Products > Test Equipment
Affordable <200MHz PDN analysis / impedance measurement hardware?
mawyatt:
--- Quote from: inevitableavoidance on November 12, 2024, 02:49:37 pm ---
--- Quote from: mawyatt on November 12, 2024, 02:41:01 pm ---Very impressive results with the low Z range covered :-+
Curious why you selected Tantalums rather than Polymer or Aluminum Electrolytic Capacitors for the coupling/decoupling, size maybe?
Best
--- End quote ---
Hey Mawyatt,
Thanks! Pretty stoked with it myself as well.
Indeed size, and with that inductance. The shunt is 500mΩ. If I would use a capacitor with an equivalent series inductance of 10nH I'd see an additional impedance of 1.57Ω in series with the rest of the circuit at 25MHz, limiting the current I'd be able to get through with a factor of 4, and with that reducing the voltage I'd read back on the second sense channel with a similar factor of 4.
Keeping the capacitor and its inductance as small as possible allows most current at high frequencies, keeping my sense voltages as high as possible there.
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WRT to the Coupling Capacitance and ESL/ESR. Have you considered using a 0.1uF C0G/NP0 ceramic in parallel with a larger polarized cap? These have a low ESL and ESR, we've done such with our DC Bias Adapter for use with Bench LCR Meters and seems to work well.
This is tempting to pull out our AD2 and put it to use ::)
Best
joeqsmith:
I am in the process of updating Solver's user manual and repeated the PDN measurements with my H4 using the latest firmware available. I had no lockups or glitches in the data.
I had damaged my H4 (suspect ESD) and when repairing it, I had added a few additional caps which greatly improved the noise floor at higher frequencies. Still, it is not good enough to resolve 100uOhms.
Link to troubleshooting, mods and performance gains of my H4.
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5695349/#msg5695349
I also have the newly release LiteVNA hardware. I was very much surprised that it performs slightly better then my other low cost VNAs at these lower impedance's, however it is still not able to resolve 100uOhms.
That said, typically when I run into problems with emissions, they are in the several MHz on up past GHz. Assuming you are wanting to measure the PDNs stability for emissions, how do you test it at these higher frequencies? Or is it not a concern?
inevitableavoidance:
--- Quote from: mawyatt on November 12, 2024, 03:35:46 pm ---Have you considered using a 0.1uF C0G/NP0 ceramic in parallel with a larger polarized cap? These have a low ESL and ESR, we've done such with our DC Bias Adapter for use with Bench LCR Meters and seems to work well.
Best
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I haven't optimized that part too much - the little coaxial cables I solder to the board have quite some inductance as well, so I think the effect on the total wouldn't be too significant.
I took a look at your DC Bias adapter posts - nice stuff too. :)
inevitableavoidance:
--- Quote from: joeqsmith on November 12, 2024, 03:44:21 pm ---That said, typically when I run into problems with emissions, they are in the several MHz on up past GHz. Assuming you are wanting to measure the PDNs stability for emissions, how do you test it at these higher frequencies? Or is it not a concern?
--- End quote ---
Nice writeup on the H4 mods!
With the measurements I did so far (of single capacitors and small PCB PDNs) I've been able to measure high enough in frequency to get down to the package- / measurement setup inductances, which is more than enough for me (I mainly have audio clients at the moment), but indeed not getting to the point of plane resonances and the like. I believe because of the inductance involved the impedances here are typically a lot higher (>100mΩ), so getting out the VNA for that would probably be fine? What do you think?
joeqsmith:
--- Quote from: inevitableavoidance on November 12, 2024, 06:42:32 pm ---
--- Quote from: joeqsmith on November 12, 2024, 03:44:21 pm ---That said, typically when I run into problems with emissions, they are in the several MHz on up past GHz. Assuming you are wanting to measure the PDNs stability for emissions, how do you test it at these higher frequencies? Or is it not a concern?
--- End quote ---
Nice writeup on the H4 mods!
With the measurements I did so far (of single capacitors and small PCB PDNs) I've been able to measure high enough in frequency to get down to the package- / measurement setup inductances, which is more than enough for me (I mainly have audio clients at the moment), but indeed not getting to the point of plane resonances and the like. I believe because of the inductance involved the impedances here are typically a lot higher (>100mΩ), so getting out the VNA for that would probably be fine? What do you think?
--- End quote ---
Without knowing if you solved the ground loop problem, its hard to say. Also, our goals for making these measurements are not the same. You may be better off with what you have for now.
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