Analog

Analog describes a continuously variable signal, or a circuit or device designed to handle such signals. The opposite of analog is "discrete" or "digital".

Background
s are much harder to design and analyze than digital ones because the designer must take into account effects such as the, and power handling of components, the ,  and  of  tracks, wires and connectors,  between signals,  stability, and more. A design, especially for high  speeds, must also take these factors into account if it is to work reliably, but they are usually less critical because most digital components will function correctly within a range of parameters whereas such variations will corrupt the outputs of an analog circuit.