AW(Andre): [sdiy] analogue phase modulation

[JH.]

>I have to admit that I didn't follow the presentation, but could you say
>again briefly how you keep the amplitude constant with this kind of phase
>shift?  You need A^2 + B^2 = const. , as I see it.  Sorry for the dumb
>question.

I run the control voltage CV thru a sin and cos converter:

A = sin (k*CV), B = cos (k*CV) , k being just a factor to get a range of 
+/-Pi for maximum CV swing.

==> A^2 + B^2 = 1    at all times.

Actually, I plan to do this:

A = 10V * sin (CV * Pi / 5V),  B = 10V * cos (CV * Pi / 5V),

for +/- 5V control voltage input range, and 10V output swing to drive a pair 
of AD633's.

The sin/cos shaper circuit needs a handful of opamps to create polygon 
approximations, and a 13600 with slight feedback for rounding.

JH.