Curvature correction method for a bandgap voltage reference

Abstract

A reference voltage based on the bandgap principle consists of the summation of two voltages having opposite variations with temperature: a forward biased p-n junction having a Complementary to Absolute Temperature (CTAT) variation and a voltage Proportional to Absolute Temperature (PTAT). The variation with temperature is approximately linear in both cases and the object of the circuit is to cancel the two opposite slopes. If the PTAT and CTAT are well balanced, all that remains is a second order curvature error of the form TlnT (where T is absolute temperature, and In is natural log), which is mainly due to the CTAT voltage component. Minimisation of this non-linear parameter is the key challenge in designing a voltage reference with low temperature coefficient (TC).This paper presents the mathematical basis of this residual non-linear component, and describes a novel circuit to reduce it.