12-Bit, 210 MSPS TxDAC Digital-to-Analog Converter

Data Sheet AD9742

Rev. C Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

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FEATURES High performance member of pin-compatible TxDAC

product family Excellent spurious-free dynamic range performance SNR at 5 MHz output, 125 MSPS: 70 dB Twos complement or straight binary data format Differential current outputs: 2 mA to 20 mA Power dissipation: 135 mW at 3.3 V Power-down mode: 15 mW at 3.3 V On-chip 1.2 V Reference CMOS compatible digital interface 28-lead SOIC, 28-lead TSSOP, and 32-lead LFCSP Edge-triggered latches

APPLICATIONS Wideband communication transmit channel:

Direct IF Base stations Wireless local loops Digital radio links Direct digital synthesis (DDS)

Instrumentation

FUNCTIONAL BLOCK DIAGRAM

1.2V REFREFLO

3.3VRSET

0.1µF

CLOCK

SLEEP 0291

3-B-

001

REFIOFS ADJ

DVDD

DCOM

CLOCK

DIGITAL DATA INPUTS (DB11–DB0)

150pF

3.3V

AVDD ACOM

AD9742CURRENTSOURCEARRAY

IOUTA

IOUTB

MODE

LSBSWITCHES

SEGMENTEDSWITCHES

LATCHES

Figure 1.

GENERAL DESCRIPTION The AD97421 is a 12-bit resolution, wideband, third generation member of the TxDAC series of high performance, low power CMOS digital-to-analog converters (DACs). The TxDAC family, consisting of pin-compatible 8-, 10-, 12-, and 14-bit DACs, is specifically optimized for the transmit signal path of communication systems. All of the devices share the same interface options, small outline package, and pinout, providing an upward or downward component selection path based on performance, resolution, and cost. The AD9742 offers exceptional ac and dc performance while supporting update rates up to 210 MSPS.

The AD9742’s low power dissipation makes it well suited for portable and low power applications. Its power dissipation can be further reduced to a mere 60 mW with a slight degradation in performance by lowering the full-scale current output. Also, a power-down mode reduces the standby power dissipation to approximately 15 mW. A segmented current source architecture is combined with a proprietary switching technique to reduce spurious components and enhance dynamic performance.

Edge-triggered input latches and a 1.2 V temperature compensated band gap reference have been integrated to provide a complete monolithic DAC solution. The digital inputs support 3 V CMOS logic families.

PRODUCT HIGHLIGHTS 1. The AD9742 is the 12-bit member of the pin-compatible

TxDAC family, which offers excellent INL and DNL performance.

2. Data input supports twos complement or straight binary data coding.

3. High speed, single-ended CMOS clock input supports 210 MSPS conversion rate.

4. Low power: Complete CMOS DAC function operates on 135 mW from a 2.7 V to 3.6 V single supply. The DAC full-scale current can be reduced for lower power operation, and a sleep mode is provided for low power idle periods.

5. On-chip voltage reference: The AD9742 includes a 1.2 V temperature compensated band gap voltage reference.

6. Industry-standard 28-lead SOIC, 28-lead TSSOP, and 32-lead LFCSP packages.

1 Protected by U.S. Patent Numbers: 5,568,145; 5,689,257; and 5,703,519.

AD9742* PRODUCT PAGE QUICK LINKSLast Content Update: 02/23/2017

COMPARABLE PARTSView a parametric search of comparable parts.

EVALUATION KITS• AD9742 Evaluation Board

DOCUMENTATIONApplication Notes

• AN-237: Choosing DACs for Direct Digital Synthesis

• AN-302: Exploit Digital Advantages in an SSB Receiver

• AN-320A: CMOS Multiplying DACs and Op Amps Combine to Build Programmable Gain Amplifier, Part 1

• AN-595: Understanding Pin Compatibility in the TxDAC® Line of High Speed D/A Converters

• AN-642: Coupling a Single-Ended Clock Source to the Differential Clock Input of Third-Generation TxDAC® and TxDAC+® Products

• AN-912: Driving a Center-Tapped Transformer with a Balanced Current-Output DAC

Data Sheet

• AD9742: 12-Bit, 210 MSPS TxDAC Digital-to-Analog Converter Data Sheet

TOOLS AND SIMULATIONS• AD9742 IBIS Models

REFERENCE MATERIALSInformational

• Advantiv™ Advanced TV Solutions

Solutions Bulletins & Brochures

• Digital to Analog Converters ICs Solutions Bulletin

DESIGN RESOURCES• AD9742 Material Declaration

• PCN-PDN Information

• Quality And Reliability

• Symbols and Footprints

DISCUSSIONSView all AD9742 EngineerZone Discussions.

SAMPLE AND BUYVisit the product page to see pricing options.

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AD9742 Data Sheet

Rev. C | Page 2 of 32

TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications ..................................................................................... 3

DC Specifications ......................................................................... 3 Dynamic Specifications ............................................................... 4 Digital Specifications ................................................................... 5

Absolute Maximum Ratings ............................................................ 6 Thermal Resistance ...................................................................... 6 ESD Caution .................................................................................. 6

Pin Configurations and Function Descriptions ........................... 7 Typical Performance Characteristics ............................................. 8 Terminology .................................................................................... 11 Functional Description .................................................................. 12

Reference Operation .................................................................. 12

Reference Control Amplifier .................................................... 13 DAC Transfer Function ............................................................. 13 Analog Outputs .......................................................................... 13 Digital Inputs .............................................................................. 14 Clock Input.................................................................................. 14 DAC Timing ................................................................................ 15 Power Dissipation....................................................................... 15 Applying the AD9742 ................................................................ 16 Differential Coupling Using a Transformer ............................... 16 Differential Coupling Using an Op Amp ................................ 16 Single-Ended, Unbuffered Voltage Output ............................. 17 Single-Ended, Buffered Voltage Output Configuration ........ 17 Power and Grounding Considerations, Power Supply Rejection ...................................................................................... 17

Evaluation Board ............................................................................ 19 General Description ................................................................... 19

Outline Dimensions ....................................................................... 29 Ordering Guide .......................................................................... 30

REVISION HISTORY 2/13—Rev. B to Rev. C Updated Format .................................................................. Universal Changes to Figure 4 and Table 6 ..................................................... 7 Moved Terminology Section ......................................................... 11 Updated Outline Dimensions ....................................................... 29 Changes to Ordering Guide .......................................................... 30 6/04—Rev. A to Rev. B Changes to the Title, General Description, and Product Highlights .......................................................................................... 1 Changes to Dynamic Specifications ............................................... 4 Changes to Figure 6 and Figure 10 ................................................. 9 Changes to Figure 12 to Figure 15 ................................................ 10 Changes to the Functional Description Section ......................... 12 Changes to the Digital Inputs Section ......................................... 14 Changes to Figure 29 ...................................................................... 15 Changes to Figure 30 ...................................................................... 16

5/03—Rev. 0 to Rev. A Added 32-Lead LFCSP Package ....................................... Universal Edits to Features and Product Highlights ...................................... 1 Edits to DC Specifications ................................................................ 2 Edits to Dynamic Specifications ...................................................... 3 Edits to Digital Specifications .......................................................... 4 Edits to Absolute Maximum Ratings, Thermal Characteristics, and Ordering Guide .......................................................................... 5 Edits to Pin Configuration and Pin Function Descriptions ........ 6 Edits to Figure 2 ................................................................................. 7 Replaced TPCs 1, 4, 7, and 8 ............................................................ 8 Edits to Figure 3 and Functional Description Section .............. 10 Added Clock Input Section and Figure 7 .................................... 12 Edits to DAC Timing Section ....................................................... 12 Edits to Sleep Mode Operation Section and Power Dissipation Section .............................................................................................. 13 Renumbered Figure 8 to Figure 26............................................... 13 Added Figure 11 ............................................................................. 13 Added Figure 27 to Figure 35 ....................................................... 21 Updated Outline Dimensions ....................................................... 26 5/02—Revision 0: Initial Version

Data Sheet AD9742

Rev. C | Page 3 of 32

SPECIFICATIONS DC SPECIFICATIONS TMIN to TMAX, AVDD = 3.3 V, DVDD = 3.3 V, CLKVDD = 3.3 V, IOUTFS = 20 mA, unless otherwise noted.

Table 1. Parameter Min Typ Max Unit RESOLUTION 12 Bits DC ACCURACY1

Integral Linearity Error (INL) −2.5 ±0.5 +2.5 LSB Differential Nonlinearity (DNL) −1.3 ±0.4 +1.3 LSB

ANALOG OUTPUT Offset Error −0.02 +0.02 % of FSR Gain Error (Without Internal Reference) −0.5 ±0.1 +0.5 % of FSR Gain Error (With Internal Reference) −0.5 ±0.1 +0.5 % of FSR Full-Scale Output Current2 2 20 mA Output Compliance Range −1 +1.25 V Output Resistance 100 kΩ Output Capacitance 5 pF

REFERENCE OUTPUT Reference Voltage 1.14 1.20 1.26 V Reference Output Current3 100 nA

REFERENCE INPUT Input Compliance Range 0.1 1.25 V Reference Input Resistance (Ext. Reference) 1 MΩ Small Signal Bandwidth 0.5 MHz

TEMPERATURE COEFFICIENTS Offset Drift 0 ppm of FSR/°C Gain Drift (Without Internal Reference) ±50 ppm of FSR/°C Gain Drift (With Internal Reference) ±100 ppm of FSR/°C Reference Voltage Drift ±50 ppm/°C

POWER SUPPLY Supply Voltages

AVDD 2.7 3.3 3.6 V DVDD 2.7 3.3 3.6 V CLKVDD 2.7 3.3 3.6 V

Analog Supply Current (IAVDD) 33 36 mA Digital Supply Current (IDVDD)4 8 9 mA Clock Supply Current (ICLKVDD) 5 6 mA Supply Current Sleep Mode (IAVDD) 5 6 mA Power Dissipation4 135 145 mW Power Dissipation5 145 mW Power Supply Rejection Ratio—AVDD6 −1 +1 % of FSR/V Power Supply Rejection Ratio—DVDD6 −0.04 +0.04 % of FSR/V

OPERATING RANGE −40 +85 °C 1 Measured at IOUTA, driving a virtual ground. 2 Nominal full-scale current, IOUTFS, is 32 times the IREF current. 3 An external buffer amplifier with input bias current <100 nA should be used to drive any external load. 4 Measured at fCLOCK = 25 MSPS and fOUT = 1 MHz. 5 Measured as unbuffered voltage output with IOUTFS = 20 mA and 50 Ω RLOAD at IOUTA and IOUTB, fCLOCK = 100 MSPS and fOUT = 40 MHz. 6 ±5% power supply variation.

AD9742 Data Sheet

Rev. C | Page 4 of 32

DYNAMIC SPECIFICATIONS TMIN to TMAX, AVDD = 3.3 V, DVDD = 3.3 V, CLKVDD = 3.3 V, IOUTFS = 20 mA, differential transformer coupled output, 50 Ω doubly terminated, unless otherwise noted.

Table 2. Parameter Min Typ Max Unit DYNAMIC PERFORMANCE

Maximum Output Update Rate (fCLOCK) 210 MSPS Output Settling Time (tST) (to 0.1%)1 11 ns Output Propagation Delay (tPD) 1 ns Glitch Impulse 5 pV-sec Output Rise Time (10% to 90%)1 2.5 ns Output Fall Time (10% to 90%)1 2.5 ns Output Noise (IOUTFS = 20 mA)2 50 pA/√Hz Output Noise (IOUTFS = 2 mA)2 30 pA/√Hz Noise Spectral Density3 −152 dBm/Hz

AC LINEARITY Spurious-Free Dynamic Range to Nyquist

fCLOCK = 25 MSPS; fOUT = 1.00 MHz 0 dBFS Output 74 84 dBc −6 dBFS Output 85 dBc −12 dBFS Output 82 dBc −18 dBFS Output 76 dBc

fCLOCK = 65 MSPS; fOUT = 1.00 MHz 85 dBc fCLOCK = 65 MSPS; fOUT = 2.51 MHz 83 dBc fCLOCK = 65 MSPS; fOUT = 10 MHz 80 dBc fCLOCK = 65 MSPS; fOUT = 15 MHz 75 dBc fCLOCK = 65 MSPS; fOUT = 25 MHz 74 dBc fCLOCK = 165 MSPS; fOUT = 21 MHz 72 dBc fCLOCK = 165 MSPS; fOUT = 41 MHz 60 dBc fCLOCK = 210 MSPS; fOUT = 40 MHz 67 dBc fCLOCK = 210 MSPS; fOUT = 69 MHz 60 dBc

Spurious-Free Dynamic Range within a Window fCLOCK = 25 MSPS; fOUT = 1.00 MHz; 2 MHz Span 80 dBc fCLOCK = 50 MSPS; fOUT = 5.02 MHz; 2 MHz Span 90 dBc fCLOCK = 65 MSPS; fOUT = 5.03 MHz; 2.5 MHz Span 90 dBc fCLOCK = 125 MSPS; fOUT = 5.04 MHz; 4 MHz Span 90 dBc

Total Harmonic Distortion fCLOCK = 25 MSPS; fOUT = 1.00 MHz −82 −74 dBc fCLOCK = 50 MSPS; fOUT = 2.00 MHz −77 dBc fCLOCK = 65 MSPS; fOUT = 2.00 MHz −77 dBc fCLOCK = 125 MSPS; fOUT = 2.00 MHz −77 dBc

Signal-to-Noise Ratio fCLOCK = 65 MSPS; fOUT = 5 MHz; IOUTFS = 20 mA 78 dB fCLOCK = 65 MSPS; fOUT = 5 MHz; IOUTFS = 5 mA 86 dB fCLOCK = 125 MSPS; fOUT = 5 MHz; IOUTFS = 20 mA 73 dB fCLOCK = 125 MSPS; fOUT = 5 MHz; IOUTFS = 5 mA 78 dB fCLOCK = 165 MSPS; fOUT = 5 MHz; IOUTFS = 20 mA 69 dB fCLOCK = 165 MSPS; fOUT = 5 MHz; IOUTFS = 5 mA 71 dB fCLOCK = 210 MSPS; fOUT = 5 MHz; IOUTFS = 20 mA 69 dB fCLOCK = 210 MSPS; fOUT = 5 MHz; IOUTFS = 5 mA 66 dB

Data Sheet AD9742

Rev. C | Page 5 of 32

Parameter Min Typ Max Unit Multitone Power Ratio (8 Tones at 400 kHz Spacing)

fCLOCK = 78 MSPS; fOUT = 15.0 MHz to 18.2 MHz 0 dBFS Output 65 dBc −6 dBFS Output 67 dBc −12 dBFS Output 65 dBc −18 dBFS Output 63 dBc

1 Measured single-ended into 50 Ω load. 2 Output noise is measured with a full-scale output set to 20 mA with no conversion activity. It is a measure of the thermal noise only. 3 Noise spectral density is the average noise power normalized to a 1 Hz bandwidth, with the DAC converting and producing an output tone.

DIGITAL SPECIFICATIONS TMIN to TMAX, AVDD = 3.3 V, DVDD = 3.3 V, CLKVDD = 3.3 V, IOUTFS = 20 mA, unless otherwise noted.

Table 3. Parameter Min Typ Max Unit DIGITAL INPUTS1

Logic 1 Voltage 2.1 3 V Logic 0 Voltage 0 0.9 V Logic 1 Current −10 +10 µA Logic 0 Current −10 +10 µA Input Capacitance 5 pF Input Setup Time (tS) 2.0 ns Input Hold Time (tH) 1.5 ns Latch Pulse Width (tLPW) 1.5 ns

CLK INPUTS2 Input Voltage Range 0 3 V Common-Mode Voltage 0.75 1.5 2.25 V Differential Voltage 0.5 1.5 V

1 Includes CLOCK pin on SOIC/TSSOP packages and CLK+ pin on LFCSP package in single-ended clock input mode. 2 Applicable to CLK+ and CLK− inputs when configured for differential or PECL clock input mode.

0.1%0.1%

tS tH

tPD

DB0–DB11

CLOCK

IOUTAOR

IOUTB

0291

2-B-

002

tLPW

tST

Figure 2. Timing Diagram

AD9742 Data Sheet

Rev. C | Page 6 of 32

ABSOLUTE MAXIMUM RATINGS Table 4.

Parameter With Respect to Min Max Unit

AVDD ACOM −0.3 +3.9 V DVDD DCOM −0.3 +3.9 V CLKVDD CLKCOM −0.3 +3.9 V ACOM DCOM −0.3 +0.3 V ACOM CLKCOM −0.3 +0.3 V DCOM CLKCOM −0.3 +0.3 V AVDD DVDD −3.9 +3.9 V AVDD CLKVDD −3.9 +3.9 V DVDD CLKVDD −3.9 +3.9 V CLOCK, SLEEP DCOM −0.3 DVDD + 0.3 V Digital Inputs, MODE DCOM −0.3 DVDD + 0.3 V IOUTA, IOUTB ACOM −1.0 AVDD + 0.3 V REFIO, REFLO, FS ADJ ACOM −0.3 AVDD + 0.3 V CLK+, CLK−, MODE CLKCOM −0.3 CLKVDD + 0.3 V Junction Temperature 150 °C Storage Temperature −65 +150 °C Lead Temperature

(10 sec) 300 °C

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

THERMAL RESISTANCE Thermal impedance measurements were taken on a 4-layer board in still air, in accordance with EIA/JESD51-7.

Table 5. Thermal Resistance Package Type θJA Unit 28-Lead SOIC 55.9 °C/W 28-Lead TSSOP 67.7 °C/W 32-Lead LFCSP 32.5 °C/W

ESD CAUTION

Data Sheet AD9742

Rev. C | Page 7 of 32

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

14

13

12

11

17

16

15

20

19

18

10

9

8

1

2

3

4

7

6

5

28

27

26

25

24

23

22

21

NC = NO CONNECT

DB7

DB6

DB5

DB4

DB3

DB2

DB1

(LSB) DB0

NC

NC

CLOCK

DVDD

DCOM

MODE

AVDD

RESERVED

IOUTA

IOUTB

ACOM

NC

FS ADJ

REFIO

REFLO

SLEEP

DB8

DB9

DB10

(MSB) DB11

0291

2-B

-003

AD9742TOP VIEW

(Not to Scale)

Figure 3. 28-Lead SOIC and 28-Lead TSSOP Pin Configuration

24 FS ADJ23 REFIO22 ACOM21 IOUTA

DB5 1DB4 2

DVDD 3

20 IOUTB19 ACOM18 AVDD17 AVDD

DB3 4DB2 5DB1 6

(LSB) DB0 7NC 8

AD9742TOP VIEW

(Not to Scale)

PIN 1INDICATOR

0291

2-00

4

NOTES1. NC = NO CONNECT.2. IT IS RECOMMENDED THAT THE EXPOSED PAD BE THERMALLY CONNECTED TO A COPPER GROUND PLANE FOR ENHANCED ELECTRICAL

AND THERMAL PERFORMANCE.

NC

9

DC

OM

10

CLK

VDD

11

CLK

+ 12

CLK

– 13

CLK

CO

M 1

4C

MO

DE

15M

OD

E 16

32 D

B6

31 D

B7

30 D

B8

29 D

B9

27 D

B11

(MSB

)26

DC

OM

25 S

LEEP

28 D

B10

Figure 4. 32-Lead LFCSP Pin Configuration

Table 6. Pin Function Descriptions (N/A = Not Applicable) SOIC/TSSOP Pin No.

LFCSP Pin No. Mnemonic Description

1 27 DB11 Most Significant Data Bit (MSB). 2 to 11 28 to 32,

1, 2, 4 to 6 DB10 to DB1 Data Bits 10 to 1.

12 7 DB0 Least Significant Data Bit (LSB). 13, 14 8, 9 NC No Internal Connection. 15 25 SLEEP Power-Down Control Input. Active high. Contains active pull-down circuit; it may be left

unterminated if not used. 16 N/A REFLO Reference Ground when Internal 1.2 V Reference Used. Connect to AVDD to disable internal

reference. 17 23 REFIO Reference Input/Output. Serves as reference input when internal reference disabled (that is, tie

REFLO to AVDD). Serves as 1.2 V reference output when internal reference activated (that is, tie REFLO to ACOM). Requires 0.1 µF capacitor to ACOM when internal reference activated.

18 24 FS ADJ Full-Scale Current Output Adjust. 19 N/A NC No Internal Connection. 20 19, 22 ACOM Analog Common. 21 20 IOUTB Complementary DAC Current Output. Full-scale current when all data bits are 0s. 22 21 IOUTA DAC Current Output. Full-scale current when all data bits are 1s. 23 N/A RESERVED Reserved. Do not connect to common or supply. 24 17, 18 AVDD Analog Supply Voltage (3.3 V). 25 16 MODE Selects Input Data Format. Connect to DCOM for straight binary, DVDD for twos complement. N/A 15 CMODE Clock Mode Selection. Connect to CLKCOM for single-ended clock receiver (drive CLK+ and float

CLK–). Connect to CLKVDD for differential receiver. Float for PECL receiver (terminations on-chip). 26 10, 26 DCOM Digital Common. 27 3 DVDD Digital Supply Voltage (3.3 V). 28 N/A CLOCK Clock Input. Data latched on positive edge of clock. N/A 12 CLK+ Differential Clock Input. N/A 13 CLK− Differential Clock Input. N/A 11 CLKVDD Clock Supply Voltage (3.3 V). N/A 14 CLKCOM Clock Common. N/A EPAD It is recommended that the exposed pad be thermally connected to a copper ground plane for

enhanced electric and thermal performance.

AD9742 Data Sheet

Rev. C | Page 8 of 32

TYPICAL PERFORMANCE CHARACTERISTICS

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

fOUT (MHz)

1 10 100

0291

2-B

-006

125MSPS (LFCSP)

165MSPS210MSPS

165MSPS (LFCSP)

210MSPS (LFCSP)125MSPS

65MSPS

Figure 5. SFDR vs. fOUT @ 0 dBFS

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

0 5 10 15 20 25

fOUT (MHz)

0291

2-B

-009

0dBFS

–6dBFS

–12dBFS

Figure 6. SFDR vs. fOUT @ 65 MSPS

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

0 5 10 15 20 25 30 35 40 45

fOUT (MHz) 0291

2-B

-012

0dBFS

–6dBFS

–12dBFS

Figure 7. SFDR vs. fOUT @ 125 MSPS

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

20 300 10 40 50 60

fOUT (MHz) 0291

2-B

-007

0dBFS (LFCSP)

0dBFS

–6dBFS (LFCSP)

–6dBFS

–12dBFS

–12dBFS (LFCSP)

Figure 8. SFDR vs. fOUT @ 165 MSPS

45

50

55

60

65

70

75

80

85

90

95SF

DR

(dB

c)

0 10 3020 40 50 60 70

fOUT (MHz)

0291

2-B

-054

–12dBFS (LFCSP)

0dBFS

–6dBFS (LFCSP)–6dBFS

0dBFS (LFCSP)

–12dBFS

Figure 9. SFDR vs. fOUT @ 210 MSPS

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

0 5 10 15 20 25

fOUT (MHz)

0291

2-B

-010

20mA

10mA

5mA

Figure 10. SFDR vs. fOUT and IOUTFS @ 65 MSPS and 0 dBFS

Data Sheet AD9742

Rev. C | Page 9 of 32

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

–25 –20 –15 –10 –5 0

AOUT (dBFS)

0291

2-B

-013

65MSPS

210MSPS

210MSPS (LFCSP)

125MSPS

165MSPS

Figure 11. Single-Tone SFDR vs. AOUT @ fOUT = fCLOCK/11

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

–25 –20 –15 –10 –5 0

AOUT (dBFS)

0291

2-B

-008

165MSPS

65MSPS

165MSPS (LFCSP)

125MSPS (LFCSP)

125MSPS

210MSPS210MSPS (LFCSP)

Figure 12. Single-Tone SFDR vs. AOUT @ fOUT = fCLOCK/5

50

55

60

65

70

75

80

SNR

25 45 65 85 105 125 145 165 205185

fCLOCK (MHz) 0291

2-B

-011

20mA

10mA5mA

Figure 13. SNR vs. fCLOCK and IOUTFS @ fOUT = 5 MHz and 0 dBFS

45

50

55

60

65

70

75

80

85

90

95

SFD

R (d

Bc)

–25 –20 –15 –10 –5 0

AOUT (dBFS)

0291

2-B

-014

65MSPS (8.3,10.3)

78MSPS (10.1,12.1)

125MSPS (16.9, 18.9)

165MSPS (22.6, 24.6) 210MSPS (29, 31)

210MSPS (29, 31)

Figure 14. Dual-Tone IMD vs. AOUT @ fOUT = fCLOCK/7

ERR

OR

(LSB

)

–1.0

–0.5

0

0.5

1.0

CODE

10240 2048 3072 4096

0291

2-B

-015

Figure 15. Typical INL

–1.0

–0.8

–0.6

–0.4

–0.2

0

0.2

0.4

0.6

0.8

1.0

ERR

OR

(LSB

)

CODE

10240 2048 3072 4096

0291

2-B

-017

Figure 16. Typical DNL

AD9742 Data Sheet

Rev. C | Page 10 of 32

50

55

60

65

70

75

SFD

R (d

Bc)

80

85

90

0 20–40 –20 40 60 80

TEMPERATURE (°C) 0291

2-B

-019

4MHz

19MHz

34MHz

49MHz

Figure 17. SFDR vs. Temperature @ 165 MSPS, 0 dBFS

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

MA

GN

ITU

DE

(dB

m)

1 6 11 16 21 26 31 36

FREQUENCY (MHz) 0291

2-B

-016

fCLOCK = 78MSPSfOUT = 15.0MHzSFDR = 79dBcAMPLITUDE = 0dBFS

Figure 18. Single-Tone SFDR

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

MA

GN

ITU

DE

(dB

m)

1 6 11 16 21 26 31 36

FREQUENCY (MHz) 0291

2-B

-018

fCLOCK = 78MSPSfOUT1 = 15.0MHzfOUT2 = 15.4MHzSFDR = 77dBcAMPLITUDE = 0dBFS

Figure 19. Dual-Tone SFDR

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

MA

GN

ITU

DE

(dB

m)

1 6 11 16 21 26 31 36

FREQUENCY (MHz) 0291

2-B

-020

fCLOCK = 78MSPSfOUT1 = 15.0MHz

fOUT2 = 15.4MHz

fOUT3 = 15.8MHz

fOUT4 = 16.2MHzSFDR = 75dBcAMPLITUDE = 0dBFS

Figure 20. Four-Tone SFDR

DIGITAL DATA INPUTS (DB11–DB0)

150pF1.2V REF

AVDD ACOMREFLO

PMOSCURRENT SOURCE

ARRAY

3.3V

SEGMENTED SWITCHESFOR DB11–DB3

LSBSWITCHES

REFIO

FS ADJ

DVDD

DCOM

CLOCK

3.3VRSET2kΩ

0.1µF

IOUTA

IOUTB

AD9742

SLEEPLATCHES

IREF

VREFIO

CLOCK

IOUTBIOUTA

RLOAD50Ω

VOUTB

VOUTA

RLOAD50Ω

VDIFF = VOUTA – VOUTB

MODE

0291

2-B-

021

Figure 21. Simplified Block Diagram (SOIC/TSSOP Packages)

Data Sheet AD9742

Rev. C | Page 11 of 32

TERMINOLOGY Linearity Error (Also Called Integral Nonlinearity or INL) Linearity error is defined as the maximum deviation of the actual analog output from the ideal output, determined by a straight line drawn from zero to full scale.

Differential Nonlinearity (or DNL) DNL is the measure of the variation in analog value, normalized to full scale, associated with a 1 LSB change in digital input code.

Monotonicity A DAC is monotonic if the output either increases or remains constant as the digital input increases.

Offset Error The deviation of the output current from the ideal of zero is called the offset error. For IOUTA, 0 mA output is expected when the inputs are all 0s. For IOUTB, 0 mA output is expected when all inputs are set to 1s.

Gain Error The difference between the actual and ideal output span. The actual span is determined by the output when all inputs are set to 1s minus the output when all inputs are set to 0s.

Output Compliance Range The range of allowable voltage at the output of a current output DAC. Operation beyond the maximum compliance limits may cause either output stage saturation or breakdown, resulting in nonlinear performance.

Temperature Drift Temperature drift is specified as the maximum change from the ambient (25°C) value to the value at either TMIN or TMAX. For offset and gain drift, the drift is reported in ppm of full-scale range (FSR) per °C. For reference drift, the drift is reported in ppm per °C.

Power Supply Rejection The maximum change in the full-scale output as the supplies are varied from nominal to minimum and maximum specified voltages.

Settling Time The time required for the output to reach and remain within a specified error band about its final value, measured from the start of the output transition.

Glitch Impulse Asymmetrical switching times in a DAC give rise to undesired output transients that are quantified by a glitch impulse. It is specified as the net area of the glitch in pV-s.

Spurious-Free Dynamic Range The difference, in dB, between the rms amplitude of the output signal and the peak spurious signal over the specified bandwidth.

Total Harmonic Distortion (THD) THD is the ratio of the rms sum of the first six harmonic components to the rms value of the measured input signal. It is expressed as a percentage or in decibels (dB).

Multitone Power Ratio The spurious-free dynamic range containing multiple carrier tones of equal amplitude. It is measured as the difference between the rms amplitude of a carrier tone to the peak spurious signal in the region of a removed tone.

150pF1.2V REF

AVDD ACOMREFLO

PMOSCURRENT SOURCE

ARRAY

SEGMENTED SWITCHESFOR DB11–DB3

LSBSWITCHES

REFIO

FS ADJ

DVDD

DCOM

CLOCK

3.3VRSET2kΩ

0.1µF

DVDDDCOM

IOUTA

IOUTB

AD9742

SLEEP50ΩRETIMED

CLOCKOUTPUT*

LATCHES

DIGITALDATA

TEKTRONIX AWG-2021WITH OPTION 4

LECROY 9210PULSE GENERATOR

CLOCKOUTPUT

50Ω

ROHDE & SCHWARZFSEA30SPECTRUMANALYZER

MINI-CIRCUITST1-1T

*AWG2021 CLOCK RETIMEDSO THAT THE DIGITAL DATATRANSITIONS ON FALLING EDGEOF 50% DUTY CYCLE CLOCK.

3.3V

MODE

50Ω

0291

2-B-

005

Figure 22. Basic AC Characterization Test Set-Up (SOIC/TSSOP Packages)

AD9742 Data Sheet

Rev. C | Page 12 of 32

FUNCTIONAL DESCRIPTION AD9742 consists of a DAC, digital control logic, and full-scale output current control. The DAC contains a PMOS current source array capable of providing up to 20 mA of full-scale current (IOUTFS). The array is divided into 31 equal currents that make up the five most significant bits (MSBs). The next four bits, or middle bits, consist of 15 equal current sources whose value is 1/16th of an MSB current source. The remaining LSBs are binary weighted fractions of the middle bits current sources. Implementing the middle and lower bits with current sources, instead of an R-2R ladder, enhances its dynamic performance for multitone or low amplitude signals and helps maintain the DAC’s high output impedance (i.e., >100 kΩ).

All of these current sources are switched to one or the other of the two output nodes (i.e., IOUTA or IOUTB) via PMOS differential current switches. The switches are based on the architecture that was pioneered in the AD9764 family, with further refinements to reduce distortion contributed by the switching transient. This switch architecture also reduces various timing errors and provides matching complementary drive signals to the inputs of the differential current switches.

The analog and digital sections of the AD9742 have separate power supply inputs (i.e., AVDD and DVDD) that can operate independently over a 2.7 V to 3.6 V range. The digital section, which is capable of operating at a rate of up to 210 MSPS, consists of edge-triggered latches and segment decoding logic circuitry. The analog section includes the PMOS current sources, the associated differential switches, a 1.2 V band gap voltage reference, and a reference control amplifier.

The DAC full-scale output current is regulated by the reference control amplifier and can be set from 2 mA to 20 mA via an external resistor, RSET, connected to the full-scale adjust (FS ADJ) pin. The external resistor, in combination with both the reference control amplifier and voltage reference ,VREFIO, sets the reference current, IREF, which is replicated to the segmented current sources with the proper scaling factor. The full-scale current, IOUTFS, is 32 times IREF.

REFERENCE OPERATION The AD9742 contains an internal 1.2 V band gap reference. The internal reference can be disabled by raising REFLO to AVDD. It can also be easily overridden by an external reference with no effect on performance. REFIO serves as either an input or an output depending on whether the internal or an external reference is used. To use the internal reference, simply decouple the REFIO pin to ACOM with a 0.1 µF capacitor and connect REFLO to ACOM via a resistance less than 5 Ω. The internal reference voltage will be present at REFIO. If the voltage at REFIO is to be used anywhere else in the circuit, an external buffer amplifier with an input bias current of less than 100 nA should be used. An example of the use of the internal reference is shown in Figure 23.

150pF

1.2V REF

AVDDREFLO

CURRENTSOURCEARRAY

3.3V

REFIO

FS ADJ

2kΩ

0.1µF

AD9742

ADDITIONALLOAD

OPTIONALEXTERNAL

REF BUFFER

0291

2-B-

022

Figure 23. Internal Reference Configuration

An external reference can be applied to REFIO, as shown in Figure 24. The external reference may provide either a fixed reference voltage to enhance accuracy and drift performance or a varying reference voltage for gain control. Note that the 0.1 µF compensation capacitor is not required since the internal reference is overridden, and the relatively high input impedance of REFIO minimizes any loading of the external reference.

150pF

1.2V REF

AVDDREFLO

CURRENTSOURCEARRAY

REFIO

FS ADJ

RSET

AD9742

EXTERNALREF

IREF =VREFIO/RSET

AVDD

REFERENCECONTROLAMPLIFIER

VREFIO

3.3V

0291

2-B

-023

Figure 24. External Reference Configuration

Data Sheet AD9742

Rev. C | Page 13 of 32

REFERENCE CONTROL AMPLIFIER The AD9742 contains a control amplifier that is used to regulate the full-scale output current, IOUTFS. The control amplifier is configured as a V-I converter, as shown in Figure 24, so that its current output, IREF, is determined by the ratio of the VREFIO and an external resistor, RSET, as stated in Equation 4. IREF is copied to the segmented current sources with the proper scale factor to set IOUTFS, as stated in Equation 3.

The control amplifier allows a wide (10:1) adjustment span of IOUTFS over a 2 mA to 20 mA range by setting IREF between 62.5 µA and 625 µA. The wide adjustment span of IOUTFS provides several benefits. The first relates directly to the power dissipation of the AD9742, which is proportional to IOUTFS (see the Power Dissipation section). The second relates to the 20 dB adjustment, which is useful for system gain control purposes.

The small signal bandwidth of the reference control amplifier is approximately 500 kHz and can be used for low frequency small signal multiplying applications.

DAC TRANSFER FUNCTION Both DACs in the AD9742 provide complementary current outputs, IOUTA and IOUTB. IOUTA provides a near full-scale current output, IOUTFS, when all bits are high (i.e., DAC CODE = 4095), while IOUTB, the complementary output, provides no current. The current output appearing at IOUTA and IOUTB is a function of both the input code and IOUTFS and can be expressed as:

( ) OUTFSICODEDACIOUTA ×= 4096/ (1)

( ) OUTFSICODEDACIOUTB ×−= /40964095 (2)

where DAC CODE = 0 to 4095 (i.e., decimal representation).

As mentioned previously, IOUTFS is a function of the reference current IREF, which is nominally set by a reference voltage, VREFIO, and external resistor, RSET. It can be expressed as:

REFOUTFS II ×= 32 (3)

where

SETREFIOREF RVI /= (4)

The two current outputs will typically drive a resistive load directly or via a transformer. If dc coupling is required, IOUTA and IOUTB should be directly connected to matching resistive loads, RLOAD, that are tied to analog common, ACOM. Note that RLOAD may represent the equivalent load resistance seen by IOUTA or IOUTB as would be the case in a doubly terminated 50 Ω or 75 Ω cable. The single-ended voltage output appearing at the IOUTA and IOUTB nodes is simply

LOADOUTA RIOUTAV ×= (5)

LOADOUTB RIOUTBV ×= (6)

Note that the full-scale value of VOUTA and VOUTB should not exceed the specified output compliance range to maintain specified distortion and linearity performance.

( ) LOADDIFF RIOUTBIOUTAV ×−= (7)

Substituting the values of IOUTA, IOUTB, IREF, and VDIFF can be expressed as:

( ) ( ) REFIOSETLOAD

DIFF

VRRCODEDACV××

−×=

/324096/40952

(8)

Equations 7 and 8 highlight some of the advantages of operating the AD9742 differentially. First, the differential operation helps cancel common-mode error sources associated with IOUTA and IOUTB, such as noise, distortion, and dc offsets. Second, the differential code-dependent current and subsequent voltage, VDIFF, is twice the value of the single-ended voltage output (i.e., VOUTA or VOUTB), thus providing twice the signal power to the load.

Note that the gain drift temperature performance for a single-ended (VOUTA and VOUTB) or differential output (VDIFF) of the AD9742 can be enhanced by selecting temperature tracking resistors for RLOAD and RSET due to their ratiometric relationship, as shown in Equation 8.

ANALOG OUTPUTS The complementary current outputs in each DAC, IOUTA, and IOUTB may be configured for single-ended or differential operation. IOUTA and IOUTB can be converted into comple-mentary single-ended voltage outputs, VOUTA and VOUTB, via a load resistor, RLOAD, as described in the DAC Transfer Function section by Equations 5 through 8. The differential voltage, VDIFF, existing between VOUTA and VOUTB, can also be converted to a single-ended voltage via a transformer or differential amplifier configuration. The ac performance of the AD9742 is optimum and specified using a differential transformer-coupled output in which the voltage swing at IOUTA and IOUTB is limited to ±0.5 V.

The distortion and noise performance of the AD9742 can be enhanced when it is configured for differential operation. The common-mode error sources of both IOUTA and IOUTB can be significantly reduced by the common-mode rejection of a transformer or differential amplifier. These common-mode error sources include even-order distortion products and noise. The enhancement in distortion performance becomes more significant as the frequency content of the reconstructed waveform increases and/or its amplitude decreases. This is due to the first-order cancellation of various dynamic common-mode distortion mechanisms, digital feedthrough, and noise.

Performing a differential-to-single-ended conversion via a transformer also provides the ability to deliver twice the reconstructed signal power to the load (assuming no source termination). Since the output currents of IOUTA and IOUTB are complementary, they become additive when processed differentially. A properly selected transformer will allow the AD9742 to provide the required power and voltage levels to different loads.

AD9742 Data Sheet

Rev. C | Page 14 of 32

The output impedance of IOUTA and IOUTB is determined by the equivalent parallel combination of the PMOS switches associated with the current sources and is typically 100 kΩ in parallel with 5 pF. It is also slightly dependent on the output voltage (i.e., VOUTA and VOUTB) due to the nature of a PMOS device. As a result, maintaining IOUTA and/or IOUTB at a virtual ground via an I-V op amp configuration will result in the optimum dc linearity. Note that the INL/DNL specifications for the AD9742 are measured with IOUTA maintained at a virtual ground via an op amp.

IOUTA and IOUTB also have a negative and positive voltage compliance range that must be adhered to in order to achieve optimum performance. The negative output compliance range of −1 V is set by the breakdown limits of the CMOS process. Operation beyond this maximum limit may result in a breakdown of the output stage and affect the reliability of the AD9742.

The positive output compliance range is slightly dependent on the full-scale output current, IOUTFS. It degrades slightly from its nominal 1.2 V for an IOUTFS = 20 mA to 1 V for an IOUTFS = 2 mA. The optimum distortion performance for a single-ended or differential output is achieved when the maximum full-scale signal at IOUTA and IOUTB does not exceed 0.5 V.

DIGITAL INPUTS The AD9742 digital section consists of 12 input bit channels and a clock input. The 12-bit parallel data inputs follow standard positive binary coding, where DB11 is the most significant bit (MSB) and DB0 is the least significant bit (LSB). IOUTA produces a full-scale output current when all data bits are at Logic 1. IOUTB produces a complementary output with the full-scale current split between the two outputs as a function of the input code.

DVDD

DIGITALINPUT

0291

2-B

-024

Figure 25. Equivalent Digital Input

The digital interface is implemented using an edge-triggered master/slave latch. The DAC output updates on the rising edge of the clock and is designed to support a clock rate as high as 210 MSPS. The clock can be operated at any duty cycle that meets the specified latch pulse width. The setup and hold times can also be varied within the clock cycle as long as the specified minimum times are met, although the location of these transition edges may affect digital feedthrough and distortion performance. Best performance is typically achieved when the input data transitions on the falling edge of a 50% duty cycle clock.

CLOCK INPUT SOIC/TSSOP Packages

The 28-lead package options have a single-ended clock input (CLOCK) that must be driven to rail-to-rail CMOS levels. The quality of the DAC output is directly related to the clock quality, and jitter is a key concern. Any noise or jitter in the clock will translate directly into the DAC output. Optimal performance will be achieved if the CLOCK input has a sharp rising edge, since the DAC latches are positive edge triggered.

LFCSP Package

A configurable clock input is available in the LFCSP package, which allows for one single-ended and two differential modes. The mode selection is controlled by the CMODE input, as summarized in Table 7. Connecting CMODE to CLKCOM selects the single-ended clock input. In this mode, the CLK+ input is driven with rail-to-rail swings and the CLK− input is left floating. If CMODE is connected to CLKVDD, the differential receiver mode is selected. In this mode, both inputs are high impedance. The final mode is selected by floating CMODE. This mode is also differential, but internal terminations for positive emitter-coupled logic (PECL) are activated. There is no significant performance difference between any of the three clock input modes.

Table 7. Clock Mode Selection CMODE Pin Clock Input Mode CLKCOM Single-Ended CLKVDD Differential Float PECL

The single-ended input mode operates in the same way as the CLOCK input in the 28-lead packages, as described previously.

In the differential input mode, the clock input functions as a high impedance differential pair. The common-mode level of the CLK+ and CLK− inputs can vary from 0.75 V to 2.25 V, and the differential voltage can be as low as 0.5 V p-p. This mode can be used to drive the clock with a differential sine wave since the high gain bandwidth of the differential inputs will convert the sine wave into a single-ended square wave internally.

The final clock mode allows for a reduced external component count when the DAC clock is distributed on the board using PECL logic. The internal termination configuration is shown in Figure 26. These termination resistors are untrimmed and can vary up to ±20%. However, matching between the resistors should generally be better than ±1%.

CLK+

TO DAC CORECLK–

VTT = 1.3V NOM

50Ω 50Ω

AD9742

CLOCKRECEIVER

0291

2-B-

025

Figure 26. Clock Termination in PECL Mode\

Data Sheet AD9742

Rev. C | Page 15 of 32

DAC TIMING Input Clock and Data Timing Relationship

Dynamic performance in a DAC is dependent on the relationship between the position of the clock edges and the time at which the input data changes. The AD9742 is rising edge triggered, and so exhibits dynamic performance sensitivity when the data transition is close to this edge. In general, the goal when applying the AD9742 is to make the data transition close to the falling clock edge. This becomes more important as the sample rate increases. Figure 27 shows the relationship of SFDR to clock placement with different sample rates. Note that at the lower sample rates, more tolerance is allowed in clock placement, while at higher rates, more care must be taken.

–3 –2 2–1 0 1

65

75

ns

dB

3

55

45

35

60

70

50

4050MHz SFDR

20MHz SFDR

50MHz SFDR

0291

2-B

-026

Figure 27. SFDR vs. Clock Placement @ fOUT = 20 MHz and 50 MHz

Sleep Mode Operation

The AD9742 has a power-down function that turns off the output current and reduces the supply current to less than 6 mA over the specified supply range of 2.7 V to 3.6 V and temperature range. This mode can be activated by applying a Logic Level 1 to the SLEEP pin. The SLEEP pin logic threshold is equal to 0.5 Ω AVDD. This digital input also contains an active pull-down circuit that ensures that the AD9742 remains enabled if this input is left disconnected. The AD9742 takes less than 50 ns to power down and approximately 5 µs to power back up.

POWER DISSIPATION The power dissipation, PD, of the AD9742 is dependent on several factors that include:

• The power supply voltages (AVDD, CLKVDD, and DVDD) • The full-scale current output IOUTFS • The update rate fCLOCK • The reconstructed digital input waveform

The power dissipation is directly proportional to the analog supply current, IAVDD, and the digital supply current, IDVDD. IAVDD is directly proportional to IOUTFS, as shown in Figure 28, and is insensitive to fCLOCK. Conversely, IDVDD is dependent on both the digital input waveform, fCLOCK, and digital supply DVDD. Figure 29 shows IDVDD as a function of full-scale sine wave output ratios (fOUT/fCLOCK) for various update rates with DVDD = 3.3 V.

IOUTFS (mA)

35

02

I AVD

D (m

A)

30

25

20

15

10

4 6 8 10 12 14 16 18 20

0291

2-B

-027

Figure 28. IAVDD vs. IOUTFS

RATIO (fOUT/fCLOCK)

20

0.01 10.1

I DVD

D (m

A)

18

16

14

12

10

8

6

4

2

0

165MSPS

125MSPS

65MSPS

0291

2-B

-028

210MSPS

Figure 29. IDVDD vs. Ratio @ DVDD = 3.3 V

0 50 250100 150 2000

2

4

6

8

12

10

fCLOCK (MSPS)

I CLK

VDD

(mA

)

DIFF

PECL

SE

0291

2-B

-029

Figure 30. ICLKVDD vs. fCLOCK and Clock Mode

AD9742 Data Sheet

Rev. C | Page 16 of 32

APPLYING THE AD9742 Output Configurations

The following sections illustrate some typical output configurations for the AD9742. Unless otherwise noted, it is assumed that IOUTFS is set to a nominal 20 mA. For applications requiring the optimum dynamic performance, a differential output configuration is suggested. A differential output configuration may consist of either an RF transformer or a differential op amp configuration. The transformer configuration provides optimum high frequency performance and is recommended for any application that allows ac coupling. The differential op amp configuration is suitable for applications requiring dc coupling, a bipolar output, signal gain, and/or level shifting within the bandwidth of the chosen op amp.

A single-ended output is suitable for applications requiring a unipolar voltage output. A positive unipolar output voltage will result if IOUTA and/or IOUTB are connected to an appropriately sized load resistor, RLOAD, referred to ACOM. This configuration may be more suitable for a single-supply system requiring a dc-coupled, ground-referred output voltage. Alternatively, an amplifier could be configured as an I-V converter, thus converting IOUTA or IOUTB into a negative unipolar voltage. This configuration provides the best dc linearity since IOUTA or IOUTB is maintained at a virtual ground.

DIFFERENTIAL COUPLING USING A TRANSFORMER An RF transformer can be used to perform a differential-to-single-ended signal conversion, as shown in Figure 31. A differentially coupled transformer output provides the optimum distortion performance for output signals whose spectral content lies within the transformer’s pass band. An RF transformer, such as the Mini-Circuits T1–1T, provides excellent rejection of common-mode distortion (that is, even-order harmonics) and noise over a wide frequency range. It also provides electrical isolation and the ability to deliver twice the power to the load. Transformers with different impedance ratios may also be used for impedance matching purposes. Note that the transformer provides ac coupling only.

RLOADAD9742

MINI-CIRCUITST1-1T

OPTIONAL RDIFF

IOUTA

IOUTB

22

21

0291

2-B-

030

Figure 31. Differential Output Using a Transformer

The center tap on the primary side of the transformer must be connected to ACOM to provide the necessary dc current path for both IOUTA and IOUTB. The complementary voltages appearing at IOUTA and IOUTB (i.e., VOUTA and VOUTB) swing symmetrically around ACOM and should be maintained with the specified output compliance range of the AD9742. A differential resistor, RDIFF, may be inserted in applications where the output of the transformer is connected to the load, RLOAD, via a passive reconstruction filter or cable. RDIFF is determined by the transformer’s impedance ratio and provides the proper source

termination that results in a low VSWR. Note that approximately half the signal power will be dissipated across RDIFF.

DIFFERENTIAL COUPLING USING AN OP AMP An op amp can also be used to perform a differential-to-single-ended conversion, as shown in Figure 32. The AD9742 is configured with two equal load resistors, RLOAD, of 25 Ω. The differential voltage developed across IOUTA and IOUTB is converted to a single-ended signal via the differential op amp configuration. An optional capacitor can be installed across IOUTA and IOUTB, forming a real pole in a low-pass filter. The addition of this capacitor also enhances the op amp’s distortion performance by preventing the DAC’s high slewing output from overloading the op amp’s input.

AD9742IOUTA

IOUTBCOPT

500Ω

225Ω

225Ω

500Ω25Ω25Ω

AD8047

0291

2-B-

031

22

21

Figure 32. DC Differential Coupling Using an Op Amp

The common-mode rejection of this configuration is typically determined by the resistor matching. In this circuit, the differential op amp circuit using the AD8047 is configured to provide some additional signal gain. The op amp must operate off a dual supply since its output is approximately ±1 V. A high speed amplifier capable of preserving the differential performance of the AD9742 while meeting other system level objectives (e.g., cost or power) should be selected. The op amp’s differential gain, gain setting resistor values, and full-scale output swing capabilities should all be considered when optimizing this circuit.

The differential circuit shown in Figure 33 provides the necessary level shifting required in a single-supply system. In this case, AVDD, which is the positive analog supply for both the AD9742 and the op amp, is also used to level shift the differential output of the AD9742 to midsupply (i.e., AVDD/2). The AD8041 is a suitable op amp for this application.

AD9742IOUTA

IOUTBCOPT

500Ω

225Ω

225Ω

1kΩ25Ω25Ω

AD8041

1kΩAVDD

22

21

0291

2-B-

032

Figure 33. Single-Supply DC Differential Coupled Circuit

Data Sheet AD9742

Rev. C | Page 17 of 32

SINGLE-ENDED, UNBUFFERED VOLTAGE OUTPUT Figure 34 shows the AD9742 configured to provide a unipolar output range of approximately 0 V to 0.5 V for a doubly terminated 50 Ω cable since the nominal full-scale current, IOUTFS, of 20 mA flows through the equivalent RLOAD of 25 Ω. In this case, RLOAD represents the equivalent load resistance seen by IOUTA or IOUTB. The unused output (IOUTA or IOUTB) can be connected to ACOM directly or via a matching RLOAD. Different values of IOUTFS and RLOAD can be selected as long as the positive compliance range is adhered to. One additional consideration in this mode is the integral nonlinearity (INL), discussed in the Analog Outputs section. For optimum INL performance, the single-ended, buffered voltage output configuration is suggested.

AD9742IOUTA

IOUTB50Ω

25Ω

VOUTA = 0V TO 0.5VIOUTFS = 20mA

50Ω

22

21

0291

2-B-

033

Figure 34. 0 V to 0.5 V Unbuffered Voltage Output

SINGLE-ENDED, BUFFERED VOLTAGE OUTPUT CONFIGURATION Figure 35 shows a buffered single-ended output configuration in which the op amp U1 performs an I-V conversion on the AD9742 output current. U1 maintains IOUTA (or IOUTB) at a virtual ground, minimizing the nonlinear output impedance effect on the DAC’s INL performance as described in the Analog Outputs section. Although this single-ended configuration typically provides the best dc linearity performance, its ac distortion performance at higher DAC update rates may be limited by U1’s slew rate capabilities. U1 provides a negative unipolar output voltage, and its full-scale output voltage is simply the product of RFB and IOUTFS. The full-scale output should be set within U1’s voltage output swing capabilities by scaling IOUTFS and/or RFB. An improvement in ac distortion performance may result with a reduced IOUTFS since U1 will be required to sink less signal current.

AD9742IOUTA

IOUTB

COPT

200Ω

U1 VOUT = IOUTFS × RFB

IOUTFS = 10mA

RFB200Ω

22

21

0291

2-B-

034

Figure 35. Unipolar Buffered Voltage Output

POWER AND GROUNDING CONSIDERATIONS, POWER SUPPLY REJECTION Many applications seek high speed and high performance under less than ideal operating conditions. In these application circuits, the implementation and construction of the printed circuit board is as important as the circuit design. Proper RF techniques must be used for device selection, placement, and routing as well as power supply bypassing and grounding to ensure optimum performance. Figure 40 to Figure 43 illustrate the recommended printed circuit board ground, power, and signal plane layouts implemented on the AD9742 evaluation board.

One factor that can measurably affect system performance is the ability of the DAC output to reject dc variations or ac noise superimposed on the analog or digital dc power distribution. This is referred to as the power supply rejection ratio (PSRR). For dc variations of the power supply, the resulting performance of the DAC directly corresponds to a gain error associated with the DAC’s full-scale current, IOUTFS. AC noise on the dc supplies is common in applications where the power distribution is generated by a switching power supply. Typically, switching power supply noise will occur over the spectrum from tens of kHz to several MHz. The PSRR versus frequency of the AD9742 AVDD supply over this frequency range is shown in Figure 36.

FREQUENCY (MHz)

85

40126 8 100

PSR

R (d

B)

80

75

70

65

60

55

50

2 4

45

0291

2-B

-035

Figure 36. Power Supply Rejection Ratio (PSRR)

Note that the ratio in Figure 36 is calculated as amps out/volts in. Noise on the analog power supply has the effect of modulating the internal switches, and therefore the output current. The voltage noise on AVDD, therefore, will be added in a nonlinear manner to the desired IOUT. Due to the relative different size of these switches, the PSRR is very code dependent. This can produce a mixing effect that can modulate low frequency power supply noise to higher frequencies. Worst-case PSRR for either one of the differential DAC outputs will occur when the full-scale current is directed toward that output. As a result, the PSRR measurement in Figure 36 represents a worst-case condition in which the digital inputs remain static and the full-scale output current of 20 mA is directed to the DAC output being measured.

AD9742 Data Sheet

Rev. C | Page 18 of 32

An example serves to illustrate the effect of supply noise on the analog supply. Suppose a switching regulator with a switching frequency of 250 kHz produces 10 mV of noise and, for simplicity’s sake (ignoring harmonics), all of this noise is concentrated at 250 kHz. To calculate how much of this undesired noise will appear as current noise superimposed on the DAC’s full-scale current, IOUTFS, one must determine the PSRR in dB using Figure 36 at 250 kHz. To calculate the PSRR for a given RLOAD, such that the units of PSRR are converted from A/V to V/V, adjust the curve in Figure 36 by the scaling factor 20 Ω log (RLOAD). For instance, if RLOAD is 50 Ω, the PSRR is reduced by 34 dB (i.e., PSRR of the DAC at 250 kHz, which is 85 dB in Figure 36, becomes 51 dB VOUT/VIN).

Proper grounding and decoupling should be a primary objective in any high speed, high resolution system. The AD9742 features separate analog and digital supplies and ground pins to optimize the management of analog and digital ground currents in a system. In general, AVDD, the analog supply, should be decoupled to ACOM, the analog common, as close to the chip as physically

possible. Similarly, DVDD, the digital supply, should be decoupled to DCOM as close to the chip as physically possible.

For those applications that require a single 3.3 V supply for both the analog and digital supplies, a clean analog supply may be generated using the circuit shown in Figure 37. The circuit consists of a differential LC filter with separate power supply and return lines. Lower noise can be attained by using low ESR type electrolytic and tantalum capacitors.

100µFELECT.

0.1µFCER.

TTL/CMOSLOGIC

CIRCUITS

3.3VPOWER SUPPLY

FERRITEBEADS

AVDD

ACOM

10µF–22µFTANT.

0291

2-B-

036

Figure 37. Differential LC Filter for Single 3.3 V Applications

Data Sheet AD9742

Rev. C | Page 19 of 32

EVALUATION BOARD GENERAL DESCRIPTION The TxDAC family evaluation boards allow for easy setup and testing of any TxDAC product in the SOIC and LFCSP packages. Careful attention to layout and circuit design, combined with a prototyping area, allows the user to evaluate the AD9742 easily and effectively in any application where high resolution, high speed conversion is required.

This board allows the user the flexibility to operate the AD9742 in various configurations. Possible output configurations include transformer coupled, resistor terminated, and single and differential outputs. The digital inputs are designed to be driven from various word generators, with the on-board option to add a resistor network for proper load termination. Provisions are also made to operate the AD9742 with either the internal or external reference or to exercise the power-down feature.

2R

13

R2

4R

35

R4

6R

57

R6

8R

79

R8

10R

9 RP5OPT

1D

CO

M161 RP3 22Ω DB13

DB12DB11DB10DB9DB8DB7DB6DB5DB4DB3DB2DB1DB0

DB13XDB12XDB11XDB10XDB9XDB8XDB7XDB6XDB5XDB4XDB3XDB2XDB1XDB0X

152 RP3 22Ω143 RP3 22Ω134 RP3 22Ω125 RP3 22Ω116 RP3 22Ω107 RP3 22Ω98 RP3 22Ω161 RP4 22Ω152 RP4 22Ω143 RP4 22Ω134 RP4 22Ω125 RP4 22Ω116 RP4 22Ω

98 RP4 22Ω107 RP4 22Ω

CKEXTCKEXTX

2R

13

R2

4R

35

R4

6R

57

R6

8R

79

R8

10R

9 RP6OPT

1D

CO

M

2R

13

R2

4R

35

R4

6R

57

R6

8R

79

R8

10R

9 RP1OPT1D

CO

M

2R

13

R2

4R

35

R4

6R

57

R6

8R

79

R8 10

R9 RP2

OPT

1D

CO

M

2 1 DB13X4 3 DB12X6 5 DB11X8 7 DB10X

10 9 DB9X12 11 DB8X14 13 DB7X16 15 DB6X18 17 DB5X20 19 DB4X22 21 DB3X24 23 DB2X26 25 DB1X28 27 DB0X30 2932 3134 33 CKEXTX36 3538 3740 39

JP3

J1

RIBBON

TB1 1

TB1 2

L2 BEAD

C70.1µF

TP4BLK

+DVDD

TP7

C60.1µF

C410µF25V BLK BLK

TP8

TP2RED

TB1 3

TB1 4

L3 BEAD

C90.1µF

TP6BLK

+AVDD

TP10

C80.1µF

C510µF25V BLK BLK

TP9

TP5RED

0291

2-B

-037

Figure 38. SOIC Evaluation Board—Power Supply and Digital Inputs

AD9742 Data Sheet

Rev. C | Page 20 of 32

R6OPT

S2IOUTA

2A BJP10

1 3IX

R1150Ω

C13OPT JP8

IOUT

S3

4

5

6

3

2

1

T1

T1-1T

JP9C12OPT

R1050ΩS1

IOUTB

12

3A BJP11

IY

1EXT

23

INTA BJP5REF

+

+

C1410µF16V

C160.1µF

C170.1µF

AVDD

DVDD

CKEXT

DB13DB12DB11DB10

DB9DB8DB7DB6DB5DB4DB3DB2DB1DB0

AVDD

C1510µF16V

C180.1µF

C190.1µF

CUTUNDER DUT

JP6

JP4

R5OPT

DVDD

R450Ω

CLOCK

S5CLOCK

TP1WHT

DVDD

AVDD

DVDD

R210kΩ

JP2

MODE

TP3WHT

REFC20.1µF

C10.1µF

C110.1µFR1

2kΩ

2827262524232221201918171615

123456789

1011121314

U1AD9742

SLEEPTP11WHT

R310kΩ

CLOCKDVDDDCOMMODEAVDD

RESERVEDIOUTAIOUTBACOM

NCFS ADJREFIO

REFLOSLEEP

DB13DB12DB11DB10DB9DB8DB7DB6DB5DB4DB3DB2DB1DB0

AVDD

0291

2-B

-038

Figure 39. SOIC Evaluation Board—Output Signal Conditioning

Data Sheet AD9742

Rev. C | Page 21 of 32

0291

2-B

-039

Figure 40. SOIC Evaluation Board—Primary Side

0291

2-B

-040

Figure 41. SOIC Evaluation Board—Secondary Side

AD9742 Data Sheet

Rev. C | Page 22 of 32

0291

2-B

-041

Figure 42. SOIC Evaluation Board—Ground Plane

0291

2-B

-042

Figure 43. SOIC Evaluation Board—Power Plane

Data Sheet AD9742

Rev. C | Page 23 of 32

0291

2-B

-043

Figure 44. SOIC Evaluation Board Assembly—Primary Side

0291

2-B

-044

Figure 45. SOIC Evaluation Board Assembly—Secondary Side

AD9742 Data Sheet

Rev. C | Page 24 of 32

CVDD

REDTP12BEAD

TB1 1

TB1 2

C70.1µF

C90.1µF

C30.1µF

BLK

TP2

TP4

TP6

BLK

BLK

C60.1µF

C80.1µF

C100.1µF

C210µF6.3V

C410µF6.3V

C510µF6.3V

L1

DVDD

REDTP13BEAD

TB3 1

TB3 2

L2

AVDD

REDTP5BEAD

TB4 1

TB4 2

L3

J1

131197531

403836343230282624222018161412108642

39373533312927252321191715

HEA

DER

STR

AIG

HT

UP

MA

LE N

O S

HR

OU

D

JP3CKEXTX

CKEXTCKEXTX

R21100Ω

R24100Ω

R25100Ω

R26100Ω

R27100Ω

R28100Ω

DB0XDB1XDB2XDB3XDB4XDB5XDB6XDB7XDB8XDB9X

DB10XDB11XDB12XDB13X

DB0XDB1XDB2XDB3XDB4XDB5XDB6XDB7XDB8XDB9XDB10XDB11XDB12XDB13X

DB13DB12DB11DB10DB9DB8DB7DB6DB5DB4DB3DB2DB1

DB0

22Ω 1622Ω 1522Ω 1422Ω 1322Ω 1222Ω 1122Ω 1022Ω 922Ω 1622Ω 1522Ω 1422Ω 1322Ω 1222Ω 1122Ω 10

22Ω 9

R20100Ω

R19100Ω

R18100Ω

R17100Ω

R16100Ω

R15100Ω

R4100Ω

R3100Ω

1 RP32 RP33 RP34 RP35 RP36 RP37 RP38 RP31 RP42 RP43 RP44 RP45 RP46 RP47 RP48 RP4

0291

2-B

-045

Figure 46. LFCSP Evaluation Board Schematic—Power Supply and Digital Inputs

Data Sheet AD9742

Rev. C | Page 25 of 32

C190.1

CVDD

CVDD

DB8DB9DB10DB11

CLKB

DB5DVDD

DB6DB7

CLK

DB0DB1DB2DB3DB4

DB13DB12

IOUT

AVDD

DVDD CVDDAVDD

DB8DB9

DB10DB11

IB

FS ADJ

CLKB

DB5DVDDDB6DB7

CLKCVDDDCOMDB0DB1DB2DB3DB4

DCOM1DB13

ACOM1AVDD

ACOMIA

REFIO

AVDD1

SLEEP

DB12

CCOMCMODEMODECMODE

MODE

T1 – 1T

T1

JP8

JP9

43

2

1

56

AGND: 3, 4, 5S3

50ΩR11

C1328

25

17

23

2122

1819

2726

24

20

29303132

DNP

DNPC12

C110.1µF

C170.1µF

C190.1µF

C320.1µF

10kΩR30

10kΩR29

U1

AD9744LFCSP

14

56789

101112

1234

13

1516

WHTTP1

WHTTP11

JP1 0.1%2kΩR1

R1050Ω

WHTTP3

TP7WHT

SLEEP

0291

2-B

-046

Figure 47. LFCSP Evaluation Board Schematic—Output Signal Conditioning

U4

U4

JP2

AGND: 5CVDD: 8

4

36

CVDD: 8

C350.1µF

C2010µF16V

S5AGND: 3, 4, 5

C340.1µF

CKEXT

CLK

CLKB

R5120Ω

R2120Ω

R650Ω

CVDD

AGND: 5

2

17

CVDD

0291

2-B-

047

Figure 48. LFCSP Evaluation Board Schematic—Clock Input

AD9742 Data Sheet

Rev. C | Page 26 of 32

0291

2-B

-048

Figure 49. LFCSP Evaluation Board Layout—Primary Side

0291

2-B

-049

Figure 50. LFCSP Evaluation Board Layout—Secondary Side

Data Sheet AD9742

Rev. C | Page 27 of 32

0291

2-B

-050

Figure 51. LFCSP Evaluation Board Layout—Ground Plane

0291

2-B

-051

Figure 52. LFCSP Evaluation Board Layout—Power Plane

AD9742 Data Sheet

Rev. C | Page 28 of 32

0291

2-B

-052

Figure 53. LFCSP Evaluation Board Layout Assembly—Primary Side

0291

2-B

-053

Figure 54. LFCSP Evaluation Board Layout Assembly—Secondary Side

Data Sheet AD9742

Rev. C | Page 29 of 32

OUTLINE DIMENSIONS

COMPLIANT TO JEDEC STANDARDS MO-153-AE

2 8 1 5

1 41

8°0°SEATING

PLANECOPLANARITY

0.10

1.20 MAX

6.40 BSC

0.65BSC

PIN 1

0.300.19

0.200.09

4.504.404.30

0.750.600.45

9.809.709.60

0.150.05

Figure 55. 28-Lead Thin Shrink Small Outline Package [TSSOP]

(RU-28) Dimensions shown in millimeters

CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FORREFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.

COMPLIANT TO JEDEC STANDARDS MS-013-AE

18.10 (0.7126)17.70 (0.6969)

0.30 (0.0118)0.10 (0.0039)

2.65 (0.1043)2.35 (0.0925)

10.65 (0.4193)10.00 (0.3937)

7.60 (0.2992)7.40 (0.2913)

0.75 (0.0295)0.25 (0.0098) 45°

1.27 (0.0500)0.40 (0.0157)

COPLANARITY0.10 0.33 (0.0130)

0.20 (0.0079)0.51 (0.0201)0.31 (0.0122)

SEATINGPLANE

8°0°

28 15

141

1.27 (0.0500)BSC

06-0

7-20

06-A

Figure 56. 28-Lead Standard Small Outline Package [SOIC_W]

Wide Body (RW-28) Dimensions shown in millimeters and (inches)

AD9742 Data Sheet

Rev. C | Page 30 of 32

COMPLIANT TO JEDEC STANDARDS MO-220-WHHD. 1124

08-A

10.50BSC

BOTTOM VIEWTOP VIEW

PIN 1INDICATOR

32

916

17

24

25

8

EXPOSEDPAD

PIN 1INDICATOR

3.253.10 SQ2.95

SEATINGPLANE

0.05 MAX0.02 NOM

0.20 REF

COPLANARITY0.08

0.300.250.18

5.105.00 SQ4.90

0.800.750.70

FOR PROPER CONNECTION OFTHE EXPOSED PAD, REFER TOTHE PIN CONFIGURATION ANDFUNCTION DESCRIPTIONSSECTION OF THIS DATA SHEET.

0.500.400.30

0.25 MIN

Figure 57. 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]

5 mm × 5 mm Body, Very Very Thin Quad (CP-32-7)

Dimensions shown in millimeters

ORDERING GUIDE Model1 Temperature Range Package Description Package Option AD9742AR −40°C to +85°C 28-Lead Standard Small Outline Package [SOIC] RW-28 AD9742ARZ −40°C to +85°C 28-Lead Standard Small Outline Package [SOIC] RW-28 AD9742ARZRL −40°C to +85°C 28-Lead Standard Small Outline Package [SOIC] RW-28 AD9742ARU −40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] RU-28 AD9742ARURL7 −40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] RU-28 AD9742ARUZ −40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] RU-28 AD9742ARUZRL7 −40°C to +85°C 28-Lead Thin Shrink Small Outline Package [TSSOP] RU-28 AD9742ACPZ −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ] CP-32-7 AD9742ACPZRL7 −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ] CP-32-7 AD9742-EBZ Evaluation Board [SOIC] AD9742ACP-PCBZ Evaluation Board [LFCSP] 1 Z = RoHS Compliant Part.

Data Sheet AD9742

Rev. C | Page 31 of 32

NOTES

AD9742 Data Sheet

Rev. C | Page 32 of 32

NOTES

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