How to simulate a frequency dependent resistor?

Yes. Well if it is the standard R=k.sqrt(f) for AC only:-)

Kevin Aylward snipped-for-privacy@anasoft.co.uk

What do you mean by "in a simulation of an amplifier"?

Yep. That's the classic paralleled conducting cylinders model. I have someone else's paper on it around here somewhere but I can't find it ;-)

...Jim Thompson

"Greg" a écrit dans le message de news: snipped-for-privacy@g14g2000cwa.googlegroups.com...

I've used this quite successfully:

Hi,

first, many thanks for the answers!

Of course I tried to give the resistor an equation with the variable freq, but the software sets freq only to the starting frequency and does not update it during the frequency sweep :-( Tried f, fr, frequency also, but they stay at their predefined value and cause errors if not predefined. Software is some IC simulation spice from tektronix.

The RL ladder network emulating coaxial sheets seems clever, but it changes L with frequency also, which I have to avoid as the L in the model is constant with frequency.

Unfortunately my spice also does not have laplace sources so I am bound with the Rskin=k*sqrt(f) model which also does not work as I described above.

Now how to make R dependent and L independent?

Greg

Get a better spice ?:-)

...Jim Thompson

Unfortunately this is not an option. Its a design system package for chip design with non-transparent customized libraries so I could not even switch to a different spice if I wanted. Also another simulator with that capabilities (suited for IC design, e.g. ability to easily converge on circuits with hundrets of transistors in it) would cost a small fortune.

Isn't there any other way of simulating that?

Greg

If there's no behavioral way to do a frequency-dependent resistor, then you're left with a lumped model, such as Fred Bartoli pointed out.

BTW, a frequency dependent resistor CANNOT exist without a reactive term.

...Jim Thompson

Yep. Somewhere back in time I posted my wirebond model that includes skin effect.

Thank god for skin effect, otherwise wirebonds would have such high Q that everything would ring.

...Jim Thompson

Well, as noted, my XSpice engine in SuperSpice does handle the sqrt(f) for resisters. Sure, it aint the best in the world for convergence, but I have been using it solidly for ic design and most of the times it converges fine for 100+ transistor circuits. You might have to set the options stiffly, like itl4=5000, and the gmin though. However, apart from LTSpice, its the only cheap simulator that handles most ic constructs directly, like the M multiplier for mosfets etc. I might be able to help with your custom lib. You can email me direct if you want.

Kevin Aylward snipped-for-privacy@anasoft.co.uk remove EXTRACT

More, the inductance *does* change with frequency, between two asymptotic values. Always. Look for internal/external inductance.