Hello Simon,
Squaring the sine wave is a good way to get a synchronized double-frequency wave, as this uses the trig identity:
sin^2(theta) = 0.5*(1-cos(2*theta))
Problem is, since the result includes a cosine, it's phase shifted 90 degrees from where you want it (or, 45 degrees from the original sine wave). To fix this, you'll need to do a 45 degree shift ahead of the square. As you pointed out, a delay or filter would work but would not be preferable. The method shown below avoids these, and in addition it keeps the two outputs correctly phased even with an adjustable frequency.
Recent versions of SigmaStudio include a Quadrature VCO block; version 3.9 Beta added this feature to the ADAU1701/2.. It outputs both a sine and a cosine wave. Adding these together provides a 45-degree shifted wave. This in turn can be squared to provide your double-frequency output. Fundamental frequency is set by the DC source:
V = 2* f / fs
In the above example, I set the frequency to only 0.1 Hz, to view the outputs on two Real-Time Displays. To make this run at 10KHz, set the DC source to 0.41667
When I tried this the two Real-Time Displays did appear to go through zero simultaneously, although the real test will be when you run it full speed and view the results on your scope.
Best regards,
Bob
