AW: [sdiy] improved dynamic range diffpair-vca

[Haible, Juergen]

> The dolby's patent shows a variable resistance cell using a 
> differential
> pair with a lot of diodes at the common emitter (Fig. 6). 
>   http://www.pat2pdf.org/patents/pat4068139.pdf
>   An OTA with 100% feedback works as a variable resistor.

Wow, that's an interesting way to look at it indeed!

My first reaction was: This has nothing to do with an OTA or
differential pair; it's just a cleverly folded diode stack. (Maybe to
avoid using a straight diode stack, who knows? EMS used  stacks of 10
diodes for the Phaser in their HiFli, for instance.)
It's also described as a diode stack in the patent text (column 7, lines
19ff).
And yet you are right: The same circuit can be considered as an OTA with
a "diode-degenerated emitter" differential pair, and 100% feedback (node
38 being both the OTA output and the inverting input).

Amazing!

JH.






> 
> It was published in 70's.  So, the Japanese patent application
> can not be patented  ;-)
> 
> Sam Hoshuyama
> Saitama, JAPAN
> 
> 
> From: Aaron Lanterman <lanterma at ece.gatech.edu>
> Date: 2007/04/26 03:28:30
> >
> > On Thu, 26 Apr 2007, HOSHUYAMA wrote:
> >
> > > Actually, what I saw the circuit topology was a patent 
> application (In
> > > Japan, almost all the patent applications becomes public 
> after one and a
> > > half years.) not a filed patent.
> > >
> > > A couple of years ago, I saw the same structure in a Japanese
> > > electronics book published in 80's. I guess, the structure was not
> > > patented.
> >
> > Interesting! Thanks!
> >
> > - Aaron
> >
> > 
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> >
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> > and Demetrius T. Paris Junior Prof.  Voice:  404-385-2548
> > College of Electri. and Comp. Eng.   Fax:    404-894-8363
> > Georgia Institute of Technology      E-mail: lanterma at ece.gatech.edu
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