A 10-Bit 400-KS/s Low Noise Asynchronous SAR ADC with Dual-Domain Comparator for Input-Referred Noise Reduction

Abstract

This paper presents a low noise 0.6-V 400-kS/s asynchronous successive approximation register (SAR) analog-to-digital converter (ADC) for input-referred noise reduction. A dual-domain comparator is proposed to optimize the power, noise, and sampling rate of the ADC in the 10-bit conversion. In order to optimize the figure of merits (FoM) of the ADC, the 10-bit conversion consists of a 7-bit coarse conversion with the double-tail dynamic comparator and a 3-bit fine conversion with the VCDL-based time-domain comparator. An asynchronous timing controller is also proposed to improve the ADC sampling rate and optimize the power consumption of the dual-domain comparator. The proposed SAR ADC is fabricated in 180-nm CMOS technology with an area of 0.836 mm2. At a 0.6-V supply voltage and a 400-kS/s sampling rate, the implemented SAR ADC achieves a signal-to-noise and distortion ratio (SNDR) of 56.59 dB and an effective number of bits (ENOB) of 9.16 bits. The peak values of DNL and INL are +0.47/−0.53 LSB and +0.92/−0.64 LSB, respectively. The FoM is 10.31 fJ/conversion step with a power consumption of 2.36 μW.