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low capacitance diodes

SMS7621-079 (Skyworks, used to be Alpha) parts run about 0.22 pF at 0 bias, according to my measurements. It's a single in a teeny SC-79 package, but they have this same chip in a dual SOT-23. It's about the lowest capacitance diode you can buy packaged. Skyworks has a dynamite free sample kit too... lots of schottkys and varicaps.

Hey, put two in series and get close to 0.1 pF! It's only rated 2 volts Vr, but is really better... I have actual reverse leakage curves somewhere around here mumble mumble. But a low barrier schottky might be a bit leaky across 390K.

John

Reply to
John Larkin
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I needed a similar diode for across a 1 meg resistor. The best I could find was the Panasonic MA3X198.

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If you find a better one, I could use it.

--
John Popelish
Reply to
John Popelish

Would a dual PIN diode work? 0.28pF @0V/1GHz for the BAR88-xx series.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Nope. Last time I needed a few Infineon parts Future had them, but not sure about these cell-phone bits.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

: Would a dual PIN diode work? 0.28pF @0V/1GHz for the BAR88-xx series.

Any source for low numbers of this diode? I don't find it with the usual suspects...

Bye

-- Uwe Bonnes snipped-for-privacy@elektron.ikp.physik.tu-darmstadt.de

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Reply to
Uwe Bonnes

Hi All,

I have an application that needs a retrofit - a pair of back-to-back "clipping" diodes across an opamp feedback resistor (which cannot be reduced below 390k for other reasons)

I want extremely low capacitance though - 1pF max, 500fF better. a pair of 1N4148s drops the gain by 60%; BAS28 and BAV99 each drop the gain by

38% - better but I'm not there yet (measured not simulated results).

Any suggestions? Its gotta be smt, and of course cheaper is better :)

Cheers Terry

Reply to
Terry Given

Vishay/Siliconix makes some low leakage diodes that may do - the JPAD5 or SSTPAD5 is 0.5 pF, and the JPAD50 is 1.5 pF - Newark has the SSTPAD5 (smd) in stock, and will sell small quantities.

--
Peter Bennett, VE7CEI  
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Reply to
Peter Bennett

Hi All,

Thanks for your comments. Very helpful. I played with the panasonic part, didnt like the pricing of the more esoteric stuff, and went and looked harder at the constraints driving the feedback resistor. The design equations were yucky when not simplified, but a little work with mathcad and I found a way to reduce it, to the point a BAV99 works. Who needs closed-form solutions when you have a numerical solver.

Cheers Terry

Reply to
Terry Given

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