# Inductor in transistor circuit

#### Sparky49

Joined Jul 16, 2011
833
Hi all,

I was wondering if anyone could tell me the use of the inductor in the follow circuit? I get that it is a common emitter with feedback resistor (R2) which reduces the effect of a different transistor gain and temperature, etc, but I am not sure about the inductor.

Many thanks,

Sparky

#### Sparky49

Joined Jul 16, 2011
833
I apologise, I forgot the input:

Sparky

#### crutschow

Joined Mar 14, 2008
26,053
A inductor can be used as a load impedance in high frequency circuits to provide a high stage gain since its impedance can be much higher at the signal frequency than a collector resistor for a given transistor bias current.

#### Sparky49

Joined Jul 16, 2011
833

If that is the case, how should one go about calculating the value for the inductor?

Sparky

#### crutschow

Joined Mar 14, 2008
26,053
You just make the inductance high enough for the inductive impedance at the signal frequency to get the gain you desire.
The gain limit is generally determined by the load impedance connected to the transistor collector, so the limits effectively how high you can go.
Thus you make the inductance no higher than the limit imposed by the load to minimize the size of the inductor.