input output circle equivalent in cadence virtuoso

LSB and SSB on the direct plot form, which are for Load Stability Circles and Source Stability Circles respectively. Strangely enough, searching for "stability circle" in the Help menu in Virtuoso points you directly at this answer...

Andrew.

Hello Andrew ,Why for stability We have in cadence both input and output plots.

But for Gain for example (where we need to conjugate match both gamma_s and gamma_L for maximal gain)

Our cadence smith shown us some Zd only.(why for other cases we dont have  input output circle)

We only get a single gamma in the results although we need both gamma_s and gamma_L for a point inside a gain circle.
Thanks. 

I have no idea how to make any sense out of what you just said. You asked earlier for how to do the equivalent of MATLAB's input and output stability circles, which I explained. You're now asking me why we have this? Didn't you just ask me how to do that? Then you have some other rather garbled sentences, and I don't know what you're trying to say.

Andrew.

Hello Andrew, i have made a comparison between the stability circles which needs both input and output  for ensuring stability of the device ,and Gain circle which we need in theory both input and output matching.
On the stability case cadence virtuoso gives us the option to plot the input and output circuit,
But on the gain circle We only have this screen and no input otput selection.
I am asking Why for GAIN we dont have input and output circle too?
In theory We need the output impedance too for setting certain gain.
Thanks.

The Gamma is the value of gamma depending on where your cursor is on the Smith chart. Whether it means Γ_L or Γ_S depends on what you're plotting. It wouldn't make any sense for the tracking cursor to have two Gamma values because it's just based on the location on the Smith chart. The tracking cursor shows the Gamma both in real+imaginary or as mag+angle.

For example, if you plot GAC (Available Gain Circles) then the peak of the contour (the trending centre of the circles) will give the Γ_S giving maximum gain (at that frequency, if sweeping power say). Similarly if you plot GPC (Power Gain Circles) then the peak of the contour (the trending centre of the circles) will give the Γ_L giving maximum gain.

This is explained in the document in the Spectre installation (the path may be different in older versions where it was not based on ADE Explorer, but it will be similarly named): <SPECTRE191_instDir>/doc/spectreRFexplorerWorkshop/spectreRFexplorerWorkshop.pdf (can also be found here on the support site: Spectre Circuit Simulator and Accelerated Parallel Simulator RF Analysis in ADE Explorer Workshop 19.1 ). The database used is at <SPECTRE191_isr>/tools/spectre/examples/SpectreRF_workshop/RF_Doc_Database.tar.gz . The LNA example in this explains pretty clearly how these two circles work.

Andrew.

Hello Andrew, i have a problem matching description and plot in the manual you said to look in.
I cant see in the smith circle 1.9 but i assume its  the smallest circle.
if we look at the table on the left we see gamma_s is 0.4 not zero
Where is gamma_s=0 in the smith plot?

Thanks.

First of all, it rather surprises me that you're attempting to do all this without at least a basic understanding of Smith Charts. Gamma=0 is at the centre of the Smith Chart. The whole point of Smith Charts is that they plot the reflection coefficient on a polar graph, and then they have additional circles drawn which have constant resistance and orthogonal to these, circles with constant reactance.

Secondly, you're actually using a document which is not the one I pointed you to - it looks rather more like the one that used to be in <SPECTRE171instDir>/tools/spectre/examples/SpectreRF_workshop/rfworkshop.tar.Z in the file doc/LNA.pdf. The wording is not as clear as it is in the newer document, but if you read the very next sentences, it explains it clearly (you can even see the start of the next sentence in the image you show above!):

In the above figure, the noise circle, NC, draws the NF on the Smith chart
of the source reflection coefficient, Γ_S . The result in the NC plot where
Γ_S = 0 and NF = 1.9 dB matches the result in the NF plot. The center of
the NC corresponds to Γ_S (that is, G_min ) which generates NF_min . The
optimum location for the center of the noise circle is at the center of the
Smith chart. However it is hard to center both the available gain circle,
GAC, and the noise circle, NC, in the Smith chart.

It would have been helpful if you'd actually mentioned which document you were using as it wasn't the same as the one I suggested you to so that I didn't have to hunt it down to find out what you might be referring to.

I knew I was going to regret answering the original question in this thread. I do wish you'd do a bit of reading and research (or ask your supervisor) first.

Andrew.

Hello Andrew,I know what gamma means. I just didnt understand how this sentence has to do with our circle.

Because Gamma_s=0 is outside of our available gain circle.

Thank you very much for pointing my error.

So in order to match available gain i need to pick a point where the input stability circle is on the same space as my available gain circle.

And in order to match power gain i need to pick a point where the output stability circle is on the same space as my power gain circle.Correct?

We dont nee both output and input stability circles for a stable functioning amplifier?

Correct?

Thanks

The purpose of these circles is that you can try to adjust the match (input or output) using the information about where they are currently centred to optimise the gain, noise and stability for a particular point (e.g. a particular frequency).

Hello Andrew, in my Cadence instalation directory  although i see here 18.1 in the following path

/cadence/tools/spectre/spectre18.1/tools.lnx86/spectre/examples/SpectreRF_workshop/

  i have only 16.1 example of the document  and i cant accsess the 19.1 link you pointed to,is there another way to download this 19.1 version?
support.cadence.com/.../techpubDocViewerPage

Thanks.