Yes, that should help due to (a) less step in width from line to pad and (b) less parasitic C to ground at the pad.Maybe I should choose a thicker dielectric substrate so that my lambda/4 lines are the same size as this resistor pad?
Yes, that should help due to (a) less step in width from line to pad and (b) less parasitic C to ground at the pad.
That said, I would compare the exact same testcase, not single stage vs. multi stage.
Are there any other options besides using a thicker substrate?Yes, that should help due to (a) less step in width from line to pad and (b) less parasitic C to ground at the pad.
That said, I would compare the exact same testcase, not single stage vs. multi stage.
The main issue seems to be the extra shunt C from pads to ground. If you can't reduce pad size, you could cut out backside ground locally underneath the pads. This is something to try in Momentum, with the ground layer modelled as a "drawn" layer which must be meshed. This takes more simulation simulation time, but enables cutout in ground.How should I deal with this problem?
My frequency is 13 GHz,0603 seems quite large for 18 GHz. Doe you need 0603 power rating or can't you go for smaller package, e.g. 0201?
this is from PCB manufact.Another question: I am a bit surprised that thickness as small as 168 um is the thickest available substrate. Why is that?
No, I would keep the RF signal in the Rogers part, the FR4 material is too lossy.However, I could probably just use IN3 instead of IN2 as Ground Plane, thus increasing the dielectric thickness?
In the simplest ideal case to minimize the effect of the pad:No, I would keep the RF signal in the Rogers part, the FR4 material is too lossy.
But according to your screenshot you have the option of using 254um instead of 168um, so why not use that? Thicker is better to solve your problem.
Ok, got it. Thanks for you support!)Yes, I would test the differnet options using Momentum.
I think it is what I wrote above: the issue is not so much a distributed line issue (discontinuity from step in width), we can look at the pad as a plate capacitor which gives too much shunt C. And one option would be to cut out the griund underneath the pad, as I mentioned above. So you have multiple options now, and can choose which is easiest to implement.
You can build such transmission line structures without ground, but it is perfectly fine to add top layer ground if needed to fulfill manufacturing rules, e.g. metal density rules. Of course, extra capacitance from the side grounds must be considered to reach the target line impedance.I found that is better to don't have any ground on the top layer
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?