Abstract: A distortion compensating circuit for a power amplifier attains raised compensating accuracy with shorter convergence time by accurately and quickly generating a distortion compensation signal for pre-distortion. An error signal representing the difference between the input and output signals of the power amplifier is generated. From the error signal and the input signal, the coefficients of the third-order intermodulation distortion, fifth-order intermodulation distortion and seventh-order intermodulation distortion are calculated. According to these coefficients, a distortion compensating signal which is characteristically opposite in phase and gain to the intermodulation distortions is generated.

Abstract: A distortion compensating circuit for a power amplifier attains raised compensating accuracy with shorter convergence time by accurately and quickly generating a distortion compensation signal for pre-distortion. An error signal representing the difference between the input and output signals of the power amplifier is generated. From the error signal and the input signal, the coefficients of the third-order intermodulation distortion, fifth-order intermodulation distortion and seventh-order intermodulation distortion are calculated. According to these coefficients, a distortion compensating signal which is characteristically opposite in phase and gain to the intermodulation distortions is generated.

Abstract: A fractional-N system frequency synthesizer and a field pickup unit which uses the synthesizer and adapts to a plurality of different channel frequencies in a microwave band. The synthesizer is made up of a fractional control unit which in turn is made up of a modulo-m counter which counts signals of a predetermined frequency fed from a reference oscillator, a channel setting unit for setting a required channel frequency in a predetermined frequency band and for outputting data on the set channel frequency, a memory which stores information on a dividing ratio at an address determined by the count of signals counted by the modulo-m counter and the data on the set channel frequency outputted by the channel setting unit, wherein switching pulses each for selecting a dividing ratio in a dual modulus prescaler are dispersively arranged at equal intervals in the counting period of the modulo-m counter. The field pickup unit is made up of a transmitter and a receiver.

Abstract: An amplifier includes an amplifying section for simultaneously amplifying a plurality of input signals having different frequency bands, a distortion extracting section for separating and extracting at every different frequency bands a distortion component from a plurality of signals having the different frequency bands outputted from the amplifying section, a distortion compensation section for adjusting independently at every different frequency bands the phase and the amplitude of the distortion component separated and extracted at every different frequency bands and a distortion eliminating section for canceling and outputting a distortion component from a plurality of signals having the different frequency bands outputted from the amplifying section based on the distortion component adjusted at every different frequency bands.

Abstract: A digital demodulator which demodulates an analog signal obtained through a quadrature amplitude modulation to produce a digital demodulated signal includes a converter to convert the analog signal into a digital signal and a signal processor to quadrature-demodulating the digital signal from the converter. Assuming that the analog signal has a carrier frequency of f.sub.IF and the signal conversion is accomplished with the sampling frequency fs, the demodulator is set to satisfy fs=4.multidot.f.sub.IF /(2n+1), where n denotes a positive integer. The signal processing section conducts the quadrature demodulation according to a quadrature local oscillation signal having a frequency fc satisfying fc=fs/4.