Tested -- works ....
This wave shaper needs an input saw that goes from Vss to
(ideally) Vdd. It works well with the 4069 VCO designed by
René Schmitz. Any saw will work as long as the wave is centered
halfway between the rails. It works as follows: The upper set of 2
linear mode gates provide an inverted and noninverted copy of the
saw. The 3 logic gates at the bottom provide a sort of comparator
that switches at halfway between the rails. The 4007 provides 2 P-MOSFETs
that alternately select the inverted or noninverted saw signal
depending on where the saw is in it's cycle. This causes the
ramp to reverse directions every half cycle. Any imperfection
in the saw will show up in the resulting output. The linear
mode gate furthest to the right provides soft clipping that turns
the triangle wave into something like a sine wave. It sounds
like it has fewer harmonics than the triangle.
To use with FatMan sawtooth output:
Power all ICs: Vdd = 0 volts, Vss = -12 volts. All ground symbols on schematic will go to -12 volts and all +V symbols go to ground.