10-Bit, Complete, 40 MSPS, dual Transmit D/A Converter

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 2x 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 2x 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 2x 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 combined 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 updated 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.

PRODUCT HIGHLIGHTS

* 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.

* 2x Digital Interpolation Filters

Dual matching FIR interpolation filters with 62.5 dB stopband rejection precede each DAC input, thus reducing the DACs’ reconstruction filter requirements.

* Low Power

Complete CMOS dual DAC function operates on a low 200 mW on a single supply from 3 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.

* On-Chip Voltage Reference

The AD9761 includes a 1.20 V temperature-compensated band gap voltage reference.

* Single 10-Bit Digital Input Bus

The AD9761 features a flexible digital interface that allows each DAC to be addressed in a variety of ways including different update rates.

* Small Package

The AD9761 offers the complete integrated function in a compact 28-lead SSOP package.

* Product Family

The AD9761 Dual Transmit DAC has a pair of Dual Receive ADC companion products, the AD9281 (8 bits) and AD9201 (10 bits).

* 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