All-digital differential VCO-based A/D conversion

Voltage-controlled oscillator-based analog-to-digital converters utilizes the superior time resolution and digital processing power of time-domain signal processing. With its inherent first-order noise shaping property, very high accuracy can be obtained while reducing both area and power consumption. An all-digital VCO-based ADC scheme is presented which combines a differential configuration with digital calibration to obtain very high linearity. A coarse-fine quantization approach is used to reduce the circuit complexity compared to the traditional multi-bit quantization The phase resolution is increased using passive interpolation coupled VCOs. These techniques are illustrated with a 65 nm CMOS implementation of a 30 MHz BW 10-bit ADC, occupying only 0.023 mm².