β Variation ParameterΒ=100Β=155 VBE672.1 mV 683.4 mV IB11.328 uA 11.317 uA IC1.1 mA1.8 mA gm43.6 mS69.2 mS Variation of gm implies that the gain of the amplifier will vary significantly as a function of beta.
Back of the Envelope Calcuation Assume the base current is negligible, i.e. negligible compared to the current in R1. IC does not depend on Beta!
Negligible Base Current V BE =R 3 /(R 1 +R 3 )V CC V BE =5.75/(5.75+17)2.5V=0.631 V I(R1)/IB=110uA/2.10=52.38
Sensitivity to Component Variation Nom.1%5% R2 (KOhm) 5.755.80756.037 VBE (mV)623626639 IB (uA)2.102.353.59 IC (uA)229262424 Gm (mS)8.810.116.3 1% error in R2 leads to 14 % error in IC. 5% error in R2 leads to 85 % in IC.
Biasing with Emitter Degeneration If R2↑→VP↑→IE↑→VRE↑→small ∆V BE →Small ∆I C An error in VX due to inaccuracies in R1, R2 and VCC is absorbed by RE, leading to a smaller change in VBE.
Sensitivity to Component Variation Nom.1%5% R3 (KOhm) 6.86.8687.140 VBE (mV)0.68 IB (uA)12.412.513.1 IC (mA)1.911.932.02 Gm (mS)73.574.277.7 1% error in R2 leads to 1.05 % error in IC. 5% error in R2 leads to 5.7 % error in IC.