smallest 0603 cap...

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
Click to expand...

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
Click to expand...

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
Click to expand...

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.
Click to expand...

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
 
On Wednesday, January 25, 2023 at 5:00:04 AM UTC-8, Phil Hobbs 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...
Click to expand...

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.
Click to expand...

Not so; this (or any) trim isn\'t intended to hit only one absolute value, it\'s for
test-and-adjust finagling. If you want to hit near-zero, any adjustable
capacitor plus a negative offset circuit (negative capacitance) seems to
me to be a suitable solution. Having a suitable length to snip on,
does eliminate the concern with an invariant element, like the end correction.
 
On Wed, 25 Jan 2023 13:45:07 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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. ;)
Click to expand...

Right. Measuring jitter requires a statistically valid number of
pulses.

We used to ship CAMAC systems that went down-hole near a nuke. They
shipped a bunch of time stamps up a long cable. Good replacement
market.

Just drilling the hole cost a million dollars.
 
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.
Click to expand...

Okay, for something like that, just dorking it to one side a bit makes
sense, assuming that the worst-case RC time constant is small enough
that it doesn\'t distort the next transition.

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)

Maybe it\'s possible to use a dpot with a shunt cap on the wiper to
balance the two sides.

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 21:26:38 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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.

Okay, for something like that, just dorking it to one side a bit makes
sense, assuming that the worst-case RC time constant is small enough
that it doesn\'t distort the next transition.

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)

Maybe it\'s possible to use a dpot with a shunt cap on the wiper to
balance the two sides.

Cheers

Phil Hobbs
Click to expand...

How about a trimmer cap? Beats soldering.

If it\'s TIA feedback, a trimpot can tweak the effective C value.

DPOTs are usually slow with the slowness code-dependent. Real trimpots
are great and easy to program.
 
John Larkin wrote:
On Wed, 25 Jan 2023 21:26:38 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

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.

Okay, for something like that, just dorking it to one side a bit makes
sense, assuming that the worst-case RC time constant is small enough
that it doesn\'t distort the next transition.

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)

Maybe it\'s possible to use a dpot with a shunt cap on the wiper to
balance the two sides.

Cheers

Phil Hobbs

How about a trimmer cap? Beats soldering.
Click to expand...

If it can be adjusted, it can be mis-adjusted, leading to
hard-to-diagnose misbehavior and reasonable-looking wrong answers. (My
least favorite kind.)

If it\'s TIA feedback, a trimpot can tweak the effective C value.

DPOTs are usually slow with the slowness code-dependent. Real trimpots
are great and easy to program.
Click to expand...

Sure, if you can still get them. Those nice Murata PVA2 things are long
gone.

A dpot is a variable RC network, so by putting the cap at the wiper, you
change the capacitive loading of the ends. There\'s some built in to the
dpot as well, as you say, but it varies with code too.

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
 
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)
Click to expand...

Did you look at parts similar to
https://www.mouser.de/c/passive-components/capacitors/silicon-rf-capacitors-thin-film/?q=0402%201pf

At least you do not start with 5 %.

Bye
--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------
 
On 26 Jan 2023 19:06:59 GMT, Uwe Bonnes
<bon@hertz.ikp.physik.tu-darmstadt.de> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)


Did you look at parts similar to
https://www.mouser.de/c/passive-components/capacitors/silicon-rf-capacitors-thin-film/?q=0402%201pf

At least you do not start with 5 %.

Bye
Click to expand...

Check out

PEREGRINE PE64907MLAA-Z

We use them for coarse-tuning an LC oscillator which is then
fine-tuned over a small range by a varicap.

It replaced a Maxim part that of course went EOL.
 
Uwe Bonnes wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)


Did you look at parts similar to
https://www.mouser.de/c/passive-components/capacitors/silicon-rf-capacitors-thin-film/?q=0402%201pf

At least you do not start with 5 %.

Bye
Click to expand...

Thanks, Uwe,

Very nice. I confess that I wasn\'t aware of the whole precision
picofarad capacitor niche--I can get 100 pF 1% NP0s for two cents in
hundreds, hurrah.

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
 
Get your xacto knife & slice across a trace on the pc board.

Hul

John Larkin <jlarkin@highlandsnipmetechnology.com> 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?
Click to expand...
 
On Fri, 27 Jan 2023 16:56:47 -0000 (UTC), Hul Tytus <ht@panix.com>
wrote:

Get your xacto knife & slice across a trace on the pc board.

Hul
Click to expand...

That\'s not very manufacturable.
 
On Friday, January 27, 2023 at 9:26:34 AM UTC-8, John Larkin wrote:
On Fri, 27 Jan 2023 16:56:47 -0000 (UTC), Hul Tytus <h...@panix.com
wrote:
Get your xacto knife & slice across a trace on the pc board.

That\'s not very manufacturable.
Click to expand...

Unknowable. Do you recall turret tuners, where each of a dozen channels\'
LC time constants were adjusted, in several places per channel,
in mass production? That started out with handwork, but got
automated, and... was actually pretty efficient.

Someone got clever and put an array of computer-controlled pistons
to work squishing coils until they hit the target value.

The \'slice across\' could be laser scan, or vibrating chisel, or
platinum-spark-plug electrode doing spark erosion, if you want
a manufacturable process. Maybe just a grinding wheel
and a jig to present the right edge to the right feed depth,
about as fast as applying an inspection stamp.
 
On Thursday, January 26, 2023 at 11:07:06 AM UTC-8, Uwe Bonnes wrote:
Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)

Did you look at parts similar to
https://www.mouser.de/c/passive-components/capacitors/silicon-rf-capacitors-thin-film/?q=0402%201pf

At least you do not start with 5 %.
Click to expand...

You beat me to it. It can be had with 10 fF tolerance. They are very repeatable. There is nothing quite like Accu-P. They can get expensive with the tight tolerance.
 
On Saturday, January 28, 2023 at 11:21:47 PM UTC-4, Simon S Aysdie wrote:
On Thursday, January 26, 2023 at 11:07:06 AM UTC-8, Uwe Bonnes wrote:
Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

I\'m actually working on a proof-of-concept that needs two separate TIAs
to have very closely similar phase and amplitude response out to a
couple of hundred kilohertz, which requires excellent phase matching.
We\'re only making 10 or so boards, so I\'m planning to put a couple of
DNP caps in parallel with the main one, to get the tolerance down from
~5% to ~0.5%. (Yes, this will require a bit of measurement and
selection on each board, but there aren\'t very many, and we have all the
stuff in stock.)

Did you look at parts similar to
https://www.mouser.de/c/passive-components/capacitors/silicon-rf-capacitors-thin-film/?q=0402%201pf

At least you do not start with 5 %.
You beat me to it. It can be had with 10 fF tolerance. They are very repeatable. There is nothing quite like Accu-P. They can get expensive with the tight tolerance.
Click to expand...

That was a trip. Accessing the German Mouser site from Puerto Rico. My choices are German or Spanish... I think!

--

Rick C.

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