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kleinesmurf69
Joined: 06 Mar 2003
Posts: 100
Helped: 3
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 24 Sep 2003 22:58 Orcad pspice oscillator problem |
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Hello,
I am trying to simulate an oscillator (4MHz) circuit that consists of a transistor and some discrete components. The only thing that comes out of the simulation is in the order of femto to pico volts. Does anyone know what I am doing wrong?
Thanks.
Regards.
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flatulent
Joined: 19 Jul 2002
Posts: 4849
Helped: 289
Location: Middle Earth
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| 25 Sep 2003 1:18 convergence problem |
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| This is the result of convergence problems. You should look at the documentation for the program to find the .options statements to use to tighten up the tolerance at each calculated point. reltol and abstol are some of these. Tighten them up by 10x and then 100x if necessary to get the waveform you expect.
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boondoggle
Joined: 05 Sep 2003
Posts: 2
Location: Somewhere in Minnesota
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| 26 Sep 2003 8:05 Re: Orcad pspice oscillator problem |
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Hi,
You might want to take a look at this document:
http://www.sss-mag.com/pdf/rfosc.pdf
It contains a number of ways to "thump" an oscillator to life in
a SPICE simulation.
-Boondoggle
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godz
Joined: 22 Sep 2003
Posts: 34
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| 02 Oct 2003 10:53 Re: Orcad pspice oscillator problem |
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Hi,
In such cases, I used to put an Initial Condition (IC) on the oscillator tank, when transient simulation starts the IC represents a disturbance in the oscillator that can trigger the oscillation, but you should take care not to set the IC value too far from the expected DC value of the node otherwise the transient simulation will take a lot of time to reach to the proper DC bias of the circuit.
I also advise you to insert an AC current source at the +ve feedback point of the oscillator and do an AC simulation before transient and notice the output at the tank, if there is peaking in the frequency of interest then the oscillator will probably oscillate when you do transient simulation.
regards,
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bastos4321
Joined: 01 Jan 1970
Posts: 333
Helped: 23
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| 02 Oct 2003 12:00 Re: Orcad pspice oscillator problem |
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Use the inicials conditions in one or two of the capacitors of the feedback network.
Cx n1 n2 xxx IC=1V
.tran 1n xx UIC
Bastos
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