Circuit for discriminating received signal modulation type

DETAILED DESCRIPTION It is an object of the present invention to provide a received signal modulation type discriminating circuit capable of correctly discriminating the modulation type of a received signal at high speed.
According to one aspect of the invention, there is provided a circuit for discriminating the modulation type of a received signal, comprising: a clock recovery circuit for recovering a data clock from received data; a phase difference detector for detecting a phase difference between the data clock recovered by the clock recovery circuit and the received data; a deviation calculation circuit for calculating a deviation between the phase difference detected by the phase difference detector and a deviation reference value preset in accordance with a modulation type; a squaring circuit for squaring the deviation calculated by the deviation calculation circuit; an average value calculation circuit for calculating an average value of a predetermined plurality number of consecutive ones of the square output calculated by the squaring circuit; and a comparator for comparing the average value calculated by the average value calculation circuit with a predetermined decision reference value and outputting a discrimination signal in accordance with the comparison results.
According to another aspect of the present invention, there is provided a circuit for discriminating the modulation type of a received signal, comprising: a clock recovery circuit for recovering a data clock from received data; a phase difference detector for detecting a phase difference between the data clock recovered by the clock recovery circuit and the received data; a deviation calculation circuit for calculating a deviation between the phase difference detected by the phase difference detector and a deviation reference value preset in accordance with a modulation type; an absolute deviation calculating circuit for calculating an absolute deviation of the deviation calculated by the deviation calculation circuit; an absolute deviation average calculation circuit for calculating an average value of a predetermined plurality number of consecutive ones of the absolute deviation calculated by the absolute deviation calculating circuit; and a comparator for comparing the absolute deviation average value calculated by the absolute deviation average calculation circuit with a predetermined decision reference value and outputting a discrimination signal in accordance with the comparison results