This circuit modifies Square input pulses into saw teeth pulses with volume potentiometer control.When input is high left PNP Tr is bias and capacitor charge that time right PNP Tr is open circuit.When input goes low then left Tr, is open (no cap charge) and the right Tr is closed circuit and capacitor discharge, and vise versa.If you change Duty cycle of the input pulse you should need change the value of resistor pot.OP amp duty is a comparator.
