1G resistor

My bad.

Version 4 SHEET 1 1072 680 WIRE 320 -192 32 -192 WIRE 448 -192 320 -192 WIRE 528 -192 448 -192 WIRE 576 -192 528 -192 WIRE 320 -128 320 -192 WIRE 448 -128 448 -192 WIRE 976 0 880 0 WIRE 224 16 176 16 WIRE 320 16 320 -48 WIRE 320 16 288 16 WIRE 448 16 448 -64 WIRE 448 16 320 16 WIRE 976 32 976 0 WIRE 176 64 176 16 WIRE 880 64 880 0 WIRE 320 80 320 16 WIRE 448 96 448 16 WIRE 32 160 32 -192 WIRE 880 192 880 144 WIRE 320 208 320 160 WIRE 448 208 448 160 WIRE 448 208 320 208 WIRE 848 208 448 208 WIRE 976 224 912 224 WIRE 1024 224 976 224 WIRE 1040 224 1024 224 WIRE 848 240 800 240 WIRE 320 256 320 208 WIRE 448 272 448 208 WIRE 32 304 32 240 WIRE 800 320 800 240 WIRE 976 320 976 224 WIRE 976 320 800 320 WIRE 448 400 448 336 WIRE 592 400 448 400 WIRE 800 400 800 320 WIRE 800 400 672 400 WIRE 880 400 880 256 WIRE 448 432 448 400 WIRE 320 448 320 336 WIRE 880 560 880 480 WIRE 448 576 448 512 FLAG 32 304 0 FLAG 320 448 0 FLAG 528 -192 PULSE FLAG 1024 224 MON FLAG 880 560 0 FLAG 976 32 0 FLAG 448 576 0 FLAG 176 64 0 SYMBOL res 304 64 R0 WINDOW 0 -65 42 Left 2 WINDOW 3 -68 81 Left 2 SYMATTR InstName R1 SYMATTR Value .5G SYMBOL res 304 240 R0 WINDOW 0 -68 40 Left 2 WINDOW 3 -87 85 Left 2 SYMATTR InstName R2 SYMATTR Value 1Meg SYMBOL cap 432 96 R0 WINDOW 0 63 10 Left 2 WINDOW 3 57 46 Left 2 SYMATTR InstName C1 SYMATTR Value 300f SYMBOL cap 432 272 R0 WINDOW 0 64 9 Left 2 WINDOW 3 53 45 Left 2 SYMATTR InstName C2 SYMATTR Value 300p SYMBOL voltage 32 144 R0 WINDOW 0 -78 146 Left 2 WINDOW 3 -260 208 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 1200 1u 10u 10u 1m) SYMBOL Opamps\\UniversalOpamp2 880 224 M180 WINDOW 0 35 46 Left 2 SYMATTR InstName U1 SYMATTR Value2 Avol=1Meg GBW=3Meg Slew=3Meg SYMBOL voltage 880 384 R0 WINDOW 0 65 37 Left 2 WINDOW 3 73 72 Left 2 SYMATTR InstName V2 SYMATTR Value 5 SYMBOL voltage 880 48 R0 WINDOW 0 -86 39 Left 2 WINDOW 3 -80 75 Left 2 SYMATTR InstName V3 SYMATTR Value 5 SYMBOL res 432 416 R0 WINDOW 0 49 55 Left 2 WINDOW 3 46 88 Left 2 SYMATTR InstName R3 SYMATTR Value 500 SYMBOL res 688 384 R90 WINDOW 0 -46 61 VBottom 2 WINDOW 3 -41 58 VTop 2 SYMATTR InstName R4 SYMATTR Value 500 SYMBOL res 304 -144 R0 SYMATTR InstName R5 SYMATTR Value .5G SYMBOL cap 432 -128 R0 SYMATTR InstName C3 SYMATTR Value 300f SYMBOL cap 288 0 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 20f TEXT -272 64 Left 2 ;1000:1 HV PICKOFF TEXT -216 192 Left 2 !.tran 2m TEXT -256 120 Left 2 ;mod Nov 21, 2015 \nterrestrial strays TEXT 560 464 Left 2 ;POT

When we were kids, LEDs were new stuff. A friend told me that he'd had LEDs for some time. When asked about it, he reached in his pile-o-parts for a glass signal diode. Then took a pair of long-nose pliers and bent the leads so they were about an inch apart and proceeded to jam the diode into an outlet. It was real bright! He said that he did have a problem with reliability.

I measured 1.1 in full 8-lead mode.

How about this?

There is a history of exploding electronics in military gear. Norden bombsights, radar, things like that. Someone made/makes ICs that have an explosive layer fabbed into the chip.

I recall an explosive chip somewhere.

James is right that the resistor has distributed RC nasties when it's flat on the board. So the only reasonable fix is to parallel it with a substantial real capacitance, to swamp out the small stuff.

How much accuracy do you need? The 1G, isolated from all things conductive, directly input to a current-to-voltage amplifier with feedback keeping the input node at constant voltage obviates problems with capacitance.

It needs to be "scope probe" sort of accuracy, so the user can see the high-voltage pulses, maybe digitize a few points to make sure the driver is working. So, a few percent accuracy and visually clean pulse response should do.

"isolated from all things conductive" would shoot down pick-and-place surface mount assembly. Even then, any shunt capacitance in the resistor will make a spike in a TIA output. A trimmer cap across the TIA feedback resistor fixes that, but that's equivalent to my circuits, but inverts.

This should be simple; it's not.

Did you see my maybe-final solution?

This uses a low-CTR optocoupler to improve the waveform.

Sure. But, not at 3kV.

On Sat, 21 Nov 2015 07:43:29 -0800, John Larkin Gave us:

The flat package devices I linked to stand perpendicular to the PCB and off of it about a quarter inch or more.

Zero leackage currents.. Near zero parasitic effects.

They might still need some sort of high-frequency compensation; I'd have to experiment to see. And we prefer to avoid hand-soldered thru-hole parts.

The Welwyn 2512 resistor costs under a dollar, and the optocoupler is

Have you tested the C value when mounted ?

Jamie

I've been on the internet too long when I parse that sentence into a hilarious image.

--sp

That will wait until we have the PCB!

It's an SO8, 1.1 pF, so it should be OK.

I measured it by pushing one down onto the surface-mount adapter of my AADE L-C meter. That's a rough approximation of real life. I might expect a bit less capacitance on the real board.

I'd be shocked if the board works first-time as-designed, so I'll probably have to write an ECO to at least change some parts values. So I can tweak the compensating cap values as needed, in that ECO.

I guess I could Dremel a closer approximation of real life, namely the ACPL mounted on a board with a layer 2 ground plane. Heck, I may as well include the 1G resistor.

An old fella walks into a taxidermist and aske if he could stuff two of his pet squirls that showed up on the door step, dead, so that he could keep them close by for all time. The taxidermist asked if he wanted them mounted and with a long look on his face, he said "No, shaking hands will do"

I don't always proof read my stuff, maybe I should. Anyway, I'll try harder next time to choice my words more carefully :)

P.S.

Voice to text does not work very well, at least the package I am using does not.

Jamie

Yes, and use a spell checker to boot.

Is English your last language? Choose would have been a better choice than choice.

So, you are using a voice-to-text program? In that case it may explain some of your problems.

I don't see that. The 'distributed RC' is just a lossy transmission line, and it's SO SHORT the timing can be ignored (and the loss is the resistance that you WANT).

The 'substantial real capacitance' looks more like a problem than a solution.

I want a high-voltage square pulse to make a small square pulse at the monitor output, attenuated 1000:1. The 1G resistor has resistance and capacitance but no significant inductance so is about as ugly as a transmission line can get. It's not short; 1G ohms times 0.05 pF (the resistor's sort of native time constant) is 50 microseconds.

It allows me to make a network that has nearly flat 1000:1 attenuation from DC to some MHz.

Isn't that the time constant of the attenuator (circa 1 Mohm parallel with 1Gohm) driving the capacitance? Which would be nanoseconds? And, it seems to be capacitance that you can bootstrap away (though I understand reulctance to start a cut-and-try exercise).

You can Spice it a number of ways. Assume that the 1G resistor has about 4 pF to ground, all along its length. Break that into a number of sections, the more the better. Like 10 sections of RCRCRC..., each

That will look ugly.