A 2-GS/s 3-bit ΔΣ-modulated DAC with tunable bandpass mismatch shaping

Direct digital synthesis of signals in the hundreds of megahertz can lead to simpler, smaller transceivers, free of images and LO feedthrough that plague systems requiring analog upconversion. We present a 3-bit, 2 GS/s, ΔΣ-modulated DAC in InP HBT technology. The DAC is linearized using bandpass mismatch shaping. The mismatch shaper uses seven tunable 1.5-bit discrete-time bandpass ΔΣ modulators to dynamically route the digital signals to the DACs. These ΔΣ modulators operate in the analog domain to decrease system complexity and power consumption. The mismatch-shaped DAC can generate narrowband signals between 250-750 MHz with >68 dB SNR in a 1-MHz bw, >74-dB SFDR, and <-80-dBc intermodulation distortion with an 8.1-W power consumption.