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

A precision bandgap reference has been developed in a 0.18 mu m BiCMOS process that achieves +/- 3 ppm/degrees C temperature drift at +/- 3 sigma from -40 degrees C to 110 degrees 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 2nd 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 pseudodifferential sampling. A new technique for sampling a V-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 V-be and the Delta V-be voltage terms independently. The bandgap reference and ADC combination have an input referred noise spectral density of 4.7 mu V/ root Hz from 0.1 to 162 Hz yielding 15 stable output bits.