Shopping for low C PFET

Oh my 'scope trace has these ~150 ns wiggles, not sure the cause. Maybe the (~4") ground lead on the x10 probes?

GH

RF MOSFETs are pretty much goneski, let alone PCHs. These are the smallest PCH for power switching I know of.

If you can't make it work, say with a little emitter follower to help gate capacitance, it ain't gonna happen with anything else. :-\

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Thanks Tim. I did search under the RF mosfet tag at DK. There was one. PN5033

listed as a p-chan J-fet! I thought they didn't make those. (?)

George H.

P-JFETs, there's still a very few of those around, yeah. No idea what people use them for...

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

Tim Williams wrote

I used a lot of BF245 A / B / C. It now is still available in a smaller package as BF545 A only

700 MHz 6.5 mA/V Only 30V. can be reverse used (drain source). The BF245 has a noise of 1.5 dB at 15V 100 MHz, I see no noise figure for BF545.

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 
https://hobbs-eo.com

If I read the scope right looks like the gate drive slews to -4V in

20ns, which if your 60pF Cin is used then grossly simplified I make the gate drive current a mere 12mA.

Also looks like the drain doesnt do much till gate hits 3.5V so if you can increase the gate drive voltage, sharpen it and make it stiffer then you'd get closer to your target?

piglet

I think less (Dang I should have put my spice sim in drop box.) I'm a brute force type. (subtle takes experience) The p-fet's source is.. (there are some 1nF and 10nF not shown)

HV---+---1mA limit---+--------+ | | | 0.1mA lim. | R4 500 | | S | +-----------------+| +---+ | | | | | R1 400k 1M? R2 | | | | | +| | +--+--|

Oh boy those look like fun... 450 bump spacing.. I assume that's um. Is it possible to dead bug hand solder such a tid bit?

George H.

How much Valium do you have on hand? :^)

Could do what JL did, spin a bunch of interposer boards. Fan it out to an SO-8 footprint, for example. Given suitable consideration for parasitics of course -- GaN screams, compared to Si.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

Of course George could get the eval board for a mere $950. ;)

I'd like to try them out too, so if you'll do the layout, George, I'll buy the boards.

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 
https://hobbs-eo.com

Not sure I understand the circuit, do you have the P-fet normally ON and want to switch it off rapidly or do you have the fet normally OFF and want to switch it on rapidly. What is the desired action?

Does that 1mA limit fight your gate drive or are there bypass caps capable of supporting brief current draws?

Looks like source and gate resistor R4 return to different points which could exceed Vgs?

piglet

Normally off.. it is getting a bit byzantine. I'm sorta blowing ~30mA on the gate to switch 3 mA across R1.

Yeah bypass caps not shown, 1nF on backside of 0.1mA limit and

10nF behind 1mA .

I hadn't thought about the separate limits turning on at different times and blowing the pfet, so I owe you another beer, or beverage of your choice.

George H.

A physics colleague would do four wire gold leads to samples with little dabs of silver paint. He claimed to need exactly 1/2 a beer, to relax just a bit.

George H.

What do want the pfet turning on to do to your SPAD? Looks like it doesn't do anything to reduce the spad bias if I read the ascii art correctly - are those diodes right?

piglet

Right, when the spad fires, all it's over voltage charge goes away. (~10-20 V over-voltage) It then takes a long time to recharge through the 400k R. (this large value 'self-quenches' the avalanche) The pfet is to speed up the recharge time... you posted some nice circuits that both quenched and recharged, I may have to do that.. But this keeps the quench and reset separate. I don't understand how the self-quench works, so I figured it might be nice to keep it separate.

Yeah diodes are right, they are meant to shield the spad C from the switch C. I figure I'll put another sting on the other side, same voltage drop.

George H.

On 21/08/2018 01:28, George Herold wrote:

Thanks, now I see. I never considered that way of speeding up recharge.

BTW I had a go at simulating an off-the-peg step up transformer quench, get 30V dip in 19ns but I think that can be improved. See below:

Version 4 SHEET 1 980 680 WIRE -592 -768 -848 -768 WIRE -592 -736 -592 -768 WIRE -592 -624 -592 -656 WIRE -464 -624 -592 -624 WIRE -368 -624 -464 -624 WIRE -368 -576 -368 -624 WIRE -352 -576 -368 -576 WIRE -272 -576 -288 -576 WIRE -256 -576 -272 -576 WIRE -176 -576 -192 -576 WIRE -160 -576 -176 -576 WIRE -80 -576 -96 -576 WIRE -64 -576 -80 -576 WIRE 16 -576 0 -576 WIRE 80 -576 16 -576 WIRE 208 -576 144 -576 WIRE 288 -576 208 -576 WIRE -592 -560 -592 -624 WIRE -464 -560 -464 -624 WIRE 288 -560 288 -576 WIRE -272 -528 -272 -576 WIRE -272 -528 -320 -528 WIRE -176 -528 -176 -576 WIRE -176 -528 -208 -528 WIRE -80 -528 -80 -576 WIRE -80 -528 -128 -528 WIRE 16 -528 16 -576 WIRE 16 -528 -32 -528 WIRE -368 -512 -368 -576 WIRE -272 -512 -272 -528 WIRE -176 -512 -176 -528 WIRE -80 -512 -80 -528 WIRE 16 -512 16 -528 WIRE 208 -512 208 -576 WIRE -592 -448 -592 -496 WIRE -464 -432 -464 -496 WIRE -368 -400 -368 -432 WIRE -320 -400 -320 -528 WIRE -320 -400 -368 -400 WIRE -272 -400 -272 -432 WIRE -208 -400 -208 -528 WIRE -208 -400 -272 -400 WIRE -176 -400 -176 -432 WIRE -128 -400 -128 -528 WIRE -128 -400 -176 -400 WIRE -80 -400 -80 -432 WIRE -32 -400 -32 -528 WIRE -32 -400 -80 -400 WIRE -464 -336 -464 -368 WIRE -368 -336 -368 -400 WIRE -368 -336 -464 -336 WIRE -352 -336 -368 -336 WIRE -272 -336 -272 -400 WIRE -272 -336 -288 -336 WIRE -256 -336 -272 -336 WIRE -176 -336 -176 -400 WIRE -176 -336 -192 -336 WIRE -160 -336 -176 -336 WIRE -80 -336 -80 -400 WIRE -80 -336 -96 -336 WIRE -64 -336 -80 -336 WIRE 16 -336 16 -432 WIRE 16 -336 0 -336 WIRE 48 -336 16 -336 WIRE 80 -336 48 -336 WIRE 208 -336 208 -432 WIRE 208 -336 144 -336 WIRE 208 -288 208 -336 WIRE -384 -256 -528 -256 WIRE 48 -256 48 -336 WIRE 48 -256 -384 -256 WIRE -848 -208 -848 -768 WIRE -528 -176 -528 -256 WIRE -384 -160 -384 -256 WIRE 208 -160 208 -208 WIRE -848 -16 -848 -128 WIRE -528 -16 -528 -96 WIRE -384 -16 -384 -96 WIRE 208 0 208 -80 FLAG 208 0 0 FLAG -848 -16 0 FLAG -592 -448 0 FLAG -528 -16 0 FLAG -384 -16 0 FLAG 288 -560 0 SYMBOL voltage -848 -224 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 200 SYMBOL voltage 208 -176 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 -5.5 100n 1.5n 1.5n 20n) SYMBOL cap -400 -160 R0 SYMATTR InstName C1 SYMATTR Value 3.3p SYMBOL res -544 -192 R0 SYMATTR InstName R1 SYMATTR Value 4meg SYMBOL res -608 -752 R0 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL cap -608 -560 R0 SYMATTR InstName C2 SYMATTR Value 1n SYMBOL ind2 -384 -528 R0 SYMATTR InstName L1

SYMATTR Type ind SYMATTR SpiceLine Rser=0.04 SYMBOL ind2 -288 -528 R0 SYMATTR InstName L2

SYMATTR Type ind SYMATTR SpiceLine Rser=0.04 SYMBOL ind2 -192 -528 R0 WINDOW 3 48 96 Left 2

SYMATTR InstName L3 SYMATTR Type ind SYMATTR SpiceLine Rser=0.04 SYMBOL ind2 -96 -528 R0 SYMATTR InstName L4

SYMATTR Type ind SYMATTR SpiceLine Rser=0.04 SYMBOL ind2 0 -528 R0 SYMATTR InstName L5

SYMATTR Type ind SYMATTR SpiceLine Rser=0.04 SYMBOL ind2 192 -528 R0 SYMATTR InstName L6

SYMATTR Type ind SYMATTR SpiceLine Rser=0.04 SYMBOL cap -288 -352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 10p SYMBOL cap -192 -352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 10p SYMBOL cap -96 -352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL cap 0 -352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 10p SYMBOL cap 144 -352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 10p SYMBOL cap 144 -592 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C8 SYMATTR Value 10p SYMBOL cap 0 -592 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C9 SYMATTR Value 10p SYMBOL cap -96 -592 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C10 SYMATTR Value 10p SYMBOL cap -192 -592 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C11 SYMATTR Value 10p SYMBOL cap -288 -592 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C12 SYMATTR Value 10p SYMBOL res 192 -304 R0 SYMATTR InstName R3 SYMATTR Value 10 SYMBOL schottky -448 -496 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky -448 -368 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode TEXT -320 -56 Left 2 ;GH SPAD Quench Aug 2018 TEXT -256 -192 Left 2 !K1 L1 L2 L3 L4 L5 L6 0.99 TEXT -488 -56 Left 2 ;SPAD TEXT -368 -704 Left 2 ;VERSA-PAC 6x3uH TEXT -136 -704 Left 2 ;LOT OF INTER WINDING STRAY CAP (C3-C12) TEXT -824 -720 Left 2 ;ANTI BURNOUT R TEXT 288 -352 Left 2 !.tran 500n TEXT 280 -160 Left 2 ;Paralled 74ABT541 line driver TEXT 288 -128 Left 2 ;or FET gate driver or similar TEXT 152 -672 Left 2 ;GUESSED AT 10pF

On Tuesday, August 21, 2018 at 6:05:06 AM UTC-4, piglet wrote:

t

with

ese

ist?

...

ver and run

n

e the

you

r then

and

d

ich

mes

choice.

nice

tch

OK thanks... I may still have to give that a try.

Hey adding a bit of inductor helped some. (matching times.. RC= L/R)

Here's my spice file.

Version 4 SHEET 1 880 680 WIRE -256 -160 -336 -160 WIRE -176 -160 -256 -160 WIRE 96 -160 -176 -160 WIRE 192 -160 96 -160 WIRE 336 -160 304 -160 WIRE 464 -160 416 -160 WIRE 592 -160 464 -160 WIRE 304 -128 304 -160 WIRE 464 -128 464 -160 WIRE 592 -128 592 -160 WIRE -176 -112 -176 -160 WIRE 96 -112 96 -160 WIRE -336 -64 -336 -160 WIRE 192 -48 192 -80 WIRE 256 -32 240 -32 WIRE -176 0 -176 -32 WIRE -128 0 -176 0 WIRE -96 0 -128 0 WIRE -64 0 -96 0 WIRE 256 0 256 -32 WIRE 304 0 304 -48 WIRE 304 0 256 0 WIRE 304 32 304 0 WIRE 368 32 368 16 WIRE 368 32 304 32 WIRE -336 48 -336 16 WIRE -176 48 -176 0 WIRE -96 48 -96 0 WIRE 96 48 96 -32 WIRE 160 48 96 48 WIRE 304 48 304 32 WIRE 0 64 0 0 WIRE 64 112 64 64 WIRE 160 112 160 48 WIRE 160 112 128 112 WIRE 192 112 192 48 WIRE 192 112 160 112 WIRE 624 112 400 112 WIRE 192 128 192 112 WIRE -176 144 -176 128 WIRE -96 144 -96 112 WIRE -96 144 -176 144 WIRE 304 160 304 128 WIRE -176 176 -176 144 WIRE 400 208 400 192 WIRE 400 208 368 208 WIRE 96 224 -192 224 WIRE 400 224 400 208 WIRE 496 224 400 224 WIRE 624 224 624 112 WIRE 400 272 400 224 WIRE 96 320 96 224 WIRE 176 320 96 320 WIRE 304 320 304 256 WIRE 304 320 256 320 WIRE -192 336 -192 304 WIRE 496 352 496 288 WIRE 496 352 400 352 WIRE 624 352 624 304 WIRE 624 352 496 352 WIRE 624 400 624 352 FLAG -192 336 0 FLAG -336 48 0 FLAG 624 400 0 FLAG -176 176 0 FLAG 192 208 0 FLAG -256 -96 0 FLAG 304 384 0 FLAG 368 16 Vgate FLAG -128 0 Vspad FLAG 592 -48 0 FLAG 464 -64 0 SYMBOL npn2 368 160 M0 SYMATTR InstName Q1 SYMATTR Value 2N5550 SYMBOL voltage -192 208 R0 WINDOW 3 -451 58 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value PULSE(5 .5 20n 3n 3n 10n 500n 2) SYMATTR InstName V1 SYMBOL voltage -336 -80 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 101V SYMBOL voltage 624 208 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value 5V SYMBOL res 384 96 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res 384 256 R0 SYMATTR InstName R2 SYMATTR Value 4k SYMBOL res 288 32 R0 SYMATTR InstName R3 SYMATTR Value 10 SYMBOL res 272 304 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 100 SYMBOL res 288 -144 R0 WINDOW 3 79 43 Left 2 SYMATTR Value 300 SYMATTR InstName R5 SYMBOL res 176 -176 R0 SYMATTR InstName R6 SYMATTR Value 1 SYMBOL res -192 -128 R0 SYMATTR InstName R7 SYMATTR Value 500k SYMBOL res -192 32 R0 SYMATTR InstName R8 SYMATTR Value 5meg SYMBOL cap -112 48 R0 SYMATTR InstName C1 SYMATTR Value 3p SYMBOL cap 480 224 R0 SYMATTR InstName C2 SYMATTR Value 1n SYMBOL diode 0 -16 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 64 48 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode 128 96 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL res 176 112 R0 SYMATTR InstName R9 SYMATTR Value 10meg SYMBOL cap -272 -160 R0 SYMATTR InstName C3 SYMATTR Value 1n SYMBOL pmos 240 48 R180 SYMATTR InstName M1 SYMATTR Value BSS84 SYMBOL res 80 -128 R0 WINDOW 0 -57 13 Left 2 WINDOW 3 -81 58 Left 2 SYMATTR InstName R10 SYMATTR Value 2meg SYMBOL voltage 592 -144 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V4 SYMATTR Value 100v SYMBOL cap 448 -128 R0 SYMATTR InstName C4 SYMATTR Value 10nF SYMBOL ind 432 -176 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 -27 3 VTop 2 SYMATTR InstName L1

TEXT -648 424 Left 2 !.tran 0 600n 0

George H. ps I've been f-ing around today trying to go from measuring 'dc' photo current (in my SPAD as only APD) to photon counting. But it's a bit of a hard hill to get over. If I have a maximum count rate of 1e6 that's ~0.1pA.. (e~ 1e-19) and APD gain of 100 gives me 10 pA. Not very much, and I'm grubbing around in dark currents/ offset voltages and bias currents.

GH

Since all you want is to replensish a little bit of lost charge I wonder if it can be done from the low side with a small capacitor?

John Larkin's resistor pullup to EHV clamped to the working voltage is gloriously simple.

piglet