# op amp

#### acw_wellsy

Joined Oct 1, 2006
3
a feedback amplifier has a closed loop gain of 100, and the negative feedback is 0.8% of the output signal. the opamp has an open loop gain which is considerably less than the ideal value of infinity.
a) what is the open loop gain?
b)what would the closed loop gain be if the opamp had an infinite open loop gain.

what equation of formula would i need i know that A = Vout/Vin = 1/B

any ideas...

cheers

#### Dave

Joined Nov 17, 2003
6,969
The equation Af = 1/B for the closed-loop gain is a special case (for where AB >> 1) of the general equation:

Af = A/(1 + AB)

Where:

Af is the closed loop gain
A is the open-loop gain
B is the feedback factor

From this equation you should be able to rearrange the equation to get A as the subject, from which you have sufficient information to answer part (a).

Part (b) can be answered using Af = 1/B

You should find your answers for (a) and (b) to be very similar. You can post up your attempts if you want to check your answers.

Dave

#### stocky

Joined Oct 18, 2006
1
acw_wellsy, do you go to swinburne as well? im struggling with exactly the same question