I will do that. IF I understand clearly what you are saying, I should connect my VNA to an oscilloscope and look at the signal generated at one frequency (let say 2.45GHz). At this point, I should observe a sine signal.OP says difference between simulation and fabrication, but
there's a third leg to that stool, which is measurement. That
holds the most potential for error and surprises, IMO.
I'd hope that there were on-same-die shorts and opens
de-embed structures for your VNA & probes, and that the
low-level layout of these matches the "access layout" for
the DUT.
The extreme behavior in the initial plots suggests a
resonant feature that a diode (oscillating types aside) ought
not to have. Could be time-of-flight in the harness and bad
termination, I dunno.
Diode DC bias and very small signal stimulus can show you
a capacitor or a resistor. Or something in between.
Large signal test stimulus can maybe bring on rectification
and multiplication / mixing. Might look at signal with a 'scope
to be sure that stimuli which "should" be ideal small signal,
are so when you put the whip to it. Like, sin(f) times cos(f)
can give you a 2f tone from only one source and its phase
shifts applied to a nonlinear (explicit, implicit, PIM...) element.
So is your diode put where it "should" be linear, or acting up?
For a realistic model fit you'd probably do some pulls at
varying DC bias, to get at those model params that emulate
bias dependent (depletion / injection) capacitance.
Here is my workspace.Your screenshots are always incomplete enough, and small enough, that we cannot exactly see what you did.
You can get much better help if upload the ADS workspace, so that we can see what you really did, including the testbench and more details.
The two libraries are not needed for the simulation. Can you also check how I define the ports of my EM simulation?I see no obvious mistakes. Mesh is fine and backside ground is modelled by boundary condition, which is fine.
The permittivity of 3.91 in your substrate definition is a bit unusual, typical FR4 would be 4.4 +/- 0.2, but if 3.91 is specified by your supplier you should use that value.
There are two missing files/libraries (Murata and HFDiode) so I could not simulate, but the EM part looks ok to me (except unusual permittivity).
View attachment 189942
Given the massive differences between your measured data, e.g. no 2.45 GHz resonance at all with your blue measurement curve, I think you should create a layout with well defined via, measure and simulate that exact version, and see what differences remain.
You should also build a layout-only testcase to exclude any effect of the diode. For that, you could use the existing layout with the diode removed. That should be sensitive to substrate permittivity. I am very surprised why your model with diode shows so little change when going from 3.91 to 4.4, because that is already a big change in electrical length. But I see the same here when running the EM models, so it might be real.
Yes, I forgot that one without diode. Looks good.but is what I made in the 11th post of this thread (Jan 24th)?
Yes, I forgot that one without diode. Looks good.but is what I made in the 11th post of this thread (Jan 24th)?
In those 3 cases, I don't have any capacitor so there is no DC current that can flow (only parasitic capacitor due to the line/diode package). There shift are thus due to current flow to the ground?Regarding the 3 cases with no gnd, one gnd and two grounds: that really changes how rectified DC current that can flow, so it is expected that results are different!? You need to decide which one is useful for your application case.
I missed that the diode configuration in your case has no obvious DC path, but now looked at the package parasitics. Please tweak your diode's parasitic CP from 80fF to 120fF, and you will see a large frequency shift for testcase 3. So that is really sensitive, and I wonder what tolerances apply there.In those 3 cases, I don't have any capacitor so there is no DC current that can flow (only parasitic capacitor due to the line/diode package). There shift are thus due to current flow to the ground?
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