Subthreshold current-mode oscillator-based quantizer with 3-decade scalable sampling rate and pico-Ampere range resolution

A current-mode oscillator-based analog-to-digital data converter (ADC) for bio-medical readout front-end systems is being presented. The core of this circuit is a current-controlled ring oscillator (CCO) whose oscillation frequency is proportional to the input current signal. To shape the quantization noise and improve the resolution, a CCO can be used as an integrator in ΔΣ configuration. Experimental results show that the proposed ADC can reach to 54 dB signal-to-noise ratio while the sampling frequency is 45.5 kHz and consuming 800 nW power (with an over-sampling ratio of 64). The sampling frequency of this ADC can be adjusted from 700 Hz to 540 kHz with a scalable power dissipation, corresponding to 17.5 pW/Hz.