A 10-hit, 771 nW Time-Mode ADC with a 2-Step TDC for Bio-Signal Acquisition

In this paper, we present the design of a low-voltage, low-power, and small-area time-mode ADC (TM-ADC) for bio-signal sensing applications. The proposed time-mode ADC (TM-ADC) consists of a programmable oversampling ratio (OSR), voltage-controlled ring oscillator (VCRO) based analog-to-time converter (ATC), followed by an asynchronous unfolded SAR coarse TDC and an asynchronous, enhanced-range fine flash TDC. The integrated circuit has been implemented in a standard CMOS 65 nm process and its performance has been evaluated through extracted transient noise simulations. The ADC consumes 771 nW at a sampling rate of 2.2 kHz from a 0.5V supply voltage and achieves 10-bit resolution in a total area of 0.014 mm
²
. The simulation results indicate DNL and INL values of +0.86/-0.83 and +0.88/-1.79, respectively, an SNDR of 60.7 dB and an ENOB of 9.8 bits for a 10mV peak-to-peak signal 1kHz input signal.