Hi Stefan,
here's a quick sketch of how I would
go about it. You wanted XORs so here's one with XORs ;-) But in this
circuit they serve basically only as inverting or noninverting opamps,
depending whether their other input is connected to the (+) supply or
(-) ground.
The top left part tries to pull the
duty cycle close to 50%. The AC voltage is reduced, and with the
negative DC feedback the comparator threshold settles to a point where
the avaerage output is at half supply voltage (eg 2.5V). BTW this is
the opposite function to the "duty cycle amplifier" which I use in
my automatic LF variometer df6nm.bplaced.net/LF/pictures/AutoTuner.zip .
The output circuit is an inverter
used for inverting one of the drives ;-) The pair of XORs should
equalize the gate delay.
The vox circuit at the bottom with
the rectifier is straightforward, including a bit of hysteresis
introduced by positive feedback.
Best 73,
Markus (DF6NM)
