Author Topic: Quality factor of an inductor (Sonnet)  (Read 1060 times)

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Offline omar32sTopic starter

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Quality factor of an inductor (Sonnet)
« on: October 05, 2022, 05:30:09 pm »
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 ?
 

Offline rfeecs

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Re: Quality factor of an inductor (Sonnet)
« Reply #1 on: October 05, 2022, 07:18:11 pm »
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.
 

Offline jonpaul

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Re: Quality factor of an inductor (Sonnet)
« Reply #2 on: October 06, 2022, 05:44:33 am »
Bonjour

Series 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 frequency

Bon courage


Jon
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Offline TheUnnamedNewbie

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Re: Quality factor of an inductor (Sonnet)
« Reply #3 on: October 06, 2022, 12:36:31 pm »
Bonjour

Series 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 frequency

Bon courage


Jon

Looking 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).
The best part about magic is when it stops being magic and becomes science instead

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Offline radiolistener

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Re: Quality factor of an inductor (Sonnet)
« Reply #4 on: October 06, 2022, 01:05:25 pm »
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 ?

Q = abs(XL) / RS
XL = 2 * pi * f * L

Note, that RS also depends on the frequency due to skin effect.
« Last Edit: October 06, 2022, 01:13:17 pm by radiolistener »
 

Offline omar32sTopic starter

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Re: Quality factor of an inductor (Sonnet)
« Reply #5 on: October 06, 2022, 05:12:06 pm »
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).
but doesn't Resistance2 equation in sonnet only computes series resistance disregarding shunt components including shunt capacitance.
« Last Edit: October 06, 2022, 05:16:18 pm by omar32s »
 


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