Radio receiver apparatus of orthogonal detection type comprising local oscillator means with improved automatic frequency control arrangement

摘要

In a radio receiver apparatus of an orthogonal detection type, a voltage controlled first local oscillator generates a first local oscillation signal, and mixers mix an inputted reception signal with the first local oscillation signal and a 90 DEG shifted signal thereof, respectively, the mixed signals respectively being passed through first and second band-pass filters to obtain desired first intermediate frequency signals. Further, a second local oscillator generates a second local oscillation signal. Further mixers mixes the first intermediate frequency signals from the first and second band-pass filters with the second local oscillation signal and a 90 DEG shifted signal thereof, respectively. Then there is calculated either one of a sum of and a difference between the resulting mixed signals, the calculated signal being passed through a third band-pass filter to obtain a second intermediate frequency signal to be demodulated. Furthermore, an average frequency detector detects an average frequency of the second intermediate frequency signal for a predetermined time interval, and a frequency correction circuit controls the first local oscillation frequency of the first local oscillation signal based on the detected average frequency.