The AD9761 is a complete dual-channel, high-speed, 10-bit CMOS DAC developed specifically for wide-bandwidth communications applications such as spread spectrum, where digital I and Q information are processed during transmit operations. 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 and can reach 40 MSPS with 2x interpolation, and then updates each DAC simultaneously.
The interleaved I and Q input data streams are submitted to a digital interface circuit consisting of I and Q latches and some additional control logic. After the data is deinterleaved, it is changed back to the original I data and Q data. The on-chip state machine ensures that the I data is properly paired with the Q data. The 2x digital interpolation filters then process the data output from each latch to simplify the refactoring filter requirements. The interpolated outputs of each filter are used as inputs to the corresponding 10-bit DAC.
These DACs feature a segmented current source architecture combined with proprietary switching technology to reduce surge energy and maximize dynamic accuracy. Each DAC provides a differential current output, thus supporting single-ended or differential applications. Both DACs are updated simultaneously and provide a nominal full-scale current of 10 mA. In addition, full-scale current matching accuracy between DACs is within 0.07 dB (i.e., 0.75%), eliminating the need for additional gain calibration circuitry.
The AD9761 is manufactured using an advanced, low-cost CMOS process and operates from a single 2.7 V to 5.5 V supply with a power consumption of 200 mW. A 1.20 V internal temperature-compensated bandgap reference is also included as a complete solution.