A VCO-Based Nonuniform Sampling ADC Using a Slope-Dependent Pulse Generator

Abstract

This paper presents a voltage-controlled oscillator (VCO)-based nonuniform sampling analog-to-digital converter (ADC) as an alternative to the level-crossing (LC)-based converters for digitizing biopotential signals. This work aims to provide a good signal-to-noise-and-distortion ratio at a low average sampling rate. In the proposed conversion method, a slope-dependent pulse generation block is used to provide a variable sample rate adjusted according to the input signal’s slope. Simulation results show that the introduced method meets a target reconstruction quality with a sampling rate approaching 92 Sps, while on the same MIT-BIH Arrhythmia N 106 ECG benchmark, the classic LC-based approach requires a sampling rate higher than 500 Sps. The benefits of the proposed method are more remarkable when the input signal is very noisy. The proposed ADC achieves a compression ratio close to 4, but with only 5.4% root-mean-square difference when tested using the MIT-BIH Arrhythmia Database.