Design and Analysis of a Power-Efficient Dynamic Comparator with an Improved Transconductance in Ultra-low Power SAR ADC Applications

Abstract

This paper presents an ultra-low power comparator with minimum delay and low offset, used in successive approximation register analog-to-digital converters (SAR ADCs) for biomedical system-on-chips (SoCs). To reduce the power consumption, the proposed comparator is designed with a minimum supply voltage in the sub-threshold region. Additionally, intermediate switches are utilized in the design to serve two purposes: 1) breaking the connection between the latch and preamplifier parts during the pre-charge phase to reduce power consumption, 2) reducing the parasitic resistance of the discharge path during the evaluation phase to enhance effective transconductance of the latch (\({g}_{meff,latch}\)). Furthermore, the proposed design incorporates, two transistors as auxiliary paths to increase the speed of discharging in the latching process. Overall, the proposed design aims to achieve a low power and high-performance comparator simulated at a frequency of 50 kHz using TSMC 65nm CMOS technology. The post-layout simulation results show that the proposed structure enjoyed from an ultra-low power consumption of 141.4 pW as well as excellent delay and offset with 357 ns and 3.32 mV values, respectively. The occupied area of the designed layout for the proposed comparator is 106.8 μm² allowed us to embed it in multi-channel recording system on chips (SoCs). The Figure of Merit (FoM) of the proposed comparator is 0.000463 fVW/Hz. Moreover, the proposed comparator has been validated by using it in successive approximation conversion algorithm with a sampling frequency of 1 kS/s.