azonenberg changed the topic of #scopehal to: libscopehal, libscopeprotocols, and glscopeclient development and testing | https://github.com/azonenberg/scopehal-apps | Logs: https://libera.irclog.whitequark.org/scopehal
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<xzcvczx> azonenberg: is sillycon coming over?
<Bird|ghosted> xzcvczx, it already exists here, see ##sillycon
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<azonenberg> oooooh
<azonenberg> So i'm thinking the ADL5569 might be a good active diff probe
<azonenberg> The s-parameters look quite nice
<azonenberg> 6.5 GHz -3 dB BW so i think a full system BW including probe tip etc of 4+ GHz should be achievable
<azonenberg> Supply voltage of 5V, differential output common mode typically Vs/2. So I should be able to run it on bipolar +/- 2.5V with output at ground
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<GenTooMan> apart from it being a dual amplifier it can convert single ended to differential also. It has more than a few gain options also.
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<GenTooMan> how much noise can the application tolerate?
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<azonenberg> GenTooMan: well thats the thing, i want differential to single ended
<azonenberg> but getting that with several GHz bandwidth is almost impossible
<azonenberg> everything is diff output and you have to just ignore one side if you want single ended output
<azonenberg> But that leads to bad uniformity between the halves
<azonenberg> As far as noise goes, less is better
<Kliment> azonenberg: why do you want single ended?
<azonenberg> Kliment: It's a probe frontend amplifier, it has to connect to a single ended BNC or whatever the host instrument input is
<azonenberg> If i was designing my own custom instrument it's plausible i could make a version that had native differential inputs
<GenTooMan> azonenberg, https://xellers.wordpress.com/electronics/1ghz-active-differential-probe/ <-- might be of some use
<azonenberg> GenTooMan: Different use case
<azonenberg> It's only 300 MHz BW (of the target 1 GHz), and very high Z
<azonenberg> I'm going for much higher loading using a resistive input stage, basically a differential transmission line probe
<azonenberg> 450 ohms on each of inP and inN across a 100 ohm differential input
<azonenberg> So 1K ohm zdiff
<azonenberg> But as a tradeoff this design is simple and should allow very high bandwidth and good flatness with only a single amplifier stage
<azonenberg> I'm targeting a minimum of 4-5 GHz with this design
<azonenberg> The ampifier in question has +/- 0.5 dB flatness out to almost 4 GHz according to the published s-parameters
<azonenberg> including PCB losses etc, i think 4 GHz -3 dB bandwidth should be very doable
<azonenberg> and probably more than that
<azonenberg> The naked amplifier quotes 6.5 GHz bandwidth
<GenTooMan> so you want a much lower input impedance to your amp?
<azonenberg> It's not that I want lower impedance so much as it's easier
<azonenberg> I might try to make a future version that has higher impedance
<azonenberg> but high bandwidth is the top requirement
<GenTooMan> lower impedance does make for higher bandwidth also it makes things more compatible with cabling that is available.
<azonenberg> Well the probe tip to amplifier connection is going to be custom flex PCB
<azonenberg> so i can do whatever on tat
<azonenberg> that*
<azonenberg> This is my current PoC design for the AKL-AD3 differential probe
<azonenberg> back area is where the amplifier and power supply will live
<azonenberg> same screw mechanism as my prototype for adjusting tips
<azonenberg> the jaws are angled about 15 degrees off of vertical so that the needles face inward toward each other
<azonenberg> full details of the jaw layout and exact spacing etc are subject to change, this is still in the "thinking about how to do it" phase
<azonenberg> Exact details of how the flex pcb bends and curves from this angle to flat is TBD
<GenTooMan> for differential to single ended conversion you may want to use a de/un compensated amplifier to have adequate bandwidth.
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<azonenberg> Ok, I think I have the AKL-AD3 amplifier board designed at a schematic level
<azonenberg> Going to be using a 10-pin LSHM to connect the flex pcb to the rigid
<azonenberg> it's simple, low cost, and has reasonably good high frequency performance
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