Modulation system capable of accurately compensating for nonlinearities of an amplifier connected thereto

摘要

In a modulation system responsive to a first sampled signal (31) of a first sampling rate for supplying a modulated analog signal to an amplifier having nonlinearities to make the amplifier produce an amplified output signal, a selector (72) selects the first sampled signal and a second sampled signal of a second sampling rate as a selected signal when supplied with first and second control signals, respectively. The second sampling rate is equal to 1/N (N: 2, 3, ...) of the first sampling rate. A processing arrangement (36) processes the selected signal with reference to a difference between the selected signal and an additional digital signal (35) to compensate for the nonlinearities to produce a processed signal. The processed signal is modulated into the modulated analog signal. The amplified output signal is demodulated and converted into the additional digital signal by a converter (40). A comparator (71) compares an absolute value of the difference with a threshold value and produces the first control signal when the absolute value is less than the threshold value. Otherwise, the second control signal is produced. A controller (78) may control a phase of a sampling signal supplied to the converter so that a quotient of the difference by a differential of the selected signal becomes equal to zero.