115A_1_EE115A_W10-Chap5

# 115A_1_EE115A_W10-Chap5 - Chapter 5 Bipolar Amplifiers h...

This preview shows pages 1–15. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 5 Bipolar Amplifiers h 5.1 General Considerations 169 h 5.2 Operating Point Analysis and Design h 5.3 Bipolar Amplifier Topologies h 5.4 Summary and Additional Examples Bipolar Amplifiers CH5 Bipolar Amplifiers 170 Voltage Amplifier CH5 Bipolar Amplifiers 171 h In an ideal voltage amplifier, the input impedance is infinite and the output impedance zero. h But in reality, input or output impedances depart from their ideal values. Input/Output Impedances CH5 Bipolar Amplifiers 172 h The figure above shows the techniques of measuring input and output impedances. x x x i V R = Input Impedance Example I CH5 Bipolar Amplifiers 173 h When calculating input/output impedance, small-signal analysis is assumed. π r i v x x = Impedance at a Node CH5 Bipolar Amplifiers 174 h When calculating I/O impedances at a port, we usually ground one terminal while applying the test source to the other terminal of interest. Impedance at Collector CH5 Bipolar Amplifiers 175 h 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 = Impedance at Emitter 1 1 + = m x x r g i v π CH5 Bipolar Amplifiers 176 h The impedance seen at the emitter of a transistor is approximately equal to one over its transconductance (if the base is grounded). ) ( 1 ∞ = ≈ A m out V g R Three Master Rules of Transistor Impedances CH5 Bipolar Amplifiers 177 h Rule # 1: looking into the base, the impedance is r π if emitter is (ac) grounded. h Rule # 2: looking into the collector, the impedance is r o if emitter is (ac) grounded. h Rule # 3: looking into the emitter, the impedance is 1/g m if base is (ac) grounded and Early effect is neglected. Biasing of BJT CH5 Bipolar Amplifiers 178 h 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. DC Analysis vs. Small-Signal Analysis CH5 Bipolar Amplifiers 179 h First, DC analysis is performed to determine operating point and obtain small-signal parameters. h Second, sources are set to zero and small-signal model is used. Notation Simplification CH5 Bipolar Amplifiers 180 h 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. Example of Bad Biasing CH5 Bipolar Amplifiers 181 h The microphone is connected to the amplifier in an attempt to amplify the small output signal of the microphone. h Unfortunately, there’s no DC bias current running thru the transistor to set the transconductance. Another Example of Bad Biasing CH5 Bipolar Amplifiers 182 h The base of the amplifier is connected to V cc , trying to establish a DC bias....
View Full Document

## This note was uploaded on 01/08/2011 for the course EE 115 taught by Professor Kaiser during the Spring '09 term at UCLA.

### Page1 / 104

115A_1_EE115A_W10-Chap5 - Chapter 5 Bipolar Amplifiers h...

This preview shows document pages 1 - 15. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online