RF SPDT gives an error: Factorization of matrix failed due to non-finite entries in the matrix

What tool are you using?  And what version?

best regards,

Tawna

Microwave Office 15.01r build 10030 Rev 9.

Its for this project: https://youtu.be/GLFeoOHoRuA

Dear Zeke KJ7NLL,

Zeke KJ7NLL said:

Microwave Office 15.01r build 10030 Rev 9.

and 

Zeke KJ7NLL said:

The schematic looks like this.  Basically when C2>0 or C3>0 it should use the capacitors, otherwise 1e9 Ohm resistors.  Can SPDT's not be used with RF circuits

I know nothing about Microwave Office, but I am wondering if in any of the simulations you are performing set C2=0 or C3=0? The motivation for the question is that the impedance of a capacitor as C gets close to 0 increases to a near infinite value. This will clearly result in a numerical error.

What I might suggest to verify this possible hypothesis, you might alter your switch condition to use a value of Cmin in lieu of 0. In essence set Cmin to say 1e-15 F and set your two conditions to C2 > Cmin and C3 > Cmin and set C2 or C3 to, for example, 1e-16 F when you want to switch the states of your switches.

Once again, I am not familiar with the tool you are using, but this came to mind as I read your error and examined your schematic and switch conditions - so I may be totally wrong! Just thought I would mention it just in case it helps...

Shawn

C1 and C2 aren't really capacitance, they are indexes into the Murata RF capacitor number (ie, C1=1 means 0.1pF because that is the first cap listed). 

C1 and C2 are always integers.  I tried setting state to 1 or 0 and it still has a problem.  It works without the SPDT's (if they are removed or disabled and then bypassed), but adding the SPDTs causes the error.

Dear Zeke KJ7NLL,

Zeke KJ7NLL said:

C1 and C2 aren't really capacitance, they are indexes into the Murata RF capacitor number (ie, C1=1 means 0.1pF because that is the first cap listed). 

C1 and C2 are always integers.  I tried setting state to 1 or 0 and it still has a problem.  It works without the SPDT's (if they are removed or disabled and then bypassed), but adding the SPDTs causes the error.

Thank you for educating me! 

One more suggestion...if you are just trying to assess how many capacitors are required to achieve a specific capacitance...you might try removing your second SPDT switches and connect the second terminal of the capacitors to ground. I can't see your entire test bench, but I don't see a circuit ground defined.

In other words, modify the topology to appear something like Figure 1.

Once again, just another hypothesis...so please don't waste your time if the suggestion does not make sense in light of your needs.

Shawn

Figure 1

Hi Zeke,

What you have looks correct.  Attached is a quick demo project using the same Murata Cap model in which you can tune the values of C1/C2/C3 to set the total capacitance.    This was built in v15.03 which is the current release using the latest Murata models.

Best Regards,
Graeme

SPDT_Cap_Tuning.zip

I forgot but Microsoft released a Windows update that broke early v15 builds.    If you download v15.03 then it should be fine.  
https://kb.awr.com/display/awrfaq/Factorization+of+Matrix+Failed+and+Other+Errors+after+Windows+10+Update).

Thank you for the example that you made, it started magically working. If it happens again we will let you know.