REV. A

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a

AD9761

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 7817/326-8703

© Analog Devices, Inc., 2000

Dual 10-Bit TxDAC+™

with 2

Interpolation Filters

FUNCTIONAL BLOCK DIAGRAM

ACOM

REFLO

"I"

DAC

FSADJ

IOUTA

IOUTB

WRITE INPUT

SELECT INPUT

DCOM

DVDD

CLOCK

AD9761

2

LATCH

"I"

REFIO

REFERENCE

COMP1

COMP2

COMP3

BIAS

GENERATOR

QOUTA

QOUTB

2

LATCH

"Q"

MUX

CONTROL

AVDD

DAC DATA

INPUTS

(10 BITS)

SLEEP

"Q"

DAC

FEATURES

Complete 10-Bit, 40 MSPS Dual Transmit DAC

Excellent Gain and Offset Matching

Differential Nonlinearity Error: 0.5 LSB

Effective Number of Bits: 9.5

Signal-to-Noise and Distortion Ratio: 59 dB

Spurious-Free Dynamic Range: 71 dB

2

Interpolation Filters

20 MSPS/Channel Data Rate

Single Supply: +2.7 V to +5.5 V

Low Power Dissipation: 200 mW (+3 V Supply @

40 MSPS)

On-Chip Reference

28-Lead SSOP

PRODUCT DESCRIPTION

The AD9761 is a complete dual channel, high speed, 10-bit

CMOS DAC. The AD9761 has been developed specifically for

use in wide bandwidth communication applications (e.g., spread

spectrum) where digital I and Q information is being processed

during transmit operations. It integrates two 10-bit, 40 MSPS

DACs, dual 2

× interpolation filters, a voltage reference, and

digital input interface circuitry. The AD9761 supports a

20 MSPS per channel input data rate that is then interpolated

by 2

× up to 40 MSPS before simultaneously updating each

DAC.

The interleaved I and Q input data stream is presented to the

digital interface circuitry, which consists of I and Q latches as well

as some additional control logic. The data is de-interleaved back

into its original I and Q data. An on-chip state machine ensures the

proper pairing of I and Q data. The data output from each latch is

then processed by a 2

× digital interpolation filter that eases the

reconstruction filter requirements. The interpolated output of each

filter serves as the input of their respective 10-bit DAC.

The DACs utilize a segmented current source architecture com-

bined with a proprietary switching technique to reduce glitch

energy and to maximize dynamic accuracy. Each DAC provides

differential current output thus supporting single-ended or

differential applications. Both DACs are simultaneously up-

dated and provide a nominal full-scale current of 10 mA. Also,

the full-scale currents between each DAC are matched to within

0.07 dB (i.e., 0.75%), thus eliminating the need for additional

gain calibration circuitry.

The AD9761 is manufactured on an advanced low cost CMOS

process. It operates from a single supply of 2.7 V to 5.5 V and

consumes 200 mW of power. To make the AD9761 complete it

also offers an internal 1.20 V temperature-compensated bandgap

reference.

TxDAC+ is a trademark of Analog Devices, Inc.

PRODUCT HIGHLIGHTS

1. Dual 10-Bit, 40 MSPS DACs: A pair of high performance

40 MSPS DACs optimized for low distortion performance

provide for flexible transmission of I and Q information.

2. 2

× Digital Interpolation Filters: Dual matching FIR interpo-

lation filters with 62.5 dB stop band rejection precede each

DAC input thus reducing the DACs’ reconstruction filter

requirements.

3. Low Power: Complete CMOS Dual DAC function operates

on a low 200 mW on a single supply from 2.7 V to 5.5 V.

The DAC full-scale current can be reduced for lower power

operation, and a sleep mode is provided for power reduction

during idle periods.

4. On-Chip Voltage Reference: The AD9761 includes a 1.20 V

temperature-compensated bandgap voltage reference.

5. Single 10-Bit Digital Input Bus: The AD9761 features a

flexible digital interface allowing each DAC to be addressed

in a variety of ways including different update rates.

6. Small Package: The AD9761 offers the complete integrated

function in a compact 28-lead SSOP package.

7. Product Family: The AD9761 Dual Transmit DAC has a

pair of Dual Receive ADC companion products, the AD9281

(8 bits) and AD9201 (10 bits).