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Unformatted text preview: Lecture 34 Wednesday April 29 EE 332 Semiconductor Devices Omit section 10.2 Problem Assignment Wednesday 9.19 and 9.23 Friday 10.1 and 10.3 HybridPi Circuit Model Identify each element with our model of a BJT AC Analysis and Modeling Write the total voltage (v EB ) as a sum of the DC component (V EB ) and an AC component (v eb ). eb EB EB v V v + = In the hybridpi model r is given by: ( ) E kT v V q E pE E pE B W e p D qA I I eb EB / + = be b v i r 1 The base current is approximately equal to I pE because: and T =1 nE T pE B I I I ) 1 ( + = Finding r The expression for r in terms of the bias current becomes: C DC B B qI kT qI kT kT qI r = = 1 ( ) kT qI W e p D qA kT q v i B E kT v V q E pE E eb b eb EB = = + / The reciprocal of this equation is r in terms of the device parameters as give in eq. 10.9 Finding r u CB C u v i r = 1 The denominator is change in current through the reverse biased collector junction with changing collector to base voltage,...
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 Spring '08
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