# Simple Opamp Problem: Pls Help

Discussion in 'General Electronics Chat' started by rajath247, Jul 23, 2008.

1. ### rajath247 Thread Starter New Member

Jul 23, 2008
1
0
I came across this problem, i tried solving it but wasnt getting the matching answers. Here's the question:
An opamp has an open-loop gain of 105 and an open-loop upper cut-off frequency of 10 Hz. If
this opamp is connected as an amplifier with a closed-loop gain of 100, then the new upper cutoff
frequency is...?

2. ### nitin.bharat Member

Sep 6, 2007
10
0
i do not know how to calculate but for close loop system cut-off frequrncy increases.

3. ### Distort10n Active Member

Dec 25, 2006
429
1

Assumptions:
Open Loop Gain (Avol) = 105dB at DC
Dominant Pole Frequency = 10 Hz
Closed Loop Gain (Acl) = 100dB

The closed loop gain may not be expressed in dB when you state 100. This is not clear in your post. So in dB it will be 40dB for a absolute gain of 100.

In either case, the roll off frequency will be:

If Avol = 105dB and Acl = 100dB: ~30 - 60 Hz.
If Avol = 105dB and Acl = 40dB: 10kHz.