Design an Amplifier with 741

Discussion in 'Homework Help' started by msr, Mar 21, 2009.

  1. msr

    Thread Starter Active Member

    Jul 8, 2008

    This is my first post here.
    I have to design an amplifier using just 741 op-amp(s) and resistors, with the following requirements:
    - closed-loop gain: 40dB
    - "3dB-frequency" (break frequency): 25kHz
    - input impedance: 47kOhm

    I'm looking at Microelectronics Circuits (Sedra) and trying to resolve this by using an inverting circuit (one op-amp and 2 resistors) but it doest seem to be a good choice. I can't acomplish all the requirements.

    Another question: how can I know the break frequency and open loop voltage gain of 741? (datasheet only mentions 1Mhz of unity-gain bandwidth)

    Any advices?

    Thanks in advance!
  2. Audioguru

    New Member

    Dec 20, 2007
    Look at the datasheet for a lousy old 741 opamp.
    Its output can go up to only 9kHz at 28V peak-to-peak.
    Its "break frequency" is only about 6kHz when its gain is 40db.

    Use a transistor at its input or another opamp to share the gain.
    Use a non-inverting circuit for the fairly high 47k input impedance.