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

On Sep 7, 10:04 am, George Herold <gher...@xxxxxxxxxxxxx> wrote:
On Sep 6, 2:42 pm, JosephKK <quiettechb...@xxxxxxxxx> wrote:



On Sat, 6 Sep 2008 07:32:27 -0700 (PDT), George Herold

<gher...@xxxxxxxxxxxxx> wrote:
On Sep 4, 2:55 am, Robert Baer <robertb...@xxxxxxxxxxxx> wrote:
Jan Panteltje wrote:
On a sunny day (Wed, 03 Sep 2008 09:42:57 -0400) it happened Steve
<st...@xxxxxxxxxx> wrote in <205tb41td5tfa5n3esvim42940ikvhh...@xxxxxxx>:

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

2 x EPROM sine and cosine lookup table,
4046 VCO variable clock generator,
binary counter on EPROM address lines,
2 x 8 bits wide DA converter, 2 x lowpass.

For a 256 values per sine wave form, your clock should be max 2560 Hz.

NOT analog.
Use a ramp oscillator for constant amplitude; one stage generates a
square wave for integrating to the ramp.
Run a comparitor off the ramp (triangle); that will be 90 degrees WRT
the square wave.
The 2 square waves can be filtered with a simple 3-stage phase retard
filter.- Hide quoted text -

- Show quoted text -

I was going to sugest a ramp generator also... as a analog
solution..But I din't know if you can build the filter to work at 0.05
Hz! How much distortion can you handle?
George

Diode ladder waveshaping can handle triangle to sine conversion, down
to about 0.1 % THD. OP does not seem to be all that distortion
sensitive.- Hide quoted text -

- Show quoted text -

There you go a diode ladder waveshaper (do you have a reference?) and
and ramp-triangle wave circuit. I've copied a ramp generator out of
H&H that I run down to 1-2 mHz or so. (That's a small m as in 10^-3
Hz.) It uses a 100uF tantalum cap at the low freq. end.

You used to be able to get the whole thing in one package. It was I
think Intersil the made it.

Since your frequency is low, there is another option that you may want
to look at.

If you make 4 inverting amplifiers from a quad rail to rail op-amp,
you can get the sine function in 8 line segments. If the supplies are
well regulated, this method is less temperature sensitive than the
diode ladder method.

.

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