Phase inversion
Encyclopedia
Phase inversion means the swapping of the two poles of an alternating current source. A phase inversion is neither a time shift nor a phase shift, but simply a swap of plus and minus.
For example, in a push-pull
power amplifier using vacuum tube
s, the signal is most often split by a phase splitter
(aka phase inverter) stage which produces two signals, one in phase, and the other out of phase, that is, phase inverted. These two signals then drive the two halves of the first push-pull stage, which may be either the output stage (in which case the phase splitter will be in between the driver stage if there is one and the output stage) or the driver stage. The other common arrangements for driving a push-pull stage are by using an isolation transformer
to produce the split signals, or by using the in-phase half of the first push-pull stage to drive the other half. A common circuit using this last technique is the long-tailed pair, often seen in television set
s and oscilloscope
s.
In solid state electronics all of these techniques can be used, and phase inversion can also be produced by the use of NPN/PNP complementary circuitry, which has no corresponding technique in vacuum tube designs.
Phase inversion may occur with a random or periodic, symmetrical or non-symmetrical waveform
, although it is usually produced by the inversion of a symmetrical periodic signal, resulting in a change in sign. A symmetrical periodic signal represented by f (t ) = A ejωt, after phase inversion, becomes f 1(t ) = Aej(ωt +π), where t is time
, A is the magnitude of the vector, ω is angular frequency
(ω = 2πf ), where f is the frequency and π ≈3.1416 and e ≈ 2.7183. The algebraic sum of f (t ) and f 1(t ) will always be zero.
For example, in a push-pull
Push-pull
Push–pull may refer to:In electronic technology:*Push–pull output, type of electronic circuit*Push–pull converter, in electronics, is a type of DC to DC converter that uses a transformer*Push–pull connector, an electronic cable connector...
power amplifier using vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s, the signal is most often split by a phase splitter
Phase splitter
A phase splitter is a device that separates a signal into multiple phases .The term is most often applied to amplifiers that produce two "balanced" voltage outputs: of equal amplitude but opposite polarity , but sometimes is used to refer to the generation of quadrature signals...
(aka phase inverter) stage which produces two signals, one in phase, and the other out of phase, that is, phase inverted. These two signals then drive the two halves of the first push-pull stage, which may be either the output stage (in which case the phase splitter will be in between the driver stage if there is one and the output stage) or the driver stage. The other common arrangements for driving a push-pull stage are by using an isolation transformer
Isolation transformer
An isolation transformer is a transformer used to transfer electrical power from a source of alternating current power to some equipment or device while isolating the powered device from the power source, usually for safety...
to produce the split signals, or by using the in-phase half of the first push-pull stage to drive the other half. A common circuit using this last technique is the long-tailed pair, often seen in television set
Television set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
s and oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
s.
In solid state electronics all of these techniques can be used, and phase inversion can also be produced by the use of NPN/PNP complementary circuitry, which has no corresponding technique in vacuum tube designs.
Phase inversion may occur with a random or periodic, symmetrical or non-symmetrical waveform
Waveform
Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...
, although it is usually produced by the inversion of a symmetrical periodic signal, resulting in a change in sign. A symmetrical periodic signal represented by f (t ) = A ejωt, after phase inversion, becomes f 1(t ) = Aej(ωt +π), where t is time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
, A is the magnitude of the vector, ω is angular frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
(ω = 2πf ), where f is the frequency and π ≈3.1416 and e ≈ 2.7183. The algebraic sum of f (t ) and f 1(t ) will always be zero.