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

On Sep 6, 9:47 am, "Ken S. Tucker" <dynam...@xxxxxxxxxxxx> wrote:
On Sep 5, 9:14 am, MooseFET <kensm...@xxxxxxxxx> wrote:



On Sep 5, 7:34 pm, "Ken S. Tucker" <dynam...@xxxxxxxxxxxx> wrote:

Hi Steve.

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.
Ken

The phase shift oscillator is a bad idea for the OP's application.
You have to control 4 time constants. The state-variable option is
better because you only have to set two gains.

I think the joke is on me.
The differential of a sine wave is a cosine wave right?
So how do we measure the "rate of change" of a sine
wave?

Avoid measuring rate of change when you can. Integration gets you
from sin() to -cos() and -cos() to -sin()

Ken

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