A fully-digital beat-frequency based ADC achieving 39dB SNDR for a 1.6mVpp input signal

A fully-digital VCO-based ADC featuring a novel beat frequency detection scheme is demonstrated in 65nm LP CMOS. The proposed beat frequency based ADC is unique compared to previous VCO-based ADCs in that it is highly effective in measuring extremely small changes (e.g., 0.01%) in the VCO frequency within a short sampling time (e.g., 100 VCO periods). Direct amplifier-less A-to-D conversion of a 1.6mV
_pp
differential input signal with 39dB SNDR and 6.2 ENOB was experimentally verified.