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The Self-heating Effects Of Bipolar Juction Transistors On The Functionality Of A Current Feedback Amplifier

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The Self-heating Effects Of Bipolar Juction Transistors On The Functionality Of A Current Feedback Amplifier

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Title: The Self-heating Effects Of Bipolar Juction Transistors On The Functionality Of A Current Feedback Amplifier
Author: Xie, Xuesong
Abstract: 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 μV/V compared with 1032 μV/V of a classical CFOA when driving a 2 kΩ 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).
URI: http://hdl.handle.net/10106/5111
Date: 2010-11-01

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