A one shot multivibrator generate a fixed width pulse at the output when the input is triggered. This fixed width output should be consistent, regardless the width of the input trigger. One example of one shot multivibrator circuit is shown in the following schematic diagram, which uses LM139 as the main active component:
The width of the output is determined by the 0.001 uF capacitor and the 1M resistor (Rp) connected to the noninverting input . The 10k resistor connected to the output of the op-amp is a pull up resistor, and you should choose the the period determining resistor (Rp) to be larger than ten times of the pull-up resistor to avoid loading effect on the output. The voltage divider resistors at the inverting input determine the minimum level of trigger’s amplitude. The thermal stability of the output’s pulse width can be kept low by choosing balanced thermal coefficient of the period determining resistor and capacitor, or use very low temperature coefficient components if not balanced. The width of this one shot multivibrator’s output pulse will be independent of the voltage supply, we can expect less than 2% pulse width changes caused by 5V changes in the supply voltage.