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Abstract

A modulation system having in-phase and quadrature phase (IQ) calibration while on-line. The modulation system includes digital filters for converting I and Q data bit streams into filtered multilevel I and Q digital data streams, digital-to-analog converters for converting the digital data streams from digital to analog form, and an IQ modulator for converting the analog I and Q data streams into a modulated output signal having a representative IQ diagram having modulation states and transition locations between the modulation states. The digital filters include forward shifting memories having several samples of the data bit streams for each data bit time. The system also includes an on-line correction data state detector, an IQ correction code, and a scalar amplitude detector. The on-line correction state detector monitors the data states in the memory and detects the presence of particular data states that are expected to result in particular modulation states or transition locations. The amplitude detector monitors the modulated output signal and provides representative detected magnitudes. When one of the particular data states is detected the IQ correction code is triggered to compare the detected magnitude with magnitudes for others of the particular data states that have been detected and stored previously. The IQ correction code then uses the comparison to generate adjustments for I and Q offsets, I/Q phase, and I/Q gain.

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