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Picotest Injector Teardowns
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Wolfgang:
Yeah, the output network is a compromise between 3dB frequency and stability. It needs to be matched to the OpAmp, thats correct.
And dont forget to simulate with all kinds of DUT PSU output impedances !
corecode:
This is what I have come up with so far; crossed out components are not part of the simulation.

Looks like R13/C1 is to compensate possible L1 wiring inductance going to the DUT.

I will simulate various DUT impedance configurations next.

I wonder whether I should add an additional op amp to optionally boost the Pr1 output gain.  In general, I'm surprised by the signal level choices of the original design.


corecode:

--- Quote from: corecode on October 14, 2020, 08:39:40 am ---
I will simulate various DUT impedance configurations next.


--- End quote ---

Doesn't look too bad - of course the wiring to the DUT has a huge impact at the high frequencies.

Wolfgang:
When you look at my webpage about it you see that the PicoTest risetime claims are only realistic if there is less than 2-3cm of wire length between output and DUT. This will not be possible in a lot of cases. IMHO, it is smarter to live with reasonable bandwidths (0-5MHz) and better stability. Most injectors are used to determine the response of switching regulators. Their regulator loop bandwidth (not the switching frequency) is normally far below 100kHz, so a few MHz of injector bandwidth is good enough.
corecode:
I agree.  This was mostly an exercise to understand the limits of this approach.  It would be nice to observe most of the PDN performance at the supply vias of a chip.  I don't have a good FRA/VNA anyways, so this probably will be good enough to be used with my RTB2004's K36 option.

Latest design attached (qucs-s).  Maybe I'll get around to building it.


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