Effects of nonideal characteristics of substrate BJT on bandgap reference circuit

The non-ideal characteristics of bipolar junction transistors (BJT) on the performance of band gap reference circuits are investigated. It is shown that the base spreading resistance (BSR) of a substrate BJT along with its temperature dependence has a significant negative impact on the performance of voltage references. It is shown that the temperature-dependent forward current gain (β) also adversely affects reference performance. In a typical application in a bulk CMOS process, the base spreading resistance causes an increase in the reference output of about 1% and the temperature dependent β introduces an inflection point shift of around 30 °C. After calibration the TC changes by 25 ppm/°C