# Gain x Bandwidth Constant

Discussion in 'Homework Help' started by Retrogalaxy, Aug 14, 2013.

1. ### Retrogalaxy Thread Starter New Member

Aug 14, 2013
4
0
i have an op-amp that a Gain x Bandwidth Constant which is equal to 500,000. What is the largest gain that the amplifier could have if the input signal was a sine wave at 100 KHz?

would i just need to do 500,000/100,000hz? = 5

a Gain of 5 Would be the largest?

2. ### WBahn Moderator

Mar 31, 2012
20,267
5,766
Basically.

Watch your units. You meant 500,000Hz/100,000Hz = 5?

Keep in mind that this nominally gives the 3dB point of the amplifier, so you probably don't want to actually run it here. If you did, you would only get a gain of 70%*5 = 3.5.

And the GBWP is not engraved in stone, so you want to give yourself some margin, or be sure to use the minimum spec'ed value that applies for your operating conditions.

3. ### xbt New Member

Aug 2, 2013
3
0
>if the input signal was a sine wave at 100 KHz?
A sine wave has a bandwidth of zero Hertz.

Is there something missing from the question ?

4. ### Retrogalaxy Thread Starter New Member

Aug 14, 2013
4
0
thats how the question in my revision notes was presented to me.

5. ### WBahn Moderator

Mar 31, 2012
20,267
5,766
But the GBWP is modelling the opamp as having a low-pass frequency response with a 1st-order skirt.