![]() RF Circuit Design by Bowick is a great reference for this. You can optimize your unloaded circuit, but then when you add your 4pFs of load you will be tuned at the wrong frequency! Unloaded-Q is theoretical, loaded-Q is reality. The denominator doesn't go to zero, it goes to the parasitic resistance. You'll have maximum Q at your resonant frequency of your RLC circuit that is where the power is 100% real and 0% imaginary. Your unloaded Q is in series with 0+j0 ohms. Note that I'm talking about parallel RLC circuits if you have a series RLC then everything is inverted. Think of your Q-value like resistance two in parallel have a lower value. Nothing has infinite Q!Īs soon as you put a load on with parasitics it has a Q less than infinity, and thus your loaded Q is lower. Unloaded Q is your tank (RLC) in parallel with nothing. Should I be optimizing the Q of _unloaded_ spiral coil inductor, or that loaded with my four puffs? Does it even make a difference? If one is improved, is the other improved? Thanks so much for the help! RE: q factor zappedagain (Electrical) 20 Aug 09 17:22 To compute Q, I am looking at the impedance over frequency (impedance magnitude) and doing the resonant frequency divided by the FWHM. I am running some EM simulations to optimize this inductor. I am trying to optimize a spiral coil inductor which will be loaded with about 4 puffs. To use this online calculator for Resistance for Series RLC Circuit given Q-Factor, enter Inductance (L), Quality Factor (q) & Capacitance (C) and hit the calculate button. Note by "reactance/resistance" above I am referring to the reactance of the entire "equivalent circuit" for the non-ideal inductor, and not just the inductor portion. Achieving this freqency would require adding a cap in parallel, no? you mentioned "it will be less than the unloaded Q due to the added load capacitance." Can you elaborate a bit on this? The reactance/resistance ratio is at its peak somewhere before the intrinsic, unloaded resonance frequency. Thank you all so much for the responses! John D.
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