with ADS using cosimulation
What models have you used for C1 and C2?
For the transistor, usually some ground path is included in the measured data, so you might have added it a again when using that S2P file with EM co-simulation (S2P ground cascaded with EM modelled ground path). Check sensitivity of ground path inductance on results.
I think the differences are coming from components' tolerances.A tuning is necessary because the frequency is pretty high..
Have you ever done a Monte Carlo Analysis ?? You'd better do it..
What are their values ?? Tune them a bit, for instance use 0.1pF or 0.2pF lower values to shift the matching frequency to the rightif they are included in matching circuit.( few pF )For C1 and C2 i used the a Murata capacitor and included its model on the simulation.
For C1 and C2 i used the a Murata capacitor and included its model on the simulation.
I'm sorry i don't understand what you just said could you please explain it a little bit more or maybe guide me to some litterature.
Capacitors are apparently 0603 size which is huge for 9 GHz range.
The models provided by Murata? I don't know how accurate these models are (possibly great), but more important: where the reference planes are (pad center? outer edge? ) and if they include some pad effects (not desirable if you include pads in EM simulation already).
You can check by moving the pin position on the pad, and check for a mistake in pad capacitance (if measured data used other substrate thickness, or measured data included pad effect and you add it again in EM) by adding a small positive/negative shunt C to model. Does it look closer to measurement then?
Modelithics have a library of substrate scalable models for different manufacturers, and what I like about their models is that it is very clearly defined where the references planes are, what is included etc.
The transistor model is based on measured data, and for measurement the transistor source is grounded. That ground path is then included in results. Now you use the S2P model and connect the ground of the S2P data to some place in layout. The path from that ground pin to PCB ground has inductance, and that is in series with the S2P ground path from measurement. This can create over-estimate of ground path inductance, because your S2P includes the measured ground path and in your EM model you add another ground path between S2P ground pin and PCB ground.
The size should be ok, it is reasonable compared to the line. But indeed, the model accuracy might be compromised. Are these just DC blocks or do they implement a specific impedance? What values and types are these caps?
Looking at the pin position on the edge, in line width the open stub, I suspect we might have an issue with ADS Momentum port width. That's an all time classic for this type of layout: when you place a pin on the edge, ADS places the EM port along the entire edge including the stub. This wrong port width then results in simulation error. More details and solution: https://muehlhaus.com/support/ads-application-notes/edge-area-pins
View attachment 146848
I actually don't include the pads in the EM simulation just the lines. the SMT are just drawn but not simulated.
In this link they explain how they got their model but it doesn't mention if it's at the center pad or the outer edge.
the model i used on ADS for the transistor is a MEXTram Model. do you think there might be the same problem even if it's a diffrent model? i'm not sur how those models are made but from my simulations they are more accurate.
it's a capacitance of 1pF, and they are just DC blocks, they are not included in my matching circuit.
I have changed it's value on my board to 10pF just to see how it'll influence the results and i got closer to 9.35GHz.
No matter if we call it "line" or "pad", the metal where the capacitor is soldered onto must not be included twice (EM + model), that was my point.
What link?
You changed the model to 10pF model of that type, or you changed it to 10pF ideal C?
Please note my comment on the ports in #10, that has been a real issue in several EM support cases that I had to handle.
Yes i do take that into account, i only use edge port in general.
Misunderstanding? When you say "edge port", do you mean placing the pin on the polygon edge? That is what will fail for your layout, because the resulting port will extend across the line width plus the stub width = too wide = wrong current distribution.
I know "pin on the edge" vs. "edge pin" sounds similar, but it describes different things. The "edge pin" in my appnote is when you explicitely draw a line of finite length and assign it to the port, to control the port with. This is what you need here! Very important error source -- I have seen companies drop Momentum and switch to another EM solver because they didn't understand the effect and got bad accuracy.
- - - Updated - - -
Let me repeat with pictures, to make it more obvious:
If you just place two pins like this
View attachment 146856
your EM ports will extend across the entire edge:
View attachment 146857
In this case, you need to use a user controlled port with as described in the appnote, to get this:
View attachment 146858
Good luck!
Volker
(Keysight Certified Expert EDA)
If this might give you any ideas, i actually had a ring resonator printed to control the permittivity, and likewise its frequency was shifted to 9.15GHz.
What makes me not convinced about this is the fact that i don't have a shift in my filter. i'm using RO4003C for the substrate.
Ok, sounds fine with the explicit width edge ports!
RO4003 is inhomogeneous, so we might expect some anisotropy between permittivity in x-y plane and z direction.
I used to work for Sonnet when they introduced support for anisotropic dielectric, and at that time they did some extensive study of substrate materials in collaboration with Rogers. If you look **broken link removed**, you will find this table:
View attachment 146859
This might be an incentive to check sensitivity to substrate permittivity, especially if your resonator/filter have different effect of er_xy vs. er_z
(edited)
What about R1 and R2 at the radial stub? I don't know their values, but the resistive sheet will have some capacitance to ground. I suspect that is not accurately captured by simulation: the resistor itself is not included in EM (only ports), and a generic resistor model connected at schematic level will not have the correct shunt capacitance for your actual substrate parameters. I would estimate the capacitance and tune that value in simulation using a shunt capacitor, to see if that effect is relevant.
We need to find out what your circuit is sensitive to.
Thank you very much for the link, it helped greatly. it does resolve the resonator's shift but I don't understand what you mean by "especially if your resonator/filter have different effect of er_xy vs. er_z"
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