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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 Hybrid-Pi 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 hybrid-pi 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