Dear All

Could I ask a silly question?
I know that almost most Transimpedance Amplifier is built with OpAmp.

However, why not use a transistor?

Thank you very much. Any thoughts are welcome.

Richie

 

Dear All

Could I ask a silly question?
I know that almost most Transimpedance Amplifier is built with OpAmp.

However, why not use a transistor?

Thank you very much. Any thoughts are welcome.

Richie

You can, but it won't be a particularly good one.

 

You can, but it won't be a particularly good one.

Thank you Steve!

Could you please explain the drawbacks a little?

Thank you
Richie

 

Thank you Steve!

Could you please explain the drawbacks a little?

Thank you
Richie

I've never tried to make one with a bipolar transistor, but I would imagine the simplest way is to inject current into the base with a voltage on the emitter. Then a resistor on the collector with a voltage on top of the resistor will allow proper biasing.

One drawback is that it will only work for one direction of the current.

Another drawback is that the current gain of the transistor will be sensitive to temperature and current and can be nonlinear. Also, it will vary from transistor to transistor.

I'm sure there are other drawbacks, depending on the exact voltages you need on input and output, and whether you are doing AC or DC coupling.

Also, output impedance will be high.

 

Here are one and two transistor transimpedance amps. Obviously, in order to get an acceptable operating point, I had to add a DC bias current.