Low Capacitance High Value Resistors

Look for high-voltage resistors, such as the larger sizes of these:

Vishay bought up lots of resistor manufacturers and I think one of them that make longer parts is Sfernice. Give them a call.

If nothing pans out or too expensive stack smaller values in series. If super-cricitcal use through-hole parts to get them off the FR-4, for less capacitance.

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Regards, Joerg

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Buy the leaded HV parts, and fashion the leads for surface mount attachment (by hand).

2kV and 4kV HV resistors fit your description. They are likely available without the ceramic dip or leads, which virtually makes the resultant an SMD part.

I have put slots like these under resistors:

to make possible cleaning underneath, and reduce possible parallel leakage paths on the board. It has not occurred to me they would have a bearing on capacitance. It would make sense because nothing has a smaller dielectric constant than air.

It is unfortunate there are never capacitance specs for resistors, or parasitic inductance specs for capacitors.

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Well, to be a bit pedantic, vacuum has a smaller dielectric constant than air. Air is 1.00059 at 20C and 1 atmosphere according to my physics book published in 1960.

Cheers, John

"Artist"

** Some makers do publish impedance curves for resistors with various values.

Small wattage composition resistors of around 150 ohms seem to have the widest bandwidths, going out to 500MHz in some cases.

I reckon any normal size, 1Mohm resistor will be droping impedance from

100kHz up.

Small wattage composition types would be likely to be the best.

** That info is published all the time - in the form of impedance curves again.

Typical through hole caps, including electros, have series inductances around 10 to 20 nH.

.... Phil

w.

L-trimmed surface mount parts seem to have lower parallel capacitance than spiral-trimmed axial leaded parts.

Making a string of SMD parts might be the best way to go.

-- Bill Sloman, Nijmegen

Sometimes, but the proximity to the FR-4 and planes doesn't play in your favor. Thru-hole parts can ride high, in the old days that was done using porcelain spacer beads. Still got some of those.

Yes. That's often the most economical way.

--
Regards, Joerg

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Artist a écrit :

Highest possible BW means almost nothing.

What BW and resistance value do you aim at?

Google usenet for hill+"R-C-R trick"

The first and last link gives you a pretty picture of it, with some nice other ideas too: "new RCR trick for transimpedance amplifier" "Capacitor-feedback for low noise"

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Thanks,
Fred.