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e.g. Tmodel
1) Determine the DC operating conditions (in particular, the collector current, IC)
2) Calculate small signal model parameters: gm, rπ, re
3) Eliminate DC sources: replace voltage sources with shorts and current sources with open circuits
4) Replace BJT with equivalent smallsignal model. Choose most convenient depending on surrounding circuitry
5) Analyze
ic
+
RC
eliminate DC sources and apply Tmodel

vc
ic
+
vbe
re
vbe

Find the gain using a small signal model:
ground
αie
voltage gain
usually re<<RE
ground
VC
rOUT
rb
Input impedanceRB
DC condition
Frequency response
Gain/Dynamic range
Impedance
ROUT
VOUT
VIN
RIN
AVIN
RS
ROUT
RIN
VOUT
AVIN
VIN
VS
RS
ROUT
RL
RIN
AVIN
VIN
VOUT
VS
RS
+
RL
vout

Ideal opampSo the equivalent circuit of an ideal opamp looks like this:
RS
ROUT
RL
RIN
AVIN
VIN
VOUT
VS
RS
ROUT
RL
RIN
AVIN
VIN
VOUT
VS
ROUT1
ROUT2
A2 VIN2
A1VIN1
VOUT2
VOUT1
RIN2
RIN1
VIN1
VIN2