Robust linear sampling switch for low-voltage SAR ADCs

Abstract

This paper presents a linear sampling switch for low-voltage successive-approximation register (SAR) analogue-to-digital converters (ADCs) operating at a frequency of tens of MHz. The proposed switch employs a bootstrapped transmission gate, where the bulk voltages are generated internally to minimize variations in the threshold voltage of transistors with input signal amplitude. Thus, ensuring almost constant and low ON-resistance ($$R_{ON}$$) over complete input signal range without using wide transistors, charge pumps, or both, at low supply voltages. The proposed switch was designed using standard 65 nm CMOS technology. The post-layout simulations have shown a signal to noise and distortion ratio (SNDR) of 87.81 dB, a spurious-free dynamic range (SFDR) of 90 dB and a total harmonic distortion (THD) of $$-91.5\,\hbox {dB}$$ at a sampling frequency and supply voltage of 100 MHz and 0.8 V, respectively. In addition, the switch has shown a maximum variation of 1% in $$R_{ON}$$ over input signal amplitude at different process corners and temperature, which is low compared to other sampling switches reported in the literature.