wien bridge oscillator with PSPICE netlist

Discussion in 'The Projects Forum' started by dagcilibili, Jan 12, 2010.

  1. dagcilibili

    Thread Starter New Member

    Jan 12, 2010
    Hello. I have a project to simulate wien bridge oscillator. I have a problem with it. The output decays although everything used in the project is ideal component. Do you have idea why it happens?

    Here is the netlist i use.

    For the project i started from the given circuit in
    the design with diodes work fine but do you know why the above circuit decays.

    Thanks for your help in advance.
    have nice days.
  2. dagcilibili

    Thread Starter New Member

    Jan 12, 2010
    no help ? =/
  3. Darren Holdstock

    Active Member

    Feb 10, 2009
    You've got amplitude stabilisation issues that are easily fixed in the real world by a thermistor in the feedback loop. Modelling this in PSPICE is much trickier, it might be easier to use a FET as the control element. This is all well documented on the web. Apart from how to model this in PSPICE... but take these clues and go google, you might get lucky.

    This amplitude drift (it can get bigger or smaller) is caused by the slightest mismatch between the two resistors in the bridge, and it will always happen unless extra stabilisation measures are employed.

    Some other oscillator designs rely on noise to kick start them, and these also cause trouble in PSPICE sims. The workaround here is to introduce a little noise spike right at the start of the simulation.
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Your gain needs to be 3. R10 and R11 theoretically will give you a gain of 3, if you have an ideal op amp. Your op amp has finite gain and finite input resistance, so you will need to make (1+R11/R10)>3 by an infinitesimal amount, or the output will indeed decay. The diode/resistor network serves this purpose, but you have omitted it from your netlist.