Patent ID: 7855523

Claim:
A motor driving circuit which supplies a drive current to a multiphase motor to drive said multiphase motor, said motor driving circuit comprising: a back electromotive detection comparator which compares a back electromotive voltage across each phase coil of said multiphase motor respectively with a common voltage of said each phase, and generates a first rectangular wave signal of each phase; a masking circuit which performs a masking process that removes a noise component from a first rectangular wave signal of said each phase output from said back electromotive detection comparator, and outputs the resultant signal as a second rectangular wave signal of each phase; an output circuit which supplies the drive current to each phase coil of said multiphase motor on the basis of the second rectangular wave signal of said each phase; a frequency generating circuit which detects the edge of the second rectangular wave signal of said each phase, and generates a frequency generation signal whose level switches at each detected edge; and a mask signal generating circuit which generates a mask signal to be at a predetermined level during an interval multiplied by a predetermined coefficient to a pulse width of the frequency generation signal after level transition of the frequency generation signal, wherein said masking circuit performs a masking process that nullifies level fluctuation of the first rectangular wave signal during an interval when the mask signal is at the predetermined level.