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Design >> Analog Design >> How to calculate and simulate impedance
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Message started by Larry_80 on Apr 17^th, 2013, 12:53pm

Title: How to calculate and simulate impedance
Post by Larry_80 on Apr 17^th, 2013, 12:53pm

Hello Guys,

Please How do i find Zin by hand calculation. Also how do i simulate the frequency dependent Zin in hspice? I would like to see if my Zin is a function (strong/weak) of the DC bias point (Vref) of my amplifier.

Title: Re: How to calculate and simulate impedance
Post by raja.cedt on Apr 17^th, 2013, 1:22pm

hello,
I guess it should be nmos rather pmos.
use small signal analysis, you will get around (1/sCdecap)+(ro)+(ro*1/scdecap*gm*(1+A)), of course it depends on vdd but as long as you have vddmin the sensitivity will be very less.

Coming to simulation, you could use ac simulation, apply some ac voltage with proper dc voltage at vdd and find ac current.

Thanks,
Raj.

Title: Re: How to calculate and simulate impedance
Post by Larry_80 on Apr 17^th, 2013, 1:31pm

Thanks Raja, i was able to do the hand calculation. I will try to do the simulation now. Could i possibly do a network impedance simulation?

Title: Re: How to calculate and simulate impedance
Post by raja.cedt on Apr 17^th, 2013, 1:33pm

what do you mean by "network impedance simulation"?

Title: Re: How to calculate and simulate impedance
Post by Larry_80 on Apr 17^th, 2013, 2:39pm

raja.cedt wrote on Apr 17^th, 2013, 1:33pm:

what do you mean by "network impedance simulation"?

Sorry i meant like 2 port network analysis. Z11 will be the input impedance...considerng Vddm as the output.

Title: Re: How to calculate and simulate impedance
Post by raja.cedt on Apr 17^th, 2013, 2:53pm

yes, indeed that's very professional way of finding impedance at any node. Use S-parameter simulation or any two port sim and find the z11.

Good night.

Title: Re: How to calculate and simulate impedance
Post by wave on Apr 18^th, 2013, 3:30pm

What is this circuit trying to accomplish??
It looks like an attempt at a DC bias circuit.
Looks like there are problems.

Title: Re: How to calculate and simulate impedance
Post by tzg6sa on Apr 19^th, 2013, 12:35am

raja.cedt wrote on Apr 17^th, 2013, 2:53pm:

yes, indeed that's very professional way of finding impedance at any node. Use S-parameter simulation or any two port sim and find the z11.

Good night.

Wouldn't it be enough to apply the AC source across the port? Of course with proper termination at the other ports if they exists.

Title: Re: How to calculate and simulate impedance
Post by raja.cedt on Apr 19^th, 2013, 2:03am

yes, sufficient.

In fact i suggested the same in my first reply.

Thanks,
Raj.