Re: Interesting inductor

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.