Clipping in inverting amplifier.

Discussion in 'Homework Help' started by analog_rex, Jan 2, 2009.

  1. analog_rex

    Thread Starter New Member

    Dec 11, 2008
    6
    0
    Hi,
    I have a question which may be a very simple one. An inverting amplifier clips the input waveform when the feedback resistance is increased. Why does it happen? What can be done to avoid this problem?

    Please give me some links to refer if you can. Thanks in advance.

    Cheers
     
    Last edited: Jan 3, 2009
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Do you have a schematic of the circuit you are seeking assistance with?

    hgmjr
     
  3. analog_rex

    Thread Starter New Member

    Dec 11, 2008
    6
    0
    Hi,

    I am using pspice to do a transient simulation of this circuit. Vin is an input sinusoidal source with f=1kHz, Amp.=1V. Rin is 1K. The value of Rf is increased from 10K to 15K and the output was plotted. At 15K the output starts to clip. Why does this happen and what can i do to avoid this? Please find the circuit diagram in the kink below.

    http://www.seas.upenn.edu/~ese205/Labs06/Lab5_files/image016.gif

    thanks
     
    Last edited: Jan 3, 2009
  4. DrNick

    Active Member

    Dec 13, 2006
    110
    2
    You are saturating the op-amp. Typically the output of an op-amp circuit can only go up to Vcc-1, and Vee+1 (approximatly). When you increase Rf, the gain of your circuit increases, the output signal will get bigger and bigger until the output saturates at about Vcc-1. To prevent this, ensure that your maximum signal level times your gain (Rf/Rin) will always be less than Vcc-1.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    You could reduce the amplitude of the input signal to eliminate the clipping.

    hgmjr
     
  6. analog_rex

    Thread Starter New Member

    Dec 11, 2008
    6
    0
    Thank you for the reply. :)

    Taking the query further, let the values of Rin and Rf be 1k and 15k. At these values of Rin and Rf, the opamp gets saturated. I want to know if there is some way to avoid the saturation of opamp without changing the values of Rin and Rf? For example, by adding an additional component or circuitry.

    It will also be very helpful if you can suggest some links to refer and study about it. I did search online but I could hardly find useful links.

    Thanks and warm regards
     
    Last edited: Jan 3, 2009
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    What suggestions to overcome clipping do you have?

    hgmjr
     
  8. DrNick

    Active Member

    Dec 13, 2006
    110
    2
    Use larger Vcc and Vee (i.e. use higher voltage for the opamp supplies). Be sure not to increase it above the rated value of the opamp. For instance if you are applying a +1V pk-pk sine wave and have a gain of 15 (Rf = 15k, Ri = 1k), use +10V for Vcc and -10V for Vee.
     
  9. silvrstring

    Active Member

    Mar 27, 2008
    159
    0
    I don't know why you don't want to change the values of Rf and Rin, but if adding components is okay, you could just throw some more resistance on the Rin side. Gain is -Rf/Rin. You need to bring it down.
     
  10. analog_rex

    Thread Starter New Member

    Dec 11, 2008
    6
    0
    Thanks to all for your help...

    cheers
     
Loading...