US 2004/0165678 A1Published application

Method for measuring and compensating gain and phase imbalances in quadrature modulators

OwnerZivi Nadiriinventor

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Abstract

A simple and efficient method to measure base-band gain and phase imbalance as well as orthogonality phase imbalance in a quadrature (IQ) modulator (12). The method comprises estimating values of modulator gain and phase imbalances (34) while the modulator is operational, by inputting at least one test signal at a base-band frequency 2 fi and computing the imbalances based on the 2 fi term, the computed imbalances then used in normal transmit operation to generate a pre-distortion transformation on the transmit signal to generate an imbalance compensation. The method can be easily expanded to cope with frequency dependent base-band amplitude and phase imbalance. This feature has an advantage when the transmitted signal is a multi-carrier signal, as the compensation can be adapted for each individual carrier.

Claims6

Dependent claims

A method for calibrating a quadrature modulator having an I input and a Q input for inputting base-band I(t) and Q(t) signals, the modulator used to transmit quadrature modulated signals, comprising

a. estimating in sequence values of modulator gain imbalances and of modulator phase imbalances while the modulator is operational, said estimating including:
i. inputting at least one test signal at a base-band frequency fi to the modulator to generate detected output signals having a term at frequency 2fi, first in said gain imbalance estimation, then in said phase imbalance estimation, and
ii. computing said gain and phase imbalances based on said 2fi term of said detected output signals, and
b. in normal transmit operation, compensating first for said gain and then for said phase imbalances to obtain an essentially ideal quadrature modulated signal, said compensating including:
iii. inputting a transmission signal to the modulator, and
iv. based on said computed gain and phase imbalances, applying a pre-distortion transformation on said input transmission signal.

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