An 8-GHz continuous-time (sigma)-(delta) analog-digital converter in an InP-based HBT technology

We report an 8-GHz clock-rate, second-order continuous-time (sigma)-(delta) analog-digital converter (ADC) that achieves 57.4-, 51.7-, and 40.2-dB SNR at signal sampling rates of 125, 250, and 500 Ms/s, respectively. The integrated circuit occupied 1.45-mm/sup 2/ die area, contains 76 transistors, is fabricated in an InP-based HBT technology, and dissipates ~1.8 W. We also study the effect of excess delay on modulator performance, and show that excess delay does not affect performance as long as the centroid-in-time of the digital-analog converter pulse remains stationary.