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# Q calculation of inductor

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#### rezaee

##### Full Member level 2
how i can measure the Q of a spiral inductor(TSMC 0.18UM) in ADS?

Inject ac current through the inductor and plot the imaginary part/real part of the voltage across the inductor across frequency. This will show you the variation in Q across the usable frequency range.

### rezaee

Points: 2

i plot Q of spiral inductor(TSMC0.18um) versus frequency(sweep 1 to 10 GHz) in ADS ,Q first increase but but from a point it decrease i cant understand why this happen? is it true that Q of a inductor is: Q=L*ω/R then what is the reason of decreasing in Q when frequency increases??

Hi

Self resonance.

Remember that a planar inductor have some parasitic components. You have a capacitance from the vindings to the ground plane, capacitance between the windings. So at some point you will have a resonance and the inductor will cease to behave as an inductor but become capacitive. You can see the picture attached.
Try and plot L versus frequency here you will properly see a constant value of L and then a sudden increase in inductance and then it goes negative. When it becomes negative it starts to act like a capacitor.

Regards

### rezaee

Points: 2
hi
tnx tyassin

its my simulation set up and here i see that Q of spiral inductor is almost 11 in 2.4GHz, is it true? because of i heard the spiral inductor that use for integration has smaller Q between 3 to 5!

yes that is true, but remember that the Q of smaller inductors is larger than larger inductors.

### rezaee

Points: 2
hi
thanks tyassin
my problem is that i want to design and simulate a power amplifier and calculate the element values. when i use lumped element (inductor&capacitor) pallate of ADS to simulate the designed circuit i achieve good result but when i use spiral inductor from TSMC0.18um pallate it is differ from good result.ofcourse i know the reason is that the lumped element in ADS are ideal and inductor has vary large Q , but i dont know how i can import the role of inductors Q to my desigining equations till when i design my circuit and i simulate it with TSMC0.18um elements the result be good, do you have any suggestion for me?

best regard

Hi

Well....this is the hard part when you design. I think it difficult to have it predicted by eqautions because the "real" parts have so many parasitic elements.

I have designed once a filter also with spiral inductors and lumped capacitors. This took some time because of the process of changing the ideal components with real components.
If would advise you to use the tune tool with the inductors.

Regards

### rezaee

Points: 2
yes i understand what u say but im beginner in ADS and i dont know how i can use tune tool or optim&goal block in my desining if you have exprince in it or having application note about this or an example and etc please help me to learn.thanks.

Hi

Look for this icon on the toolbar. This is for tuning. When you press it you have to select the parameters on the schematic you want to tune.

Regards

### rezaee

Points: 2
hi
thanks for your answer to my questions, i find this icon and i apply it for tuning inductor value in circuit.
now i have several questions:

in TSMC0.18um (ver2) there are 2 kinds of spiral inductor that the minimum correct value they can accept are 2.369nH and 3.494nH but i need smaller inductor for example 1nH in my circuit so i dont know how i can tune this? on the other hand how can i import smaller inductor in my circuit?
1nH or smaller inductor isnt usuall in ICs?

what is the application of optim/goal block and how i can use it and for what kind of simulation i can use it?

Regards

draw your own inductor in momentum and characterize it with sp simulation

### rezaee

Points: 2
hi
thanks oermens

i want to design my circuit in TSMC0.18um technology for integration and if i draw my own inductor (out of the TSMC inductor range for example 1.6nH ) in momentum and i use it in my shematic isnt wrong?? my means is when i want to design a circuit with TSMC0.18um technology for integration isnt important for me to use just elements from TSMC pallate in ADS ?

im beginner in ADS, how i can draw for example 1.6nH inductor in momentum and then how i can import it in my shematic window for simulating the whole circuit?

Best Regards

the passive devices provided by the pdk are ones which have been fabricated and characterized to be included in the PDK, so their performance should pretty much be guaranteed. if you need something which is not available through the pdk Pcells, you should make it yourself and perform whatever simulations to characterize it.

custom inductors from scratch is not easy, unless you really want to work out the hand models before drawing. do you have ASITIC tek file for your pdk? that way you can use asitic, give it a set of constraints (i.e. max diameter, max winding width, max winding spacing, required inductance and Q, etc) and it will generate the topology which best meets your constraints. then use that geometry and draw it in momentum, taking into consideration the DRC rules which asitic sometimes ignores (i.e allowable angles), and characterize it with sp simulation. then create an instance based on sp results using broadband or narrowband spice model generator.

### rezaee

Points: 2
hi
thanks
my OS is windows XP and just i have ADS2008UP1 and i install on it the designkit of ( TSMC RF CMOS O.18um v2.0) i am not familiar with ASITIC and i dont have this software but now i search on the net and see somethings about it but i cant understand what files i should download and how i can install it because of i see i must be familiar with UNIX operating system but i dont have information about this OS
Isnt any way for me to just simulation my circuit with cmos TSMC0.18um in ADS?? I just want simulate my circuit and see resylt and i dont want to draw layout.

Best Regards

rezaee said:
hi
how i can draw for example 1.6nH inductor in momentum and then how i can import it in my shematic window for simulating the whole circuit?

rezaee said:
Isnt any way for me to just simulation my circuit with cmos TSMC0.18um in ADS?? I just want simulate my circuit and see resylt and i dont want to draw layout.

I don't understand, you want to do layout or not?? I just explained how to draw the layout and make the spice model for simulation. I have TSMC CL018 180nm pdk, there are fitting equations for spiral inductors. if you don't want to use one that comes with the pdk, use the equation to determine the geometry of a suitable inductor.

sorry if my means isnt clear now i can describe my means clearly
In first step i just want to simulate my circuit with ADS in cmos TSMC0.18um technology , layout isnt important for me in this step because of im not familiar with ASITIC & UNIX & momentum ... Drawing layout is second step for me on the other hand and for example think i want to simulate a simple RLC circuit in schematic window of ADS and layout isnt important for me at first time but its important for me that my circuit simulated in cmos TSMC0.18um technology
now think the value of inductor is 1.6nH, when i want to select an inductor from TSMC0.18um pallete to drag in schematic window for simulation i can select 2 kinds of spiral inductors that the minimum values of these for one of them are 2.369nH and for other one is 3.494nH but i need 1.6nH for my circuit. and when i change the value of it to 1.6nH appears a warning message : "The minimum inner radius is 30 um ." my question is what i do now? i dont see any fitting equation.

Your PDK pcells do not have an inductor of value 1.6nH characterized, so you can not use the instance that is available in the "ADS palette". You have to draw an inductor yourself in Momentum and generate the spice model.

### rezaee

Points: 2
OK but i dont know how i can draw a 1.6nH in cmos TSMC0.18um technology in ADS with momentum and then how i can generate spice model
is it necessary to use ASITIC for this?? if your answer is yes then can you tell me how i can install ASITIC on windows XP and from which site i can download all require files??

of course i must tell you that when i change the value of TSMC0.18um inductor to 1.6nH appears the warning message but the value changes to 1.6nH. if i simulate the circuit with this condition ( with warning message ) in this way i dont know the result is wrong or true??

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