Single-ended signaling is the simplest and most commonly used method of transmitting electrical signals over wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

s. One wire carries a varying voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 that represents the signal, while the other wire is connected to a reference voltage, usually ground

Ground (electricity)

In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....

.

The main alternative to single-ended signaling is called differential signaling

Differential signaling

Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analog signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, Ethernet , PCI Express and USB...

. There is also the historic alternative of ground return, rarely used today.

Single ended signaling is less expensive to implement than differential, but it lacks the ability to reject noise caused by:

1. differences in ground voltage level between transmitting and receiving circuits
2. induction picked up on the signal wire

The main advantage of single-ended over differential signaling is that fewer wires are needed to transmit multiple signals. If there are n signals, then there are n+1 wires - one for each signal and one for ground. (Differential signaling uses at least 2n wires.) A disadvantage of single-ended signaling is that the return currents for all the signals share the same conductor (even if separate ground wires are used, the grounds are inevitably connected together at each end), and this can sometimes cause interference ("crosstalk") between the signals.

Standards

Single-ended signaling is widely used, and can be seen in numerous common transmission standards, including:

• RS-232
  RS-232
  In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
  
   serial communications
• PS/2
  IBM Personal System/2
  The Personal System/2 or PS/2 was IBM's third generation of personal computers. The PS/2 line, released to the public in 1987, was created by IBM in an attempt to recapture control of the PC market by introducing an advanced proprietary architecture...
  
   mouse and keyboard connectors
• I²C
  I²C
  I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
  
   serial bus
• TTL
  Transistor-transistor logic
  Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...
  
   circuits
• CMOS
  CMOS
  Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
  
   logic circuits
• ECL
  Emitter coupled logic
  In electronics, emitter-coupled logic , is a logic family that achieves high speed by using an overdriven BJT differential amplifier with single-ended input, whose emitter current is limited to avoid the slow saturation region of transistor operation....
  
   circuits
• Most parallel computer buses, such as:
  • VMEbus
    VMEbus
    VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...
    
    
  • PCI
    Peripheral Component Interconnect
    Conventional PCI is a computer bus for attaching hardware devices in a computer...
    
    
• VGA
  Video Graphics Array
  Video Graphics Array refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution...
  
   video connectors
• SCSI
  SCSI
  Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
  
   interfaces for hard drives and other peripherals

Some kinds of connectors, though more often used for balanced pairs, are sometimes used for single-ended operation:

• RCA jacks for audio signals
• TRS connector
  TRS connector
  A TRS connector is a common family of connector typically used for analog signals including audio. It is cylindrical in shape, typically with three contacts, although sometimes with two or four . It is also called an audio jack, phone jack, phone plug, and jack plug...
  
  s for audio signals