Automatic frequency control method and device for use in receiver

Claim 2

The method according to claim 1, characterized in that the step of outputting frequency correction data comprises comparing digital data when the received signal is modulated with specific transmit data with a theoretical value when a received signal modulated with specific transmit data is converted to the normal intermediate frequency signal and outputting frequency correction data which permits the difference between the digital data and the theoretical value to be minimized.

Claim 3

The method according to claim 1, characterized in that when the received signal is modulated with plural pieces of specific transmit data, the step of outputting frequency correction data comprises comparing digital data of each of the plural pieces of specific transmit data with a corresponding theoretical value when a received signal modulated with each of the plural pieces of specific transmit data is converted to the normal intermediate frequency signal and outputting frequency correction data which permits the average of amounts of errors between corresponding digital data and theoretical value to be minimized.

Claim 4

The method according to claim 1, characterized in that the step of controlling the local oscillator frequency is performed at a time when a received signal which is not related to information is being received.

Claim 5

The method according to claim 4, characterized in that the step of controlling of the frequency of the local oscillator signal is performed during a pause of the received signal.

Claim 6

The method according to claim 4, characterized in that the step of controlling of the frequency of the local oscillator signal is performed at a time when dummy data is being received prior to information of the received signal.

Claim 8

The method according to claim 7, characterized in that the received signal consists of GMSK modulated waves, and only when three or more successive bits of the binary identification data is identical to one another, the step of outputting frequency correction data comprises comparing a digital information value at the timing corresponding to the center of the neighboring bit of the binary identification data with each one bit before and after a point at which the binary identification data changes with a digital theoretical value at the timing corresponding to the center of the second bit when an intermediate frequency, obtained when three bits of a signal modulated with transmit data which is the same as the binary identification data whose three or more successive bits are identical is received successively, becomes the normal frequency and outputting frequency correction data which permits the difference to be minimized.

Claim 9

The method according to claim 7, characterized in that the received signal consists of GMSK modulated waves, and only when three or more successive bits of the binary identification data is identical to one another, the step of outputting frequency correction data comprising sampling a digital information value at the time corresponding to the center of neighboring the bit of the binary identification data with each one bit before and after a point at which the binary identification data changes, obtains the average of sample values obtained by performing the sampling a predetermined number of times and including the latest sample value, comparing the average with a digital theoretical value at the timing corresponding to the center of the second bit when an intermediate frequency, obtained when three bits of a signal modulated with transmit data which is the same as the binary identification data whose three or more successive bits are identical is received successively, becomes the normal frequency and outputting frequency correction data which permits the difference to be minimized.

Claim 10

The method according to claim 7, characterized in that the step of outputting frequency correction data comprises, when binary identification data is 1, outputting frequency correction data which permits the difference to be minimized only when a voltage signal level after conversion to an intermediate frequency signal is greater than a high-level theoretical value which is preset on the basis of frequency deviation of a received signal and, when identification data is 0, outputting frequency correction data which permits the difference to be minimized only when a voltage signal level after conversion to an intermediate frequency signal is smaller than a low-level theoretical value which is preset on the basis of frequency deviation of a received signal.

Claim 11

An automatic frequency control device for use in a receiver comprising: mixing means for mixing a received signal with a local oscillator signal to produce an intermediate frequency signal; frequency to voltage converting means for converting the frequency of the intermediate frequency signal from the mixing means to a voltage signal; analog to digital converting means for converting the voltage signal from said frequency to voltage converting means to digital data; arithmetic means for performing comparison operation on the digital data from said analog to digital converting means and a theoretical value to output frequency correction data; and local oscillator means responsive to the frequency correction data for controlling the frequency of the local oscillator signal to be applied to said mixing means.

Claim 12

The device according to claim 11, characterized in that said arithmetic means comprises a microprocessor.

Claim 13

The device according to claim 11, further comprising sampling clock generating means connected to said analog to digital converting means and said arithmetic means for generating sampling clocks for timing an input signal and memory means connected to said arithmetic means for storing the theoretical value to be compared with digital data from said analog to digital converting means.