problem with AC analisys Cadence- output differential signal

[macg84]

AC analisys Cadence

Hello,
i have some problem with AC analysis, I have to compute for the circuit in attached this value:
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Run an AC–analysis to simulate the small signal properties at the resonance frequency,which means the input impedance, voltage gain and small signal parameters of the transistors.

How will i measure the output differential signal?

Run an AC–analysis where you choose a suitable frequency sweep.
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This circuit is a low noise amplifier the works at frequency oh 1.8Ghz
Can you help me?

 

[erikl]

Re: AC analisys Cadence

How will i measure the output differential signal?

It's already available in your schematic: The vcvs (E6) delivers it to the output PORT3 .

Run an AC–analysis where you choose a suitable frequency sweep.

That's the correct method!

 

[macg84]

Re: AC analisys Cadence

I have take this output with calculator:VF("/net28")-VF("/net36"), is it correct?
i used an AC analysis with sweep range start 1G stop 3G, e sweep type logarithmic with 10 points per decade. In imput there is a PORT with AC magnitude equal to 1. This LNA has to work at 1.8GHz, is this differential output output correct???it'isn't , I think becouse the differential output is very low
Why in output do i have to put a port with in output a generator VCVS with gain 1???
I have to take my differential output between 1 nad 2 (look schematic 2) .
Thank you very much!!!!!!!!!!!!!!!!!!!!

 

[erikl]

Re: AC analysis Cadence

I have take this output with calculator:VF("/net28")-VF("/net36"), is it correct?

Yes, just a bit long-winded, s. below.

i used an AC analysis with sweep range start 1G stop 3G, sweep type logarithmic with 10 points per decade. In input there is a PORT with AC magnitude equal to 1.

This is normal in small-signal analysis.

This LNA has to work at 1.8GHz, is this differential output correct???

Surely not!

it'isn't , I think because the differential output is very low

Right. Did you declare your variables reasonably? You must define reasonable values for all the variables in your circuit (Ibias, Vgbias1, Vgbias2, Ls, Lg, Rin, Rtank, Ltank, Cload) in order to achieve correct biasing of the MOSFETs and the right gain at the desired frequency. That's the job you have to do! Play with the variables, assigning reasonable values to them, corresponding to the knowledge you (should) have acquired!

Why in output do i have to put a port with in output a generator VCVS with gain 1???

Because it's convenient. It calculates the difference and relates it to GND.

I have to take my differential output between 1 and 2 (look schematic 2) .

... and the VCVS (E6) does this for you! ;-)