What is Analog-to-digital converters (ADC)? 

Before we dive into theory, we see how it look likes…

This is the pic of 8-channel, 50 ksps to 1 Msps, 12-bit A/D converter, manufactured by ST Microelectronics, a European company.

Can you count the pins in the above A/D convertor? yes, it has got 16 pins (only 8 pins are visible in the above pic since 8 are on another side which is not shown in the above pic).

So, what exactly a A/D convertor does?

In the A/D convertor, A stands for analog, D for digital … means a device that convertor analog to digital is known as A/D convertor.

but what is analog and what is digital.

for understanding this,

businesswoman talking on cell making notes

Here there is a woman holding a mobile in her hand and talking to someone.

her sound is analog sound waves means a sound signal is here an analog signal.

Now her sound (analog signal) is converted to digital signal (binary 0 or 1) by the A/D convertor.

The processor and SIM than transmit the voice available in the binary to Electromagnetic waves.

Now the person on another side receives/hear her voice after his/her phone converts the electromagnetic waves into digital signal than from digital signal to sound signal (analog signal).

Now at this end, this conversion from digital to analog signal (sound signal) is done by D/A Digital to Analog convertor.