Importance

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Abstract

Methods and apparatus for dynamically calibrating a modulator in a radio transmitter are provided. In a preferred embodiment an In-Phase and Quadrature (I/Q) modulator in a radio modem is calibrated by means of a modulator, a digital signal processor and a power sensor. The modulator being electrically adapted to receive a local oscillator input having a carrier frequency and a substantially direct current (DC) input having an amplitude in order to produce an output having a power magnitude at the carrier frequency in a frequency defined power spectrum. The power sensor being in electrically succession to the modulator to measure the power magnitude of the output to permit the digital signal processor (DSP), electrically between the modulator and the power sensor, to compare the measured power magnitude with a minimum threshold power magnitude to determine which is greater. If the power magnitude is greater, the DSP reiteratively alters the amplitude of the DC input until the measured power magnitude of the output is less than the minimum threshold power magnitude. The minimum threshold power magnitude is preferably stored in the digital signal processor and defines a suitable power magnitude threshold at the carrier frequency beneath which the carrier frequency component will be substantially suppressed. Thereafter, the appropriate amplitude of the DC input which enabled the power magnitude of the output to fall below the minimum threshold is established in the DSP as a temporary calibration coefficient for a selected duration of time. The selected duration of time being the time from the powering on until the powering off of the radio modem or until the transmitter is selected for re-calibration by the user.

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First Claim