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From: Cursitor Doom
Newsgroups: sci.electronics.design
Subject: Re: Interesting inductor
Date: Thu, 14 Mar 2024 01:00:18 +0000
Organization: A noiseless patient Spider
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On Thu, 14 Mar 2024 00:03:54 -0000 (UTC), Phil Hobbs
wrote:
>Cursitor Doom wrote:
>> On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs
>> 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:
>>> .
>>>
>>> 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.