FIRDAC with RTZ/RTO voltage-mode elements

摘要

A FIRDAC with a return-to-zero or return-to-open drive uses multiple DACs receiving delayed copies of a digital input data signal to reduce thermal noise and intersymbol interference to produce a summed analog output. The SNR of sigma-delta ADCs using current-source-based DACs is significantly limited by the thermal noise of the DAC current sources. DACs using a switched voltage connected via a resistor or other passive element are quieter, but in a non-return-to-zero configuration tend to suffer from intersymbol interference if used at GHz clock frequencies. The intersymbol interference can be avoided by using a return-to-zero or return-to-open drive using multiple DACs clocked on successive half clock cycles (a finite-impulse-response DAC).