Chapter 4 BJT3 - Chapter 4 Bipolar Junction Transistor (BJ...

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SJTU J. Chen 1 3/2/12 Chapter 4 Bipolar Junction Transistor (BJ T)
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3/2/12 2 The analysis process (1) Determine the dc operating point of the BJT, in partic ular I c (2) Calculate the values of the small-signal model param eters: (3) Give the AC circuit: eliminate the dc source by replac ing each dc voltage source with a short circuit and e ach dc current source with an open circuit (4) Replace the BJT with one of its small-signal equivale nt circuit models (5) Analyze the resulting circuit to determine the require d quantities, e.g. voltage gain, input resistance and o utput resistance m E T e m T C m g I V r g r V I g 1 , , 2245 = = = β π
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3/2/12 3 J. P C h e n Ø Expression for the output resistance. Ø Output resistance represents the Early Effect(or base width modulation) Augmenting the Hybrid- Model ' 1 . C A const v CE C o I V v i r BE = = - =
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3/2/12 4 J. P C h e n Models derived from npn type transistor apply eq ually well to pnp transistor with no changes of pol arities. Because the small signal can not change t he bias conditions, small signal models are indep endent of polarities. No matter what the configuration is, model is uniq ue. Which one to be selected is only determined b y the simplest analysis. Models for pnp Type
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3/2/12 5 Summary of model parameters (1) Model parameters in terms of DC bias currents: (2) Model parameters in terms of g m : (3) Model parameters in terms of re: (4) Relationships between αandβ : = = = C T B T T C m I V I V r V I g β π C A o C T E T e I V r I V I V r = = = α m m e g r g r = = , ( 29 e m e e m r r g r r r g 1 1 , 1 , = + + = = - = + + = - = 1 1 1 , 1 , 1
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6 J. P
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This note was uploaded on 03/02/2012 for the course EI 207 taught by Professor Chengjianping during the Fall '10 term at Shanghai Jiao Tong University.

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Chapter 4 BJT3 - Chapter 4 Bipolar Junction Transistor (BJ...

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