Products > Test Equipment
> 1 GHz DIY differential probes
nctnico:
--- Quote from: mawyatt on April 13, 2021, 01:57:14 pm ---Nico,
Are these differential probes still available?
--- End quote ---
Yes but I'm currently out of stock; a new batch is being produced.
beardedhustler:
Sorry for hijacking the thread, but since it's a bit related and I eventually will look into the topic (differential design) of this thread as well I hope it's ok.
We have a Signatone probing station with (passive) "micropositioners" (probes) that we use to probe on bonding pads on various chips and read data with some reader attached. Coaxial cables from probes to reader are ~1m, so signal integrity isn't always great when the frequency increases, thus the need to add an active stage/probe. For now we've mostly dealt with various SPI flash chips, eMMC chips in 1-bit bus width mode, up to ~36MHz clk speed (I got enough probes that I can go for the 4-bit bus width mode which supports clk speeds up to 200MHz if I want, but it's not always beneficial to spend time and energy trying to place six probes within the small area where the bonding pads are located and at the same time not break any bonding wire between the pads and the controller, etc, so usually I stick to using a 1-bit bus width..).
Due to the possibility of using the HS200 mode for eMMCs I think a 1GHz BW is an ok goal to aim for here, and since eMMCs use single ended signals I don't have the need for a differential probe (for now - that might change later on if we decide to try probing UFS chips, but that's another story - we'll cross that bridge when we get to it...). Another important thing to mention is that the goal here is to make the pcb that we can custom fit on the micropositioners in some way to utilize what we already have and thus buying a general purpose probe isn't an option for this now.
I've started on a few single-stage designs trying out various op-amps from TI (LMH3401, LHM6702, OPA855/OPA858), and getting a BW > 1GHz seems quite straight forward with the op-amps mentioned, but I'm a bit unsure on the pitfalls when it comes to designing a active "probe". I guess trying to get as high input impedance / low input capacitance should be a goal as well. Anything else to consider other than trying to impedance match output from op-amp to 50Ohm (coax cable) to maximize power transfer?
It's been a few years since I did design and back then it was mainly high power RF PAs with different things to consider during the design process. I've only used TI's spice simulator for now, and although it's a nice tool I guess it has its limitations. I tried importing some of the spice models they offer on their web page into Keysight ADS, and although I get almost identical results for similar simulations I'm not sure if e.g. the models are valid for other simulations, e.g. S-parameter simulations, which for some devices result in S11>0dB for a wide frequency range (and in my experience from the RF PA design days that's a big no-no).
Suggestions to components, literature, etc, is greatly appreciated!
tggzzz:
--- Quote from: beardedhustler on June 04, 2021, 11:52:09 am ---Sorry for hijacking the thread, but since it's a bit related and I eventually will look into the topic (differential design) of this thread as well I hope it's ok.
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You would probably get better responses if you started a new thread with your questions. Plus, if the responses are useful, other people are more likely to find them and benefit from them.
beardedhustler:
--- Quote from: tggzzz on June 04, 2021, 03:13:43 pm ---
--- Quote from: beardedhustler on June 04, 2021, 11:52:09 am ---Sorry for hijacking the thread, but since it's a bit related and I eventually will look into the topic (differential design) of this thread as well I hope it's ok.
--- End quote ---
You would probably get better responses if you started a new thread with your questions. Plus, if the responses are useful, other people are more likely to find them and benefit from them.
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You're probably right; I'll make a new thread about it.
Edit: new thread up at https://www.eevblog.com/forum/projects/input-to-single-ended-probe-designs/
Any suggestions are greatly appreciated!
LooseJunkHater:
--- Quote from: nctnico on April 13, 2021, 05:17:10 pm ---
--- Quote from: mawyatt on April 13, 2021, 01:57:14 pm ---Nico,
Are these differential probes still available?
--- End quote ---
Yes but I'm currently out of stock; a new batch is being produced.
--- End quote ---
Do you have any intention of making some high voltage (500v+) differential probes?
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