Chapter13 - Chapter 13 Small-Signal Modeling and Linear Amplification Microelectronic Circuit Design Richard C Jaeger Travis N Blalock Jaeger\/Blalock

# Chapter13 - Chapter 13 Small-Signal Modeling and Linear...

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Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill Chapter 13 Small-Signal Modeling and Linear Amplification Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock Chap 13 - 1
Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill Chapter Goals Understanding of concepts related to: Transistors as linear amplifiers dc and ac equivalent circuits Use of coupling and bypass capacitors and inductors to modify dc and ac equivalent circuits Small-signal voltages and currents Small-signal models for diodes and transistors Identification of common-source and common-emitter amplifiers Amplifier characteristics such as voltage gain, input and output resistances and linear signal range Rule-of-thumb estimates for voltage gain of common-emitter and common-source amplifiers. Chap 13 - 2
Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill Introduction to Amplifiers BJT is used as an amplifier when biased in the forward-active region FET can be used as amplifier if operated in the pinch-off or saturation region In these regions, transistors can provide high voltage, current and power gains Bias is provided to stabilize the operating point in a desired operation region Q-point also determines Small-signal parameters of transistor Voltage gain, input resistance, output resistance Maximum input and output signal amplitudes Power consumption Chap 13 - 3
Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill BJT Amplifier BJT is biased in active region by dc voltage source V BE . Q-point is set at ( I C , V CE ) = (1.5 mA, 5 V) with I B = 15 μ A. Total base-emitter voltage is: v BE = V BE + v be Collector-emitter voltage is: This is the load line equation. v CE = 10 i C R C Chap 13 - 4
Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill BJT Amplifier (cont.) 8 mV peak change in v BE gives 5 μ A change in i B and 0.5 mA change in i C . 0.5 mA change in i C produces a 1.65 V change in v CE . If changes in operating currents and voltages are small enough, then i C and v CE waveforms are undistorted replicas of input signal. Small voltage change at base causes large voltage change at collector. Voltage gain is given by: Minus sign indicates 180 0 phase shift between input and output signals. A v = V ce V be = 1.65 180 0.008 0 = 206 180 = 206 Chap 13 - 5
Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill MOSFET Amplifier MOSFET is biased in active region by dc voltage source V GS . Q-point is set at ( I D , V DS ) = (1.56 mA, 4.8 V) with V GS = 3.5 V. Total gate-source voltage is: v GS = V GS + v gs 1 V p-p change in v GS gives 1.25 mA p-p change in i D and 4 V p-p change in v DS . Chap 13 - 6
Jaeger/Blalock 7/20/07 Microelectronic Circuit Design, 3E McGraw-Hill Coupling and Bypass Capacitors AC coupling through capacitors is used to inject ac input signal and extract output signal without disturbing Q-point Capacitors provide negligible impedance at frequencies of interest and provide open circuits at dc.

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• Voltage source, Electrical parameters, Microelectronic Circuit Design

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