Digital electronics involves the study and engineering of digital signals in contrast to analog signals. Digital circuits are made from assemblies of logic gates that are often packaged into integrated circuits. There are two types of signals - analog or continuous signals, and digital or discrete signals. Digital electronics deals with processing digital signals for controlling systems. Logic gates are basic building blocks of digital systems, with inputs and a single output. Common logic gates include AND, OR, and NOT gates. AND gates output high only when all inputs are high, while OR gates output high if any input is high. NOT gates invert the input signal.