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emitter-follower ef amplifier

Ch. 7 Frequency Response Part 4. 2. EF Amplifier - DC Analysis (Nearly the Same as CE Amplifier). GIVEN: Transistor parameters: Current gain

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emitter-follower ef amplifier

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    1: Ch. 7 Frequency Response Part 4 1 Emitter-Follower (EF) Amplifier DC biasing Calculate IC, IB, VCE Determine related small signal equivalent circuit parameters Transconductance gm Input resistance rp Midband gain analysis Low frequency analysis Gray-Searle (Short Circuit) Technique Determine pole frequencies ?PL1, ?PL2, ... ?PLn Determine zero frequencies ?ZL1, ?ZL2, ... ?ZLn High frequency analysis Gray-Searle (Open Circuit) Technique Determine pole frequencies ?PH1, ?PH2, ... ?PHn Determine zero frequencies ?ZH1, ?ZH2, ... ?ZHn

    2: Ch. 7 Frequency Response Part 4 2

    3: Ch. 7 Frequency Response Part 4 3 EF Amplifier - Midband Gain Analysis

    4: Ch. 7 Frequency Response Part 4 4 Analysis of Low Frequency Poles Gray-Searle (Short Circuit) Technique Draw low frequency AC circuit Substitute AC equivalent circuit for transistor (hybrid-pi for bipolar transistor) Include coupling capacitors CC1, CC2 Ignore (remove) all transistor capacitances Cp , C Turn off signal source, i.e. set Vs= 0 Keep source resistance RS in circuit (do not remove) Consider the circuit one capacitor Cx at a time Replace all other capacitors with short circuits Solve remaining circuit for equivalent resistance Rx seen by the selected capacitor Calculate pole frequency using Repeat process for each capacitor finding equivalent resistance seen and corresponding pole frequency Calculate the final low 3 dB frequency using

    5: Ch. 7 Frequency Response Part 4 5 Emitter Follower - Analysis of Low Frequency Poles Gray-Searle (Short Circuit) Technique

    6: Ch. 7 Frequency Response Part 4 6 Emitter Follower - Analysis of Low Frequency Poles Gray-Searle (Short Circuit) Technique

    7: Ch. 7 Frequency Response Part 4 7 Emitter Follower - Low Frequency Zeros

    8: Ch. 7 Frequency Response Part 4 8 Emitter Follower - Low Frequency Poles and Zeros Magnitude Bode Plot

    9: Ch. 7 Frequency Response Part 4 9 Emitter Follower - Low Frequency Poles and Zeros Phase Shift Bode Plot

    10: Ch. 7 Frequency Response Part 4 10 Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique Draw high frequency AC equivalent circuit Substitute AC equivalent circuit for transistor (hybrid-pi model for transistor with Cp, C) Consider coupling and emitter bypass capacitors CC1 and CC2 as shorts Turn off signal source, i.e. set Vs = 0 Keep source resistance RS in circuit Neglect transistors output resistance ro Consider the circuit one capacitor Cx at a time Replace all other transistor capacitors with open circuits Solve remaining circuit for equivalent resistance Rx seen by the selected capacitor Calculate pole frequency using Repeat process for each capacitor Calculate the final high frequency pole using

    11: Ch. 7 Frequency Response Part 4 11 Emitter Follower - Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique

    12: Ch. 7 Frequency Response Part 4 12 Emitter Follower - Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique

    13: Ch. 7 Frequency Response Part 4 13 Emitter Follower - Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique

    14: Ch. 7 Frequency Response Part 4 14 Emitter Follower - Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique

    15: Ch. 7 Frequency Response Part 4 15 Emitter Follower - Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique

    16: Ch. 7 Frequency Response Part 4 16 Emitter Follower - Analysis of High Frequency Poles Gray-Searle (Open Circuit) Technique

    17: Ch. 7 Frequency Response Part 4 17 Emitter Follower - High Frequency Zeros

    18: Ch. 7 Frequency Response Part 4 18 Emitter Follower - High Frequency Poles and Zeros Magnitude

    19: Ch. 7 Frequency Response Part 4 19 Emitter Follower - High Frequency Poles and Zeros Phase Shift

    20: Ch. 7 Frequency Response Part 4 20 Comparison of EF to CE Amplifier (For RS = 5O )

    21: Ch. 7 Frequency Response Part 4 21 Conclusions Voltage gain Can get good voltage gain from CE but NOT from EF amplifier (AV ? 1). Low frequency performance better for EF amplifier. EF amplifier gives much better high frequency performance! CE amplifier has dominant pole at 5.0x107 rad/s. EF amplifier has dominant pole at 1.0x1010 rad/s. Bandwidth approximately 200 X larger! Miller Effect multiplication of C? by the gain is avoided in EF. Current gain For CE amplifier, current gain is high ? = Ic/Ib For EF amplifier, current gain is also high Ie/Ib = ? +1 ! Frequency dependence of current gain similar to voltage gain. Input and output impedances are different for the two amplifiers!

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