Digital signal








The term digital signal has related definitions in different contexts.

In digital electronics

A five level PAM digital signal

In digital electronics, a digital signal is a pulse train (a pulse amplitude modulated signal), i.e. a sequence of fixed-width square wave electrical pulses or light pulses, each occupying one of a discrete number of levels of amplitude.[6][7] A special case is a logic signal or a binary signal, which varies between a low and a high signal level.

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, BJT transistors more slowly generate analog signals resembling sine waves.[8]

In signal processing


In digital signal processing, a digital signal is a representation of a physical signal that is sampled and quantized. A digital signal is an abstraction that is discrete in time and amplitude. The signal's value only exists at regular time intervals, since only the values of the corresponding physical signal at those sampled moments are significant for further digital processing. The digital signal is a sequence of codes drawn from a finite set of values.[10] The digital signal may be stored, processed or transmitted physically as a pulse-code modulation (PCM) signal.

In communications

A frequency shift keying (FSK) signal is alternating between two waveforms and allows passband transmission. It is considered a means of digital data transmission.

In digital communications, a digital signal is a continuous-time physical signal, alternating between a discrete number of waveforms,[3] representing a bitstream. The shape of the waveform depends the transmission scheme, which may be either a line coding scheme allowing baseband transmission; or a digital modulation scheme, allowing passband transmission over long wires or over a limited radio frequency band. Such a carrier-modulated sine wave is considered a digital signal in literature on digital communications and data transmission,[11] but considered as a bit stream converted to an analog signal in electronics and computer networking.[12]


Logic voltage levels



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. Two ranges of voltages are typically defined for each logic family, which are frequently not directly adjacent. The signal is low when in the low range and high when in the high range, and in between the two ranges the behaviour can vary between different types of gates.




To create a digital signal, an analog signal must be modulated with a control signal to produce it. The simplest modulation, a type of unipolar encoding, is simply to switch on and off a DC signal so that high voltages represent a '1' and low voltages are '0'.


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.


Clocking digital signals through a clocked flip-flop

Digital signals may be sampled by a clock signal at regular intervals by passing the signal through a flip-flop. When this is done, the input is measured at the clock edge, and the signal from that time. The signal is then held steady until the next clock. This process is the basis of synchronous logic.


See also

  • Intersymbol interference


  1. Robert K. Dueck (2005). Digital Design with CPLD Applications and VHDL. ISBN 1401840302. Archived from the original on 2017-12-17. Retrieved 2017-08-30. A digital representation can have only specific discrete values
  2. Proakis, John G.; Manolakis, Dimitris G. (2007-01-01). Digital Signal Processing. Pearson Prentice Hall. ISBN 9780131873742. Archived from the original on 2016-05-20. Retrieved 2015-09-22.
  3. Analogue and Digital Communication Techniques Archived 2017-12-17 at the Wayback Machine: "A digital signal is a complex waveform and can be defined as a discrete waveform having a finite set of levels"
  4. "Digital Signal". Archived from the original on 2016-03-04. Retrieved 2016-08-13.
  6. B. SOMANATHAN NAIR (2002). Digital electronics and logic design. PHI Learning Pvt. Ltd. p. 289. ISBN 9788120319561. Digital signals are fixed-width pulses, which occupy only one of two levels of amplitude.
  7. Joseph Migga Kizza (2005). Computer Network Security. Springer Science & Business Media. ISBN 9780387204734.
  8. "Applying MOSFETs to Today's Power-Switching Designs". Electronic Design. 23 May 2016. Archived from the original on 10 August 2019. Retrieved 10 August 2019.
  9. 2000 Solved Problems in Digital Electronics. Tata McGraw-Hill Education. 2005. p. 151. ISBN 978-0-07-058831-8.
  10. Vinod Kumar Khanna (2009). Digital Signal Processing. p. 3. ISBN 9788121930956. A digital signal is a special form of discrete-time signal which is discrete in both time and amplitude, obtained by permitting each value (sample) of a discrete-time signal to acquire a finite set of values (quantization), assigning it a numerical symbol according to a code ... A digital signal is a sequence or list of numbers drawn from a finite set.