Electronic – How to turn continuous signal into a short pulse using logic gates


Basically, I want to turn a continuous "1" into a short "1" pulse then "0". I'm new to logic gates, apologies if it's too obvious.

Best Answer

An XOR gate and a pair of inverters will do this if you don't need precise control over the pulse width.


simulate this circuit – Schematic created using CircuitLab

How it works:

An XOR gate output is high only when its inputs are at different states (i.e. 10 or 01). The two inverters add a small amount of delay to the signal seen on the bottom leg which gives you a brief moment when the inputs are different, leading to a pulse on the output whenever the line changes high or low. This is a very simple edge detector circuit.

If you need more delay you can add a resistor between the two inverters along with a capacitor between the resistor and input to the second inverter:


simulate this circuit

This adjusts the pulse delay by slowing down the signal even more. The values of the resistor and capacitor determine the delay. If you're going to be sticking analog elements into your digital design you may want to use Schmitt trigger inverters as they can better handle input signals which "wander" through the boundary between a logic 0 and logic 1.