Quality factor of an inductor (Sonnet) - Page 1
Forum section: electronics / rf-microwave

author: omar32s
author_rank: Newbie
timestamp: October 05, 2022, 05:30:09 pm
content: When I create a series (floating) 2-port inductor in sonnet I know it is equivalent to a pi model where we have a series R and series L and shunt components at the 2 ports.after eming the inductor using sonnet, I knew that inductance 2 represents the series inductance and same for resistance 2 also represents series resistance.1) I wanted to know what is the quality factor of that (series/floating) inductor, as Q represents quality factor if port 2 is grounded and Q3 represents quality factor for differential inductor, but how to calculate quality factor for the floating inductor ?2) After I emmed an inductor I found that resistance 2 has negative value at some frequencies is that even possible or did I do something wrong ?I have added a photo at which resistance 2 has a negative value with frequency, and would it be in that case the quality factor (w*L2/R2) even if R2 has a negative value ? or what should be the quality factor of a 2 port floating inductor ?

author: rfeecs
author_rank: Frequent Contributor
timestamp: October 05, 2022, 07:18:11 pm
content: Your model is wholly inadequate to go up to 20GHz. You have capacitance between turns and capacitance to ground. Look up "planar inductor lumped model" for lots of more complicated models.At low frequencies, the models will just reduce to a series resistance, so use your low frequency resistance for that value.

author: jonpaul
author_rank: Super Contributor
timestamp: October 06, 2022, 05:44:33 am
content: BonjourSeries resistance is a function of the frequency, rising due to well known skin effect.The layout will have substantial shunt capacité turn to turn and all turns to earth and infinity.Suggest you find a microwave pcb layout and, inductor design référence.Coilcraft and others make SMD wire wound inductors. very well characterized at microwave frequencyBon courageJon

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: October 06, 2022, 12:36:31 pm
content: Quote from: jonpaul on October 06, 2022, 05:44:33 amLooking at the OP I suspect this is a MMIC or similar inductor. From that perspective, the layout seems fine, though I prefer having ground traces around to more accurately simulate the return current (sonnet and other 2.5 D simulators use an idealized groundat a distance but in practice that ground doesn't exist, your current needs to go somewhere and you want to know how it does that, thus you better include it in your simulation instead of hoping its negligeable).I suspect the reason your 'resistance' has gone negative is because you are actually seeing the parasitic capacitance from input to output that is shorting (parts of) this resistor. Plotting the effective inductance from simulated sparameters can be a good way to see also how close to self-resonance you are which will give you an idea how well such a simple model will work (spoiler: probably not at all at anywhere near 20 GHz).

author: radiolistener
author_rank: Super Contributor
timestamp: October 06, 2022, 01:05:25 pm
content: Quote from: omar32s on October 05, 2022, 05:30:09 pmQ = abs(XL) / RSXL= 2 * pi * f * LNote, that RSalso depends on the frequency due to skin effect.

author: omar32s
author_rank: Newbie
timestamp: October 06, 2022, 05:12:06 pm
content: Quote from: TheUnnamedNewbie on October 06, 2022, 12:36:31 pmbut doesn't Resistance2 equation in sonnet only computes series resistance disregarding shunt components including shunt capacitance.