The self-heating effects of bipolar junction transistors on the functionality of a current feedback amplifier

Self-heating effects strongly affect the performance of modern silicon-on-insulator (SOI) bipolar junction transistors. This research work does an extensive analysis of self-heating effects on large-signal behavior, small-signal behavior and transient operation of bipolar junction transistors. The two mechanisms in which device temperature affects large-signal behavior of a BJT transistor are investigated, i.e. the common-emitter (CE) configuration is to be driven by a constant base-emitter voltage and a constant base current. It is shown that the output characteristic of a BJT transistor is less sensitive to self-heating under a fixed base current than a fixed base-emitter voltage. A simple method of extracting the thermal resistance and the Early voltage is proposed. Self-heating effects on the BJT small-signal behavior are examined by investigating the two-port network parameters. It is shown that the gain of an amplifier and the output impedance of a current mirror can be affected significantly by self-heating effects. The mechanism of self-heating in transient operation is investigated and the transient operation of a high speed voltage buffer is analyzed. A method for estimating the thermal tail of a voltage buffer is presented.;An approach to analyze the contribution of each transistor to the overall thermal tail of current feedback operational amplifiers is presented. It is shown that the overall thermal tail of a current feedback operational amplifier (CFOA) is a linear superposition of each individual transistor. Techniques to minimize the thermal tail are proposed. A cascode bootstrapped CFOA is designed and optimized to minimize the thermal tail. The overall thermal tail is reduced to 9 muV/V compared with 1032 muV/V of a classical CFOA when driving a 2 kO load in a unity gain feedback configuration. Also the common mode rejection ratio (CMRR) is greatly improved to 92 dB compared with 60 dB of the classical CFOA.;The Vertical Bipolar Inter Company (VBIC) model is used for all the simulations. Simulations are performed using Cadence and Advanced Design System (ADS).