A VCO-ADC Linearized by a Capacitive Frequency-to-Current Converter

Abstract

In this brief we propose a technique to compensate the distortion of an open-loop VCO-based ADC. The VCO is linearized by placing an analog feedback loop based on a frequency-to-current converter which uses an asynchronous switched capacitor circuit. The feedback loop relies on the VCO gain to linearize the ADC without requiring additional amplifiers. This permits the use of a ring oscillator with small input range to efficiently encode a large signal. The proposed technique has been experimentally demonstrated in an audio ADC. The proof-of-concept chip was fabricated in 130nm CMOS and achieves 76.64 dBA of peak SNDR with a Dynamic Range of 90dB and a power consumption of 482μW in 20kHz.