Two periodic waveforms whose phase difference is of their output period are said to have a quadrature phase relationship. The term is also used in communication systems to describe one of the components of orthogonal decomposition.
A composite signal described by its envelope-and-phase form can be decomposed to an equivalent quadrature-carrier (IQ) form as:
where represents a carrier frequency, and:
and represent possible modulation of a pure carrier wave: . The modulation alters the original component of the carrier, and creates a (new) component, as shown above. The component that is in phase with the original carrier is referred to as the direct or in-phase component. The other component, which is always 90° ( radians) out of phase, is referred to as the quadrature component.
Read more about Quadrature Phase: Uses
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