I'd like to generate a 90 degree version of a sine wave concurrent with
the original. So far -

Digitise using an A2D and then output D2A 1/4f later. The limitations
would seem to be resolution and bandwidth. Advantage is that it would
work for any shape that's set by the duty cycle and for triangle too. And
the phase angle would be adjustable

But I wonder if there's an analogue way to delay a sinewave, nominally
at 50% duty cycle, over a wide band. From previous experience with
music effects I know that a capacitor is used to deliberately change the
phase in filters, tone controls and so on. And that the capacitor is active
at a particular frequency. I'm also aware of an op-amp as a capacitance
multiplier, which suggests, maybe, that a frequency tracking system could
be made to alter the capacitance and maintain the 90 degree shift. Is it
possible to make the angle of an analogue phase shifter adjustable ?

Any of that analogue idea practical, or should I just go with digitising and
make the best of it ?

TIA

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.