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Larry_80 Community Member Offline Posts: 61	How to calculate and simulate impedance 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.
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raja.cedt

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Posts: 1516
Germany

Re: How to calculate and simulate impedance
Reply #1 - 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.

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Larry_80 Community Member Offline Posts: 61	Re: How to calculate and simulate impedance Reply #2 - 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?
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to calculate and simulate impedance Reply #3 - Apr 17^th, 2013, 1:33pm what do you mean by "network impedance simulation"?
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Larry_80 Community Member Offline Posts: 61	Re: How to calculate and simulate impedance Reply #4 - 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.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to calculate and simulate impedance Reply #5 - 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.
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wave Senior Member Offline Posts: 117 Silicon Valley	Re: How to calculate and simulate impedance Reply #6 - 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.
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Horror Vacui

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Posts: 127
Dresden, Germany

Re: How to calculate and simulate impedance
Reply #7 - 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.

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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to calculate and simulate impedance Reply #8 - Apr 19^th, 2013, 2:03am yes, sufficient. In fact i suggested the same in my first reply. Thanks, Raj.
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