Lect_07 - ECE442 SolidStateDevices&Circuits...

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ECE 342–Jose Schutt Aine 1 ECE 442 Solid State Devices & Circuits 7. BJT Amplifiers Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois jschutt@emlab.uiuc.edu
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ECE 342–Jose Schutt Aine 2 Definitions – Used to increase the amplitude of an input signal to a desired level – This is a fundamental signal processing function – Must be linear (free of distortion) – Shape of signal preserved Amplifiers () , oi v t Av t where A is the voltage gain = v i (t) v o (t) AMP : o v i v Voltage Gain A v = : L p I Load Power P Power Gain A Input Power P =
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ECE 342–Jose Schutt Aine 3 Amplifiers : pv i Note A A A = : o i i i Current Gain A i = oo p I I vi A = 20log V Voltage gain in dB A = I Current gain in dB A = 10log P Power gain in dB A = Expressing gain in dB (decibels)
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ECE 342–Jose Schutt Aine 4 Amplifiers 11 2 2 DC P VI VI = + 100 L DC P Power Efficiency P η = Since output associated with the signal is larger than the input signal, power must come from DC supply DC I L dissipated P PPP + =+
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ECE 342–Jose Schutt Aine 5 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 Ω 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 η Problem 9 9 1 o v i V A V == = 9 ˆ 9 1 o I mA k Ω 20log 20log 9 19.1 vd B v A Ad B = ˆ 9 90 ˆ 0.1 o i i I A I = The current gain is
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ECE 342–Jose Schutt Aine 6 Problem 40.5 810 0.05 d v I P A P == = 20log90 39.1 id B Ad B 99 40.5 22 Lo r m s o r m s Power at Load P V I mW −− = = 10 . 1 0.05 II r m s I r m s Power at input P V I mW = = 10log810 29.1 vd B B 10 9.5 10 9.5 190 dc P mW = dissipated dc I L P PP P = +− 190 0.05 4.05 149.6 dissipated Pm W =− = 100 21.3% L dc P P η =
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ECE 342–Jose Schutt Aine 7 Biasing of Amp () IQ I I Vt V vt =+ Bias will provide quiescent points for input and output about which variations will take place. Bias maintain amplifier in active region.
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Lect_07 - ECE442 SolidStateDevices&Circuits...

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