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

A precision bandgap reference has been developed in a <inline-formula> <tex-math notation="LaTeX">$0.18~\mu \text {m}$ </tex-math></inline-formula> BiCMOS process that achieves ±3 ppm/°C temperature drift at ±3 <inline-formula> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">$2^{{\textrm {nd}}}$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">$\text {V}_{{\textrm {be}}}$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">$\text {V}_{{\textrm {be}}}$ </tex-math></inline-formula> and the <inline-formula> <tex-math notation="LaTeX">$\Delta \text {V}_{{\textrm {be}}}$ </tex-math></inline-formula> voltage terms independently. The bandgap reference and ADC combination have an input referred noise spectral density of <inline-formula> <tex-math notation="LaTeX">$4.7~\mu \text {V}/\surd $ </tex-math></inline-formula>Hz from 0.1 to 162 Hz yielding 15 stable output bits.

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