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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Interesting inductor
Date: Thu, 14 Mar 2024 00:03:54 -0000 (UTC)
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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 


-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics