EE3110 AECL1 Revision & frequency response_2007

EE3110 AECL1 Revision & frequency response_2007 -...

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Unformatted text preview: REVISION 1 Transistor Amplifier Circuit Analysis 1.1 Amplifier Characteristics R C R 1 V CC I/ P O/ P C C C B R 2 R E C C Comm on-Em itter configured ampl ifier Low-frequency Effects due to coupling capacitor C C and bypass capacitor C B is dominant and reduces the gain (transfer function). ∞ ⇒ = C j jX C ϖ 1 as ⇒ ϖ High-frequency Effects due to junction capacitance and stray capacitance in parallel with the amplifier reduces the gain (transfer function). 1 ⇒ = C j X C ϖ as ∞ ⇒ ϖ mid-frequency low-freq. high-freq. Transfer function Frequency Mid-frequency low-frequency effects of coupling and bypass capacitors negligible since ⇒ C X high-frequency effects of junction and stray capacitance negligible since ∞ ⇒ C X 1.2 A.C. Small Signal Analysis at Mid-frequency The power supply is an ideal voltage source and therefore behaves as an a.c. short circuit. The coupling and bypass capacitors also behaves like an a.c. short circuit, since its impedance is zero. Small signal parameters remain constant and operation is linear. Using the previous circuit as an example, R C R 1 I/ P I/ P O/ P O/ P R 2 BJT Mo del R // R 1 2 R C A.C. Small signal equivalent circuit at mid-frequency BJT model : approximate π model BJT model : approximate transconductance model FET model : transconductance Once an equivalent circuit is obtained, circuit analysis can be applied to determine, voltage gain A v input impedance Z in output impedance Z out 1.2.1 Approximate π Model (BJT) v be i b i c v ce v h i h v i h i h v be ie b re ce c fe b oe ce = + = + ⇒ v i h h h h i v be c ie re fe oe b ce = common-emitter h-parameter matrix h-parameter model h V I v i ie BE B be b V CEQ = = ∆ ∆ Input impedance,...
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This note was uploaded on 01/11/2011 for the course EE 3110 taught by Professor Wingshingchan during the Fall '08 term at City University of Hong Kong.

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EE3110 AECL1 Revision & frequency response_2007 -...

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