electronic-devices-9th-edition-by-floyd pp19a

39
© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Electronic Devices Ninth Edition Floyd Chapter 19

Transcript of electronic-devices-9th-edition-by-floyd pp19a

Page 1: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

Electronic DevicesNinth Edition

Floyd

Chapter 19

Page 2: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

Modulation

Modulation is the process of converting a signal containing information to a form suitable for transmission from a transmitter to a receiver. Circuits designed for this conversion are called modulators.

SummarySummary

Audio signals are far too low in frequency for direct radio transmission. The signal is impressed onto a carrier, which is a high-frequency wave called RF (for radio-frequency) that can be radiated from an antenna.

Page 3: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

Amplitude Modulation

Amplitude modulation (AM) is the process of varying the amplitude of the carrier with the information signal such that the carrier amplitude varies in the same way as the information.

SummarySummary

Amplitudemodulatedenvelope CarrierFor an AM radio station, the

carrier is the assigned frequency for that station. The commercial AM broadcast band extends from 535 kHz to 1605 kHz and each station has a 10 kHz bandwidth (with some exceptions).

Page 4: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

AM Radio Receiver

SummarySummary

The receiver recovers the audio signal from the modulated carrier. Since the early 1920’s all receivers convert signals from various stations to a single intermediate frequency (IF).The IF amplifier is optimized for this frequency and contributes most of the gain for the receiver. This greatly simplified tuning different stations.

540 kHz–1640 kHzelectromagnetic waves

Soundwaves

Localoscillator,

LO

455 kHzmodulated IF

Audio modulatedcarrier fc

455 kHz modulatedIF amplified Amplified

audio

Audio

Tuned to fc

fc + 455 kHz

Audio andpower

amplifiersDetectorMixerRF

amplifierIF

amplifier

Page 5: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

AM Radio Receiver

SummarySummary

The idea for the IF amplifier is credited to Edward Armstrong, in 1918. This concept is what defines a superheterodyne receiver. He was credited with numerous inventions for radio and held 42 patents.

540 kHz–1640 kHzelectromagnetic waves

Soundwaves

Localoscillator,

LO

455 kHzmodulated IF

Audio modulatedcarrier fc

455 kHz modulatedIF amplified Amplified

audio

Audio

Tuned to fc

fc + 455 kHz

Audio andpower

amplifiersDetectorMixerRF

amplifierIF

amplifier

Page 6: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

Frequency Modulation

In frequency modulation (FM), the modulating signal, which carries information, varies the instantaneous frequency of the carrier signal. The amplitude of the frequency modulated signal remains fixed.

The assigned frequencies for FM broadcasting is between 88 and 108 MHz. NTSC television also uses FM for the audio portion of the TV signal, which is transmitted just above the video signal within the channel.

SummarySummary

Modulating signal

Frequency-modulated carrier

Page 7: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

FM Radio Receiver

The superheterodyne FM receiver has many of the same blocks as the AM receiver. The main difference is the manner of recovering the signal. The FM receiver uses a discriminator (or phase-locked loop) rather than a detector to recover the modulating signal. Note that the IF frequency is 10.7 MHz, but some receivers use double-conversion to 455 kHz.

SummarySummary

De-emphasisnetwork

DiscriminatorLimiter

88 MHz–108 MHzelectromagneticwaves

Audio

MixerRFamplifier

IFamplifier

10.7 MHz FMFM fc

fc + 10.7 MHz

Localoscillator

Audio andpower

amplifiersSound

10.7 MHzAmplified FM

10.7 MHzLimited FM

Compensatedaudio

Amplifiedaudio

Page 8: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

The Linear Multiplier

A linear multiplier generates the scaled product of two input voltages. A two-quadrant multiplier has only positive outputs whereas a four-quadrant multiplier can accept either polarity.

SummarySummary

V OU

T, ou

tput

vol

tage

(vol

ts)

+10

+8.0

+6.0

+4.0

+2.0

0

–2.0

–4.0

–6.0

–8.0

–10–10 –8.0 –6.0 –4.0 –2.0 0 +2.0 +4.0 +6.0 +8.0 +10

VX, input voltage (volts)

+

K = 110

V Y= +10 V

VY= +6.0 V

VY = +2.0 V

VY = 0 VVY = –2.0 V

VY = – 6.0 VV

Y = –10 V

KXYXYThe transfer curve for a four-

quadrant multiplier is shown. On the transfer curve, one input is along the x-axis, the other is represented by the blue lines. The output is the product multiplied by a scale factor, K and is read on the y-axis.

Transfer curve

Page 9: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

The Linear Multiplier

SummarySummary

V OU

T, ou

tput

vol

tage

(vol

ts)

+10

+8.0

+6.0

+4.0

+2.0

0

–2.0

–4.0

–6.0

–8.0

–10–10 –8.0 –6.0 –4.0 –2.0 0 +2.0 +4.0 +6.0 +8.0 +10

VX, input voltage (volts)

+

K = 110

V Y= +10 V

VY= +6.0 V

VY = +2.0 V

VY = 0 VVY = –2.0 V

VY = – 6.0 VV

Y = –10 V

KXYXY

Transfer curve

From the transfer curve, what is VOUT when Vx = +6 V and Vy = 8 V?

See red lines for the inputs and the green line for the output, which is 4.8 V. This is the product of the inputs and the scale factor of 1/10.

Page 10: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Applications for linear multipliers include modulators and phase detectors in communication systems as well as processing circuits such as these.

V KV2V

KVX

XVV

YY

R2

R1

VX

KVYVOUT

0 V

VY

VOUT= –VXVY

+

I2

I1

R2

R1

VX

KVOUT

0 V VOUT= VX

+

I2

I1

2

Multiplier Squaring circuit

Square root circuitDivide circuit

1. 2.

3. 4.

The Linear Multiplier

Page 11: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Amplitude modulation is a multiplication process, so the linear multiplier is ideally suited as a modulator.

Amplitude Modulation

Amplitudemodulator

Carrier signal

Modulating signal

fc

fm

fout

If the gain of the carrier frequency is made to vary sinusoidally at a certain frequency, the output will vary with the shape of the sinusoidal signal.

Page 12: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Recall from basic studies that a sinusoidal voltage can be expressed as v = Vpsin 2ft. If you multiply two sinusoidal voltages of different frequencies together, the result is the product of two sine terms:

Amplitude Modulation

1 2 1( ) 2( ) 1 2(sin 2π )(sin 2π )p pv v V V f t f t

A trigonometric identity for the product of two sinusoidal functions is(sin A)(sin B) = ½ [cos (A – B) – cos (A + B)]

By applying this identity to the equation for v1v2, the following result is obtained.

1( ) 2( ) 1( ) 2( )1 2 1 2 1 2cos 2π( ) cos 2π( )

2 2p p p pV V V V

v v f f t f f t

Page 13: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

The equation on the previous slide (equation 19-2) illustrates an important idea. The product of two frequencies creates two new frequencies, which are the difference frequency and the sum frequency of f1 and f2.

Amplitude Modulation

f

f

1

f1 f1

2

f2 f2f

When the two frequencies have the same amplitude, the difference and sum frequencies are ½ this amount.

Page 14: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Amplitude Modulation

1( ) 2( ) 1( ) 2( )1 2 1 2 1 2cos 2π( ) cos 2π( )

2 2p p p pV V V V

v v f f t f f t

From the equation for the product of two sine waves, what is the relative amplitude of the output signals if f1 = ½ f2?

f

f

1

f1 f1

2

f2 f2f

1( ) 2( )

2p pV V

Let V2(p) = 1; then V1(p) = ½. The amplitude of each output

is given by:

Substituting, 1

1( ) 2( ) 2 12 2 4

1p pV V

The outputs are ¼ the size of V2(p).

Page 15: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Amplitude Modulation

For communication systems, there are several different types of modulators available. Balanced modulators multiply the carrier signal, fc, and the modulating signal, fm, together, resulting in only sidebands in the output spectrum. If there is no modulating signal, there is no output.This is called double sideband suppressed carrier modulation. As in other cases, a sine wave modulating signal is assumed.

Suppressed carrier modulation is efficient, but it is not used in commercial radio broadcasting. One problem is that the receiver must insert the missing carrier at the correct frequency to avoid distortion.

fm fmfc ff ccf

Page 16: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Amplitude Modulation

In standard amplitude modulation, the carrier is added to the signal before transmission. A dc level representing the carrier peak is added to the signal.

This is called double sideband full carrier modulation. The spectrum in the yellow box represents 100% modulation by a sine wave.

Vc(p)

Vm(p)sin 2fmt.

Vc(p)sin 2fct.

V c(p) + Vm(p)sin 2fmt.

The output will have a carrier term, as given in Equation 19-3.

fm fmfc ff ccf

output

Page 17: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Amplitude Modulation

The line spectrum shown on the previous slide represents a sine wave because it is a pure frequency. With music and voice, the spectrum is no longer lines but varies according to the information being transmitted. The green boxes represent the limits to the spectrum for a commercial AM station.In general, commercial stations are restricted to ±5 kHz on either side of fc to avoid interference with other stations. f f +5 kHzf 5 kHz c cc

f

Page 18: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

AM Mixer and Demodulator

The receiver mixes the incoming RF signal local oscillator in a mixer (linear multiplier) to produce the IF. After mixing, the original modulation signal can be recovered using a linear multiplier followed by a low-pass filter.

IF

0

Low-passfilter

Audio modulated IFAudio

Filter responsef

Page 19: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

IF Amplifier

The IF amplifier is a tuned-resonant amplifier. The resonant frequency is 455 kHz for AM radios, which is less than the RF to insure there is no interference from the input signal.

450455460f (kHz)

IF

An IF amplifier passes only the signals of interest because it has a relatively narrow bandwidth (10 kHz) that is the same bandwidth as broadcast stations; further it is less prone to oscillate than RF amplifiers.

Page 20: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Audio Amplifier

After detection, the signal is amplified by an audio amplifier. One popular audio amplifier in IC form is the LM386. A typical low-power amplifier is shown.

10 C20.1 mF

mFmF

mF

R2–

+

1.0 k

Input fromdetector

R110 kW W

W

C1

1

Volumecontrol

C30.0022

C4+ 9 V

LM386

C510

C60.047

R3

47

C7

220

(1)(6)

(2)

(3) (7)

(4)

(8)(5)

mF

mF mF

Page 21: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Frequency Modulation

In an FM signal, the carrier frequency is increased or decreased by the modulating signal. FM signals are less susceptible to noise because most noise changes the amplitude of the signal.

FM modulators often use a varactor diode to change the frequency according to the modulating signal. A varactor diode VCO is shown in which Vm modifies the resonant frequency.

VFM

Vm

+

Page 22: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Frequency Modulation

In applications where the frequency deviation is smaller (such as mobile FM radios), a crystal-controlled modulator can be used. The varactor can still modify the output frequency of the modulator.The varactor is reverse-biased by R1 and R2. Positive alterations of Vm increase the reverse bias.

+VCC

RER2

C

C

4

3

C C1 2

VFM

Vm

XTAL

R1

Varactordiode

RFC

RFC

RFC

Does a positive alteration increase or decrease the frequency?An increase in reverse-bias will decrease C and increase frequency.

Page 23: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

The Phase-Locked Loop

The phase-locked loop is used extensively in communication systems as an FM modulator, demodulator, frequency generation and multiplication. It is feedback circuit consisting of a phase-detector, a low-pass filter, and a VCO.

Vifi

Output is proportional tophase difference of Vi and Vo.Phase

detectorθ

Low-passfilter

Voltage-controlledoscillator

VCO

Vo fo

The phase detector is a linear multiplier and therefore the output contains the sum and difference frequencies between Vi and Vo. The low-pass filter sends the difference frequency back to the VCO as a control voltage.

Page 24: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

The Phase-Locked Loop

PLLs are characterized by a lock range and a capture range.

Lock range, f lock

Capture range, fcap

f0

A popular PLL is the LM565. The basic VCO frequency is set by external components and is given by

The lock range is the range of frequencies over which the PLL can track the incoming frequency. The capture range is the range of frequencies over which the PLL can acquire lock.

(3)

(5)(4)

(7)(2)

(1)(9)(8)

(10)

–V

(6)

+V

LM565

Diff inputs Output

Phase comparatorinput

VCO output

Ref output

Low-pass filter

3.6 kW

R1C1

C2

VCO

Phasedetector Amplifier

01 1

1.24

fR C

Page 25: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

The Phase-Locked Loop

As an FM demodulator, the VCO input on the PLL is compared to the IF, which is a frequency modulated signal. As the IF deviates from the center frequency, the voltage on the VCO control line varies in proportion to the IF changes, forming the demodulated output.

(7)(2)

(1)(9)(8)

FM input Demodulated output(10)

–V

R1

(3)

(5)

(4)

(6)

+V

C1

C2

LM565

Page 26: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

SummarySummary

Fiber Optics

Fiber optic cables transmit light rather than electrical pulses. Light can be transmitted in the cable with extremely low loss because of a phenomena known as total internal reflection. In recent years, fiber optic cables have replaced many miles of copper wire for phone lines, cable TV, industrial plants, and other large communication systems.

Signalsource User

Electricalto light

conversion

Transmitter

Fiber optic cable

Receiver

Opticalconnector

Light toelectrical

conversion

Opticalconnector

Page 27: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

Selected Key TermsSelected Key Terms

Amplitude modulation

Frequency modulation

Four-quadrant multiplier

A communication method in which a lower frequency signal modulates (varies) the amplitude of a higher frequency signal (carrier).

A communication method in which a lower frequency intelligence-carrying signal modulates (varies) the frequency of a higher frequency signal.

A linear device that produces an output voltage proportional to the product of two input voltages.

Page 28: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

Selected Key TermsSelected Key Terms

Phase-locked loop (PLL)

Lock range

Capture range

Fiber optics

A device for locking onto and tracking the frequency of an incoming signal.

The range of frequencies over which a PLL can maintain lock.

The range of frequencies over which a PLL can acquire lock.

The use of light for the transmission of information through tiny fiber cables.

Page 29: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

1. The normal bandwidth of commercial AM radio stations is

a. 5 kHz

b. 10 kHz

c. 20 kHz

d. 455 kHz

Page 30: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

2. The IF amplifier in an AM superheterodyne receiver has a bandwidth of

a. 5 kHz

b. 10 kHz

c. 100 kHz

d. 455 kHz

Page 31: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

3. In a FM signal, amplitude variations in the transmitted signal

a. depend on the amplitude of fm

b. depend on the frequency of fm

c. both of the above

d. none of the above

Page 32: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

4. The plot shows the inputs and output for a four-quadrant multiplier. This is called the

a. transfer curve

b. response curve

c. product curve

d. load response V OU

T, ou

tput

vol

tage

(vol

ts)

+10

+8.0

+6.0

+4.0

+2.0

0

–2.0

–4.0

–6.0

–8.0

–10–10 –8.0 –6.0 –4.0 –2.0 0 +2.0 +4.0 +6.0 +8.0 +10

VX, input voltage (volts)

+

K = 110

V Y= +10 V

VY= +6.0 V

VY = +2.0 V

VY = 0 VVY = –2.0 V

VY = – 6.0 VV

Y = –10 V

KXYXY

Page 33: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

5. There are two inputs to the circuit, VX and VY. With proper scaling of the resistors, the output can represent

a. – (VX + VY)

b. – (VX – VY)

c. – (VX VY )

d. – (VX / VY )

R2

R1

VX

VY

VOUT

+

Page 34: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

6. Amplitude modulation is a

a. summing process

b. multiplication process

c. squaring process

d. division process

Page 35: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

7. The spectrum shown shows a carrier that is modulated by

a. a sine wave

b. a square wave

c. a triangle wave

d. voice and musicfm fmfc ff cc

f

Page 36: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

8. The circuit shown is

a. an FM modulator

b. an AM modulator

c. a VCO

d. a mixer

+VCC

RER2

C

C

4

3

C C1 2

VFM

Vm

XTAL

R1

Varactordiode

RFC

RFC

RFC

Page 37: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

9. The block diagram represents a phase-locked loop. The yellow box represents a

a. low-pass filter

b. VCO

c. phase detector

d. input amplifier

OutputInput

Page 38: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

10. A phase-locked loop can be used as a

a. FM modulator

b. FM demodulator

c. frequency generator

d. all of the above

Page 39: electronic-devices-9th-edition-by-floyd pp19a

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Electronic Devices, 9th editionThomas L. Floyd

QuizQuiz

Answers:

1. b

2. b

3. d

4. a

5. d

6. b

7. a

8. a

9. c

10. d