Conventional continuous-time modulators that use non-return-to-zero (NRZ) feedback DACs suffer from distortion due to inter-symbol-interference (ISI) and are sensitive to clock jitter. Using a return-to-zero (RZ) DAC solves the problem of ISI, but exacerbates clock jitter sensitivity. The clock jitter sensitivity of an NRZ DAC can be reduced using a switched-capacitor (SC) DAC, but the large peak-to-average ratio of the DAC waveform degrades modulator linearity. In this work, we introduce the Switched-Capacitor Return-to-Zero (SCRZ) DAC, which combines the low clock jitter sensitivity of the SC DAC with the low distortion of an RZ DAC. Measured results from a test chip fabricated in 0.18um CMOS demonstrate the efficacy of the SCRZ technique.
Thursday, February 28, 2013
Free and open to the public