Common Emitter BJT Amplifier Design Current Mirror Design
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Some Random Observations
● Conditions for stabilized voltage source biasing
● Emitter resistance, RE, is needed.
● Base voltage source will have finite resistance, RB.
● needs to be much larger than RB.
● Small RB - relative to RS - will attenuate input signal.
● Larger RE permits larger RB, but results in lower gain.
● Gain = -RC/RE for RE >> re.
● Split RE with bypassing increases gain.
● Requires large bypass capacitor.
● Limiting case - entire RE bypassed: Gain = - gmRC.


Bias Setting
1. Since RB does not interfere with
the bias, the signal source can be
connected to the base without need
for a blocking capacitor.
2. Choose Rb “ large” compared to
RS to avoid attenuating vsig.
3. Choose Rref to set IC



Gain Setting
1. Connect the source to the base.
2. Provide a path for the small
signal emitter current.
3. Choose RE for the desired gain
(G = - RC/RE).
4. CE is nearly a short circuit for f ≥ fmin
Calculate CE to have negligible
reactance at the lowest frequency
of interest fmin.