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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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