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# ch05 - Fundamentals of Microelectronics CH1 CH2 CH3 CH4 CH5...

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1 Fundamentals of Microelectronics CH1 Why Microelectronics? CH2 Basic Physics of Semiconductors CH3 Diode Circuits CH4 Physics of Bipolar Transistors CH5 Bipolar Amplifiers CH6 Physics of MOS Transistors CH7 CMOS Amplifiers CH8 Operational Amplifier As A Black Box

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2 Chapter 5 Bipolar Amplifiers 5.1 General Considerations 5.2 Operating Point Analysis and Design 5.3 Bipolar Amplifier Topologies 5.4 Summary and Additional Examples
CH5 Bipolar Amplifiers 3 Bipolar Amplifiers

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CH5 Bipolar Amplifiers 4 Voltage Amplifier In an ideal voltage amplifier, the input impedance is infinite and the output impedance zero. But in reality, input or output impedances depart from their ideal values.
CH5 Bipolar Amplifiers 5 Input/Output Impedances The figure above shows the techniques of measuring input and output impedances. x x x i V R =

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CH5 Bipolar Amplifiers 6 Input Impedance Example I When calculating input/output impedance, small-signal analysis is assumed. π r i v x x =
CH5 Bipolar Amplifiers 7 Impedance at a Node When calculating I/O impedances at a port, we usually ground one terminal while applying the test source to the other terminal of interest.

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CH5 Bipolar Amplifiers 8 Impedance at Collector With Early effect, the impedance seen at the collector is equal to the intrinsic output impedance of the transistor (if emitter is grounded). o out r R =
CH5 Bipolar Amplifiers 9 Impedance at Emitter The impedance seen at the emitter of a transistor is approximately equal to one over its transconductance (if the base is grounded). ) ( 1 1 1 = + = A m out m x x V g R r g i v π

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CH5 Bipolar Amplifiers 10 Three Master Rules of Transistor Impedances Rule # 1: looking into the base, the impedance is r π if emitter is (ac) grounded. Rule # 2: looking into the collector, the impedance is r o if emitter is (ac) grounded. Rule # 3: looking into the emitter, the impedance is 1/g m if base is (ac) grounded and Early effect is neglected.
CH5 Bipolar Amplifiers 11 Biasing of BJT Transistors and circuits must be biased because (1) transistors must operate in the active region, (2) their small-signal parameters depend on the bias conditions.

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CH5 Bipolar Amplifiers 12 DC Analysis vs. Small-Signal Analysis First, DC analysis is performed to determine operating point and obtain small-signal parameters. Second, sources are set to zero and small-signal model is used.
CH5 Bipolar Amplifiers 13 Notation Simplification Hereafter, the battery that supplies power to the circuit is replaced by a horizontal bar labeled Vcc, and input signal is simplified as one node called V in.

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CH5 Bipolar Amplifiers 14 Example of Bad Biasing The microphone is connected to the amplifier in an attempt to amplify the small output signal of the microphone.
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