Patent Number:
6,298,096
Title:
Method and apparatus for determination of predistortion parameters for aquadrature modulator
Abstract:
A transmit modulator which uses a quadrature modulator has a predistortionblock which produces a predistorted output signal. The predistortion blockpre-compensates for errors introduced by the quadrature modulator based ona set of predistortion parameters. The quadrature modulator receives theoutput signals from the predistortion block. The quadrature modulatorup-converts the I and Q channel signals and combines them. In the process,the quadrature modulator introduces errors. In calibration mode, asinusoidal wave at frequency f.sub.cal is applied to the input of thepredistortion block and a transformer is coupled to the output of thequadrature modulator. The transformer produces a digital representation ofa spectrum of the output of the quadrature modulator converted tobaseband. Spurious energy produced by the quadrature modulator errors butreduced by the effect of the predistortion block is generated at f.sub.caland .sup.2*f.sub.cal. A quadratic polynomial minimization calculatorreceives the output of the transformer. The quadratic polynomialminimization calculator determines a subsequent value of the predistortionparameters based upon a quadratic relationship between energies present inthe digital representation of the spectrum of the output of the quadraturemodulator at frequencies f.sub.cal and 2*f.sub.cal and the values of theprevious predistortion parameters.
Inventors:
Burgin; George H. (La Jolla, CA)
Assignee:
International Classification:
Expiration Date:
10/02/2013