# Lect_07 - ECE!442 Solid"State!Devices!Circuits...

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1 Jose E. Schutt " Aine " ECE 442 ECE 442 Solid " State Devices & Circuits 7. BJT Amplifiers Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois [email protected]

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2 Jose E. Schutt " Aine " ECE 442 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 !
3 Jose E. Schutt " Aine " ECE 442 Amplifiers : p v 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 ! 20log I Current gain in dB A ! 10log P Power gain in dB A ! Expressing gain in dB (decibels)

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4 Jose E. Schutt " Aine " ECE 442 Amplifiers 1 1 2 2 DC P V I V I ! " 100 L DC P Power Efficiency P # ! \$ ! Since output associated with the signal is larger than the input signal, power must come from DC supply DC I L dissipated P P P P " !"
5 Jose E. Schutt " Aine " ECE 442 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 # Problem 9 9 1 o v i V A V ! ! ! 9 ˆ 9 1 o I mA k !! & 20log 20log 9 19.1 v dB v A A dB ! ! ! ˆ 9 90 ˆ 0.1 o i i I A I ! ! ! The current gain is

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6 Jose E. Schutt " Aine " ECE 442 Problem 40.5 810 0.05 d v I P A P ! ! ! 20log90 39.1 i dB A dB !! 99 40.5 22 L o rms o rms Power at Load P V I mW ’’ ! ! ! ! 1 0.1 0.05 I I rms I rms Power at input P V I mW ! ! ! ! 10log810 29.1 v dB A dB 10 9.5 10 9.5 190 dc P mW ! \$ " \$ ! dissipated dc I L P P P P ! "’ 190 0.05 4.05 149.6 dissipated P mW ! ! 100 21.3% L dc P P #! \$ !
7 Jose E. Schutt " Aine " ECE 442 Biasing of Amp ( ) ( ) I QI I V t V v t !" 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 - ECE!442 Solid"State!Devices!Circuits...

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