Lect_07 - ECE 442 ECE 442 SolidState Devices & Circuits 7....

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CE 442 ECE 442 Solid State Devices & Circuits 7. BJT Amplifiers Jose E. Schutt-Aine lectrical & Computer Engineering Electrical & Computer Engineering University of Illinois jschutt@emlab.uiuc.edu ECE 442–Jose Schutt Aine 1

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Amplifiers Definitions – Used to increase the amplitude of an input signal to a desired level his is a fundamental signal processing function – This is a fundamental signal processing function – Must be linear (free of distortion) – Shape of signal preserved v i (t) v o (t) AMP () , oi v t Av t where A is the voltage gain : o v i v Voltage Gain A v : Load Power P ower Gain A ECE 442–Jose Schutt Aine 2 p I Power Gain A Input Power P
Amplifiers oo p I I vi A i ote A A A : o i i i Current Gain A i : pv Note A 0log l t i i dB A Expressing gain in dB (decibels) 20log V Voltage gain in dB I Current gain in dB A 10log P Power gain in dB A ECE 442–Jose Schutt Aine 3

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Amplifiers Since output associated with the signal is larger than the input signal, power must come from DC supply 11 2 2 DC P VI VI DC I L dissipated P PPP  100 L DC P Power Efficiency P  ECE 442–Jose Schutt Aine 4
n amplifier has 0 V power supplies and an input current of 0.1 Problem An amplifier has 10 V power supplies and an input current of 0.1 mA (sine wave) input voltage 1 V peak-to-peak and an output voltage with a peak of 9V. The load impedance is 1 k and the amp draws 9.5 mA from each power supply. Determine: - the voltage gain - the current gain - the power gain - the power drawn from supplies - the power dissipated and 9 o V 9 1 v i A V  20log 20log 9 19.1 vd B v A Ad B 9 ˆ 9 1 o I mA k ˆ 9 90 ˆ o I A he current gain is ECE 442–Jose Schutt Aine 5 0.1 i i I The current gain is

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Problem 20log90 39.1 id B Ad B  99 0 5 ower at Load P V I mW 40.5 22 Lo r m s o r m s Power at Load 10 . 1 0.05 I r m s I r m s Power at input P V I mW 40.5 810 05 d v P A II dissipated dc I L P PP P  0.05 I P 10log810 29.1 vd B B 190 0.05 4.05 149.6 dissipated Pm W  10 9.5 10 9.5 190 dc P mW   100 21.3% L dc P P ECE 442–Jose Schutt Aine 6
Biasing of Amp ias will provide quiescent points for input and output about which Bias will provide quiescent points for input and output about which variations will take place. Bias maintain amplifier in active region. () IQ I I Vt V vt  oQ O o V ov I A o v I at Q dv A dv ECE 442–Jose Schutt Aine 7 Amplifier characteristics are determined by bias point

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Voltage Amplifier A R vo i L A vR v : ov o L v iL o vA Voltage gain is A vR R i R put v v o L o RR Want R o small (as small as ossible) to achieve maximum is iS Input v Want R i large ( so v i v s ) possible) to achieve maximum gain ideal R o =0 (actually want R
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This note was uploaded on 05/05/2010 for the course ECE 329 taught by Professor Franke during the Spring '08 term at University of Illinois at Urbana–Champaign.

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Lect_07 - ECE 442 ECE 442 SolidState Devices & Circuits 7....

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