Coherent demodulator preceded by non-coherent demodulator and automatic frequency control circuit

A demodulating device comprising:

• non-coherent demodulating means for performing orthogonal detection of a received modulated signal with a signal having frequency close to a frequency of the modulated signal to produce first pseudo baseband signals having frequency error;
• automatic frequency control means responsive to the first pseudo baseband signals to produce second pseudo baseband signals having smaller frequency error;
• and
• narrow band coherent demodulating means for performing orthogonal detection of the second pseudo baseband signals with a reproduced carrier to produce baseband signals.

An automatic frequency controller for receiving a first pseudo baseband signal having frequency error obtained by orthogonally detecting a received modulated signal with a signal having frequency close to a frequency of the modulated signal and outputting a second pseudo baseband signal having smaller frequency error to a narrow band coherent demodulator, said automatic frequency controller comprising:

• first oscillator means;
• first multiplying means for multiplying the first pseudo baseband signal with an output signal of said first oscillator means;
• phase detecting means for producing a first phase error signal from an output of said first multiplying means;
• a loop filter having wider band width than said coherent demodulating means, for producing a first control signal from the first phase error signal for controlling said first oscillator means;
• filtering means for removing noise component of the first control signal to produce a second control signal;
• second oscillation means adapted to be controlled by the second control signal;
• and
• second multiplying means for multiplying the first pseudo baseband signal with an output of said second oscillation means to produce the second pseudo baseband signal.