OP-amp and transistor

1. Sep 1, 2011

rama1001

What is the meaning of differential gain?
Iam studying a document that says, opamp can provide differential gain unlike transistor. I don,t know what does it mean. Can some clear me out.

More, what is meant by bias volatge in case of op-amp. I am very beginer to electronics.

2. Sep 1, 2011

Floid

Differential gain means that your op-amp's output is related to the difference between it's positive and negative inputs.

So if you had an differential amplifier with a gain of 1 and applied +5V to the + input and +3V to the - input you would get a +2V output.

Bias voltage on an op-amp is the output value with no inputs applied to the op-amp. Generally it will be about zero but you can construct your circuit so that it has a different value.

3. Sep 1, 2011

Staff: Mentor

The input of most opamps uses a differential transistor gain stage, and there are more gain stages after that. So you get high effective differential gain with opamps -- the output is a function of the difference of the two inputs, multiplied by a very large number.

http://en.wikipedia.org/wiki/Opamp

The bias voltages on an opamp are the input quiescent voltages. You will generally set the bias voltage at the + terminal explicitly, and use negative feedback to set the bias voltage at the - terminal.