In electronics, an analog-to-digital converter (AD converter, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal . An AD converter may also provide an isolated measurement such as an electronic device that converts an input analog voltage or current to a digital number representing the magnitude of the voltage or current. A different approach to convert analogue voltage to a digital number has a comparator.