A monostable multivibrator has one stable state in which it can remain indefinitely. It can be triggered externally to another quasi-stable state. A monostable multivibrator can thus be used to generate a pulse of desired width.
The desired pulse width is set by adjusting the values of C2 and R4. The resistor divider of R1 and R2 can be used to determine the magnitude of the input trigger pulse. The output will change state when V1 < V2. Diode D2 provides a rapid discharge path for capacitor C2 to reset at the end of the pulse. The diode also prevents the non-inverting input from being driven below ground.