Assimilation of Negative Feedback in Bandgap Reference Circuits for Subsiding the Variation of Reference Voltages Over the Temperature Range from 55 C to +165 C

Abstract

Latest technologies demand for low voltage and low power in designing both analog and digital integrated circuits. The purpose is to incorporate as much devices as possible into a single chip and to operate them in low voltage in order to minimize power loss. On the other hand, many electronic blocks such as oscillator, data converter (AID or Df A) etc. require a precise reference yoltage so as to work properly even when there is supply, process and temperature variations. A Bandgap reference circuit (BGR) plays a vital role, in this case, that provides a low reference yoltage that is exempt to temperature, process and supply variations. In this project, a 1.2V CMOS Bandgap reference circuit with supply voltage range of 1.8V to 2V in associated with active regulated circuits is proposed. The reference circuit is designed to operate at an ambient temperature of 27°C with line regulation of 177.5mVN and a temperature coefficient of 241 ppm/DC. The reference circuit composed of a supply independent block (which is basically a common-gate-Op Amp) that keeps the reference immune to supply variation to some extent. Another part of the reference circuit is the temperature independent block that is designed in such a way that the reference has negligible impact with temperature variation and also it debilitates the effect of process variation with temperature. An equation is derived for the clear understanding of how process variation is affecting the reference voltage. Lastly, the values obtained from the design simulation are compared with the other proposals. A two stage operational amplifier with a gain of around 70dB is designed to demonstrate the adverse effect of varying reference on its gain. Owing to its high open loop dc gain, the Op Amp shows a significant change due to small change in its biasing voltage. The gain of the Op Amp varies from 13%-15% due to variation in temperature and 60%-130% due to the variation in supply. So active regulated circuits are proposed that incorporate negative feedback mechanisms, in order, to subside the reference voltage to 1.2V, for a wide range of temperature from -55DC to +1650C. The analyses are carried out in Advanced Design System (ADS) software using TSMC 0.18wn technology.