Simple Emitter Follower Amplifier.

Bias Point Analysis: Is = 5x10^-17 β = 100 Vτ = 0.026 (From Simulation) Ic = 2.34 mΑ Ib = Ic/β = 23.4 μΑ Ιe = Ic + Ib = 2.36 mA Ve = Re*Ie = 1.18 V Small Signal Analysis: gm = Ic/Vτ = 0.09 S = 1/11.111 (1/Ω) Rπ = β/gm = 2254.79 Ω Gain = Re/(Re + 1/gm) = 0.9783 (suppose Ro->Inf, so without Early Effect) By observing the smaller than unity gain of the emitter follower, we can see that it doesn't amplify the input signal,it only increases it by Ve . Thats because the primary usage of an emitter follower is not to amplify a signal,but to act as an intermidiate buffer of high input impedance and small output impedance. In the case in which we use a current source as biasing device of the emitter follower we get an gain of unity. Input Impedance: Rin = Rπ + (β+1)*Re = 52.75 kΩ Output Impedance: Rout = Re||(1/gm) = 10.8696 Ω

published 7 years ago