US 5,493,710 AGranted

Communication system having oscillation frequency calibrating function

AssigneeHitachi, Ltd.

InventorsYasuaki Takahara, Shigeyuki Sudo

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Abstract

A communication system which includes a receiving section having a frequency convertor for converting a received signal into an intermediate frequency signal by mixing with a local oscillation signal, and a demodulator for demodulating the received signal converted into the intermediate frequency signal, a transmission section for modulating a transmission signal received thereby, to transmit the so modulated signal, and an input/output section for receiving the demodulated signal from the receiving section and outputting it externally and receiving the transmission signal externally and outputting it to the transmission section. The receiving section includes a local oscillator for generating the local oscillation signal, reference frequency generator for generating a reference signal, calibration signal generator for generating a calibration signal having a predetermined frequency based upon the reference signal, to input the calibration signal to the frequency converter, counter for counting the frequency of the intermediate frequency signal, and corrector for detecting a frequency error based upon the counted value of the intermediate frequency signal. The frequency converter converts the calibration signal into the intermediate frequency signal by mixing with the local oscillation frequency. The counter counts the frequency of the calibration signal converted by the frequency converter as the intermediate frequency signal. The corrector detects the frequency error from a frequency difference between the counted value of the calibration signal and a predetermined intermediate frequency reference value, thereby generating a signal for frequency correction based upon the thus detected frequency error.

Claims17

Dependent claims

A mobile communication system comprising:

a receiving section which includes first and second local oscillating means each for generating first and second local oscillation signals, respectively, first frequency converting means for converting a received signal into a first intermediate frequency signal by mixing with said first local oscillation signal, second frequency converting means for converting the received signal converted into said first intermediate frequency signal into a second intermediate frequency signal by mixing with said second local oscillation signal, reference frequency oscillating means for generating a reference signal having a predetermined reference frequency, calibration signal generating means for generating a calibration signal based on said reference signal generated from said reference frequency oscillating means, and a demodulator for demodulating the received signal converted into said second intermediate frequency signal;
a transmission section for modulating a transmission signal;
and
an input/output section for receiving the demodulated signal and outputting the transmission signal,
wherein said receiving section has frequency control means for controlling an oscillation frequency of said reference frequency of said reference frequency oscillating means based on the received signal converted into said second intermediate frequency signal, and correcting means for correcting said second local oscillating means based on a calibration signal converted into said second intermediate frequency signal in which said calibration signal from said calibration signal generating means is inputted to an input of said second frequency converting means;
said first local oscillating means generates said first local oscillation signal based on the controlled reference signal of said reference frequency oscillating means;
and
said calibration signal generating means generates said calibration signal which is controlled based on said reference signal generated by the controlled reference frequency oscillating means.

5 more elements

A communication system comprising a receiving section which includes first frequency converting means for converting a received signal into a first intermediate frequency signal by mixing with a first local oscillation signal, second frequency converting means for converting the received signal converted into said first intermediate frequency signal into a second intermediate frequency signal by mixing the received signal converted into the first intermediate frequency signal with a second local oscillation signal, a demodulator for demodulating the received signal converted into the second intermediate frequency signal, a transmission section for modulating a transmission signal and an input/output section for receiving the demodulated signal from the receiving section and outputting it externally and receiving the transmission signal externally and outputting it to the transmission section,

said receiving section including:
reference frequency generating means for generating a reference signal;
calibration signal generating means for generating a calibration signal of said first intermediate frequency based on said reference signal;
and
frequency estimating and correcting means for detecting a frequency error of said reference frequency generated by said reference frequency generating means and outputting an oscillation frequency control signal to said reference frequency generating means based on the detected frequency error,
said reference frequency generating means being controlled based on said oscillation frequency control signal, with respect to an oscillation frequency of said reference signal,
said second frequency converting means converting, in addition to the received signal converted into said first intermediate frequency signal, said calibration signal of said first intermediate frequency signal into a second intermediate calibration frequency signal by mixing said calibration signal of said first intermediate frequency signal with said second local oscillation signal;
and
said frequency estimating and correcting means detecting a frequency error A between said second intermediate frequency calibration signal converted by said second frequency converting means and a predetermined reference intermediate frequency, detecting a frequency error C which is determined by subtracting the frequency error A from a frequency error B which is a frequency difference between the received signal converted into said second intermediate frequency signal and said predetermined reference intermediate frequency and outputting said oscillation frequency control signal based on the detected frequency error C.

6 more elements

Dependencies are inferred from the claim text.