Balanced
From Free net encyclopedia
See also balance, equilibrium.
In electronics, a balanced signal is one that is expressed as the difference between two conductors, as opposed to an unbalanced signal that is expressed as the difference between one conductor and a reference earth.
Low voltage differential signaling, twin-lead and standard low-impedance microphone cables are all examples of balanced signals. In all three of these applications, noise in a cable run is reduced by the fact that the noise is picked up equally by both conductors, and so the signal expressed as the difference between them is unaffected, with the noise cancelling out.
Practically: In a balanced system there are 3 wires carrying the signal: ground, hot and cold. Hot and cold have the signal but inverted compared to each other (eg. +2V and -2V). If we would just combine both signals, they would cancel each other out. On the receiving end however, we invert the 'cold' signal to get the correct output signal. Since any interference is introduced in the same way on both wires (for example +1V), the hot wire will have the interference (+1V) and the cold wire after inverting will have the interference in the opposite way (-1V) and when both signals are combined, the interference is cancelled out.
A push-pull amplifier stage is another example of a balanced circuit. In the traditional push-pull power amplifier circuit, the unbalanced signal is converted to balanced by a phase-splitter stage between the driver and power stages. The balanced signal may then be converted back to unbalanced by an output transformer (common in valve amplifiers) or may be used directly (common in transistor amplifiers).
A device that converts a balanced signal to unbalanced or vice versa is known as a balun.