Sub-ppm/°C Bandgap References With Natural Basis Expansion for Curvature Cancellation

Abstract

A general approach based on a natural basis function expansion to cancel the temperature-curvature of the base-emitter voltage in the bipolar transistors embedded in bandgap references is presented. The proposed method can be applied to the widely used Banba, Kuijk, and Brokaw structures to build references with sub-ppm/°C temperature coefficients. Current version and voltage version embodiments based on a self-bootstrapping concept are provided. Error sources that can potentially affect the reference performance are analyzed and their effects on the temperature coefficient are minimized after trimming. Monte Carlo simulation results confirm that after calibration, temperature drift performance is within the design/trimming target 0.5 ppm/°C. A partially integrated Kuijk-based prototype reference has been designed and fabricated in a 65nm UMC process. Measurement results demonstrated a 1.5 ppm/°C temperature coefficient over a temperature range of 0 °C to 80 °C with a low-cost two-temperature trimming method. With additional trimming, 0.8 ppm/°C performance was achieved.