# Design an Op Amp circuit to meet specs

#### Robert Murch

Joined Nov 2, 2015
43
So for a class activity in school we are to design an Op Amp circuit (any number of 741 Op Amp's) that must have the following characteristics:

DC voltage gain (Vout/Vin) of 40 dB +- 1 dB
DC phase shift of 180 degrees (input to output)
Gain to be achieved with a Thevenin equivalent resistance of 10k Ohm's driving the amplifier
Gain to be achieved with a 10k Ohm load
3dB Bandwidth >= 40 kHz
Bipolar supplies of +-15V

So me and my partner have completed the project but we had to use two Op Amp's to do it. What I was wondering is could it be done with one and if so could you tell me what kind of configuration would be required.

#### WBahn

Joined Mar 31, 2012
30,034
What is the gain-bandwidth product of a 741 op amp?

What is the gain-bandwidth product of your amplifier?

#### Robert Murch

Joined Nov 2, 2015
43
Ah I see now the GBP of the 741 is just too small 10 kHz. So, I am assuming I could complete this with only one Op Amp if i was not using 741's?

#### WBahn

Joined Mar 31, 2012
30,034
I think the GBP for the 741 is generally given as being about 1 MHz, not 10 kHz. But with a voltage gain of 40 dB (or 100) and a bandwidth of 40 kHz, you would need a GBP of about 4 MHz.

There are numerous op amps that satisfy that requirement. Though there are other performance parameters that would have to be considered as well.

#### Robert Murch

Joined Nov 2, 2015
43
Okay here's my next question in our circuit we utilized a few capacitors and some resistors along with two Op Amp's. I was told by another student that it could be done with one inverting Op Amp and one non-inverting Op Amp a few resistors and no energy storage element, is that possible? I was under the impression that the energy storage elements are what's creating the pols and zeros (sorry just starting learning about network functions).

#### WBahn

Joined Mar 31, 2012
30,034
But do you need any poles or zeros?

Remember, the bandwidth spec is a minimum.