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From: Cursitor Doom <cd@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Interesting inductor
Date: Thu, 14 Mar 2024 01:00:18 +0000
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On Thu, 14 Mar 2024 00:03:54 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>Cursitor Doom <cd@notformail.com> wrote:
>> On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> 
>>> So I'm doing a new lab amp product.
>>> Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz).
>>> 
>>> The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz).  The 
>>> spherical cows love it, so we'll see when the test boards arrive later 
>>> this week.
>>> 
>>> As part of the design, I wanted to make an emitter follower with a 
>>> decent amount of inductance in series with its tail resistor, to avoid 
>>> the transistor turning off on fast negative edges and causing linearity 
>>> problems.
>>> 
>>> Searching on Digikey, I found this very interesting part:
>>> <https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82498F1472J000/697521>.
>>> 
>>> 4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_, 
>>> which is several times higher than many other parts of that description. 
>>> That corresponds to an effective parallel capacitance of 0.12 pF, 
>>> about that of a resistor of the same size, despite all the copper windings.
>>> 
>>> Pretty nifty, if true.  (Parts on order.)
>> 
>> As you say, nifty. Do you have some means of verifying that Fo claim,
>> Phil? Even a NanoVNA would give a pretty good idea if it's really that
>> high.
>> 
>Sure, SRF measurements aren’t super subtle. 
>
>Cheers 
>
>Phil Hobbs 

Good show. I'd be interested to know the result.