Re: square to sine

On Sun, 06 Nov 2005 15:57:29 +0000, Bob Eldred wrote:

> Another idea is the synthesizer scheme: Use the squarewave to switch an
> integrator to ramp positive then negative on each half cycle producing a
> triangle wave from the square wave. Run the triangle wave into an automatic
> gain stage to generate a constant amplitude. Use a diode-resistor shaping
> network to round the triangle wave into a sine wave form. Run this into
> another variable gain stage controlled by the amplitude of the original
> square wave to re-constitute the original amplitude of the square wave for
> the sine wave.
>
> This scheme creates a sine and triangle wave out of the square wave and can
> work over a range of frequencies. If the amplitude is not important, the
> variable gain stages can be ommited.

The OP can see this in action (or a similar scheme in action) by searching
for and viewing the ICL8038 datasheet. It uses this scheme by making a
triangle wave from a couple of current sources and a flipflop, and runs it
through an array of PNP transistors. There is a schematic for the chip in
the datasheet.

The ICL8038 is now quite pricy, since it appears to be out of production.
However, so you may as well go for the Cadillac:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/650

or

http://www.futurlec.com/Maxim/MAX038CPP.shtml

For $20, you can get a signal generator on a chip that goes from .1Hz to
20MHz. It also appears to feature a PLL input, which allows the chip to
lock the chip to an external reference, such as a square wave. I haven't
spent much time looking at it, but it might be just the thing the OP needs.

---
Regards,
Bob Monsen

When earlier, new functions were invented, the purpose was to apply them.
Today, on the contrary, one constructs functions to contradict the
conclusions of our predecessors and one will never be able to apply them for
any other purpose.
- Poincare
.

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