Nikolai Golovchenko wrote:

> Is this the same as phase accumulators?

  I beg to differ from Tracy.  I think it is.  Phase accumulators are
based on the principle of - as the name suggests - adding up little
pieces of the cycle and "rolling over" when the sum of these amounts to
or in fact exceeds, a full cycle.

  That appears to be exactly what is suggested here; you would be using
a phase accumulator to control the up/ down ramp of the wave, then
filtering it further in analogue circuitry.  It begs the question though
of using a full-blown phase accumulator/ DDS with (a number of stages
of) integration.

  Once you go the DDS path, you are in a position to vary the slope of
the waveform during the cycle, by using even a simple resistive DAC,
(or perhaps PWM) which *greatly* eases the requirements on your
integration/ low-pass filtering.

  I would think that even a 3-bit (six resistor) ADC would considerably
improve performance, and perhaps allow output of both tones via the one
channel (though Dave Van Horn's "twist" would still be a difficulty).
--
  Cheers,
        Paul B.  (away from home for a day or so!).