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differential signal detector

I probably won't use this one, but it is pleasingly weird.

Watch for line wrap on the BAT15 model.

Version 4 SHEET 1 1724 680 WIRE -416 -352 -480 -352 WIRE -368 -352 -416 -352 WIRE -208 -352 -288 -352 WIRE -128 -352 -208 -352 WIRE 32 -352 -128 -352 WIRE 192 -352 112 -352 WIRE -208 -304 -208 -352 WIRE 192 -304 192 -352 WIRE -480 -224 -480 -352 WIRE -576 -208 -608 -208 WIRE -528 -208 -576 -208 WIRE -208 -192 -208 -240 WIRE -160 -192 -208 -192 WIRE -32 -192 -96 -192 WIRE 80 -192 -32 -192 WIRE 240 -192 160 -192 WIRE 320 -192 240 -192 WIRE 384 -192 320 -192 WIRE 240 -176 240 -192 WIRE 384 -176 384 -192 WIRE -528 -160 -560 -160 WIRE -32 -160 -32 -192 WIRE -560 -96 -560 -160 WIRE -480 -96 -480 -144 WIRE -480 -96 -560 -96 WIRE -208 -80 -208 -192 WIRE -160 -80 -208 -80 WIRE -32 -80 -32 -96 WIRE -32 -80 -96 -80 WIRE 80 -80 -32 -80 WIRE 240 -80 240 -112 WIRE 240 -80 160 -80 WIRE 384 -80 384 -96 WIRE 384 -80 240 -80 WIRE -480 -64 -480 -96 WIRE -32 -16 -32 -80 WIRE 384 0 384 -80 WIRE -928 96 -992 96 WIRE -896 96 -928 96 WIRE -656 96 -752 96 WIRE -608 96 -656 96 WIRE -448 96 -480 96 WIRE -368 96 -448 96 WIRE -128 96 -288 96 WIRE -32 96 -32 48 WIRE -32 96 -128 96 WIRE 32 96 -32 96 WIRE 192 96 112 96 WIRE -992 112 -992 96 WIRE -752 112 -752 96 WIRE -480 128 -480 96 WIRE 192 144 192 96 WIRE -992 240 -992 192 WIRE -752 240 -752 192 WIRE -480 240 -480 208 FLAG -752 240 0 FLAG -480 240 0 FLAG -656 96 sig FLAG -992 240 0 FLAG -928 96 gate FLAG -448 96 GEN+ FLAG -480 -64 0 FLAG -576 -208 GEN+ FLAG 192 -304 0 FLAG 192 144 0 FLAG 384 0 0 FLAG -416 -352 GEN- FLAG -128 96 SFP+ FLAG -128 -352 SFP- FLAG 320 -192 DET SYMBOL voltage -752 96 R0 WINDOW 0 31 93 Left 2 WINDOW 3 12 126 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName Vclk SYMATTR Value SINE(0 1 {F} 10u) SYMBOL bv -480 112 R0 WINDOW 0 17 108 Left 2 WINDOW 3 38 157 Left 2 SYMATTR InstName B1 SYMATTR Value V=V(gate) * 0.25*(tanh(1e6*(V(sig)))) SYMBOL voltage -992 96 R0 WINDOW 0 28 124 Left 2 WINDOW 3 -33 180 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName Vgate SYMATTR Value PULSE(0 1 10u 0 0 100u) SYMBOL res -272 80 R90 WINDOW 0 67 56 VBottom 2 WINDOW 3 82 55 VTop 2 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL res 128 80 R90 WINDOW 0 68 59 VBottom 2 WINDOW 3 72 58 VTop 2 SYMATTR InstName R2 SYMATTR Value 50 SYMBOL e -480 -240 R0 SYMATTR InstName E1 SYMATTR Value -1 SYMBOL res -272 -368 R90 WINDOW 0 70 61 VBottom 2 WINDOW 3 79 61 VTop 2 SYMATTR InstName R3 SYMATTR Value 50 SYMBOL res 128 -368 R90 WINDOW 0 71 83 VBottom 2 WINDOW 3 79 84 VTop 2 SYMATTR InstName R4 SYMATTR Value 50 SYMBOL cap -224 -304 R0 WINDOW 0 -46 24 Left 2 WINDOW 3 -43 51 Left 2 SYMATTR InstName C3 SYMATTR Value 5p SYMBOL cap -48 -16 R0 WINDOW 0 -46 24 Left 2 WINDOW 3 -43 51 Left 2 SYMATTR InstName C4 SYMATTR Value 5p SYMBOL diode -160 -176 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value BAT15 SYMBOL res 176 -96 R90 WINDOW 0 72 59 VBottom 2 WINDOW 3 76 59 VTop 2 SYMATTR InstName R5 SYMATTR Value 10K SYMBOL res 368 -192 R0 WINDOW 0 50 39 Left 2 WINDOW 3 48 66 Left 2 SYMATTR InstName R7 SYMATTR Value 1e6 SYMBOL cap -48 -160 R0 WINDOW 0 60 8 Left 2 WINDOW 3 54 40 Left 2 SYMATTR InstName C5 SYMATTR Value 100p SYMBOL diode -96 -64 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value BAT15 SYMBOL cap 224 -176 R0 WINDOW 0 55 29 Left 2 WINDOW 3 46 60 Left 2 SYMATTR InstName C1 SYMATTR Value 100p SYMBOL res 176 -208 R90 WINDOW 0 -13 61 VBottom 2 WINDOW 3 47 59 VTop 2 SYMATTR InstName R6 SYMATTR Value 10K TEXT -1016 -16 Left 2 !.MODEL BAT15 D(IS=130n RS=4.5 N=1.08 XTI=1.8 EG=.68\n+ CJO=260f M=.047 VJ=.11 FC=.5 BV=4 IBV=10U TT=25p) TEXT -1016 -144 Left 2 !.tran 200u TEXT -976 -312 Left 2 ;K420 Differential Signal Detector TEXT -888 -216 Left 2 ;JL Oct 17 2020 TEXT -1016 -112 Left 2 !.param F = 5e6 TEXT -1016 -80 Left 2 !.step param F list 5e6 500e6 2e9 TEXT -952 -264 Left 2 ;ECL or CML into SFP Module

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin
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Fun--a floating one-stage Cockroft-Walton. ;)

Who says you need a transformer?

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
Reply to
Phil Hobbs

I was considering using a Mini-Circuits wideband transformer to pick off the diff signal, but this circuit occurred to me and is suitably strange.

But I think I'll use a 1K resistive pickoff from just the high side, into a 5 GHz MMIC, then a fairly normal diode doubler detector. We might allow the user to apply a wide range of inputs, including single-ended.

An SAV551 source follower would be fun as the pickoff too, but might get risky. Have you tried that?

I've been playing with 10G SFP modules. They seem to accept single-ended or diff inputs, from about 50 mV p-p to full 5 volt CMOS, and just work. They are amazing for $20.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

SAV551s (like other 3-GHz class pHEMTS) are amazingly stable. I've run one (without beads) bootstrapping a 100-pF Hamamatsu MPPC at the wrong end of a 50-mm flex. The bootstrap bandwidth wasn't nearly as wide as if it had been on the right end, but it worked very well.

I've used SKY65050s as followers--they work about as well as JFETS, only

10 times faster. (The Avago parts were the pits for this because their drain impedance was so low--I measured an ATF38143 as having a voltage gain of less than 0.7 as a follower.)

Yup. Funny how that happens when there's a huge development effort with a multi-year roadmap. ;)

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
Reply to
Phil Hobbs

Did you play with my SFP board? I have more.

The 10G Cisco that I like is hard to get, but we've found some cheap equivalents that look good. Cisco's list price is $1200 or something silly now.

We have a new 1 GHz analog o/e converter, something I did for fun during lockdown. Jonathan will test it with an SFP as the light source. Directly pulsing vcsels gets weird.

My o/e was crazy slow, and he discovered that the pin photodiode has

20 pF from the cathode lead to the TO18 can. The spec is 1p max. 
--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

Not yet. Last week I built a test setup for my new laser noise canceller idea.

Since there are no really good fast matched BJT chips(*), trying to extend the original MAT04 versions to much higher bandwidth is a problem.

There are two basic approaches: use the DC precision of the slowish MAT04/MAT14 and put a bandaid on to reach higher frequency, or take some amazingly good disctete transistors, e.g. the BFP640H (45 GHz, VAF > 1 kV beta ~700) and make them act as though they were monolithic. (Mainly that means getting their die temperatures to track accurately from DC out to highish speeds, like 50 kHz or so.)

The first approach might put fast cascode transistors on the MAT14 diff pair to get rid of their output capacitance, and use Darlington base drive to recycle the base current to the collector circuit, so that (in the required bandwidth) nothing was lost to base current.

Turns out, of course, that the collector-base time constant puts a fairly sharp limit on how far you can go with the bandaid approach--the extrinsic base resistance and BC capacitance prevent the recycling at high frequencies.

So this gizmo uses a BFP640 diff pair, exploiting the very high VAF to allow equalization of the power dissipation on the two sides by dorking the V_CE of one side to match the ratio of I_C. We'll see how it works this week.

Cheers

Phil Hobbs

(*) The Infineon HFA series has very disappointing R_ee' and R_bb'.

--
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
Reply to
Phil Hobbs

Am 18.10.20 um 03:47 schrieb Phil Hobbs:

Do you mean these? Renesas?

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I've used the HFA3096 in a pretty good 1:5000 time stretcher. It was available in a hermetic flat pack for space apps. Might have been still Intersil. The 3096 family seems to be bond out options of the same SOI chip. The last fast-ish PNPs alive?

cheers, Gerhard

Reply to
Gerhard Hoffmann

Right. I meant Intersil, not Infineon.

Yeah. Unfortunately they have ridiculously high R_bb' and R_ee', which makes them unsuitable for noise cancellers. By a combination of bootstrapping and cascoding, with various tricks for bias current cancellation, I managed to get the whole thing going with no PNPs at all. (Noise cancellers need to use both ends of the photodiodes, which makes it trickier.) Those SiGe:C things really are amazing, all for 20 cents in reels.

In the spherical cow universe, that gets me >60 dB cancellation out to

30 MHz or thereabouts, over a pretty wide range of photocurrents. We'll find out what the real ruminants can do in the next few days. ;)

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
Reply to
Phil Hobbs

My new o/e converter uses both ends of the photodiode, one for a fast AC path and the other end for a slow DC path. I merge them back together later. That's how I got into trouble with that crazy pd, the one with 20 pF from the cathode to the can. Only the 850 pd does that... it works great with the longer wavelength parts.

I wonder if using a balun could help in situations like this.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

Or plastic-packaged PDs. We use a 300 um Hamamatsu one in a TMB package that costs $5.

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
Reply to
Phil Hobbs

We buy this one in a metal sugar-cube package, ST or FC fiber connector, all aligned and stuff. 20 pF from cathode to TO18 can, then xx pF from the can to the metal housing. Yuk.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

One gathers that they expect you to use a positive bias supply. That's a pain.

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
Reply to
Phil Hobbs

Given that my circuit takes signals out of both ends, I just used the wrong ends.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard
Reply to
jlarkin

Using a negative bias supply makes TIA design easier, because you can easily make zero volts = zero photocurrent, simply by grounding the + input, which means coming out the cathode. For single-ended photodiode circuits, you normally don't care how much capacitance they want to hang on the anode, because it's connected to the bias supply anyhow.

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
Reply to
Phil Hobbs

I'm hanging the PD between a -5 supply and the input of a MMIC which biases itself up about +2 volts, 7 volts net. Seemed all nice until the capacitance glitch. We can probably find another supplier for the

850 nm connectorized photodiode. Lots of people make them.

More voltage makes the photodiodes faster. Not all capacitive... seems like more voltage sweeps charges out faster. Does that keep happening, or does it level off like capacitance?

Reply to
John Larkin

Depends on the device. If the high-doped regions are thin enough, you can deplete them before the device breaks down. That sometimes leads to quite startling speedups.

The physics of that is similar to forward recovery in PN diodes--due to Debye shielding, the carriers nearest the junction don't get the message until it's had a chance to get there by diffusion.

Schottky photodiodes are very fast too, but the interdigitated metal fingers block a lot of the light, and you have to bias them above reachthrough because there are two barriers back-to-back.

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
Reply to
Phil Hobbs

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