Automatic frequency control apparatus for FSK receiver and FSK receiver including the same

A frequency shift keying signal receiver with automatic frequency controlling, having a receiving and detection circuit for receiving and detecting an in-phase and quadrature signals using a local oscillation signal from a received first frequency shift keying signal having a data rate, for outputting a demodulated result, said frequency shift keying receiver comprising:

• a frequency controlled local oscillator for generating said local oscillation signal, a frequency of said local oscillation signal being controlled in accordance with a frequency control signal;
• a frequency shift keying modulation circuit for generating a frequency signal and a second frequency shift keying modulation signal by frequency shift modulating said in-phase and quadrature signals using said frequency signal having a substantially predetermined frequency lower than a carrier frequency of said first frequency shift keying signal;
• a first frequency to voltage converter for converting a frequency of said second frequency shift keying modulation signal into a first voltage signal;
• a second frequency to voltage converter for converting said substantially predetermined frequency of said frequency signal into a second voltage signal;
• a voltage comparing circuit for comparing first and second voltage signals and outputting said demodulation result;
• and
• an averaging circuit for averaging said demodulation is result successively outputted for a predetermined interval which is sufficiently long compared with said data rate and for generating said frequency control signal.

A frequency shift keying signal receiver with automatic frequency controlling, having a receiving and detection circuit for receiving and detecting an in-phase and quadrature signals using a local oscillation signal from a received first frequency shift keying signal having a data rate, for outputting a demodulated result, said frequency shift keying signal receiver comprises:

• a local oscillator for generating said local oscillation signal, a frequency of said local signal being controlled in accordance with a frequency control signal;
• a frequency shift keying modulation circuit for generating a frequency signal and a second frequency shift keying modulation signal by frequency shift modulating said in-phase and quadrature signals using said frequency signal having a predetermined frequency lower than a carrier frequency of said first frequency shift keying signal;
• a first switch for outputting either said second frequency shift keying modulation signal or said frequency signal in response to a switch control signal;
• a frequency to voltage converter for converting a frequency of an output of said first switch into a voltage signal;
• a second switch for said voltage signal at a first terminal or a second terminal in response to said switch control signal;
• a holding circuit for holding said voltage signal from said second terminal;
• a voltage comparing circuit for comparing said voltage signal from said first terminal and said held voltage signal from said holding circuit and outputting a demodulation result;
• a control circuit for generating said switch control signal such that when said first switch outputs said second frequency shift keying signal, said second switch outputs said voltage signal to said at said first terminal and when said first switch outputs said frequency signal, said second switch outputs said voltage signal at said second terminal and said first and second switches switch periodically;
• and
• an averaging circuit for averaging said demodulation result successively outputted for a predetermined interval which is sufficiently long compared with said data rate and for generating said frequency control signal.

An automatic frequency controlling circuit for a frequency shift keying receiver having a receiving and detection circuit for receiving and detecting an in-phase and quadrature signals using a frequency controlled local oscillation signal from a received first frequency shift keying signal having a data rate, and a demodulator for demodulating said in-phase and quadrature baseband signals and outputting mark and space data, said automatic frequency controlling circuit comprising:

• a local oscillator for generating said frequency controlled local oscillation signal;
• a frequency shift keying modulation circuit for generating a frequency signal and a second frequency shift keying modulation signal by frequency-shift-modulating said in-phase and quadrature signals using said frequency signal having a substantially predetermined frequency lower than a carrier frequency of said first frequency shift keying signal;
• a first frequency to voltage converter for converting a frequency of said second frequency shift keying modulation signal into a first voltage signal;
• a second frequency to voltage converter for converting said predetermined frequency of said frequency signal into a second voltage signal;
• a voltage comparing circuit for comparing first and second voltage signals and outputting a demodulation result;
• and
• an averaging circuit for averaging said demodulation result successively outputted for a predetermined interval which is sufficiently long compared with said data rate and for generating said frequency control signal.