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Affordable <200MHz PDN analysis / impedance measurement hardware?
inevitableavoidance:
I’ve been stepping up my low noise game, took a deep dive into decoupling (simulations), and am feeling a lot more confident about the performance of the boards I design. The only problem - I don’t have anything to verify this / measure PDN impedances above 5MHz or below 200mOhm.
The pros seem to use €30k VNAs and with €5k ground loop isolators to run S21 shunt through measurements. Is there a more affordable alternative out there? I’d be happy to get up to 200MHz / down to 5mOhm.
Would the cheaper VNAs suffice for this? Or do they not have the performance for it? Do I really need the ground loop isolators? Could I spin my own with a GHz differential amplifier?
I feel this is slightly out general hobby territory (but also feel people have to stop putting 100nFs everywhere like it’s the 80s, route those with way to long / thin traces compared to the capacitors ESL, and call it a day)
I’d love some advice - thanks!
ch_scr:
I would say this is the realm of devices like the Bode 500.
While not 30k€, it' still "comfortably" into the 5 digits. It's more specialized to the task than a general purpose VNA, though, on the hard and software side.
A LiteVNA64 is a lot cheaper, can be run from battery and joeqsmiths "" software might enable the kind of low impedance measurement you'd need ("shunt-through measurement") - I'm not sure of the latter, though. If you're comfortable with software you should be able to implement the needed post processing yourself (on a quick glance "shunt-through" is based on S21 so a LiteVNA should get you there)
nctnico:
There are various low cost network analysers. Problem is though that many don't work well below -say- 20MHz while PDN analysis is most interesting int the range from several kHz to 200MHz.
inevitableavoidance:
That software looks like it makes those cheap VNAs into quite powerful tools!
I just bought a NanoVNA-H4, with a dynamic range of 70dB from 50kHz-300MHz, specified with a minimum frequency of 10khz. Cheap enough to play around with as a start. :)
Now I use my scope with its generator, a voltage + current channel, and a math channel, but it doesn't have the resolution / current capacity to measure low impedances, and doesn't have the bandwidth for the high frequencies. I might be able to wing a combination of the two to still measure DC to 50kHz it the impedance is high enough to measure on the scope.
Thanks for the advice! I'll post an update on how it goes
Someone:
Do you already have a modern oscilloscope? A signal generator and some amplification will get you into milliohms.
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