auto duty cycle - for asymmetrical signals

for asymmetrical signals It is quite a common practice to use a schmitt trigger to generate a rec- tangular waveform from some other signal. The duty cycle and frequency at the output do, of course, depend on the form of the signal at the in- put but, other than that, the shape of this latter signal is relatively unim- portant. The one essential require- ment is that the signal must exceed, or at least reach, the triggering threshold of the schmitt trigger. With the circuit shown in figure 1 that is not necessarily so. In order to be able to process smaller signals a.c. coupling may be used and the signal need then only be greater than the hysteresis. The same sensitivity irrespective of the shape of the input signal. The ideal input to this circuit is a small signal fed to the schmitt trigger inverter via capacitor C1. The value at the output is averaged by means of R2/C2 and fed back to the input. The d.c. setting at the input is thus "tailored" to the amplitude of the in- put s...