This paper describes a voltage controlled oscillator (VCO)-based ADC for biomedical applications which employs a relaxation oscillator for voltage-to-frequency conversion. The proposed circuit uses a redundant pair of capacitors to mitigate the conversion error resulting from the time required for resetting the capacitor. A switch matrix with feedback helps sustain oscillations. Further, the VCO frequency approaches zero as the input voltage approaches zero unlike a converter with ring oscillator, thereby reducing power consumption. Post-layout simulation of the proposed ADC designed with a 28 nm FDSOI CMOS technology shows an ENOB of 8 and power consumption of 12 W from a 0.7 V supply.

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