Oh, OK, the fet is both the follower into the amp and the bootstrap. I didn't understand where Rfb connected.
Some of our fast o/e conveters use an un-bootstrapped photodiode right into the inverting input of a nasty gnarly cfb amp (opamps have feelings too!) but we use pd's with under 1 pF capacitance, and we work with milliwatts of light.
-- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
"nasty gnarly" is a term of adulation in some circles. ;) My current fave is the EL5166. Its gnarliness knows few bounds.
Nice when that happens. Then you can concentrate on making the step response beautiful.
BTW we've been using the P400 to calibrate out 24-channel time stretcher, which uses an RC ramp and one FIN1002 per channel, switching a SAV-551+ via a fast Schottky diode. (We talked about that a month or so ago--it's the one where I'm forward-biasing the gate.)
Looks like we can get 25-ps accuracy and single-digit picosecond jitter, which I would not have expected. We've got it taking a whole bunch of data over TxG so that we can look at the effects of (1) ramp slope on propagation delay and (2) signal voltage on the aperture time. (The pHEMT switches at V_GS ~ 0.3V, but that happens near the top of the switching edge at high signal voltages and near the bottom at low voltages.
Merry Thanksgiving, all.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Jitter in the 10s of fs RMS can be done nowadays with affordable, or frankly cheap, parts.
What's the effective sampler bandwidth? It's a change from using diodes.
Happy HolidaySicles! They look like little hanging Christmas trees to me.
Gotta start cooking soon.
-- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
The SJ capacitance is 2.4 pF, as measured on a Boonton, about
I have one a bit like that, but with a better base:
It does need a rubber band to apply a rotational preload to the arm.
Top-to-bottom dimension is 18 mm.
Sure, but we're calibrating with this big complicated DDG thing. ;) We're using a 20-ns RC time constant on the ramp
Around 1 GHz. The pHEMT charges up an 8-pf cap connected directly to the input of a 6-channel simultaneous-sampling ADC, so effectively the sampling circuit is a switch driving 8 pF, a very short trace, and the ADC input, which (apart from pad capacitance) looks basically like a
40-ohm resistor and a 12-pF cap. So there's a fast bit and a slow bit that have to be fixed in software.Sure is. I'm trying to use SAV-5xx+es in everything, to help persuade MCL to keep making them. (They're generally very good about doing that anyway.)
BTW I notice that NTE is selling the NTE2403, a near-replica of the BFT92 5-GHz PNP. They cost $3, and have a sucky datasheet, but what can you do? Digikey claims they're in active production.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Am 27.11.20 um 15:02 schrieb Phil Hobbs:
For me, DK claim not know it at all. I got a google hit that leads to DK, but even when I copy the complete part number from there and search it from my account, they suppose a typo. Weird.
Gerhard
I'd expect a single sampler could be made faster. The gate transfer curve is steep and squares up the sanpling signal. Might be fun to play with.
Is NTE for real? I remember their dusty bubble-packed parts way in the back at Radio Shack.
-- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
The product page is at
and the sucky datasheet is at
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
The sampler is much, much faster than that--like 50 ps or so---but is slowed down by the ADC front end. The 8-pF number is a compromise between speed on the one hand (which favours a larger C in this regime because the voltage-divider effect with the ADC's C_hold gets better), and on the other hand stability. To save parts, we're driving three samplers from each EL5167 CFA, and there's no buffer between the sampling cap and the ADC input. (That saves us 40 op amps right there.) Having one amp per three samplers per amp means that the poor thing has to drive 24 pF of fast capacitance, and cope with not only the charge injection but the sudden change of load capacitance when a pHEMT turns off.
We're sampling round-robin fashion, so that the amps get the maximum time to recover (i.e. 8 sample periods), but that's still only a few nanoseconds.
There's some signal-level dependence of the aperture time because of the finite slope of the FIN1002's output (about 4V/150ps), but since the pHEMT's f_max is about 12 GHz, and it turns off in about 300 mV, that ~25V/ns slope makes a very nice abrupt turn-off.
Well, they claim to have some thousands in stock. The datasheet parameters don't match any of the old NXP parts AFAICT, so maybe they're actually getting them fabbed someplace. At $3 apiece sold direct, they don't need to move 10**7 of them to make it worthwhile.
I have a reel of BFT92s, so we're set for internal use, but having an actual supplier out there means that we can potentially keep using them in licensed designs. (That three bucks will put a big dent in my average BOM, of course.)
My main applications for fast PNPs are (a) folded cascodes, and (b) the PNP wraparound trick for JFETs. You know the one--you put a resistor in the drain and wrap a PNP around it--emitter to supply, base to drain, collector to source.
That gets you the equivalent of a CPH3910 or BF862 with 20 times the transconductance but the same noise. There are other ways of doing it, but they take more parts and run slower because the signal path goes through more stages.
The CPH3910 has an f_max ~ 700 MHz, so having a 5-GHz PNP means you can run the local feedback loop at full speed without stability worries.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
That's what I found by g**gling, but C-C C-V ing it into my own order form gives "device not found". Just trying to change to digikey.de from the above address throws an error 404.
Try a VPN maybe? Mine (privateinternetaccess) has exit points in Kazakhstan and Greenland as well as NA and mainland Europe.
Cheers
Phil
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Thanks, though the second reminds me of the 'classic' PH front end where you return the current though the summing junction, and so have an offset.
George H.
Thanks, though the second reminds me of the 'classic' PH front end where you return the current though the summing junction, and so have an offset.
George H.
Well, the one in the book has a first-order temperature compensated fix for that. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
What's the bandwidth and latency like from there though? I usually prefer to surface my VPN in a country with good internet and short ping times.
CH
From here, I just measured 55/10 and 280 ms pings through Poland, and
39/26 with 250 ms pings through Bangladesh via Singapore. Not awful.From a Frankfurt exit node, I can get to that page on digikey.com but not digikey.de. Same from a NJ exit node.
So it's a digikey.de issue.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
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