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Metal inductance Negligible or not?

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kenambo

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Hi

As we are talking about parasitic cap and res, why inductance is not considered in Inter chip metal routing? Can it be negligible for routing? If so why inductance is considered for transmission line model in IC circuits?

how about the inductance value for a short wire using metal?

Thanks
 

Because for most of the time effects of RC dominates it in ICs. Main reasons are because the interconnections are short for the frequencies that propagate and inductance of very thin lines are low. The connections are more lossy than inductive, which is why we can't have nice on-chip inductances. Also, including inductance in simulations cause simulations to take about forever, RC is good enough in most cases.

Inductance matters in transmission lines because in transmission lines you're specifically interested in inductances, which affect the characteristics of the transmission line. Using a transmission line model implies that you are in the region (high frequency, high inductance) where you'd care about inductances.
 
kemiyun said:
Inductance matters in transmission lines because in transmission lines you're specifically interested in inductances, which affect the characteristics of the transmission line. Using a transmission line model implies that you are in the region (high frequency, high inductance) where you'd care about inductances.
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Hi
Thanks for the reply. I understand your points. While we consider Transmission line model, the same frequency which I use in my internal circuits, is going to transmit. So For the same frequency itself I am considering inductance for the transmission line. So What makes the difference Here?

Thanks.
 

You make the difference, you chose to use transmission line model for one and RC for the other :-D . Are you asking me why you chose it? I guess you needed to match lines, or maybe you were interested in reflections? I don't know.

Transmission line that is made out of G, L, R, C is more accurate but harder to simulate and extract from layout. So it's only used when the accuracy is needed, which is usually the RF applications. For most of digital and analog stuff RC model is good enough for most of the time. Distributed RC is close to transmission line anyways.
 

Hi

Yeah Ok. I know that when a ordinary line has comparable length with respect to the wavelength of a signal, then that line is considered as Transmission line. So at that time, we employ Transmission line theory.
Thanks.
 

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