AW: Re[4]: F-V converter and Ring Mod. stuff

[Haible_Juergen#Tel2743]

> Note that, with an exponential VCO, the loop gain increases
> exponentially with frequency.  This is a good thing for tracking, as
> the tracking actually gets faster at higher pitches, but you'll get
> more of a spring effect too.  I 'spose it would be best if the filter
> could change tuning in parallel with the VCO.
>
> Some nonlinearities before the VCO could also help.

Just an idea:

The "nonlinearity" could be a logging circuit!
So we'd have:  Phase Comparator -> RC-Filter -> Log -> ExpVCO
The PLL loop sees a linear VCO then, and all the well-known PLL
theory would apply. And we could use the Log output for deriving
a V/8ve CV as desired.
Note that the Log circuit could be a very cheap one (without
temperature compensation), because the accuracy is only determined
by the exponential VCO (closed loop).

What do You think?

JH.