[time-nuts] how to find low noise transistors

Charles Steinmetz csteinmetz at yandex.com
Sat Jul 25 01:45:50 UTC 2015


Brooke wrote:

>Does hFE (DC) have much relevance to this?  Would hfe (AC) be the 
>important one?

It depends on whether you are more interested in the 1/f noise, which 
causes most of the phase noise in oscillators and the additive 
("residual") PN in amplifiers, or the in-band noise.  As I said in 
the message to which you replied:

>Note that these are static (DC) curves, which are good 
>approximations for the 1/f region.  The curves in the white noise 
>region, even at relatively low frequencies like 1 kHz, generally 
>fall off faster than this as current is reduced, so the effect of 
>reduced beta on in-band noise figure is greater.

Best regards,

Charles






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