| 摘要 |
A transmit modulator which uses a quadrature modulator (102) has a predistortion block (100) which produces a predistorted output signal. The predistortion block (100) pre-compensates for errors introduced by the quadrature modulator (102) based on a set of predistortion parameters. The quadrature modulator (102) receives the output signals from the predistortion block (100). The quadrature modulator (102) up-converts the I and Q channel signals and combines them. In the process, the quadrature modulator (102) introduces errors. In calibration mode, a sinusoidal wave at frequency fcal is applied to the input of the predistortion block (100) (while the modulator output is downconverted with an AM-detector). Spurious energy produced by the quadrature modulator errors but reduced by the effect of the predistortion block (100) is generated at fcal and 2*fcal. The quadratic polynomial minimization calculator (166) determines a subsequent value of the predistortion parameters based upon a quadratic relationship between energies present in the digital representation of the spectrum of the output of the quadrature modulator (102) at frequencies fcal and 2*fcal and the values of the previous predistortion parameters.
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