I am having a problem replicating some lab results in the PSPICE/capture CIS program for an assignment. I have this circuit right here: which is an oscillator using the uA741 op-amp which is supposed to output an oscillation through its output pin(pin 6). After doing this experiment in the lab i found out that oscillations begin at about 220 ohms but after doing a parametric sweep for r between the values of 10 and 300, with an increment of 10, i am getting only a stable voltage of a few mV and not an oscillation of any kind. Is there any mistake i'm not seeing?
The issue you are facing, is that, your oscillator has a stable DC operating point.
Imagine you open-circuit the capacitors. You now have a zero volt input with 100 kOhm source resistance being amplified by U1, which regardless of gain is a 0 V output.
A real oscillator circuit relies on the noise voltage/current generated in circuit to initiate the oscillator.
In a spice simulation you can try:
- Skipping the DC operating point solution
- Injecting a small transient current pulse just after t=0
- Force a non-steady-state value to one of the circuit nodes in the oscillator loop