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
    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


    Sep 6, 2007
    i do not know how to calculate but for close loop system cut-off frequrncy increases.
  3. Distort10n

    Active Member

    Dec 25, 2006

    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.