Return-to-zero (RZ or RTZ) describes a
line code
In telecommunications, a line code is a pattern of voltage, current, or photons used to represent digital data transmission (telecommunications), transmitted down a communication channel or written to a storage medium. This repertoire of signal ...
used in
telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
signals in which the signal drops (returns) to zero between
pulses. This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal is
self-clocking. 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 format.
The "zero" between each bit is a neutral or rest condition, such as a zero amplitude in
pulse-amplitude modulation (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 carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. I ...
(PSK), or mid-
frequency
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
in
frequency-shift keying
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used fo ...
(FSK).
That "zero" condition is typically halfway between the
significant condition 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
In signal processing, when describing a periodic function in the time domain, the DC bias, DC component, DC offset, or DC coefficient is the mean value of the waveform. A waveform with zero mean or no DC bias is known as a ''DC balanced'' or ''DC ...
resulting in “baseline wander” during long strings of 0 or 1 bits, just like the line code
non-return-to-zero.
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 (shorter than a
clock cycle) 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 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 bus.
See also
Other line codes that have 3 states:
*
Hybrid ternary code
*
Bipolar encoding
*
MLT-3 encoding
*
4B3T
References
Further reading
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{{DEFAULTSORT:Return-To-Zero
Encodings
Line codes