A drive control signal is effectively obtained. An offset is added to a rotational state signal. A drive control signal having a period which is reduced by a predetermined period compared to the sine wave form signal is generated between a crossing of a reference value for a second time and a crossing of the reference value for a next time by an added signal obtained by sequentially offsetting the rotational state signal in a direction reaching the reference value. A pulse indicating that the polarity has been reversed when the offset is added is added to the crossing of the reference value for the first time, to reliably detect crossing of the reference value for the second time.
1. A drive circuit which generates a drive control signal based on a rotational state signal of a sine wave form which indicates a rotational state of a motor, wherein
an added signal is obtained by adding an offset to the rotational state signal by repeating a process in which,
upon detection of crossing of a reference value for a first time, from a first direction, by an added signal having a predetermined amount of offset added to the rotational state signal in a direction approaching the reference value, the predetermined amount of offset is added to the rotational state signal in a direction away from the reference value,
upon detection of crossing of the reference value for a second time, from the first direction, by the obtained added signal, no offset is added to the rotational state signal, and
upon detection of crossing of the reference value for a first time, from a second direction approaching the reference value from a direction opposite of the first direction, by the added signal, the predetermined amount of offset is added to the rotational state signal in a direction approaching the reference value,
in response to crossing of the reference value by the added signal based on a comparison of the obtained added signal and the reference value, a rise signal or a fall signal is obtained based on a direction of the crossing, and in response to the detection of the crossing of the reference value for the first time, a fall signal or a rise signal is added at a time delayed from the rise signal or the fall signal generated in the detection of the crossing, and
a drive control signal having a period which is reduced by a predetermined period compared to the rotational state signal is generated using the obtained rise signal or the obtained fall signal between the detection of the crossing of the reference value for the second time and a detection of the crossing of the reference value for a next time.
2. The drive circuit according to claim 1 , wherein
the detection of the crossing of the added signal and the reference value is executed by generating a rise signal or a fall signal based on a change of a read signal obtained by reading, at a predetermined clock, a raw output of a comparator which compares the added signal and the reference value.
3. The drive circuit according to claim 1 , wherein
addition of the rise signal or the fall signal is prohibited by a control signal from outside.
4. The drive circuit according to claim 2 , wherein
addition of the rise signal or the fall signal is prohibited by a control signal from outside.