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ADS EM model problem s-parameter simulation

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Kooky613

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I am designing a differential amplifier (6-9 GHz) and I have created some footprints for smt components (Infenion transistor 2 pins for emmiter).
I run the simulation in momentum (0-30 GHz) and i create the EM MODEL and the symbol but when i go back to the schematic and i insert it and i connect it to the transistor the s-parameters simulation does not run...!!! it shows me the following:

Error detected by hpeesofsim during DC analysis 'SP1'.
No DC convergence.


Warning detected by hpeesofsim during termination.
Could not free saved data for Momentum component

Does anyone knows what does it mean?
Thanks in advance!!!
 

Try to fix the DC convergence issue.

Does the DC path result look ok?
Have you simulated using Momentum RF mode or µW mode?
 
I use an inductor and a bybass capacitor to bias each of the 2 bases of transistors....I also have add only the pads for this components... I have not look for discontinuities between the pads. I have only add them to see what i take... and i see this error....
Must i change something?
 

I don't understand your answer. Check DC results from Momentum if that looks good and physical. Show screenshots.
 

I use Momentum μW mode..
I can not understand what i must check
How can i check dc results from momentum?
 

Kooky613 said:
How can i check dc results from momentum?
Click to expand...

Look at low frequency and DC S-params. In data display, you can switch to log frequency scale. Curves should be smooth (no glichtes) down to DC. Evaluate resistances in the connected & isolated paths if they make physical sense.

It is difficult to help you without knowing your models & settings & results.
 

I get these from momentum.... I have shortcircuit pins 1 and 4 (the 2 emitter pins)
5.JPG
6.JPG
7.JPG

When i insert the symbol to the schematic and i connect it to the transistor in the schematic i have the problem i mentioned above
 

I see no mistake with those S-params.
It is difficult to help you without knowing your models & settings & results.
 

what else do you want to see? I cannot understand
 

0.JPG
When i put the footprints the s parameters are failing
 

Kooky613 said:
what else do you want to see? I cannot understand
Click to expand...

Can you show a screenshot of your transistor pad layout for EM, including the EM pins/ports?
Your use of small EM pieces for pad capacitance is a bit unusal, I think it's not accurate.
 

Kooky613 said:
View attachment 149689
When i put the footprints the s parameters are failing
Click to expand...
Your set-up and simulation method both are essentially wrong.You connected both layout and electrical component to the same PIN.
What you would expect this set-up ?? In other-words which component will be valid ?? electrical component or layout ??
There are serious mistakes, please review your set-up and search-please-application of Momentum Simulation examples on the internet.
 

Big Booss thanks for the reply.
how can i simulate the effect of footprints?
how can i connect them?
please explain more

- - - Updated - - -

volker@muehlhaus said:
Can you show a screenshot of your transistor pad layout for EM, including the EM pins/ports?
Your use of small EM pieces for pad capacitance is a bit unusal, I think it's not accurate.
Click to expand...

The layout of the transistor pads have the dimension given in datasheet. I put the ports in the middle of each pad and i use NONE calibration
 

Kooky613 said:
The layout of the transistor pads have the dimension given in datasheet. I put the ports in the middle of each pad and i use NONE calibration
Click to expand...

Yes, but pads have more complex behaviour than just shunt C. They have a size, and different locations for input pin and component connection, which makes them 2-port model for each pad.

Your "small pieces" use of EM is not appropriate for RF PCB analysis. Have a look at the ADS examples for Momentum to see how larger layout sections are analyzed, including the routing (interconnect) between components.

If you insist on using shunt C only, extract shunt C values in ADS data display and use that in schematic. But that method is not accurate at your frequencies.

Good luck,
Volker
(Keysight Certified Expert EDA)

cosim.PNG
 
Last edited:

I understand what you say
It is a first approach to add parasitics in my schematic
The problem is that s parameters does not run!!! (Not how accurate is my model)
 

Kooky613 said:
It is a first approach to add parasitics in my schematic
The problem is that s parameters does not run!!! (Not how accurate is my model)
Click to expand...

It is related. Your small models have S-params that are close to open circuit, and such near-0dB-data can easily become slightly larger than 0dB (from numercial precision issues) and then your analysis blows up due to non-passive S-params. Simulating along the outer boundary of the Smith chart means asking for trouble in transient analysis.

That's why I wrote "If you insist on using shunt C only, extract shunt C values in ADS data display and use that in schematic". To avoid S-params that are slightly non-passive from numerical precision issues with all these tiny pieces of copper that have no series loss.

Also, as BigBoss mentioned, you have that EM-modelled dual emitter path in parallel to an ideal wire connection, that makes no sense.
 
Last edited:

Thanks for the reply Volker
So if i create an accurate EM model for the pads, how could I connect the 3 pin electical model in the schematic with the 4 pins EM model, which i create?
 

Kooky613 said:
Thanks for the reply Volker
So if i create an accurate EM model for the pads, how could I connect the 3 pin electical model in the schematic with the 4 pins EM model, which i create?
Click to expand...

For such small details, it is important to model accurately, so I would do the EM model like this:

pads2.PNG

All pins are created using the edge/area pin concept with user drawn size, by drawing an additional line that controls the exact port size. This gives controlled port size instead of just placing a pin and let Moment decide. Without such user controlled size, Momentum picks the entire edge of the polygon (on edge) or a point (inside pad). We want to control port size, to accurately model the step in width and the reference plane of the SMD. Appnote on edge/area ports: click.

Then, the 2-port SMD data is embedded at the inner ports of the 4-port EM structure.

pads.PNG
 
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