[sdiy] improved dynamic range diffpair-vca

[JH.]

> To me that looks almost like a free meal. Where's the drawback?

Is it true that it has 6dB SNR improovement?
I would expect 3dB ( SQRT(2) times noise, vs. 2 times signal level ) - just 
as with two pairs in parallel.

JH.

----- Original Message ----- 
From: "np" <np at planetarc.de>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, April 24, 2007 11:08 PM
Subject: [sdiy] improved dynamic range diffpair-vca


Hi list, and hello to some old-timers who remember me.. I've been away
from the list for several years....

Is anyone familiar with this circuit here:

http://www5b.biglobe.ne.jp/~houshu/synth/Vca0302.gif

It's a long tailed pair with two extra transistors working as diodes.
Not the same configuration as the linearization diodes we have in some
OTA's. I gave it a try using a CA3046 transistor array, and it just
magically works. I can drive the input up to 50mVpp with low distortion.
Nearly twice as much as without the extra trannies.

To me that looks almost like a free meal. Where's the drawback?

And could someone please shed some light on why these "diodes" work and
what they do? They somehow linearize the input for sure, but I have no
clue what exactly is going on here.

Thanks in advance,
  Nils




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