Publisher Summary This chapter explains analog and digital signals and their interconversion. Bridging the gap between the analog and the digital at some point is important if one wants to market the latest gadget. The chapter discusses how to make the analog-to-digital leap. Analog means a continuously variable signal. It means that the item being measured can be chopped up into infinite little pieces over time. The simplest form of digital is two states: It's either there or not. Digital signals could be used to represent Boolean statements, one level indicating true and the other indicating false. Boolean logic is based on a digital representation of the world. Digital processing speeds eventually increased enough to take over almost all applications. An analog signal is converted to digital by chopping it up into chunks at predetermined time intervals. (This chopping is called the sample rate. The faster the sample rate, the higher the frequency that can be digitized.) Then the signal is measured at that point in time and assigned a digital value, which is called sampling the signal. Digital signals (typically represented as 1 or 0) can be crammed together to indicate different levels of analog. A single digit can indicate two levels. To convert a digital signal back to analog, the circuit has to simulate the analog signal it represents. This always requires some kind of filtering. There are many ways to convert digital to analog. One is by pulse width modulation (PWM). The digital PWM is fed into a low-pass filter that removes the switching frequency of the signal, essentially leaving an analog signal.