Digital signal
Simple digital signals represent information in discrete bands of analog levels.
In a digital signal, the physical quantity representing the information may be a variable electric current or voltage, the intensity, phase or polarization of an optical or other electromagnetic field, acoustic pressure, the magnetization of a magnetic storage media, etcetera.
The pulse trains in digital circuits are typically generated by metal–oxide–semiconductor field-effect transistor (MOSFET) devices, due to their rapid on–off electronic switching speed and large-scale integration (LSI) capability.
[8][9] In contrast, bipolar junction transistors more slowly generate analog signals resembling sine waves.
The effects of interference are typically minimized by filtering off interfering signals as much as possible and by using data redundancy.
The two states are usually represented by some measurement of an electrical property: Voltage is the most common, but current is used in some logic families.
This means that during a short, finite transition time the output may not properly reflect the input, and will not correspond to either a logically high or low voltage.
Asymmetric Digital Subscriber Line (ADSL) over telephone wires, does not primarily use binary logic; the digital signals for individual carriers are modulated with different valued logics, depending on the Shannon capacity of the individual channel.
Asynchronous logic also exists, which uses no single clock, and generally operates more quickly, and may use less power, but is significantly harder to design.
