I need a tiny cap.

This one is interesting

https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D

Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
pF. Maybe a couple in series? Maybe a network?

John Larkin wrote:
> I need a tiny cap.
>
> This one is interesting
>
> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>
> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
> pF. Maybe a couple in series? Maybe a network?
>
>
>

I have some 0.1 pF caps in stock too, primarily for adjusting the
transfer functions of high-Z TIAs.

You could maybe make a poor man's 3-terminal cap using two of those in
series--the capacitance to ground from the midpoint would reduce the
end-to-end capacitance.

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

On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>John Larkin wrote:
>> I need a tiny cap.
>>
>> This one is interesting
>>
>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>>
>> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>> pF. Maybe a couple in series? Maybe a network?
>>
>>
>>
>
>I have some 0.1 pF caps in stock too, primarily for adjusting the
>transfer functions of high-Z TIAs.
>
>You could maybe make a poor man's 3-terminal cap using two of those in
>series--the capacitance to ground from the midpoint would reduce the
>end-to-end capacitance.
>
>Cheers
>
>Phil Hobbs

One end of my cap will be ground already.

I could just use PCB capacitance, but that's hard to tune. I'd just
have to get it right first try.

John Larkin wrote:
> On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> John Larkin wrote:
>>> I need a tiny cap.
>>>
>>> This one is interesting
>>>
>>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>>>
>>>
>>>
Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>>> pF. Maybe a couple in series? Maybe a network?
>>>
>>>
>>>
>>
>> I have some 0.1 pF caps in stock too, primarily for adjusting the
>> transfer functions of high-Z TIAs.
>>
>> You could maybe make a poor man's 3-terminal cap using two of those
>> in series--the capacitance to ground from the midpoint would reduce
>> the end-to-end capacitance.
>>
>> Cheers
>>
>> Phil Hobbs
>
> One end of my cap will be ground already.
>
> I could just use PCB capacitance, but that's hard to tune. I'd just
> have to get it right first try.

It's already not that easy to get less than 0.1 pF to ground from a PCB
pad, let alone a trace.

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

On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:

> It's already not that easy to get less than 0.1 pF to ground from a PCB
> pad, let alone a trace.

Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
so you can get your 0.1 pf by soldering a short length onto the board, and then
with flush nippers, cut it off.

On Tuesday, January 24, 2023 at 4:10:41 PM UTC-5, whit3rd wrote:
> On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:
>
> > It's already not that easy to get less than 0.1 pF to ground from a PCB
> > pad, let alone a trace.
> Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
> so you can get your 0.1 pf by soldering a short length onto the board, and then
> with flush nippers, cut it off.

0.04 inches for 0.1 pf. How does that work exactly?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

On Tuesday, January 24, 2023 at 1:28:22 PM UTC-8, Ricky wrote:
> On Tuesday, January 24, 2023 at 4:10:41 PM UTC-5, whit3rd wrote:

> >... the usual trim techniques still work; RG174 is 30 pF/foot,
> > so you can get your 0.1 pf by soldering a short length onto the board, and then
> > with flush nippers, cut it off.

> 0.04 inches for 0.1 pf. How does that work exactly?

That's why it takes flush nippers. :-)

On Tuesday, 24 January 2023 at 19:17:17 UTC, John Larkin wrote:
> On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
> >John Larkin wrote:
> >> I need a tiny cap.
> >>
> >> This one is interesting
> >>
> >> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
> >>
> >> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
> >> pF. Maybe a couple in series? Maybe a network?
> >>
> >>
> >>
> >
> >I have some 0.1 pF caps in stock too, primarily for adjusting the
> >transfer functions of high-Z TIAs.
> >
> >You could maybe make a poor man's 3-terminal cap using two of those in
> >series--the capacitance to ground from the midpoint would reduce the
> >end-to-end capacitance.
> >
> >Cheers
> >
> >Phil Hobbs
> One end of my cap will be ground already.
>
> I could just use PCB capacitance, but that's hard to tune. I'd just
> have to get it right first try.

Yes, but when you look at the tolerances are you really gaining much?

John

Am 24.01.23 um 19:41 schrieb Phil Hobbs:
> John Larkin wrote:
>> I need a tiny cap.
>>
>> This one is interesting
>>
>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>>
>> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>> pF. Maybe a couple in series? Maybe a network?
>>
>>
>>
>
> I have some 0.1 pF caps in stock too, primarily for adjusting the
> transfer functions of high-Z TIAs.
>
> You could maybe make a poor man's 3-terminal cap using two of those in
> series--the capacitance to ground from the midpoint would reduce the
> end-to-end capacitance.

That's why ADS or other CAD systems have these capacitor-less
capacitors with interdigitated layout models that can be tuned
with a scalpell if really needed on the hardware board.
A 0201 cap that swims around during soldering?

--------
| --------|
-----*------- *--------
| --------|
--------

> Cheers

Gerhard

whit3rd wrote:
> On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:
>
>> It's already not that easy to get less than 0.1 pF to ground from a PCB
>> pad, let alone a trace.
>
> Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
> so you can get your 0.1 pf by soldering a short length onto the board, and then
> with flush nippers, cut it off.

I invite you to try getting the fringing capacitance of an actual piece
of RG-174, connected to a circuit, to be that low. Show your work. ;)

(The capacitance per unit length only applies when the fringing
capacitance is negligible.)

Cheers

Phil Hobbs

On Tuesday, January 24, 2023 at 5:36:47 PM UTC-8, Phil Hobbs wrote:
> whit3rd wrote:
> > On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:
> >
> >> It's already not that easy to get less than 0.1 pF to ground from a PCB
> >> pad, let alone a trace.
> >
> > Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
> > so you can get your 0.1 pf by soldering a short length onto the board, and then
> > with flush nippers, cut it off.
> I invite you to try getting the fringing capacitance of an actual piece
> of RG-174, connected to a circuit, to be that low. Show your work. ;)
>
> (The capacitance per unit length only applies when the fringing
> capacitance is negligible.)

But, because this is a trimming technique, there's an end correction BEFORE the
snip as well as after. At least, there is until the two ends of the cable coincide...

I'm not concerned with high frequencies much, so I might apply a negative capacitor
first, swamp it with the long-RG174 trimmer, then trim down to get near zero. Negative
impedance converter, you know...

<https://wiki.analog.com/university/courses/electronics/text/chapter-4>

On a sunny day (Tue, 24 Jan 2023 10:37:01 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<n390th9l7dkb25tai5g3aj4cesoe6n0u5u@4ax.com>:

>I need a tiny cap.
>
>This one is interesting
>
>https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D

LOL looks like a type by them
value .1 pF
tolerane .1 pF
multilayer???
LOL

likely 100 nF!
At 10V must be!

>Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>pF. Maybe a couple in series? Maybe a network?
>
>
>
>

On a sunny day (Tue, 24 Jan 2023 11:17:06 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<o5b0thlfg6oiep66l7om8tcnns6hldcbfq@4ax.com>:

>On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
><pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>>John Larkin wrote:
>>> I need a tiny cap.
>>>
>>> This one is interesting
>>>
>>>
>>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>>>
>>> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>>> pF. Maybe a couple in series? Maybe a network?
>>>
>>>
>>>
>>
>>I have some 0.1 pF caps in stock too, primarily for adjusting the
>>transfer functions of high-Z TIAs.
>>
>>You could maybe make a poor man's 3-terminal cap using two of those in
>>series--the capacitance to ground from the midpoint would reduce the
>>end-to-end capacitance.
>>
>>Cheers
>>
>>Phil Hobbs
>
>One end of my cap will be ground already.
>
>I could just use PCB capacitance, but that's hard to tune. I'd just
>have to get it right first try.

Bended wire, twisted wire...
done it.

On a sunny day (Tue, 24 Jan 2023 10:37:01 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<n390th9l7dkb25tai5g3aj4cesoe6n0u5u@4ax.com>:

>I need a tiny cap.
>
>This one is interesting
>
>https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D

I wrote:

>LOL looks like a type by them
>value .1 pF
>tolerane .1 pF
>multilayer???
>LOL
>
>likely 100 nF!
>At 10V must be!

So, even if it is really .1 pF the capacitance between the soldering masses at the ends will change that!
It seems that sort of stuff (and I joked about that a while back here)
is sold to clueless Spice users who never build a RF circuit and
are now looking for .1 pF ??? SMDs

How many THz and what sort of peeseebee they use?

What a crap world of snake oil sellers
Reminds me of the F35, likely also spice designed...

My predictions come true, US military now goes
for nuculear space propulsion, pick up where they
left in the sixties....
https://www.rt.com/news/570435-nasa-darpa-nuclear-mars/

Well, nothing to worry about, anything metal floating next to it will detune its .001 pF peeseebees.

If they even can get it of the ground.

>Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>pF. Maybe a couple in series? Maybe a network?

2 drops of solder.. add more when needed, better is to design a circuit that does not need .1 pF caps.
o o
- -
==============

////
0 0
/
<0>
^
| cookie

On Wednesday, January 25, 2023 at 12:49:32 AM UTC-5, Jan Panteltje wrote:
> On a sunny day (Tue, 24 Jan 2023 10:37:01 -0800) it happened John Larkin
> <jla...@highlandSNIPMEtechnology.com> wrote in
> <n390th9l7dkb25tai...@4ax.com>:
> >I need a tiny cap.
> >
> >This one is interesting
> >
> >https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
> LOL looks like a type by them
> value .1 pF
> tolerane .1 pF
> multilayer???
> LOL
>
> likely 100 nF!
> At 10V must be!

LOL! But the part number matches a 0.1pF, ±0.1pF cap. So they can ship you an empty reel and claim they are within tolerance!

No need for multilayer... no need for any layers!! The un-capacitor!

A friend pointed out once that zero ohm resistors had amazingly tight tolerances, considering they were specified as ±10%, which would be ±0 ohms! That's a tough spec to meet. In fact, impossible.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

On Wednesday, January 25, 2023 at 12:52:24 AM UTC-5, Jan Panteltje wrote:
> On a sunny day (Tue, 24 Jan 2023 11:17:06 -0800) it happened John Larkin
> <jla...@highlandSNIPMEtechnology.com> wrote in
> <o5b0thlfg6oiep66l...@4ax.com>:
> >On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
> ><pcdhSpamM...@electrooptical.net> wrote:
> >
> >>John Larkin wrote:
> >>> I need a tiny cap.
> >>>
> >>> This one is interesting
> >>>
> >>>
> >>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
> >>>
> >>> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
> >>> pF. Maybe a couple in series? Maybe a network?
> >>>
> >>>
> >>>
> >>
> >>I have some 0.1 pF caps in stock too, primarily for adjusting the
> >>transfer functions of high-Z TIAs.
> >>
> >>You could maybe make a poor man's 3-terminal cap using two of those in
> >>series--the capacitance to ground from the midpoint would reduce the
> >>end-to-end capacitance.
> >>
> >>Cheers
> >>
> >>Phil Hobbs
> >
> >One end of my cap will be ground already.
> >
> >I could just use PCB capacitance, but that's hard to tune. I'd just
> >have to get it right first try.
> Bended wire, twisted wire...
> done it.

I don't recall what gadget it was in, had such a wire indicated on the silkscreen of the circuit board. Seems a wire was soldered to the board, then bent over to create a capacitor to some other part. The board had a single through hole, and a line toward the part it was to be bent over.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

On 2023-01-25 07:57, Ricky wrote:
> A friend pointed out once that zero ohm resistors had amazingly tight tolerances, considering they were specified as ±10%, which would be ±0 ohms! That's a tough spec to meet. In fact, impossible.

I still have a package of 0 Ohm 5% resistors (actually, about 20 mOhm).

The company switched to 1% resistors and discarded all stock of 5% reels.
I saved them from the dumpster, stripped them, and repacked in 1.5x1.5" ZIP-bags.

Arie

On 2023-01-25, Jan Panteltje <alien@comet.invalid> wrote:
> On a sunny day (Tue, 24 Jan 2023 10:37:01 -0800) it happened John Larkin
><jlarkin@highlandSNIPMEtechnology.com> wrote in
><n390th9l7dkb25tai5g3aj4cesoe6n0u5u@4ax.com>:
>
>>I need a tiny cap.
>>
>>This one is interesting
>>
>>https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>
> LOL looks like a type by them
> value .1 pF
> tolerane .1 pF
> multilayer???

one layer of metal, one layer of alumina, one layer of metal

> LOL
>
> likely 100 nF!
> At 10V must be!

datasheet says 0.1pf

--
Jasen.
pǝsɹǝʌǝɹ sʇɥƃᴉɹ ll∀

whit3rd wrote:
> On Tuesday, January 24, 2023 at 5:36:47 PM UTC-8, Phil Hobbs wrote:
>> whit3rd wrote:
>>> On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:
>>>
>>>> It's already not that easy to get less than 0.1 pF to ground from a PCB
>>>> pad, let alone a trace.
>>>
>>> Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
>>> so you can get your 0.1 pf by soldering a short length onto the board, and then
>>> with flush nippers, cut it off.
>> I invite you to try getting the fringing capacitance of an actual piece
>> of RG-174, connected to a circuit, to be that low. Show your work. ;)
>>
>> (The capacitance per unit length only applies when the fringing
>> capacitance is negligible.)
>
> But, because this is a trimming technique, there's an end correction BEFORE the
> snip as well as after. At least, there is until the two ends of the cable coincide...
>
> I'm not concerned with high frequencies much, so I might apply a negative capacitor
> first, swamp it with the long-RG174 trimmer, then trim down to get near zero. Negative
> impedance converter, you know...
>
> <https://wiki.analog.com/university/courses/electronics/text/chapter-4>
>

Yes and no. Given invariant fringing capacitance, changing the length
incrementally does give a nice predictable delta-C. Trombone line is
good that way down at low frequency, for instance.

This is because, in a nice long piece of coax, the E field inside is
purely radial almost everywhere, and any departure from the pure TEM
mode at the ends dies off exponentially, roughly as exp(-2 pi L/r),
where L is the distance from the open end and r is the radius. (That's
a consequence of Laplace's equation, and is also why perforated metal
makes good electrostatic shielding.)

However, John asked for a small absolute capacitance. A picofarad or so
of end effect doesn't fit that bill.

Plus when the coax gets too short, the approximation you're relying on
starts getting inaccurate because (a) there are varying axial fields
throughout the length of the coax, and (b) the fields at the two ends
interact.

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

On Wed, 25 Jan 2023 05:48:33 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

>On a sunny day (Tue, 24 Jan 2023 11:17:06 -0800) it happened John Larkin
><jlarkin@highlandSNIPMEtechnology.com> wrote in
><o5b0thlfg6oiep66l7om8tcnns6hldcbfq@4ax.com>:
>
>>On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
>><pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>>John Larkin wrote:
>>>> I need a tiny cap.
>>>>
>>>> This one is interesting
>>>>
>>>>
>>>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>>>>
>>>> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>>>> pF. Maybe a couple in series? Maybe a network?
>>>>
>>>>
>>>>
>>>
>>>I have some 0.1 pF caps in stock too, primarily for adjusting the
>>>transfer functions of high-Z TIAs.
>>>
>>>You could maybe make a poor man's 3-terminal cap using two of those in
>>>series--the capacitance to ground from the midpoint would reduce the
>>>end-to-end capacitance.
>>>
>>>Cheers
>>>
>>>Phil Hobbs
>>
>>One end of my cap will be ground already.
>>
>>I could just use PCB capacitance, but that's hard to tune. I'd just
>>have to get it right first try.
>
>Bended wire, twisted wire...
>done it.

This used to be called a gimmick capacitor.

..<https://en.wikipedia.org/wiki/Gimmick_capacitor>

Joe Gwinn

On Wed, 25 Jan 2023 07:59:52 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>whit3rd wrote:
>> On Tuesday, January 24, 2023 at 5:36:47 PM UTC-8, Phil Hobbs wrote:
>>> whit3rd wrote:
>>>> On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:
>>>>
>>>>> It's already not that easy to get less than 0.1 pF to ground from a PCB
>>>>> pad, let alone a trace.
>>>>
>>>> Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
>>>> so you can get your 0.1 pf by soldering a short length onto the board, and then
>>>> with flush nippers, cut it off.
>>> I invite you to try getting the fringing capacitance of an actual piece
>>> of RG-174, connected to a circuit, to be that low. Show your work. ;)
>>>
>>> (The capacitance per unit length only applies when the fringing
>>> capacitance is negligible.)
>>
>> But, because this is a trimming technique, there's an end correction BEFORE the
>> snip as well as after. At least, there is until the two ends of the cable coincide...
>>
>> I'm not concerned with high frequencies much, so I might apply a negative capacitor
>> first, swamp it with the long-RG174 trimmer, then trim down to get near zero. Negative
>> impedance converter, you know...
>>
>> <https://wiki.analog.com/university/courses/electronics/text/chapter-4>
>>
>
>Yes and no. Given invariant fringing capacitance, changing the length
>incrementally does give a nice predictable delta-C. Trombone line is
>good that way down at low frequency, for instance.
>
>This is because, in a nice long piece of coax, the E field inside is
>purely radial almost everywhere, and any departure from the pure TEM
>mode at the ends dies off exponentially, roughly as exp(-2 pi L/r),
>where L is the distance from the open end and r is the radius. (That's
>a consequence of Laplace's equation, and is also why perforated metal
>makes good electrostatic shielding.)
>
>However, John asked for a small absolute capacitance. A picofarad or so
>of end effect doesn't fit that bill.

And I want something that can be manufactured, not a hobby fiddle
thing.

Something like this:

https://www.dropbox.com/s/z4vevjyuflm732l/T578_LVDS.jpg?raw=1

It needs extreme CMRR to work. If C1 is just a resistor parasitic, I
can make C2 a bit larger and the CMRR error becomes positive feedback,
which is OK in moderation. High voltage Schmitt trigger.

I could just use a digital isolator to drive the GaN fet, but they are
slow. The modulated ones may add jitter, too.

Of course, detonators probably don't care about a bit of jitter.

On Wed, 25 Jan 2023 05:45:41 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

>On a sunny day (Tue, 24 Jan 2023 10:37:01 -0800) it happened John Larkin
><jlarkin@highlandSNIPMEtechnology.com> wrote in
><n390th9l7dkb25tai5g3aj4cesoe6n0u5u@4ax.com>:
>
>>I need a tiny cap.
>>
>>This one is interesting
>>
>>https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>
>LOL looks like a type by them
>value .1 pF
>tolerane .1 pF

Yes, that was the interesting part.

On a sunny day (Wed, 25 Jan 2023 10:49:52 -0500) it happened Joe Gwinn
<joegwinn@comcast.net> wrote in <jpj2tht5cdbd666u4pu937ftqki68s3ah2@4ax.com>:

>On Wed, 25 Jan 2023 05:48:33 GMT, Jan Panteltje <alien@comet.invalid>
>wrote:
>
>>On a sunny day (Tue, 24 Jan 2023 11:17:06 -0800) it happened John Larkin
>><jlarkin@highlandSNIPMEtechnology.com> wrote in
>><o5b0thlfg6oiep66l7om8tcnns6hldcbfq@4ax.com>:
>>
>>>On Tue, 24 Jan 2023 13:41:52 -0500, Phil Hobbs
>>><pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>>John Larkin wrote:
>>>>> I need a tiny cap.
>>>>>
>>>>> This one is interesting
>>>>>
>>>>>
>>>>>
>>>>> https://www.mouser.com/ProductDetail/Walsin/RF03N0R1B100CT?qs=sGAEpiMZZMvsSlwiRhF8qtsBU8Zhqm2Ra%2Fa5698GTEQZP2uSIBTS%2FQ%3D%3D
>>>>>
>>>>> Below 0.1 pF, maybe I can use a 10 meg resistor, which is around 0.04
>>>>> pF. Maybe a couple in series? Maybe a network?
>>>>>
>>>>>
>>>>>
>>>>
>>>>I have some 0.1 pF caps in stock too, primarily for adjusting the
>>>>transfer functions of high-Z TIAs.
>>>>
>>>>You could maybe make a poor man's 3-terminal cap using two of those in
>>>>series--the capacitance to ground from the midpoint would reduce the
>>>>end-to-end capacitance.
>>>>
>>>>Cheers
>>>>
>>>>Phil Hobbs
>>>
>>>One end of my cap will be ground already.
>>>
>>>I could just use PCB capacitance, but that's hard to tune. I'd just
>>>have to get it right first try.
>>
>>Bended wire, twisted wire...
>>done it.
>
>This used to be called a gimmick capacitor.
>
>.<https://en.wikipedia.org/wiki/Gimmick_capacitor>

http://panteltje.com/pub/twisted_wire_oscillator_IMG_6629.JPG
http://panteltje.com/pub/2.4GHz_twisted_oscillator_IMG_3629.GIF
http://panteltje.com/pub/GPS_jammer_board_twisted_wire_1.57GHz_oscillator_IMG_3622.GIF

....

On a sunny day (Wed, 25 Jan 2023 08:02:22 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<tlj2th5frqrbrvhf8mjrgup4df34lgq2j2@4ax.com>:

>Something like this:
>
>https://www.dropbox.com/s/z4vevjyuflm732l/T578_LVDS.jpg?raw=1

2 twisted wire caps?

John Larkin wrote:
> On Wed, 25 Jan 2023 07:59:52 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> whit3rd wrote:
>>> On Tuesday, January 24, 2023 at 5:36:47 PM UTC-8, Phil Hobbs wrote:
>>>> whit3rd wrote:
>>>>> On Tuesday, January 24, 2023 at 12:47:09 PM UTC-8, Phil Hobbs wrote:
>>>>>
>>>>>> It's already not that easy to get less than 0.1 pF to ground from a PCB
>>>>>> pad, let alone a trace.
>>>>>
>>>>> Yeah, but the usual trim techniques still work; RG174 is 30 pF/foot,
>>>>> so you can get your 0.1 pf by soldering a short length onto the board, and then
>>>>> with flush nippers, cut it off.
>>>> I invite you to try getting the fringing capacitance of an actual piece
>>>> of RG-174, connected to a circuit, to be that low. Show your work. ;)
>>>>
>>>> (The capacitance per unit length only applies when the fringing
>>>> capacitance is negligible.)
>>>
>>> But, because this is a trimming technique, there's an end correction BEFORE the
>>> snip as well as after. At least, there is until the two ends of the cable coincide...
>>>
>>> I'm not concerned with high frequencies much, so I might apply a negative capacitor
>>> first, swamp it with the long-RG174 trimmer, then trim down to get near zero. Negative
>>> impedance converter, you know...
>>>
>>> <https://wiki.analog.com/university/courses/electronics/text/chapter-4>
>>>
>>
>> Yes and no. Given invariant fringing capacitance, changing the length
>> incrementally does give a nice predictable delta-C. Trombone line is
>> good that way down at low frequency, for instance.
>>
>> This is because, in a nice long piece of coax, the E field inside is
>> purely radial almost everywhere, and any departure from the pure TEM
>> mode at the ends dies off exponentially, roughly as exp(-2 pi L/r),
>> where L is the distance from the open end and r is the radius. (That's
>> a consequence of Laplace's equation, and is also why perforated metal
>> makes good electrostatic shielding.)
>>
>> However, John asked for a small absolute capacitance. A picofarad or so
>> of end effect doesn't fit that bill.
>
> And I want something that can be manufactured, not a hobby fiddle
> thing.
>
> Something like this:
>
> https://www.dropbox.com/s/z4vevjyuflm732l/T578_LVDS.jpg?raw=1
>
> It needs extreme CMRR to work. If C1 is just a resistor parasitic, I
> can make C2 a bit larger and the CMRR error becomes positive feedback,
> which is OK in moderation. High voltage Schmitt trigger.
>
> I could just use a digital isolator to drive the GaN fet, but they are
> slow. The modulated ones may add jitter, too.
>
> Of course, detonators probably don't care about a bit of jitter.

Well, not repeatable jitter, anyway. ;)

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