A memory effect distortion component compensating unit compensates for a distortion component caused by a memory effect of an amplifier by using a time difference of results from raising an input signal to even power. For example, the amplifier may include a memory effect distortion component compensating unit having an even power raising unit for raising an input signal to even power, an even power raising result delaying unit for delaying a signal of a result of even power raising, an even power raising result time difference detecting unit for detecting a difference between a signal of an even power raising result and a delayed signal, an input signal multiplying unit for multiplying a signal of a detection result by an input signal, a distortion compensation coefficient multiplying unit for multiplying a signal of a multiplication result by a distortion compensation coefficient, and a distortion compensation coefficient multiplication result adding unit for adding an input signal and a signal of a multiplication result.
A digital predistorter comprises a module J for producing a counteracting signal V.sub.m1 for combination with the input signal of a power amplifier to correct the output of the amplifier for distorting memory effects within the amplifier. The module J produces the contracting signal V.sub.m1 by convolving (see FIG. 6) functions of the input signal with impulse response characteristics related to the memory effects being corrected. The counteracting signal V.sub.m1 is produced by a function f.sub.m and parameters in that function are adjusted to minimize any residual distortion in the amplifier output.
A predistorter for correcting distortion caused by a memory effect in amplifying a signal by an amplifier is provided. In the memory PD 2 provided to the predistorter, the level detection means 21 detects the level of the signal, the coefficient output means 22 outputs the coefficient corresponding to the detected level, the delay means 23 delays the output coefficient, the difference detection means 24 detects the difference between the output coefficient and the delayed coefficient, the multiplication means 25 multiplies the detected difference with the signal, and the combination means 26 combines the result of the multiplication and the signal. Thus, the result of the combination is output to the amplifier.
