Hello guys,
I'm learning how this simple circuit works just for a hobby.
The circuit is a common emitter amp with fixed bias and grounded emitter.
I'm trying to calculate its input impedance. As I understand the input signal current flows through Q1 baseemitter (re) to the ground and through R2 to the ground.
So:
Zin = R2  βre
β = 100
re = 25/IE Ohm ≈ 25mV/50mA = 0.5 Ohm
Then:
Zin = 50KOhm  50Ohm = 49.95Ohm
But when I run a simulation the current through the input voltage source V1 is
56μA PP.
As V1 voltage is 5mV this gives
Zin = 5mV / 56μA ≈ 89.29Ohm
which is far away from 49.95Ohm I get from my calculations.
Could anyone help to figure out what am I doing wrong?
I'm learning how this simple circuit works just for a hobby.
The circuit is a common emitter amp with fixed bias and grounded emitter.
I'm trying to calculate its input impedance. As I understand the input signal current flows through Q1 baseemitter (re) to the ground and through R2 to the ground.
So:
Zin = R2  βre
β = 100
re = 25/IE Ohm ≈ 25mV/50mA = 0.5 Ohm
Then:
Zin = 50KOhm  50Ohm = 49.95Ohm
But when I run a simulation the current through the input voltage source V1 is
56μA PP.
As V1 voltage is 5mV this gives
Zin = 5mV / 56μA ≈ 89.29Ohm
which is far away from 49.95Ohm I get from my calculations.
Could anyone help to figure out what am I doing wrong?
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