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Simulators >> Circuit Simulators >> fast inductor
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Message started by raja.cedt on Sep 21^st, 2010, 7:15am

Title: fast inductor
Post by raja.cedt on Sep 21^st, 2010, 7:15am

hi,
can any one please tell me what is fast inductor corner, when i am ding vco corner simulation with fast inductor i am getting higher frequency, through this i got fats means less value of inductance. But i want to know what is the mean by fast inductor from process perspective (means thin metal width or less radius ..some thing like this ?

Thanks.

Title: Re: fast inductor
Post by Geoffrey_Coram on Sep 22^nd, 2010, 5:54am

I expect that the relevant process variation would be over- or under-etch in the plane of the inductor (the metal lines would be narrower or wider than intended), or a change in the thickness in the vertical direction, from when the metal layer is planarized (ground and polished).

Title: Re: fast inductor
Post by RFICDUDE on Sep 22^nd, 2010, 5:24pm

I suspect that the corner variation of an integrated inductor is mainly due to the variation in parasitic capacitance to the substrate and the interwinding dielectric capacitance. These capacitances impact the self resonant frequency of the inductor, and the effective inductance increases as the frequency approaches the self resonant frequency. It is not that the inherent inductance changes, rather it is that the reactance changes more rapidly because of the second order resonant response (hope that is clear).

The metal spacing and width tolerances mainly impact capacitance. Inductance is fairly insensitive to these variations, but the effective inductance at a given frequency can vary substantially with the capacitance if the self resonant frequency of the inductor is within a couple of octaves of the operating frequency.

This is one reason why VCO inductors tend to be quite small in self inductance (to minimize the impact of parasitic capacitance variation).

I suspect your fast inductor corner corresponds to thick oxide thickness (between substrate and inductor metal) and maybe wide separation between windings.

Title: Re: fast inductor
Post by vp1953 on Sep 22^nd, 2010, 5:49pm

Hi Raja,

The higher VCO frequency may in fact have nothing to do with the inductance. Fast generally means smaller capacitance (slow is larger capacitance, though may not always hold) - if the capacitance for the LC tank has come down this can increase the oscillating frequency

Title: Re: fast inductor
Post by raja.cedt on Sep 22^nd, 2010, 10:52pm

HI,
thanks for every one who contributed some thing here. From the above discussion this is my understanding.

1.Mainly inter winding cap will effect due to spacing between turns (which is mainly under etching), metal width.
2.Thick oxide

Thanks..