azonenberg changed the topic of #scopehal to: libscopehal, libscopeprotocols, and glscopeclient development and testing | | Logs:
<azonenberg> AKL-PD1 panel received from fab, waiting for it to ship
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<d1b2> <Hardkrash> @azonenberg The USB-C cables you linked at 2m length had DCR of 1.2Ω to 1.5Ω for all 8 SS conductors. Tested at 100mA load, includes the test boards trace resistance which could be resistance difference.
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<azonenberg> hardkrash: individually 1.2 to 1.5?
<azonenberg> using the worst case 1.5 ohms we'll call it 375 milliohms for both positive and negative (four lines in parallel), or 750 mR total series resistance in the power loop
<d1b2> <Hardkrash> yes, each conductor. using 2 pairs 4 conductors for a circuit would yield about 375mΩ
<d1b2> <Hardkrash> one direction, not loop
<azonenberg> let's say 250 mA current drawn by a probe (so far this sounds high, the AKL-AD1 prototype doesn't get over 100 mA)
<azonenberg> Which comes out to 188 mV drop
<d1b2> <Hardkrash> and this is a cable twice as long as the original specified.
<azonenberg> And 47 mW of total joule heating in the cable
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<azonenberg> So i think we have plenty of margin here
<d1b2> <Hardkrash> so to me, a 200mV drop and the 50mW is very acceptable.
<azonenberg> Yes i would be inclined to agree
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<d1b2> <Hardkrash> I also just did a quick calculation, if 32AWG wire for STP conductor, it's ~165mΩ per foot, so about an Ohm for 6 feet. if 34AWG it would be 260mΩ per foot, so about 1.56Ω at 6ft
<d1b2> <Hardkrash> so theory and measurements are of the same order.
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<azonenberg> Interesting
<azonenberg> I probably should have looked at the ADL5565 s-parameters more before designing the first rev of the AKL-AD1
<azonenberg> Lesson learned
<azonenberg> They only go to 3 GHz despite the part being advertised as a 6 GHz amplifier
<azonenberg> there's also visible crossover in the P/N response just as you can see in the actual VNA data
<azonenberg> So the basic shape is about the same although the sub 1 GHz response of the measured data is less nice than the sim
<azonenberg> (this is a Sonnet sim of the actual PCB layout, slightly simplified, with the ADL5565 S-parameter model inserted into it)
<azonenberg> So you can see there's a substantial amount of variability between the P vs N to output response
<azonenberg> as well as the crossover in the ~500 MHz range
<azonenberg> I guess i need to find another amplifier lol
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<azonenberg> What do you folks think of the LMH3401 for the AKL-AD1 v0.2?
<azonenberg> vs the ADL5565
<azonenberg> 7 GHz -3 dB BW, but it says "usable" bandwidth of 2 GHz which i'm not clear on the meaning of
<azonenberg> Fixed gain of 16 dB differential
<azonenberg> BiCMOS process, vs the ADL5565 is SiGe
<azonenberg> also compatible with the +/- 2.5V target power supply range i'm going for
<azonenberg> 7 GHz small signal bandwidth, 4 GHz large signal bandwidth (2V p-p output, which is a lot)
<azonenberg> Or LMH5401
<azonenberg> ooooh ADL5580
<azonenberg> lain: ^
<azonenberg> i think i found a better amp
<azonenberg> explicitly states dc coupling is ok
<azonenberg> There is a little bit of P-to-N mismatch which i'm not thrilled about. but it's not huge
<azonenberg> although it does pull a lot of power
<azonenberg> 276 mA @ 5V, 224 mA @ -1.8V
<lain> :o
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<azonenberg> New MEAD MMCX input board came in. This one actually fits the connectors without needing any machining, which is nice
<azonenberg> gonna populate one tonight probably then if all looks good order enough to outfit the rest of my pods
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<_whitenotifier> [starshipraider] davidlenfesty opened pull request #5: Active probe testing PCB -
<d1b2> <david.lenfesty> Probably gonna order the PCBs sometime this weekend
<d1b2> <david.lenfesty> (and do a final final check)
<d1b2> <david.lenfesty> I really shouldn't be working on this too much over the next few weeks (the semester is starting and I have some other commitments to work on), but I do have a decent chunk of the base FUSB302 and PD library done.
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