# Lecture 10 - Last Week Three Terminal Devices Bipolar...

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1 ECTE290 Spring 2007 Lecture 10 2 Last Week Three Terminal Devices: Bipolar Junction Transistors V BE I B I C β I B DC equivalent Hybrid π Model T C m V I g = m g r β π = be m c v g i = DC Analysis AC Analysis C B E B C I I I I I + = = V BE = 0.7V I C is controlled by I B i c is controlled by v be B E C 3 Example Find A V = v out /v i , ( β = 100) DC problem Short AC source v i , determine I C and V CE a) BE voltage loop 3 = I B R B + V BE I B = (3 - 0.7)/R B = 0.023mA b) CE voltage loop V CE = 10 - I C R C V CE = 10 – 100*(0.023)(3) V CE = 3.1V Q point: V CE = 3.1V, I C = 2.3mA v out B C E 4 AC problem Short DC sources, input and output circuits are separate, only coupled mathematically g m = I C /V T = 2.3mA/25mV = 92mA/V r π = β / g m = 100/92mA/V = 1.1K v be = v i [r π / (100K + r π )] = 0.011v i i c =g m v be v out = - i c R C v out = - 92 (0.011v i )3K Æ A V = v out /v i = -3.04 + v out - e b c + v be - Example R π g m v be

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2 5 Outline ± Operational amplifier ± Open loop ± Close loop ± Typical circuits ± Digital to analog converters 6 Ideal Amplifier Characteristics ) ( ) ( t Av t v s L = The source has been modeled as a thevenin equivalent, and the load as an equivalent resistance. The equivalent source circuit is the circuit the amplifier “sees” from its input port; and R L , the load is the equivalent resistance seen from the output port of the amplifier Ideal amplifier will perform consistently for different sources and loads, that is, same A 7 Ideal Amplifier Characteristics cont s L out L in s in L L out L in L s in s in in v R R R R R R A v R R R Av v v R R R v + + = + = + = The amplification factor is now dependent on both the source and load impedances, and on the input and output resistance of the amplifier. Thus, a given amplifier would perform differently with different loads or sources. If R in is very large and R out is very small , 1 + + L out L in s in R R R R R R s L Av v = Ideal Amplifier has 0 , = = out in R R 8 Overview– Operational Amplifier ± Often Abbreviated : Op-Amp ± Versatile Circuit Element ± Monolithic Integrated Circuit (many transistors inside) ± But we don’t care… ± Because to use an Operational amplifier does not require an in depth knowledge of the internal circuitry ± Model the “Op-Amp” as a simple 3-port element
3 9 Real Op-Amp Components Dual OP Single OP Find the pin definition from data sheet Don’t forget to connect the power. Op-Amp is an active component, it won’t work if there is no power supply. Dot indicates pin 1 10 What’s Inside the Op-Amp? Monolithic Integrated Circuit (Many transistors inside) Circuitry inside the LM741, one popular type of op-amp + _ + _ + V POS + V NEG + v OUT 11 How to Connect the Power Supply? Both positive and negative power must be supplied, Three terminal device with two input and one output POS OUT NEG V V V < < Negative input Positive input Output +15V -15V POS V NEG V They may not always be shown.

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Lecture 10 - Last Week Three Terminal Devices Bipolar...

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