For detecting short pulses from a single sensor, a pulse stretcher is often required. The circuit of the figure above acts as a one-shot, stretching the width of an incoming pulse to a consistent ~100ns. The circuit works as follows: Comparator U1 functions as a threshold detector, and Comparator U2 functions as a one-shot. Comparator U1 is biased with a threshold of 11mV to overcome comparator and system offsets, and establish a low output in the absence of an input signal. An input pulse causes the output of U1 to go high, which then causes the output of U2 to go high. The output of U2 is fed back to the input of the 1st comparator, Timing Capacitor C now begins charging through R. After 100ns, U2 goes low, allowing U1 also to go low. A new pulse at the input of U2 can now restart the process. Timing capacitor C can be increased without limit for longer output pulses.
Tools & Simulations
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.
To launch ready-to-run LTspice demonstration circuits for this part:
Step 1: Download and install LTspice on your computer.
Step 2: Click on the link in the section below to download a demonstration circuit.
Step 3: If LTspice does not automatically open after clicking the link below, you can instead run the simulation by right clicking on the link and selecting “Save Target As.” After saving the file to your computer, start LTspice and open the demonstration circuit by selecting ‘Open’ from the ‘File’ menu.