Switched-Capacitor Bandgap Voltage Reference for IoT Applications
U Chi-Wa, Man‐Kay Law, Chi‐Seng Lam, Rui P. Martins
Abstract
This paper presents a switched-capacitor network (SCN) based bandgap voltage reference (BGR) for IoT applications. The proposed BGR employs a dual proportional-to-absolute-temperature (PTAT) clock topology to achieve both high precision and low power over a wide temperature range while relaxing the capacitor size requirements. Specifically, the fast PTAT clock assists in reducing the output voltage ripple of the dual-branch interleaved <inline-formula> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> charge pump (CP). Meanwhile, the slow PTAT clock controls the voltage divider SCN to relax the settling error at low temperature and the leakage-induced error at high temperature simultaneously, resulting in lower power consumption and smaller temperature coefficient (TC). We also propose a replica <inline-formula> <tex-math notation="LaTeX">$V_{\mathrm {EB}}$ </tex-math></inline-formula> generation branch in the series-parallel SCN to improve the BGR output TC due to the finite settling time during switching. Fabricated in 65nm standard CMOS, measurement results show that the proposed BGR obtains a TC of 32 ppm/°C at 0.5V supply within −40 °C to 120 °C. The line regulation is 3.3mV/V or 0.66%/V from 0.5V to 1V. Based on 10-chip measurement results, we obtain a <inline-formula> <tex-math notation="LaTeX">$3\sigma / \mu $ </tex-math></inline-formula> variation of 1.37% before trimming, while 0.25% after applying one-point trimming at 20°C.