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I am trying to get the Q factor for this circuit but I don't know how to simulate it properly.

I did a frequency sweep from 1 Hz - 30 MHz. The oscillating frequency is 16 MHz. I can't get the bandwidth around that frequency.

How should I simulate it to get the obvious shape of the Q factor for the RLC circuits?

NOTE: The diagram is wrong, L1 = 21.23mH

schematic

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EDIT: With the I probes set on R,L or C I get only a fixed value for everything.

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  • \$\begingroup\$ It looks like you ran a transient analysis (.TRAN) rather than an ac analysis (.AC). Please replace the sinusoidal transient source by a regular voltage source with an ac value of 1 and run an ac analysis from 1 Hz to 100 MHz for instance. Then plot the current in \$R_1\$ in dbA and you should obtain a meaningful graph. \$\endgroup\$ – Verbal Kint Sep 11 '19 at 14:49
  • \$\begingroup\$ It's also pretty easy to calculate the Q, so if that's all you're after you don't really need to simulate. If learning how to run AC simulations on LC circuits is the goal, then @VerbalKint has the answer. \$\endgroup\$ – John D Sep 11 '19 at 14:55
  • \$\begingroup\$ Try setting the number of frequency points in the AC analysis to be much higher and try setting Flow and Fhigh to be much closer to 16 MHz. \$\endgroup\$ – Andy aka Sep 11 '19 at 15:33
  • \$\begingroup\$ Yes, 100 points per decade is usually too low for peaky responses. Pushing this number to 1000 usually gives adequate results. \$\endgroup\$ – Verbal Kint Sep 11 '19 at 16:59
  • \$\begingroup\$ The 2nd schematic doesn't have the same values for the C and L as does the 1st schematic. Just FYI. \$\endgroup\$ – jonk Sep 11 '19 at 18:11
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It looks to me like the second circuit that resonates around 16 MHz has a Q of about 95000 and a 3 dB bandwidth of 166 Hz. The frequency resolution (step size) of your simulation needs to be smaller then that. Usually I zoom way in to see a high Q resonance by setting the limits of the AC analysis to be say 100-500 KHz either side of resonance

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