A Precision CMOS Bandgap Reference

Abstract

This paper describes the design of a precision on-chip bandgap voltage reference for applications with CMOS analog circuits. The circuit uses naturally occurring vertical n-p-n bipolar transistors as reference diodes. P-tub diffusions are used as temperature-dependent resistors to provide current bias, and an op-amp is used for voltage gain. The circuit is simple. Only two reference diodes, three p-tub resistors, and one op-amp are necessary to produce a reference with fixed voltage of —1.3 V. An additional op-amp with two p-tub resistors will adjust the output to any desired value. The criteria for temperature compensation are presented and show that the properly compensated circuit can in principle produce thermal drift which is less than 10 ppm/°C. Process sensitivity analysis shows that in practical applications it is possible to control the output to better than 2 percent, while keeping thermal drift below 40 ppm/°C. Test circuits have been designed and fabricated. The output voltage produced was -1.30 + 0.025 V with thermal drift less than 7 mV from 0°C to 125°C. Significant improvements in performance, at modest cost in circuit complexity, can be achieved if the op-amp offset contribution to the output voltage is reduced or eliminated. © 1984 IEEE