ANALOG DEVICES AD9785 Service Manual

Dual 12-/14-/16-Bit 800 MSPS DAC

with Low Power 32-Bit Complex NCO

FEATURES

Analog output: adjustable 8.7 mA to 31.7 mA,

= 25 Ω to 50 Ω

Low power, fine complex NCO allows carrier placement

anywhere in DAC bandwidth while adding <300 mW power Auxiliary DACs allow I and Q gain matching and offset control Includes programmable I and Q phase compensation Internal digital upconversion capability Multiple chip synchronization interface High performance, low noise PLL clock multiplier Digital inverse sinc filter 100-lead, exposed paddle TQFP package

APPLICATIONS

Wireless infrastructure

WCDMA, CDMA2000, TD-SCDMA, WiMAX, GSM Digital high or low IF synthesis Transmit diversity Wideband communications

LMDS/MMDS, point-to-point

AD9785/AD9787/AD9788

GENERAL DESCRIPTION

The AD9785/AD9787/AD9788 are 12-bit, 14-bit, and 16-bit, high dynamic range TxDAC® devices, respectively, that provide a sample rate of 800 MSPS, permitting multicarrier generation up to the Nyquist frequency. Features are included for optimizing direct conversion transmit applications, including complex digital modulation, as well as gain, phase, and offset compensation. The DAC outputs are optimized to interface seamlessly with analog quadrature modulators, such as the ADL537x family from Analog Devices, Inc. A serial peripheral interface (SPI) provides for programming and readback of many internal parameters. Full-scale output current can be programmed over a range of 10 mA to 30 mA. The AD978x family is manufactured on a 0.18 m CMOS process and operates from 1.8 V and 3.3 V supplies. It is enclosed in a 100-lead TQFP package.

PRODUCT HIGHLIGHTS

1. Low noise and intermodulation distortion (IMD) enable

high quality synthesis of wideband signals from baseband to high intermediate frequencies.

2. Proprietary DAC output switching technique enhances

dynamic performance.

3. CMOS data input interface with adjustable setup and hold.

4. Low power complex 32-bit numerically controlled

oscillators (NCOs).

TYPICAL SIGNAL CHAIN

COMPLEX I AND Q

FPGA/ASI C/DSP

Rev. A

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DIGITAL INTERPOL ATION FILTERS

QUADRATURE

MODULATOR/

MIXER/

AMPLIFIER

I DAC

POST DAC

ANALOG FILTER

Q DAC

Figure 1.

07098-001