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From: email@example.com (Jorge Omar)
Subject: Re: Diodes as collector load?
Date: 3 Sep 2002 05:38:10 -0700
NNTP-Posting-Date: 3 Sep 2002 12:38:10 GMT
I will try the Vbe multiplier solution and compare distortion.
Re transistors - the ZTX1048 is a 5A TO-92 super beta device...
Back in '75 I've used a VHF one (BF200), which also had very low
Any suggestion for lower noise (and low distortion)?
Win Hill wrote in message news:...
> Jim Thompson wrote...
> >firstname.lastname@example.org (Jorge Omar) wrote:
> >| Re gain - 10 is enought for most decent phono inputs, and easily
> >| achievable with a string of 10 diode connected transistors of same
> >| type as the gain one.
> > I've designed variable gain amplifiers using "diodes" as loads
> > (everything was differential) and controlling gain by current
> > diversion. [ snip ]
> > For those of you not conversant with I/C techniques the use of diode
> > loads allows larger signal-handling (less distortion) in the input
> > differential-pair without using resistors.
> Right on. The transconductance gain of an un-degenerated common-
> emitter stage is qIc/kT, which creates considerable distortion into
> a fixed resistor R_L. On the other hand the resistance of a diode-
> connected transistor is kT/qIc, which nicely cancels the distortion,
> yeilding a gain of 1x. Ten transistor-diodes in series would give a
> gain of 10x, as would a single-transistor load, if its base was fed
> from its collector via a 9:1 resistive divider. Jim, what's your
> approach to retain a good noise figure for the first stage?
> - Win
> - Win
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