I have simulated an oscillator circuit using OTA in SPICE. It is a self starting oscillator.

However, the frequency of oscillation does not change with the bias current but changes with the duration specified in the .TRAN command. Eg - .TRAN 20ms and .TRAN 50ms will give oscillations of different frequencies.

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  • 2
    \$\begingroup\$ Circuit please. \$\endgroup\$ – Andy aka Jul 30 at 7:00
  • \$\begingroup\$ Eg - .TRAN 20ms and .TRAN 50ms will give oscillations of different frequencies. That might be due to the simulator changing the timestep. I suggest that you do what I always do and that is to set a maximum timestep. I usually set it such that there will be at least 1000 timepoints so for a 20 ms TRAN, I set max step to 20 us (or smaller). And add a schematic! \$\endgroup\$ – Bimpelrekkie Jul 30 at 7:21
  • \$\begingroup\$ Added the schematic. I keep timestep to 25Ns for 20ms duration. The Oscillation Freq was supposed to change with Bias current not with the time duration but it's happening totally opposite. \$\endgroup\$ – Anirban Choudhury Jul 30 at 8:02
  • \$\begingroup\$ There is a general rule for oscillator simulation: Select a minimum time step that is so small that the expected waveform (mostly sinus) can be fully recognized without remarkable edges. Then, the shown result does not depend on the selection (rule of thumb: App. 100 simulation points within one period) \$\endgroup\$ – LvW Jul 30 at 13:05
  • \$\begingroup\$ How did you measure the oscillation frequency? If you read it off the output plot, are you sure the plot is not aliased? \$\endgroup\$ – The Photon Jul 30 at 16:03

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