The pulse wave on the right represents the assumed regular discharge mechanism* of the oscillator (i.e. pin 3 of a 7555 chip); the 100k resistor under the charge capacitor and discharge MOSFET represents the oscillator's voltage-controlled current source. The button on the left represents an external Sync input signal. The bottom op-amp buffers the combined discharge pulses for the Sync output. *Note the simulation limitation of using the righthand pulse wave to represent the discharge mechanism; in reality, the oscillator will start back at phase 0 every time the external sync trigger occurs. I'm a self-taught noob, so comments and suggestions are most welcome. I'm working on a prototype VCO, of which this subcircuit will be a part.
