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

> On a sunny day (Wed, 03 Sep 2008 09:42:57 -0400) it happened Steve

> > wrote in : > > >>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. =A0Is there an > >>analog design that uses a single potentiometer or perhaps is voltage > >>controlled ? =A0Low 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. > > =A0 =A0NOT analog. > =A0 =A0Use a ramp oscillator for constant amplitude; one stage generates =
a
square wave for integrating to the ramp. > =A0 =A0Run a comparitor off the ramp (triangle); that will be 90 degrees =

WRT

the square wave. > =A0 =A0The 2 square waves can be filtered with a simple 3-stage phase ret=

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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

Reply to
George Herold
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The component values aren't too bad. 1M and 33uF can be had. You need to make it so it can be adjusted from the frequency. This is the hard part.

Reply to
MooseFET

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.

Reply to
JosephKK

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I was thinking about his driving home... I have a wavetek that does just this, (0.05 Hz to 10 Hz) with just one knob. What does that circuit look like? I also remeber these triangle wave "modifiers" that involved transistors in the feedback loop to give some sort of log(X)?? function that turned the triangle waves into approximate sine wave.

Reply to
George Herold

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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.

Reply to
George Herold

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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.

Reply to
MooseFET

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