The AD9761 is a complete dual, high speed, 10-bit CMOS DAC developed specifically for wide bandwidth communication applications such as spread spectrum where digital I and Q information is processed during transmit operation. It integrates two 10-bit, 40 MSPS DACs, two 2x interpolation filters, a voltage reference, and digital input interface circuitry. The device supports an input data rate of 20 MSPS per channel, up to 40 MSPS after 2x interpolation, and then updates each DAC simultaneously.
The interleaved I and Q input data streams are submitted to the digital interface circuit, which consists of I and Q latches and some additional control logic. After deinterlacing, the data is transformed back to the original I data and Q data. An on-chip state machine ensures that I data is properly paired with Q data. The 2x digital interpolation filter then processes the data output from each latch to simplify the reconstruction filter requirements. The interpolated output of each filter is used as the input to the corresponding 10-bit DAC.
These DACs use a segmented current source architecture combined with proprietary switching techniques to reduce surge energy and maximize dynamic accuracy. Each DAC provides a differential current output to support single-ended or differential applications. Both DACs are updated simultaneously and provide a nominal full-scale current of 10 mA. In addition, the full-scale current matching accuracy between the DACs is within 0.07 dB (0.75%), eliminating the need for additional gain calibration circuitry.
The AD9761 is manufactured on an advanced, low cost CMOS process and operates from a single 2.7 V to 5.5 V supply and consumes 200 mW. An internal 1.20 V temperature-compensated bandgap reference is also included to make it a complete solution.