The two main problems that face designers who have to integrate analog and digital circuits on the same PCB are:
• preventing digital switching noise from contaminating the analog signal, and
• interfacing the wide range of analog input voltages to the digital circuit.
Generating analog outputs from digital signals is not usually a problem. Generating digital inputs from analog signals is.
The high-frequency switching noise that was discussed earlier must be kept out of analog circuits at all costs. An analog-to-digital interface quantizes a variable analog signal into a digital word, and the number of bits in the word determines the resolution that can be achieved ...