Return-to-zero (RZ or RTZ) describes a
line code
In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained ...
used in
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...
s
signals in which the signal drops (returns) to zero between each
pulse
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the n ...
. This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal is
self-clocking
In telecommunications and electronics, a self-clocking signal is one that can be decoded without the need for a separate clock signal or other source of synchronization. This is usually done by including embedded synchronization information withi ...
. This means that a separate clock does not need to be sent alongside the signal, but suffers from using twice the bandwidth to achieve the same data-rate as compared to
non-return-to-zero
In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negat ...
format.
The "zero" between each bit is a neutral or rest condition, such as a zero amplitude in
pulse-amplitude modulation
Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulse ...
(PAM), zero
phase shift in
phase-shift keying
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs ...
(PSK), or mid-
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
in
frequency-shift keying
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather bal ...
(FSK).
That "zero" condition is typically halfway between the
significant condition
In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in ''b ...
representing a 1 bit and the other significant condition representing a 0 bit.
Although return-to-zero (RZ) contains a provision for synchronization, it still has a
DC component
DC, D.C., D/C, Dc, or dc may refer to:
Places
* Washington, D.C. (District of Columbia), the capital and the federal territory of the United States
* Bogotá, Distrito Capital, the capital city of Colombia
* Dubai City, as distinct from t ...
resulting in “baseline wander” during long strings of 0 or 1 bits, just like the line code
non-return-to-zero
In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negat ...
.
Return-to-zero in optical communication
Return to zero, inverted
Return-to-zero, inverted (RZI) is a method of mapping for transmission. The two-level RZI signal has a
pulse
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the n ...
(shorter than a
clock cycle
In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits.
A clock sig ...
) if the binary signal is 0, and no pulse if the binary signal is 1. It is used (with a pulse 3/16 of a bit long) by the
IrDA
The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1994 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and the name "IrDA" also ...
serial infrared (SIR) physical layer specification. Required bandwidth for this kind of modulation is: BW = R(data rate).
Bipolar return-to-Zero (bipolar RZ)
For bipolar return-to-zero (bipolar RZ), a binary one is encoded as +V volts, a binary zero is encoded as −V volts, and 0 volt is used to provide padding and separation between bits.
Bipolar return-to-zero encoding is used by the
ARINC 429
ARINC 429, "Mark33 Digital Information Transfer System (DITS)," is also known as the Aeronautical Radio INC. (ARINC) technical standard for the predominant avionics data bus used on most higher-end commercial and transport aircraft. It defines the ...
bus.
See also
Other line codes that have 3 states:
*
Hybrid ternary code
*
Bipolar encoding
*
MLT-3 encoding
*
4B3T
References
Further reading
*
{{DEFAULTSORT:Return-To-Zero
Encodings
Line codes