[time-nuts] Re: +1/f of transistors

[Joseph Gwinn]

On Sun, 03 Apr 2022 03:30:27 -0400, time-nuts-request at lists.febo.com 
wrote:
time-nuts Digest, Vol 216, Issue 4

> ------------------------------
> 
> Message: 6
> Date: Sat, 2 Apr 2022 07:36:27 -0700
> From: "Lux, Jim" <jim at luxfamily.com>
> Subject: [time-nuts] Re: +1/f of transistors
> To: time-nuts at lists.febo.com
> Message-ID: <fa51db42-c572-810f-785c-3763ef25ee86 at luxfamily.com>
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> On 4/2/22 3:31 AM, Leon Pavlovic wrote:
>> Hello to all,
>> 
>> as Gerhard already mentioned, the 1/f data of transistors is really a
>> kind-of black magic stuff and almost never present in the datasheets.
> 
> Not only that, but it potentially changes from lot to lot.
> 
> Lately, I've been seeing papers using various microwave pHEMTs but, by 
> the time you find and read the paper, the part is no longer available. 
> And, of course, just like low noise MMICs (PGA-103, GALI-74) you have to 
> measure them yourself to find out - because the mfr only measures from 
> 50 MHz and up.

It's a big problem.  Nor do they specify DC parameters all that well.

 
> A good example is the 2018 paper by Chen, et al. which references the 
> ATF54143 - a 3 year old paper, and the part isn't available any more.  
> The 2SK117 shows up a lot in some older articles and app notes (e.g. 
> from Wenzel) - it's discontinued, but potentially available from some 
> surplus/obsolete dealers.
> 
> Exp Astron (2018) 45:231–253 <https://doi.org/10.1007/s10686-018-9576-3> 
> <https://link.springer.com/article/10.1007/s10686-018-9576-3>
>
> 
> There is a list in The Art of Electronics, but some of them won't be 
> available.   Some datasheets do have the curve - the JFE150 from TI has 
> its voltage noise curve right on the front page.

What those folk are currently using for capacitance multipliers and 
the like (where low 1/f noise is also essential) are SiGe transistors 
like the following:  BFP640H (Infineon), BFP780, SAV541 
(MiniCircuits), and 2S2114K (NPN, beta 1200) for high current 
applications.  And the best choices do keep going obsolete.  These 
have GHz gain-bandwidth products, and want to oscillate, so some base 
or gate resistance (often a ferrite bead) is necessary.  

There would be two applications in a low-noise oscillator.  One would 
be as a capacitance multiplier to filter the Vcc provided to the 
oscillator circuit, giving considerable PSRR.  The other would be in 
the oscillator circuit itself.

Joe Gwinn