

16M

20191817161514131211

12345678910

AC Characteristics Test Circuit

No. 6655-20/54

LA1787M

12

34

56

78

910

1112

1314

1516

4847

4645

4443

4241

4039

3837

3635

3433

17181920212223242526272829303132

64636261605958575655545352515049

AN

TD

BU

FF

AM

1ST

OS

C

AG

CT

RIG

GA

TE

HP

F

FF

19<

90 k

LPF

SN

C

MR

C

FF

19<

0

F

F38

k<0

FF

PH

AS

EC

OM

P

VC

O

TR

IGP

ILO

TD

ET

P-C

AN

SU

BD

EC

MA

TR

IX

VC

OS

TO

P

MA

INH

C

HC

C

AN

TD

HO

LED

ET

MU

TE

DR

IVE

AM

VS

MA

M S

D IF B

UF

FFM

VS

MF

M S

DD

ET

IFA

GC

BU

FF

L.C

.

OS

CB

UF

FO

SC

DC

-CD

ET

AF

CC

IAM

P

Q.D

ET

MU

TE

AM

P

MIX

AM

/FM

MIX

RF

AG

CW

.B. A

GC

TW

EE

T

BU

FF

AM

FM

VR

EF

KE

YE

DA

GC

FF

RE

GF

M/A

MS

W

W.B

.AG

C

RF

AG

C

+

+–

+

+

++

++

+ ++

+

+

+

+ +

ANT D

RF AGC

FE GND

OS

C

20kΩ

SW

1

VA

1V

A9

8V

VC

C

VA

6

10kΩ

20pF

300pF

6800

pF0.

01µF

10µF

0.015µF

0.015µF

0.01

µF

0.22

µF

0.47

µF

1µF

BA

SW

4 (T

)

1µF

AM

HC

AM

LE

VE

L

1µF 1µF

20kΩ

20kΩ

3pF

100k

Ω

VR

1

VR

2

8VS

W9

5.6k

Ω

8200

pF

0.04

7µF

0.02

2µF

10.2

6MH

zX

TA

L

5pF

25pF 20pF

1µF

0.022µF 0.022µF

0.01µF

0.47µF

1MΩ

50kΩ

50kΩ

VD

2

VA

3

FM

/AM

IFB

UF

F.V

D4

SW

5

4.3k

Ω

100kΩ

100kΩ

+

AM

OS

CM

PX

OU

T

PI.C

AN

AD

J

SE

P.

AD

J

CS

B91

2JF

108

AM

/FM

S-M

ET

ER

GN

D

SN

C

HC

C

NC

-IN

DE

T O

UT

FM

S-M

ET

ER

N.C.MPX GND

MU

TE

DR

IVE

0.1µF

0.47µF

0.22µF

0.022µF

2.2µF

3.3µF

1µF

15kΩ

180kΩ

IF7

100µF

2200pF

AFC IN

QD OUT

QD IN

VREF

FM SD ADJ.

AM LC

CHCC

PILOT DET

MUTE OR ADJ

KEYED AGC

10kΩ

10kΩ

22kΩ

240k

Ω

6.8kΩ

0.1µ

FR

FA

GC

IF O

UT

B A

IF IN

SW

3

SW

2 (

i )M

IX

GN

D

VC

C

0.02

2µF

0.022µF

100µ

H

47µF

20kΩ

0.022µF

100µ

H

0.02

2µF

30Ω 100kΩ

1.6k

Ω

510Ω

30Ω

25Ω

50Ω

10pF

330Ω

FC

18

AN

TD

VD

6

SW

8S

W7

1mH

6.8mH

FM

IFIN

FM

IF O

UT

AM

IF IN

FE

IF IN

330Ω

200Ω

0.02

2µF

18pF

AM

MIX

OU

T

FM

WB

AG

CIN

AM

SD

AD

J

MU

TE

AT

T

FE

VC

CV

CC

5pF

5pF

3pF

39pF 100kΩ

50Ω

10kΩ

1MΩ

100Ω

100Ω

GN

D

VT

0.02

2µF

0.02

2µF

1000

µF

0.02

2µF

15pF

JIS

DU

MM

Y

30Ω

50Ω

65pF

30kΩ

RIGHT CH.

LEFT CH.

AM/FM OSC BUFF

VA

2

FM GND

FM VCC

SE

EK

→A

M/F

M S

DS

TO

P→

AM

ST

BU

FF

ER

F

M S

T IN

D.

AD

J

VD

1

200kΩ

30kΩ

VC

C2

VD

3

VC

C2

VD

5

MR

C-I

N

VC

C8V

VC

C3

HC

C

NC

-IN

SN

C

PG

1(A

C1)

+

VC

C1

5V

100kΩ

SW

6

+

+

AC

5

+

AC

1S

G1

300Ω

50Ω

50Ω

+

AC

3S

G3

+

AC

2S

G2

A13

598

3pF

0.02

2µF

10kΩ

10kΩ

VC

C

VA

7

8VS

W10

10µF

+

10kΩ

1MΩ

VA

8

IF li

mite

ram

plifi

er

No. 6655-21/54

LA1787M

Parameter SymbolSwitch states

SW1 SW2 SW3 SW4 SW5 SW6 SW7 SW8 SW9 SW10

Current drain ICCO-FM ON b OFF b — ON OFF OFF ON —

Demodulation output VO-FM ON b OFF b — ON OFF OFF ON —

Pin 31 demodulation output VO-FM31 ON b OFF b — ON OFF OFF ON —

Channel balance CB ON b OFF b — ON OFF OFF ON —

Total harmonic distortion (FM) THD-FMmono ON b OFF b — ON OFF OFF ON —

Signal-to-noise ratio: IF S/N-FM IF ON b OFF b — ON OFF OFF ON —

AM suppression ratio: IF AMR IF ON b OFF b — ON OFF OFF ON —

Att-1 ON b OFF b — ON OFF OFF ON —

Muting attenuation Att-2 ON b OFF b — ON OFF OFF ON —

Att-3 ON b OFF b — ON OFF OFF ON —

Separation Separation ON b OFF b — ON OFF OFF ON —

Stereo on level ST-ON ON b OFF b — ON OFF OFF ON —

Stereo off level ST-OFF ON b OFF b — ON OFF OFF ON —

Main total harmonic distortion THD-Main L ON b OFF b — ON OFF OFF ON —

Pilot cancellation PCAN ON b OFF b — ON OFF OFF OFF/ON —

SNC output attenuation AttSNC ON b OFF b — ON OFF OFF ON —

HCC output attenuation 1 AttHCC-1 ON b OFF b — ON OFF OFF ON —

HCC output attenuation 2 AttHCC-2 ON b OFF b — ON OFF OFF ON —

Input limiting voltage Vi-lim ON b OFF b — ON OFF OFF ON ON

Muting sensitivity Vi-mute ON b OFF b — ON OFF OFF ON —

SD sensitivity 1 SD-sen1 FM ON b OFF b OFF OFF OFF OFF ON —

SD sensitivity 2 SD-sen2 FM ON b OFF b ON OFF OFF OFF ON —

IF counter buffer output VIFBUFF-FM ON b OFF b OFF OFF OFF OFF ON —

VSM FM-1 ON b OFF b — ON OFF OFF ON —

Signal meter output (FM)VSM FM-2 ON b OFF b — ON OFF OFF ON —



Muting bandwidth BW-mute ON b OFF b — ON OFF OFF ON —

Mute drive output VMUTE-100 ON b OFF b — ON OFF OFF ON —

N-AGC on input VNAGC ON a ON b — ON OFF OFF — —

W-AGC on input VWAGC ON a ON b — ON OFF OFF — —

Conversion gain A.V ON a ON b — ON OFF OFF — —

Oscillator buffer output VOSCBUFFFM ON a ON b — ON OFF OFF — —

Gate time 1 τGATE1 ON — OFF a — ON OFF OFF — —

Noise sensitivity SN ON — OFF a — ON OFF OFF — —

NC effect SN-NC ON/OFF — OFF a — ON OFF OFF — —

MRC output VMRC ON — OFF b — ON OFF OFF — —

MRC operating level MRC-ON ON — OFF b — ON OFF OFF — —

Practical sensitivity S/N-30 OFF — OFF b ON ON — — — —

Detection output VO-AM OFF — OFF b ON ON — — — —

Pin 31 detection output VO-AM31 OFF — OFF b ON ON — — — —

AGC F.O.M. VAGC-FOM OFF — OFF b ON ON — — — —

Signal-to-noise ratio S/N-AM OFF — OFF b ON ON — — — —

Total harmonic distortion (AM) THD-AM OFF — OFF b ON ON — — — —

Signal meter output (AM)VSM AM-1 OFF — OFF b ON ON — — — —

VSM AM-2 OFF — OFF b ON ON — — — —

Oscillator buffer output VOSCBUFF AM-1 OFF — OFF b ON ON — — — —

Wide band AGC sensitivityW-AGCsen 1 OFF — OFF b ON ON — — — —

W-AGCsen 2 OFF — OFF b ON ON — — — —

SD sensitivitySD-sen1 AM OFF — OFF b OFF OFF — — — —

SD-sen2 AM OFF — OFF b OFF OFF — — — —

IF buffer output VIFBUFF-AM OFF — OFF b OFF OFF — — — —

Test Conditions

Usage Notes

1. Notes on VCC and Ground

* : When applying the VCC voltage to pin 6, that voltage must not exceed the pin 40 and pin 61 VCC voltages.(This condition must be checked carefully when first applying the pin 6 voltage.)

2. Notes on AM Coil ConnectionThe VCC used for the first oscillator coil connected to pin 7 must be at the same potential as pin 61.Connect to the IFT connected with pin 45, and to the MIX coil connected with pin 54. VCC must be at the same potentialas pin 40.

3. AM/FM SwitchingPin 6 is also used as the FM front end and RF AGC VCC

No. 6655-22/54

LA1787M

Pin 40 VCC for the FM IF, AM, NC, MPX, and MRC blocks

Pin 25 Ground for the FM IF and AM blocks

Pin 14 Ground for the NC, MPX, and MRC blocks

Pin 61 VCC for the FM front end, AM first mixer, and first oscillator blocks

* Pin 6 VCC for the FM front end and AGC blocks, and the AM/FM switching pin

Pin 3 Ground for the FM front end, first mixer, and first oscillator blocks

Pin 6 voltage Mode

8 FM

OPEN AM

Fig. 1

LA1787M Overview

1. Notes on the LA1781M, LA1784M, and LA1787M

The LA1784M is a version of the LA1781M that uses an external oscillator circuit, and has the same characteristics asthe LA1781M.The LA1787M is a version of the LA1784M that features improved characteristics.

LA1781M LA1784M LA1787M

This product is a version of the LA1781Mwith the oscillator circuit removed. Itsupports the use of an external oscillatorcircuit.It has the same characteristics as theLA1781M.

The LA1787M features improvedcharacteristics over the LA1781Mand LA1784M.

No. 6655-23/54

LA1787M

2. Modified circuits

The following characteristics have been improved over those of the The LA1784M.

• The AM adjacent channel interference characteristics (∆40 kHz) have been improved.• The AM S-meter curve slope has been increased.• The FM separation temperature characteristics have been improved.• The stereo indicator sensitivity has been improved.• The FM oscillator circuit has been omitted.

(1) AM interference characteristics improvement

The second signal interference and suppression have been improved for adjacent channels (±40 kHz) by increasingthe AM second mixer input dynamic range.

(2) The AM S-meter curve slope has been increased.

The slope of the AM S-Meter curve has been increased from that of the LA1781M and LA1784M.

–20 00

2

3

4

5

6

7

1

20 40 60 80 100 120 140

LA1787MLA1780M

LA1781M

AM S-Meter Voltage

Antenna input — dBµ

S-m

eter

vol

tage

— V

(3) FM separation temperature characteristics improvement

The temperature characteristics have been improved, the amount of change in the separation due to drift when atpower on has been stabilized. This makes it easier to adjust the separation.

35

40

45

50

55

60

0 1 2 335

40

45

50

55

60

0 1 2 3

Change in Separation (LA1781M): First IF Input

Time after power on — minutes

Cha

nge

in s

epar

atio

n —

dB

Change in Separation (LA1787M): First IF Input

Time after power on — minutes

Cha

nge

in s

epar

atio

n —

dB

No. 6655-24/54

LA1787M

(4) Stereo indicator sensitivity improvement

The stereo indicator sensitivity (on/off) is equivalent to that of the LA1780M

Stereo on level Stereo off level

LA1781M/1784M 4.1% 3.1%

LA1787M/1780M 2.6% 1.6%

* : The pilot level such that the stereo indicator goes on or off for a 10.7 MHz unmodulated IF input.

(5) FM oscillator circuit removed

The internal FM oscillator circuit provided in the LA1781M has been removed. The FM oscillator level can beadjusted by constructing an external circuit block.

*: However, this requires 4 more external parts than the LA1781M: 1 transistor and 3 resistors/capacitors.

4

Vt

VCCVCC

A13600

4

Vt

VCC

IC internalIC internal

A13601

LA1787M/1784M FM OSC LA1780M/1781M FM OSC

3. Gain distribution

The table below shows the gain distribution of the LA1780M, LA1784M, and LA1787M. (These are measuredvalues.) Compared to the LA1784M, the total gain is lower.

1st MIX (10.7) 1st IF (10.7) 2nd MIX (450) 2nd IF (450)

LA1780M 10 dB 3.3 dB 3.2 dB 69 dB

LA1784M 7.5 dB 13 dB 7 dB 66 dB

LA1787M 7.5 dB 3.5 dB 8.6 dB 67 dB

First mixer : No circuit changes from the LA1784M.

First IF amplifier : Equivalent to the LA1780M circuit. (The gain is lower than that in the LA1781M and LA1784M.)

Second mixer : The mixer circuit has been modified to improve adjacent channel suppression and interference.

Second IF amplifier : Equivalent to the LA1780M circuit.

(Typical value)

No. 6655-25/54

LA1787M

4. Changes to applications

Component values that change from LA1781M/LA1784M applications(Since the total AM gain has changed in the LA1787M)

• AM SD adjustment resistor (pin 55): Because Vsm is higher.• AM level adjustment resistor (pin 31):Since the post-detection audio amplifier gain is higher than in the LA1781M

and LA1784M, the output level is also higher. This resistor must be changedto match the set value.

• AM mixer coil (pin 54), IFT coil (pin 45) damp resistor:Since the IF block gain is increased, the mixer (pin 54) andIFT (pin 45) coil damping must be adjusted.

• Separation adjustment resistor (pin 19):Since an internal 4 kΩ resistor has been added to the pin 19 input circuit toimprove the separation temperature characteristics, the value of the externalresistor must be reduced from that used with the LA1780M, LA1781M, andLA1784M. (See the following page.)

19

30kΩ

0.047µF

DECODERComposite Sign

19

30kΩ

Added 4 kΩ resistor

5kΩ

0.047µF

DECODERComposite Sign5kΩ

A13602 A13603

LA1781M/1784M LA1787M

1. Notes on the FM Front EndNotes on interference rejection characteristics

• Intermodulation characteristicsThe LA1787M applies two high-band AGC functions to prevent IM (the generation of intermodulation). These arethe narrow AGC (pin 58: mixer input detection type) and the wide AGC (for the pin 55 input), and this results in theantenna frequency characteristics shown in figure 2. The levels at which the AGC functions turn on are determinedby the capacitors attached at pins 55 and 58.

–4–5 –2–3 –1 050

70

80

90

100

110

60

1 2 3 4 5

When ∆f = 0, 98.1 MHz

The wide AGC sensitivity when pin 39 is 5 V.

AG

C s

ensi

tivity

— d

Bµ

∆f — MHz

∆f — AGC Sensitivity

The narrow AGC sensitivity when pin 39 is at ground.

Fig. 2

Functions

No. 6655-26/54

LA1787M

• Notes on second-channel attenuation suppressionKeyed AGC (3D AGC) is a technique for achieving good characteristics for both intermodulation and second-channel attenuation at the same time. When the desired signal is faint or nonexistent, the high-band AGC level willbe essentially 0, and as a result automatic tuning may malfunction and blocking oscillation may occur in thepresence of strong interfering stations. Keyed AGC helps resolve these problems.This 3D AGC technique uses information that has the following three frequency characteristics and is a uniqueSanyo-developed system for determining the high-band AGC level.

RF and ANT circuit information: Mixer input AGCMixer circuit information: Mixer output AGCCF selectivity information: S-meter output

–4–5 –2–3 –1 050

70

80

90

100

110

60

1 2 3 4 5

Pin 58 capacitor: 10 pF

Nar

row

AG

C o

n le

vel —

dB

µ

∆f — MHz

∆f — AGC on Level (ANT input)


39

keyed AGC

Fig.3

140

130

120

110

100

90

80

70

7 1.0 2 3 5 7 10 2 3 5 7 100 2 3 5

Wide AGC on level frequency characteristics

Narrow AGC on level frequency characteristics

AGC input level frequency characteristics such that VRFAGC (pin 2) falls under 2 V.

Pin

59 n

arro

w A

GC

and

pin

55 w

ide A

GC

inpu

t lev

els —

dBµ

Frequency, f — MHz

W-AGC, N-AGC — f Fig.5

–4–5 –2–3 –1 050

60

70

80

90

100

110

1 2 3 4 5



Wid

e A

GC

on

leve

l — d

Bµ

∆f — MHz


39

5V

keyed AGC

Fig.4

• 3D AGC Features

Feature Merit

Only the narrow AGC sensitivity (operation at ∆f < 1.5 MHz) is • Effective in resolving second-channel attenuation problems.controlled by the field strength of the desired station.

The narrow AGC sensitivity is controlled by a voltage (V23) that is • Allows effective resolution of second-channel attenuation problems without under 0.5 V. degrading three-signal characteristics.

• Seek operations may stop incorrectly due to the occurrence of

The wide AGC can operate even when V23 = 0 (when the desired intermodulation.

station is not present).• It is possible to prevent the occurrence of intermodulation in the RF tuning

circuit and antenna in the presence of strong interfering stations, and blocking oscillation due to AGC operation can be prevented.

The narrow and wide AGC sensitivities can be set independently.• Settings can be optimized for the field conditions.(See figure 3 and 4.)

The system has two AGC systems: narrow and wide AGC. • Since the narrow AGC operates for the desired station and adjacent

(See figure 5.)stations, the wide AGC sensitivity can be lowered and AGC malfunction due to local oscillator signal can be prevented.

3D AGC Sensitivity Characteristics

No. 6655-27/54

LA1787M

Second-channel attenuation improvement

Desired station AGC sensitivity

4

3

2

1

∆F

Narrow AGC sensitivity

V23 (Desired station field strength)

Wide AGC sensitivityAGC sensitivity

A12075

3D AGC Sensitivity — ∆f, V23 characteristics• The wide AGC sensitivity is determined by the antenna and RF circuit selectivity, regardless of V23.• The narrow AGC sensitivity is determined by the following.

The total selectivity of the antenna, RF circuit, and mixer when V23 ≥ 0.5 VThe above selectivity and V23 when V23 < 0.5 V

• The improvement in the second-channel attenuation corresponds to the area occupied by the narrow AGC in thetotal AGC sensitivity area.Figure 8 on the next page shows the actual operation of the circuit.

–4–5 –2–3 –1 050

60

70

80

90

100

110

1 2 3 4 5

The f

u in

put l

evel

at wh

ich an

tenna

dam

ping

turn

s on

— d

Bµ

∆f — MHz


A12076

ANT INVIN

Second-channel padfD = 98.1 MHz

fu = 98.1 MHz + ∆f

Fig. 6

Fig. 7

Notes on 3D AGC (Keyed AGC)

• The antenna damping current from the pin due to the pin diode flows when the V2 pin reaches the VCC - VBElevel.

• The narrow AGC operates as follows.When pin V39 > pin V24: The narrow AGC turns off.When pin V39 < pin V24: The narrow AGC turns on.

No. 6655-28/54

LA1787M

+

55W-AGC

DET

58

1 2 39 24

N-AGCDET

+

–

+

–

VCC

VCC

ANTDUMPING

90µA S-meter

VS-meter

A11763

Fig. 8

• The LA1787M includes two AGC circuits in its front end block.— Antenna input limiter using a pin diode.— FET second gate controlThe AGC input pin is pin 59, and the AGC circuit turns on when a signal of about 30 mVrms is input.

AGC activationThe pin diode drive circuit turns on when VCC – V2 is greater than or equal to about 1 V, and input limitation isapplied to the antenna circuit. In application circuits, there will be an attenuation of about 30 to 40 dB. Next, whenan adequate current flows in the antenna attenuator pin diode, the inductance falls, the FET second gate voltagedrops, the FET gm falls, and the AGC operates. The recommended FET is the Sanyo 3SK263, which is anenhancement-type MOSFET. Therefore, full AGC is applied when the voltage, VG2-S, between the second gate andthe source is 0. Note that if a depletion-type MOSFET is used, AGC will not be applied unless VG2-Sis less than 0.

No. 6655-29/54

LA1787M

0

1

2

3

4

5

6

7

8

9

–10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

fr = 98.0 HzVCC = 8 VTa = 25°C

Range where the AGC does not operate

AGC level due to the MOSFET second gate: about 35 dB

AGC level due to the pin diode: about 35 dB

V2A

GC

—

V

ANT IN — dBµ

V2 AGC Characteristics Fig.9

5964 60 63 62

OSC

A12077

MIX

INP

UT

MIX

OU

T

MIX

OU

T

MIX

INP

UT

MIX

VC

C

MIX

Mixer circuit

• MixerThe mixer circuit in this IC is a double-balanced mixer with bothbalanced input and balanced output.Input circuit typeEmitter inputInput impedance: 25 Ω

Due to optimized device geometry, emitter current, the bias, this ICachieves the following performance.

Mixer input usable sensitivity: 15 dBµMixer input IMQS: 90.5 dBµ(For an oscillator level of 200 mVrms)

* The mixer input IMQS is defined as:

fr = 98.8 MHz, no inputfu1 = 98.8 MHz, 1 kHz, 30% modulationfu2 = 99.6 MHz, no modulation

The interference 1 and 2input levels such thatgenerated intermodulationoutput signal-to-noise ratiobecomes 30 dB when aninterference signal with thesame level as the mixer inputis input, and distortion occursin the mixer.

Fig. 10

• OscillatorFigure 11 shows the type of oscillator circuit used in this IC. It includes both an oscillator and an oscillator buffer.

No. 6655-30/54

LA1787M

5

4

VT

18pF

25pF

20pF

VCC

AM/FMOSC BUFFER OUT

A12078

56 53

+

–

TO MIX

330Ω

330Ω

330Ω

FM IF input

A12079

• Figure 12 shows the type of FM first IF amplifier used in this IC. It is a differential single-stage amplifier.

SpecificationsInput impedance: 330 ΩOutput impedance: 330 ΩGain: 20 dB

Fig. 11

Fig. 12

2. FM IF• Notes on the FM SD and SD adjustment

The figure below presents an overview of the FM SD and the IF count buffer.

No. 6655-31/54

LA1787M

S-meter

FM IF

HOLECLET

Mutingdrive

outputSTEREO

IND

Bandmuting

39 24 33 23 26

+

–

+

–

+

–

4.9V R

R

R

IF count buffer

IF count output

2.5V 5V

SDSTEREO/MONO

5V

A11759

V23DC

V23AC

V26

V33

V38

V24

5 V

Larger values of R33

Smaller values of R33

S-meter

V33 over 0.7 V

V33 over 0.7 V

On as anSD signal

SDON

SDON Stereo

Mono

0.7 V

OFF OFFIF countbuffer

5 V

2.5 V 0 V

IF counter output off

RDS and other types of SD detection can be used by switching these modes.

A11758

For stereo input (when the V26 pin voltage is 0.7 V), when this pin is shorted to ground (0.1 V or lower) the IC will operate in forced mono mode.

New LA1784M functionality:

Fig. 13

Fig. 14

Figure 14 shows the relationship between the FM SD, the IF count buffer output, the S-meter, and the muting driveoutput.

• Transient response characteristics during automatic tuningThe transient characteristics for SD and IF count buffer on/off operation are determined by the time constants ofthe RC circuits attached to the following pins.(1) Muting time constant: pin 33(2) S-meter time constant: pin 24(3) AFC time constant: pin 34

There are two points that require consideration when using fast tuning.(1) The SD time constant due to the S-meter time constant

Since the current I24 (pin 24) varies with the field strength, the time constant also changes. There is no hysteresisin the comparator.If a smaller value is used for C24, you must select a value for C such that the AGC does not become unstablewhen the pin 24 voltage is used for keyed AGC.

(2) The SD time constant due to the pin 33 muting voltage time constantThe changes in volume due to field fluctuation during weak field reception can be made smoother by setting theattack and release times during soft muting operation.

No. 6655-32/54

LA1787M

24

S-meter

C24

A12080

10k

Muteamp

Mutedrive

10kΩ 50kΩ

C33

A11766

33

Attack Release

0

10

20

30

40

50

6 10 14 18 22 26 30 34

Ant

enna

inpu

t suc

h th

at p

in 5

goe

s hi

gh —

dB

µ

Resistance between the pin and ground — kΩ

SD Sensitivity Adjustment Fig.17

Fig. 15

Fig. 16

Muting time constants

Attack: 10 kΩ × C33

Release: 50 kΩ × C33

However, when testing this stop sensitivity, note that when checking the waveform on the IF count buffer output(pin 23), there are cases, such as that shown below, where current in the test system may be seen as flowing toground and cause oscillation that causes the IF count buffer output to go to the output state.

• FM Muting control pin (pin 47) (R47: 30 kΩ variable resistor)The –3 dB limiting sensitivity can be adjusted with R47.

• FM muting attenuation adjustment (pin 58)The muting attenuation can be switched between the three levels of –20, –30, and –40 dB by the resistor insertedbetween pin 58 and ground. (Note that the exact values depend on the total tuner gain.)The noise convergence with no input is determined by the pin 58 voltage.

The attenuation can be set by making R33 smaller as listedin the table above.

No. 6655-33/54

LA1787M

IF bufferampIFF.E.

5 V 0.022 µF

The 10.7 MHz feeds back through ground.

Test system capacitance

A12081

FM Soft Muting (1)


Out

put n

oise

— d

B

DET out

Noise

15 kΩ

10 kΩ

20 kΩ

R47 = 7.5 kΩ

Fig.19

58

100Ω R58

A11764

R33

A11765

33

Fig. 18

Fig. 20

R58 Mute ATT

Open –20 dB

200 kΩ –30 dB

30 kΩ –40 dB

Out

put,

nois

e —

dB

No. 6655-34/54

LA1787M

FM Soft Muting (2) FM Soft Muting (3)

Antenna input — dBµ Antenna input — dBµ

Out

put n

oise

— d

BO

utpu

t —

dB

Out

put

— d

B

10 kΩ

10 kΩ

20 kΩ

2 0kΩ

15 kΩ

15 kΩ

DET out DET out

Noise Noise

R47 = 7.5 kΩR47 = 7.5 kΩ

Fig.21 Fig.22

200 kΩ

30 kΩ

+

–

+

–

58 33 31

200 kΩ R

VCC

R

R

N-AGC

To MIX out

Open

200 kΩ 30 kΩ

Mutedrive

Limiter

Quadrature detector Mute amp.(VCA)

DET out

A11767

20

1

0Detector output

Antenna input

When the pin is at the ground level, the noise convergence will be 10 dB and the –3 dB limiting sensitivity will be about 0 dBµ.

A12082

• FM muting off functionForcing this pin to the ground level turns muting off.

Fig. 23

Fig. 24

Out

put,

nois

e —

dB

• Hall detectionThe Hall detection function detects the level of the pin 36 quadrature input signal and then applies peak detectionto that result. The result is output from pin 33. This circuit has three effects.(1) It assures that muting will be applied for weak inputs with an antenna input of under 5 dBµ. The amount of

attenuation is referenced to an antenna input of 60 dBµ, fm = 1 kHz, and a 22.5 kHz dev output, and is variablefrom 10 dB to 40 dB when there is no input. Thus one feature of this circuit is that the weak input noiseattenuation and the –3 dB limiting sensitivity for over 5 dBµ inputs can be set independently.

(2) When the pin 36 quadrature input is a saturated input, the pin 36 noise level (Va) is detected and a peak-holdfunction is applied to pin 33 (Vb) for locations rapid field strength variations and severe multipath occurs forfields that result in an antenna input level of over 5 dBµ.

(3) Unique featuresOne unique feature of the LA1784M is that if there are adjacent stations such that f1 = 98.1 MHz and f2 = 97.9 MHz, a search operation will not stop at 98.0 MHz. Since VAFC = 0 V and VSM = 3.6 V at 98.0 MHz inthe situations shown in figure 27 and 28, even though Hall detection would normally not operate and SD wouldbe high, in this IC the Hall detection circuit will operate, VMute will be set to 1.2 V (over 0.7 V) and the SDsignal will go low, thus preventing incorrect stopping of the search.

No. 6655-35/54

LA1787M

0

1

2

3

4

5

–20 –10 0 10 20 30

Area muted by Hall detection

V38

pin

—

V


Hall Detection Output — Antenna Input Characteristics Fig.25

36

33

+

0 0

0.1µFVaVb

A12083

Fig. 26

No. 6655-36/54

LA1787M

0

2

4

6

8

0

2

4

6

0

2

4

6

–1

0

1

2

97.7 97.8 97.9 98.0 98.1 98.2 98.3

f2 = 97.9 MHz, 120 dBµfm = 400 Hz, 22.5 kHz dev.

When the tuner is moved in 50 kHz steps.With a 51 kΩ resistor between pins 37 and 34.With the SD sensitivity adjusted to be 20 dBµ.

f1 = 98.1 MHz, 120 dBµfm = 1 kHz, 22. 5kHz dev.

Pin

26 (

SD)

— V

Pin

24, V

SM —

VPi

n 33

, VM

ute

— V

Vol

tage

bet

wee

n pi

ns 3

7 an

d 34

, VA

FC —

V

Frequency, fr — MHz

Unique Features of the LA1784M Hall Detection Circuit (1)

f1

f2

ANTIN

Fig.27

0

2

4

6

8

0

2

4

6

0

2

4

6

–1

0

1

2

97.7 97.8 97.9 98.0 98.1 98.2 98.3

f2 = 97.9 MHz, 40 dBµfm = 400 Hz, 22.5 kHz dev.

When the tuner is moved in 50 kHz steps.With a 51 kΩ resistor between pins 37 and 34.With the SD sensitivity adjusted to be 20 dBµ.

f1 = 98.1 MHz, 40 dBµfm = 1 kHz, 22.5 kHz dev.

Pin

26 (

SD)

— V

Pin

24, V

SM —

VPi

n 33

, VM

ute

— V

Vol

tage

bet

wee

n pi

ns 3

7 an

d 34

, VA

FC —

V

Frequency, fr — MHz

Unique Features of the LA1784M Hall Detection Circuit (2) Fig.28

• Notes on the quadrature input levelWhen a strong field is being received the quadrature signal input (pin 36) requires a 200 mV rms input, and thedetection transformer and the damping resistor between pins 36 and 37 must be designed.(We recommend the Sumida SA-208 transformer and a 10 kΩ resistor between pins 36 and 37.)When the pin 36 input level falls below 160 mV rms, the Hall detection circuit operates and the pin 33 mute driveoutput voltage increases. Therefore, when pin 36 input is from 160 to under 200 mV rms during strong fieldreception, the muting circuit may or may not operate due to sample-to-sample variations between individual ICs.Furthermore, the SD function may not operate, and the audio output level may be reduced. Incorrect operation dueto sample-to-sample variations and temperature characteristics can be prevented by keeping the pin 36 voltage at200 mVrms or higher.

0

1

2

3

4

5

6

92 94 96 98 100 102 104 106

With pins 34 and 37 shorted.With 5 V applied to pin 24.

Vm

ute

—

V

QD input level — dBµ

Pin 33 VMute — QD Input Level

36 37

SG

10.7 MHz LA1888M

75 Ω 75 Ω+

0.022 µF

Fig.29

–0.8

–0.6

–0.4

–0.2

0.2

0.4

0.6

0.8

1

2

3

4

–100 –80 –60 –40 –20 0 20 40 60 80 100 120–120

With the resistor between pins 36 and 37 open.

∆f — kHz

∆f=0→ 10.7 MHzWith a 10 kΩ resistor

between pins 36 and 37.

Voltage between pins 37 and 34 (referenced to the pin 37 voltage)

THD 1 kHz75 kHz dev

SA208 + LA1787M IF Input Characteristics

TH

D

—

%

Fig.30

No. 6655-37/54

LA1787M

Detector output Pin 36 AC levelMPX OUT

R36-37 Vo QDIN

Open 330 mVrms 235 mVrms

10 kΩ 280 mVrms 200 mVrms

• Band Muting Adjustment ProcedureThe muting bandwidth can be modified as shown in figure 31 with the resistor RBW between pin 34 and 37.

3. AM• AM AGC system

The LA1787M RF AGC circuit takes its input from three sources: the WIDE AGC pin (pin 46), the MIDDLEAGC pin (pin 49) and NARROW AGC. There is also an IF AGC circuit.

0

40

80

120

160

200

240

280

1.0 2 3 5 7 10 2 3 5 1007 2

SA208Sumida

Band

wid

th su

ch th

at th

e pin

33

volta

ge ≥

2 V

— k

Hz

Resistor RBW between pins 34 and 37 — kΩ

37 36 35 34

+ +

1 µF 0.47 µF

10 kΩ

RBW

ANT IN 98 MHz 100 dBµ

Fig.31RBW — Muting Bandwidth

+

62

46

57

49RF 52 31

+

48

44

42

RW

1st MIX 10.7MHz CF 2nd MIX 450kHz CF IF Amp. DET

1st OSC X'tal

Middle AGC INNarrow AGC IN

Wide AGC IN

ANTdamping

RF AGC

47 µF 3.3 µF

Amp. IF AGC2.2 µF

240 kΩ

VCC

VCC

A11762

Fig. 32

No. 6655-38/54

LA1787M

800 900 100060

80

70

90

100

1100 1200

AG

C o

n le

vel

Frequency — Hz

AM AGC f characteristics

Wide AGCOperates for wide band interference

Wide AGCOperates for wide band interference

Middle AGCOperates for interference within ±70 kHz of the received frequency.

Middle AGCOperates for interference within ±70 kHz of the received frequency.

Narrow AGCOperates at the received frequency.

Fig.33

70

80

90

100

110

120

21.0 3 5 7 10 2 3 5

Received frequency: 1 MHz

Ant

enna

dam

ping

on

inpu

t lev

el —

dB

µ

Pin 46 input — MHz

Wide Band AGC Circuit

30 Ω 0.022 µF

0.022 µF

0.022 µF

4650 Ω

510 Ω

50 Ω

–6dB

SG

ANTD

Fig.34

62

57

+

VCC

0.022 µF30 Ω

620 Ω 1MH

100 µH

100 µH

30M

H

15 p

F

15 p

F

47 µ

F

100

kΩ

0.02

2 µF

Wide band AGC adjustment resistor

A12084

FC18

The wide band AGC circuit in this IC has the frequency characteristics shown above. The pin 46 input frequencycharacteristics are identical to those of the RF amplifier gate. This AGC circuit serves to prevent distortion at theFET input when a strong signal is applied to the antenna circuit. The level at which the AGC circuit turns on can beadjusted to an arbitrary level with the wide band AGC adjustment resistor. A delayed AGC on level can be handledby reducing the value of the adjustment resistor.

Fig. 35

• Notes on AM SD (pin 26) and the SD adjustment pinSD and the IF buffer are operated by comparing the S-meter level (V24) and the 5 V reference voltage as shown infigure 36.

Figure 37 shows the relationship between the AM SD, the IF count buffer, and the S-meter.

No. 6655-39/54

LA1787M

55 24 23 26

AM IF

+

–

S-meter

100 kΩ0.47 µF

51 kΩ

Seek

5 V

5 V

IF buffer

IF buff amp.

SD

0.022 µF

100 kΩ

50 pF

Comparator

50 µA

VCC

A12085

V23DC

V23AC

V26

V55

V24PIN

Larger values of R55

Smaller values of R55

5 VPin 55: AM SD adjustment pin

OFF IF buffer on

SD on

S-meter

0 V

A11760

Fig. 36

Fig. 37

• AM high band cut and detector output level adjustment methodsThe pin 31 AM and FM tuner output has an impedance of 10 kΩ in AM mode and a few tens of Ohms in FMmode. Therefore, R31 is used to lower the AM detector output level and C31 determines the AM high bandfrequency characteristics.

• AM stereo system pins

No. 6655-40/54

LA1787M

Fig. 39

31

30

+

FMdetector

AMdetector

VCC

VCC

10 kΩ

Noise canceler input

50 kΩ

R31 C31

A12086

45 39

VCC

VCC

IFT

50 pF 150 Ω

IF AMP.

Keyed AGC

GND

To the AM stereo decoder

400 mV rms 450 kHz output

A11761Fig. 40

No. 6655-41/54

LA1787M

• AM low band cut adjustment methodThe AM low band frequency characteristics can be adjusted with C42, which is inserted between pin 42 and VCC.Since the detector is designed with VCC as the reference, C42 must be connected to VCC.

AMdetector

42

+

–

50 kΩ

50 kΩ

10 kΩ10 kΩ

10 kΩ

C42

VCC

To pin 31

A12087

–40

–30

–20

–10

0

10

3 5 70.010.001 2 3 5 72 3 5 72 3 5 720.1 1.0 10

0.043 µF (41pin)% with no used (31pin)

0.022 µF (41pin)With no used (31pin)

0.022 µF (41pin)8200 pF (31pin)

0.022 µF (41pin)With no used (31pin)

fr = 1000 kHzfm = 1 kHz, 30%

Det

ecto

r ou

tput

— d

B

Frequency — Hz

Detector Output — Frequency Fig.42

Fig. 41

31 30+

–IF output Noise canceler input1 kΩ

1 µF2200 pF

A12089

H1 W12.5OU

–2.5OU–19.00 µs 981.00 µs

IF audio output f = 10 kHz,180 kHz dev

A12088Fig. 43

Fig. 44

4. Noise Canceler Block• The noise canceler input (pin 30) has an input impedance of about 50 kΩ. Check the low band frequency

characteristics carefully when determining the value of the coupling capacitor used. Note that fC will be about 3 Hzwhen a 1 µF capacitor is used in the application.

• Pins 8 and 9 are used to set the noise detector sensitivity and the noise AGC. It is advisable to first set the noisesensitivity for a medium field (an antenna input of about 50 dBµ) with pin 8 (the noise sensitivity setting pin), andthen set the AGC level for a weak field (20 to 30 dBµ) with pin 9 (the AGC adjustment pin). If the noise sensitivityis increased, the AGC will become more effective but, inversely, the weak field sensitivity will be reduced.

Noise canceler 10 kHz overmodulation malfunction may be a problem. In particular, when an overmodulatedsignal is input, the noise canceler may, in rare cases, malfunction. This is due to the fact that the IF detector outputhas a waveform of the type shown in figure 43 due to the bands of the IF ceramic filters as shown below. (Here, theantenna input is 60 dBµ, the ceramic filters are 150 kHz × 1 and 180 kHz × 2, f = 10 kHz, 180 kHz dev.) The noisecanceler reacts to the spikes (whiskers) generated due to this overmodulation, which results in distortion to theaudio output. (The spike components due to overmodulation occur due to the bands of the ceramic filters in thetuner.) The following describes a method for resolving this problem. This incorrect operation due toovermodulation is prevented by removing the spike components due to this overmodulation with a low-pass filterconsisting of a 1 kΩ resistor and a 2200 pF capacitor shown in figure 44. However, note that the FM separationcharacteristics in the high band and the AM frequency characteristics will change.

No. 6655-42/54

LA1787M

41

20 kΩ

C

To the matrix

A12090

VO(dB)

f(Hz)

2πC × 20 kΩ1

A12091

–60

–50

–40

–30

–20

–10

0

10

3 5 7 100 2 3 5 7 1k 2 3 5 7 10k 2 3

VCC = 8.0 Vf = 98 MHz 100%mod80 dBµ IN

Changes in the pin 41 capacitor capacitance (for a 100% high cut ratio)

0.0047 µF

0.0022 µF

0.001 µF

0.01 µF0 µF

Atte

nuat

ion,

HC

C —

dB

Frequency, f — Hz

Frequency Characteristics Fig.47

5. Multiplexer Block• HCC (high cut control) frequency characteristics (pin 41)

When the HCC function operates, the frequency characteristics of the output signal are determined by thecapacitance of the external capacitor connected to pin 41.

1fC = ——————— [Hz]

2π× C × 20 kΩ

Fig. 45

Fig. 46

17

30 –

1211

6800 pF 3.9 kΩ

18

0.01 µF 50 kΩ

Pilotcancel

Gate

To the multiplexer

Noise canceler input

A12092

• Pilot canceler adjustment (pins 17 and 18)

Fig. 48

The pilot canceler signal waveform (pin 19) is a 19 kHz signal that contains no third harmonic as shown in figure48. Since this signal has the same phase as the pilot signal, no capacitor is required between pin 18 and ground.Since it has no third harmonic component, excellent pilot cancellation can be acquired in both the left and rightchannels by adjusting with a variable resistor.

19

5 kΩ

0.047 µF C

To the subdecoder

A12093

20 kΩ

Larger

A12094

• Separation adjustment (pin 19)

The separation is adjusted by modifying the input level to the subdecoder with the variable resistor connected topin 19. Since only the sub-modulation level is changed by changing the variable resistor setting, the monaural(main) output level is not changed. Furthermore, degradation of high band separation in the decoder can be avoidedif the impedance of the external capacitor (C) in the subchannel frequency band (23 to 53 kHz) is made sufficientlysmaller than the variable resistor.

No. 6655-43/54

LA1787M

Fig. 49

++

24

S-meter

32 27

FMS-meter

MRC

6.4 kΩ10 kΩ

30 kΩ

3.6 kΩ 75 pF 1 kΩ

DC buffer

VCC

2 µA

100 Ω

QMRC

C27 VCC

To the SNC, pin 28

Noise amplifierHigh-pass filter with Fc = 70 kHz + amplifier

An external transistor equivalent to the 2SC536 is requiredReason: A QMRC level shifter is required to allow a simplified MRC circuit to be used in the LA1787M.

A11768

6. MRC Circuit

Fig. 50

No. 6655-44/54

LA1787M

+

32

A11769

(1) When there is no AC noise on pin 32V24 = V27–VBE

↑QMRC

V27 is about 2.5 V when the antenna input is 60 dB or higher.

(2) Since the MRC noise amplifier gain is fixed, the MRC circuit is adjusted by reducing the AC input level.

(3) The MRC attack and release are determined by C27 on pin 27.Attack: 7 µA · C27 → 2 µA · C27Release: 500 Ω · C27 → 100 Ω

Notes on the Noise CancelerThe noise canceler characteristics have been improved by implementing the circuit that determines the gate time inlogic. Since the time constant in earlier noise cancelers was determined by an RC circuit such as that shown in figure52, the rise time shown in figure 53 was influenced by the values of the resistor and capacitor used. As a result thenoise exclusion efficiency was reduced by this delay in the rise time. In the LA1787M, this rise time was shortened byimplementing the circuit that determines the gate time in logic, allowing it to reliably exclude noise.

Fig. 51

A11771 A11772

Fig. 52 Fig. 53

No. 6655-45/54

LA1787M

FM

RF

MIX IN 64 pin

1st IF IN 56 pin

2nd IF IN 51 pinANT IN

11 dB 12 dB 18 dB

A11773

Fig. 54

Gain Distribution (FM)This section investigates the gain in each block in the LA1787M when the Sanyo recommended circuits are used.

(Test conditions)Ambient temperature: 26°CAntenna and mixer input frequency: 98.1 MHzFirst and second IF input frequency: 10.7 MHz

The input levels when VSM = 2 V will be as follows.ANT IN: 19 dBµMIX IN: 30 dBµ1st IF IN: 42 dBµ2nd IF IN: 60 dBµ

When the gains for each block are determined according to the above, the results are as follows.RF GAIN: 11 dBMIX GAIN: 12 dB1st IF GAIN: 18 dB

No. 6655-46/54

LA1787M

(AM)This section investigates the gain in each block in the LA1787M when the Sanyo recommended circuits are used.

(Test conditions)Ambient temperature: 26°CAntenna and mixer input frequency: 1 MHzFirst and second mixer input frequency: 10.7 MHzSecond IF input frequency: 450 kHz

The gains at each stage will be as follows.RF Gain (ANT IN-pin62): 17 dB1st MIX Gain (pin62-pin56): 8 dB1st IF Gain (pin55-pin53): 15 dB

AM

RF

RFGain

1st MIXGain

1st IFGain

2nd MIXGain

2nd IFGain

A11774

1st MIX 1st IF 2nd MIX 2nd IF AM DET

Fig. 55

Input Circuits for Each Stage

[FM]• Mixer input • First IF input

No. 6655-47/54

LA1787M

A11775A11776

6250 Ω 0.022 µF

50 Ω

A11778

fr = RF

5250 Ω 0.022 µF

50 Ω

A11780

fr = 450 kHz

4550 Ω 0.022 µF

50 Ω

IFT

A11781

fr = 450 kHz

4950 Ω 0.022 µF

50 Ω

A11779

fr = 10.71 MHz (f2nd osc + 0.45 MHz)

A11777

63

64

75 Ω 0.022 µF

75 Ω

VIN

Actual measurement

5675 Ω 300 Ω 0.022 µF

75 Ω

fr = 10.7 MHz

51

50

75 Ω 300 Ω 0.022 µF

75 Ω 330 Ω

0.022 µF

fr = 10.7 MHz

• IF input

• IF input • Del input

[AM]• First mixer input • Second mixer input

Sample AM tuner Circuit with the LC72144 Used Together

No. 6655-48/54

LA1787M

RFCF CF CF

1st IF

2nd MIX

450K

300 Ω

IF

A11782

LC72144XBUFF

fosc

RFCF CF CF

1st MIX10.71 MHz

2nd OSC 1st OSC

IF

A11783

10.26 MHz

62

10 kΩ

AF

AFRF

CF CF Quadraturedetector

10.7 MHzIF

NC MPXRchLch

59 56 53 49 54 52

31

60

6364

60 56 53 5159

AM 1st IF Step FM IF

1 fOSC 10.25 MHz 10.7 MHz 10 kHz, 11 kHz 10.7 MHz

2 fOSC 10.35 MHz 10.8 MHz 9 kHz, 10 kHz 10.8 MHz

No. 6655-49/54

LA1787M

1 2 3

6 4

3

2

4

1 6

S

3

2

4

1 6

S

S S

3

2

4

1 6

S

[AM Block]AM FILTEER (SA-1051)

AM IF1 (SA-264)

AM OSC (SA-359)

AM IF2 (SA-1063)

3

2

4

1 6

S

3

2

4

1 6

S

AM loading (SA-1062)

0.1ø2UEW

AM RF amplifier (RC875-222J)

AM ANT IN (SA-1048)

3

2

4

1 6

S3

2

4

1 6

S

3

2

4

1 6

S

3

2

48

71 6

A136

S

SC1

C2

[FM Block]FM RF (SA-1060)

FM OSC (SA-1052)

FM ANT (SA-1061)

FM MIX (SA-266)

3

2

4

1 6

S S

FM DET (SA-208)

Crystal Oscillator ElementKinseki, Ltd.

Frequency: 10.26 MHzCL: 20 pFModel No.: HC-49/U-S

Coil SpecificationsSumida Electronics, Ltd.

No. 6655-50/54

LA1787M

1 2 3

6 4

3

2

4

1 6 0.1ø2UEW

3

2

4

1 6 0.05ø3UEW

3

2

4

1 6 0.05ø3UEW

[AM Block]

The Toko Electric Corporation

AM FILTEER (A2861BIS-15327)

AM IF1 (7PSGTC-5001A)

AM OSC (V666SNS-214BY)

AM IF2 (7PSGTC-5002Y)

3

2

4

1 6 0.05ø3UEW

3

2

4

1 6

S

S

AM loading (269ANS-0720Z)

0.1ø2UEW

AM RF amplifier (187LY-222)

AM ANT IN (385BNS-027Z)

3

2

4

1 6 S

S

ø0.1–2UEW

3

2

4

1 6 Sø0.1–2UEW

3

2

4

1 6 Sø0.12–2UEW

3

2 5

4

1 6 S

S

ø0.07–2UEW

[FM Block]FM RF (V666SNS-208AQ)

FM OSC (V666SNS-205APZ)

FM ANT (V666SNS-209BS)

FM MIX (371DH-1108FYH)

3

2

4

1 6 0.07ø2MUEW

FM DET (DM600DEAS-8407GLF)

No. 6655-51/54

LA1787M

1 2 3

6 4

3

2

4

1 6

S

5.1µH

3

2

4

1 6S S

180pF

3

2

4

1 6

S

180pF

[AM Block]

Sagami Elec Co., Ltd.

AM FILTEER (000021055)

AM IF1 (000021057)

AM OSC (000021056)

AM IF2 (000021059)

3

2

4

1 6

S

30mH

3

2

4

1 6

S

100µH

AM loading (000021061)

2.2mH

AM RF amplifier (000021063)

AM ANT IN (000021062)

3

2

4

1 6

S

S3

2

4

1 6

S

105.5nH

3

2

4

1 6

S

62.7nH

3

2 5

4

1 6

1-2 : 100pF2-3 : 100pF

S

S

[FM Block]FM RF (000021064)

FM OSC (000021066)

FM ANT (000021065)

FM MIX (000021067)

3

2

4

1 6

1-3 : 20µH3-4 : 120pF

SS

FM DET (010021075)

Coil Specifications

No. 6655-52/54

LA1787M

Out

put,

nois

e, A

M o

utpu

t, LR

out

put —

dB

HC

C, S

NC

, RF

AG

C, m

utin

g vo

ltage

,S

-met

er v

olta

ge, V S

M—

V


Tot

al h

arm

onic

dis

tort

ion,

TH

D —

%


Out

put,

nois

e —

dB

Out

put,

nois

e, A

M o

utpu

t — d

B

DC

V —

V

Mix

er o

utpu

t — d

Bµ

Input — dBµ Input — dBµ

Mixer input — dBµ

Firs

t IF

out

put —

dBµ

First IF input — dBµ

No. 6655-53/54

LA1787M

–100

–80

–60

–40

–20

0

20

–20 0 20 40 60 80 100 120 140

VCC = 8.5 Vf = 1 MHzmod = 1 k 30%

NOISE

OUT

ANT input, IN — dBµ

AM I/O Characteristics

Out

put,

nois

e —

dB

0

1.0

2.0

3.0

4.0

5.0

7.0

6.0

–20 0 20 40 60 80 100 120 140

VCC = 8.5 Vf = 1 MHz

RF AGC

IF AGC

VSM


AM DC Characteristics

AG

C, S

-met

er v

olta

ge —

V

0

1.0

2.0

3.0

4.0

5.0

7.0

6.0

–20 0 20 40 60 80 100 120 140

VCC = 8.5 Vf = 1 MHzmod = 1 k 30% 80%

fm =

1 k

Hz

80%

fm =

1 k

Hz

30%


AM Distortion

Tot

al h

arm

onic

dis

tort

ion,

TH

D —

%

Firs

t IF

out

put —

dB

Frequency, — MHz

Firs

t IF

out

put —

dB

Ant

enna

inpu

t — d

Bµ

S/N

, AM

out

put —

dB

AG

C o

n, s

epar

atio

n, in

put l

evel

— d

Bµ

Frequency, — MHz

Ambient temperature, Ta — °CAmbient temperature, Ta — °C

Sep

arat

ion,

Sep

— d

B

Ambient temperature, Ta — °C

LA1787M

PS No.6655-54/54

ON Semiconductor and the ON logo are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a numberof patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed atwww.onsemi.com/site/pdf/Patent-Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes nowarranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of theapplication or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidentaldamages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actualperformance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technicalexperts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for useas components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application inwhich the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products forany such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributorsharmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury ordeath associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of thepart. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

–80

–60

–40

–20

0

20

40 60 80 100 120 140

desire mod ON

Δ40 kHz

100 dBμ

80 dBμ60 dBμ40 dBμ

100 dBμ80 dBμ

60 dBμ

40 dBμdesiremodOFF

ANT input, IN — dBμ

AM Second-Channel Interference Rejection Characteristics

Out

put,

nois

e —

dB

50Ω

50Ω 50/3Ω

50/3Ω50/3Ω

30ΩVIN

15pF ANT IN

65pF

JIS ANT. DUMMYfu=1040kHzfm=400Hz 30%

fD=1MHzfm=1kHz 30%

–80

–60

–40

–20

0

20

40 60 80 100 120 140

desire mod ON

Δ400kHz

100 dBμ

80 dBμ60 dBμ40 dBμ

100

dBμ

80 d

Bμ

60 dBμ

40 dBμ

ANT input, IN — dBμ

Out

put,

nois

e —

dB

desiremodOFF

50Ω

50Ω 50/3Ω

50/3Ω50/3Ω

30ΩVIN

15pF ANT IN

65pF

JIS ANT. DUMMYfu = 1400 kHzfm = 400 Hz 30%

fD = 1 MHzfm = 1 kHz 30%

AM Second-Channel Interference Rejection Characteristics

ON Semiconductor · SD sensitivity SD-sen1 AM 1 MHz, the ANT input level such that the IF counter...

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