"Alan B. Pearce" <A.B.Pearce@RL.AC.UK> wrote:
> The only concern I see for these is the non-linearity of the LED versus
> the supplied voltage. Not sure how the circuit gets around this.

The LEDs are driven by current, not voltage. The 100K resistor makes sure
of that. Optoisolators are fairly linear with respect to current.

Russell McMahon <apptech@PARADISE.NET.NZ> wrote:
> Plus lack of matching plus aging.

Well, it does show a single-package quad optoisolator, but I don't know
whether those are usually monolithic internally. Even if they're not, the
individual pieces can probably be expected to come from the same batch,
maybe even the same wafer.

BTW, Googling for "Gilbert Cell" came up with this:
   http://www.ieee.org/organizations/pubs/newsletters/sscs/apr03/jssc2.html

-- Dave Tweed

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