A ± 3 ppm/°C Single-Trim Switched Capacitor Bandgap Reference for Battery Monitoring Applications

Abstract

A precision bandgap reference has been developed in a $0.18~\mu \text {m}$ BiCMOS process that achieves ±3 ppm/°C temperature drift at ±3 $\sigma $ from −40 °C to 110 °C. The reference is designed to utilize single temperature trim and standard components. A 3.65 V switched capacitor reference voltage is provided to a $2^{{\textrm {nd}}}$ order delta-sigma modulator ADC to digitize a battery cell voltage. The switched capacitor reference utilizes fully differential sampling which reduces the errors from channel charge injection and clock feedthrough introduced by pseudo-differential sampling. A new technique for sampling a $\text {V}_{{\textrm {be}}}$ voltage directly onto the output of the reference’s differential amplifier has been developed that removes the error that would be introduced from differentially sampling the $\text {V}_{{\textrm {be}}}$ and the $\Delta \text {V}_{{\textrm {be}}}$ voltage terms independently. The bandgap reference and ADC combination have an input referred noise spectral density of $4.7~\mu \text {V}/\surd $ Hz from 0.1 to 162 Hz yielding 15 stable output bits.