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Nov 2, 2013 (4 years and 7 days ago)

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Re: low-noise sot-23 BJT transistors
Source: http://sci.tech-archive.net/Archive/sci.electronics.design/2007-08/msg00682.html
From: "Howard Swain" <hswain@xxxxxxxxxxxxx>·
Date: Fri, 3 Aug 2007 11:19:11 -0700·
Hi Win,
"Winfield" <winfieldhill@xxxxxxxxx> wrote in message
news:1186103561.731608.237960@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'd like to take noise measurements now, but my
venerable HP 4470A has just gone on the fritz.
Perhaps in a week or two I can find the time to
repair it. Meantime, I've ordered a selection
of currently-available transistors from several
manufacturers to evaluate.
Actually, all the '6429 datasheets I have in my
computer show it to be a small-die transistor,
best suited to operation below 100uA or so.
What 2N6429 datasheet do you have that shows
better results for low-Z source impedances
(e.g., under 500-ohms)?
The Motorola data sheet for 2N6428 and 2N6429 dated 1977.
At 1 mA and 1kHz, this shows En as about 1.4 nV per root Hz and
In as 0.8 pA per root Hz as typical. I assume this is for the 2N6429,
which had the higher hFE.
Cob is spec'ed as 3 pF max at 10 V.
fT typically peaks at 400 MHz at about 10 mA and 5 V Vce.
Where it really shown for us was with a 50 ohm source
impedance and 10 Hz. I calculate about a 6 dB noise figure
at 1 mA bias.
--
Regards,
Howard
hswain@xxxxxxxxxxxxx
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