producing gain circles in cadence virtuoso

Did you check that the transistors are not just completely off? Check the bias point (show the operating point and node voltages annotated on the schematic). I didn't spend any time thinking about the circuit, but it seems rather unlikely that it's anything other than your circuit not working!

Andrew.

Hello Andrew the problem came from the DC value ,i specified 0.8V dc in the port but it showed 1.6V

Why its biasing twice the specified value?

Another question , is there some option in cadence virtuoso where we can convert the source reflection coefficient(shown in the photo bellow)?

into load reflection coefficient(automatickly converting using the formula shown bellow)

Thanks.

You've rather annoyingly updated your question after posting to add more, so a quick answer to the question you originally posted. I don't know the answer to the second question off the top of my head (and it's the weekend, so I have less time to look it up).

Anyway, for the first question, the port has output impedance (by default 50 ohms) and if you specify a voltage, it is driven assuming that the output of the port is matched. So because of this the internal voltage source (before the port impedance) is twice the value you specify, so that if it was matched the output voltage would be the value you specified. In this case the port is driving a gate, so is very high impedance, and hence you don't see the potential divided down at all, and so see twice the specified value. This is expected.

Andrew.

Dear robert21,

robert 21 said:

Another question , is there some option in cadence virtuoso where we can convert the source reflection coefficient(shown in the photo bellow)?

into load reflection coefficient(automatickly converting using the formula shown bellow)

If I am understanding your question correctly, I believe you are misinterpreting the elements of the formula you provided and the resulting  question you pose that I have quoted. The S parameters of the 2 port referred to in the source reflection coefficient formula you refer to remain the same in source and load reflection coefficient formuals, the values of the source and load reflection coefficients within the two formulas are not. In the case of the formula for the source reflection coefficient, the value of gamma within the formula refers to the gamma of the load. In the case of the formula for the load reflection coefficient, the value of gamma within the formula refers to the gamma of the source. There is no guarantee that the source and load reflection coefficients of the two port source and load elements are the same. Hence,, you cannot simply convert one to the other. To hopefully make this more clear for you, I am including a reference to a Rutger's University document.

Shawn

Hello Shawn ,My final goal is to get the impedance to which i need to match on the source and on the load from the point in the circle shown bellow.
So the Gamma we get from the point  shown in red arrow is it Gamma_L or Gamma_G?

I see that its much easyer to use the Z_params because our Z_G=Z_L=50 ohms and getting z11 z22 z12 z21 are straight forward from cadence .So if i want to go that way of using Z_params what is zd shown the circle plot result bellow?

given that Zd is Zin  how do i know what is that Zout in that point on the circle?

Thanks.

Dear robert21,

robert 21 said:

So the Gamma we get from the point  shown in red arrow is it Gamma_L or Gamma_G?

Since you selected GAC in the Direct Plot form, my understanding is that the gamma shown represents the source reflection coefficient. The helpful link below to an example set of analyses indicates the following:

"Available Gain (GA) is solely a function of the source reflection coefficient Γ_S . "

Hence, it is neither "Gamma_L" nor "Gamma_G" as you state. The values of "Gamma_L" and "Gamma_G", as shown in the reference I provided, refer to the reflection coefficients of the impedances ZL and ZG respectively. Neither of these is the source reflection coefficient.

https://support.cadence.com/apex/techpubDocViewerPage?xmlName=spectrerfworkshop.xml&title=Spectre%20Circuit%20Simulator%20and%20Accelerated%20Parallel%20Simulator%20RF%20Analysis%20in%20ADE%20Workshop%20--%201%20-%20SP%20Analysis%20and%20Small%20Signal%20Gain&hash=1084997&c_version=16.1&path=spectreRFworkshop/spectreRFworkshop16.1/AppA.html#1084997

Shawn

Hello Shawn, given what you said i assume that Zd shown by the program is Z_in.

Is there a way in cadence to automatickly get Z_out two? (without using Zout= Z22-Z12*Z21/(Z11+ZG))

Thanks.

Hello Shawn, given what you said i assume that Zd shown by the program is Z_in.

Is there a way in cadence to automatickly get Z_out two? (without using Zout= Z22-Z12*Z21/(Z11+ZG))

Thanks.

Point of reference only... because it's a commonly asked question.  Do you have access to Cadence Online Support?  

In the sp Direct Plot form, what is the difference between Z11 and ZM1, Z22 and ZM2?

The equations behind the Direct Plot buttons are in the Spectre and APS Analysis in ADE User Guide.  Look for the following topics.

• Network Parameters
• Two Port Scalar quantities
• Two Port Gain quantities
• Two Port Network circles
• Equation for VSWR
• Equation for Group Delay

best regards,

Tawna

Dear Tawna,

Thank you Tawna! Your links saved me from a bunch of typing!

Hopefully, robert21, you can find what you need in the two port network circles. The data regarding the output reflection coefficient (i.e. your "Z_out") was also present in the reference I provided you yesterday.

Shawn

I need the Zm1 and Zm2(zin and zout) at a certain point in the circle i showed .

So i get to the conclution that if i put the mouse on a  point in a cicrle, Zin is the Zd and Zout i get from

Zout= Z22-Z12*Z21/(Z11+ZG))

Thanks