Re: Dual sine wave generator with variable frequency and 90 degree phase difference

On Sep 6, 12:29 am, Rich Grise <r...@xxxxxxxxxxx> wrote:
On Fri, 05 Sep 2008 04:34:24 -0700, Ken S. Tucker wrote:
On Sep 3, 6:42 am, Steve <st...@xxxxxxxxxx> wrote:
I'm looking for a waveform generator that outputs two sine waves of
the same frequency with 90 degree phase difference (sine and cosine).
I need a variable frequency between 0.05 Hz and 10 Hz. Is there an
analog design that uses a single potentiometer or perhaps is voltage
controlled ? Low distortion is not a requirement.
Steve

You have a good idea. Use a phase shift oscillator,
http://en.wikipedia.org/wiki/Phase-shift_oscillator
but use 4 filters and make each filter shift 90 degrees
then lightly tap into the filter at any 90 degree point.
After that, I think MOSFETs can replace the resistors,
to provide a single voltage control or you'll need 4 pots.

I wonder howcome nobody's mentioned a "quadrature oscillator" e.g.http://www.ecelab.com/circuit-quadrature-oscillator.htm

Of course, with those low freqs, you'd need CMOS opamps and some
BMF caps and resistors. :-)

"state variable" == quadrature

It is being discussed in another subthread.
.

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