Demodulator for digitally modulated wave

A demodulator for demodulating a digitally modulated wave, comprising:

• a first local oscillation unit for modulating a first frequency converting carrier and a second frequency converting carrier, wherein said first frequency converting carrier and said second frequency converting carrier have carrier phase axes which are different;
• a frequency converting unit for converting components of a first phase axis and a second phase axis of a digital modulated wave to a frequency band in accordance with said first frequency converting carrier and said second frequency converting carrier, respectively, thereby producing a first frequency converted signal and a second frequency converted signal, respectively, wherein said frequency band is substantially a base band;
• analog to digital conversion means for digitally converting said first frequency converted signal and said second frequency converted signal, thereby producing a first digital signal and a second digital signal, respectively;
• first complex multiplier means for multiplying said first digital signal and said second digital signal by a third reproducing carrier and a fourth reproducing carrier and for obtaining a first calculation output and a second calculation output, wherein said first calculation output and said second calculation output each having an expression which comprises a complex number;
• digital low pass filters for spectrum-shaping said first calculation output and said second calculation output, thereby producing a first digitally shaped output and a second digitally shaped output;
• second complex multiplier means for multiplying said first digitally shaped output and said second digitally shaped output by a fifth reproducing carrier and a sixth reproducing carrier and for obtaining a third calculation output and a fourth calculation output, wherein said third calculation output and said fourth calculation output each having an expression which comprises a complex number;
• means for obtaining phase difference data and quadrant data corresponding to a phase expressed by said third calculation output and said fourth calculation output, and for obtaining a demodulation output having a multi-phase from said phase difference data and said quadrant data;
• phase lock loop means, for producing said fifth reproducing carrier and said sixth reproducing carrier, wherein said phase lock loop comprises:
• a first loop filter for filtering said phase difference data, thereby producing filtered phase difference data;
• a first numerical value control oscillator for receiving said filtered phase difference data, and for generating oscillated phase difference data in accordance with said filtered phase difference data;
• and
• data conversion means for converting said oscillated phase difference data, thereby producing said fifth reproducing carrier and said sixth reproducing carrier;
• and
• automatic frequency control means for controlling an oscillation frequency of said third reproducing carrier and said fourth reproducing carrier, wherein said automatic frequency control means comprises:
• a second loop filter for filtering a frequency error data, thereby outputting filtered frequency error data;
• latch means for latching said filtered frequency error data, thereby outputting latched frequency error data;
• frequency error detection means for receiving said phase difference data, and for producing and outputting said frequency error data in accordance with said received phase difference data, wherein said frequency error detection means comprises:
• means for continuing an operation state of said automatic frequency control means by setting said output of said latch means to be in a through state and said output of said phase lock loop means to be in a fixing state when a value of said frequency error data is larger then a predetermined value, and for controlling said phase lock loop means to be in an operating state by maintaining said output of said latch means when said value of said frequency error data is smaller than said predetermined value;
• a second local oscillation unit comprising a second numerical value control oscillator for receiving said latched frequency error data, and for generating an oscillated frequency error in accordance with said latched frequency error data;
• and
• data converters for modulating said oscillated frequency error, thereby producing said third reproducing carrier and said fourth reproducing carrier, wherein said third reproducing carrier and said fourth reproducing carrier each having a conversion characteristic which is one of a sine conversion characteristic and a cosine conversion characteristic, and wherein said conversion characteristic of said third reproducing carrier is different from said conversion characteristic of said fourth reproducing carrier.