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LC parallel circuit at resonant frequency

baristaskin

Dear All,

I am trying to simulate a simple LC parallel circuit when it is drived by a voltage source.

I'm expecting the current of the voltage source V1 to get smaller as its frequency gets closer to the resonant frequency.

When I simulate this circuit at the resonant frequency, with spectre default values, I get:

I tried to play around with the following parameters:

maxstep, reltol, vabstol, iabstol

without success.

My question is: how do I setup Spectre in order to get consistent and accurate results?

What I expect to see is a sine-shaped current signal with no DC value.

I'm including the netlist of the simulation shown above:

// Generated for: spectre
// Generated on: Mar 2 16:11:27 2015
// Design library name: paper3
// Design cell name: LC_osc
// Design view name: schematic
simulator lang=spectre
global 0
parameters _EXPR_8=1.986858915135295e-08 C=1p L=100n vdd=1 \
freqC=503.30696M cycles=10 L_IC=-sqrt(C/L)*vdd/2

// Library name: paper3
// Cell name: LC_osc
// View name: schematic
L1 (Vin 0) inductor l=L r=1a ic=0
V1 (Vin 0) vsource type=sine freq=freqC ampl=vdd/2 sinephase=90 sinedc=0
C1 (Vin 0) capacitor c=C ic=vdd/2
simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \
checklimitdest=psf
tran tran stop=_EXPR_8 errpreset=conservative write="spectre.ic" \
writefinal="spectre.fc" annotate=status maxiters=5
finalTimeOP info what=oppoint where=rawfile
modelParameter info what=models where=rawfile
element info what=inst where=rawfile
outputParameter info what=output where=rawfile
designParamVals info what=parameters where=rawfile
primitives info what=primitives where=rawfile
subckts info what=subckts where=rawfile
save Vin V1:p L1:1
saveOptions options save=allpub

 

Thank you in advance.

Parents

  • Dear Shawn,

    Thank you for your reply, I appreciate it.

    Regarding your points:

    1) This non-linear network has been already used in a cross-coupled LC oscillators as the capacitive load; without the voltage source and with correct initial conditions the circuit oscillates with the inductance (it's a damped oscillation of course). These are the reasons why I'm assuming it would oscillate. What do you mean by "the voltage source acts as an infinite capacitance"?

    I am not interested in the impedance of the non-linear network, but only in its oscillation with an inductor.

    2) I specified that I needed an oscillation of 1V simply to emphasize that I can't use a small signal analysis. What I am trying to do is forcing an oscillation with the voltage amplitude that I decide. In the simple LC circuit the amplitude of the oscillation is given by the initial condition on the capacitor (if you choose to start from there, otherwise it's given by the initial current of the inductor).

    The bottom line is that I am interested in computing the power dissipated by the voltage source, at the resonant frequency of the system.

    I already know that my non-linear network can oscillate with an inductor, so the problem is finding the right settings for Spectre in order to get rid of all that numerical gibberish.

    I hope this helps understand better what I am trying to do.

Reply

  • Dear Shawn,

    Thank you for your reply, I appreciate it.

    Regarding your points:

    1) This non-linear network has been already used in a cross-coupled LC oscillators as the capacitive load; without the voltage source and with correct initial conditions the circuit oscillates with the inductance (it's a damped oscillation of course). These are the reasons why I'm assuming it would oscillate. What do you mean by "the voltage source acts as an infinite capacitance"?

    I am not interested in the impedance of the non-linear network, but only in its oscillation with an inductor.

    2) I specified that I needed an oscillation of 1V simply to emphasize that I can't use a small signal analysis. What I am trying to do is forcing an oscillation with the voltage amplitude that I decide. In the simple LC circuit the amplitude of the oscillation is given by the initial condition on the capacitor (if you choose to start from there, otherwise it's given by the initial current of the inductor).

    The bottom line is that I am interested in computing the power dissipated by the voltage source, at the resonant frequency of the system.

    I already know that my non-linear network can oscillate with an inductor, so the problem is finding the right settings for Spectre in order to get rid of all that numerical gibberish.

    I hope this helps understand better what I am trying to do.

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