| 摘要 |
PROBLEM TO BE SOLVED: To obtain an output of a rotating speed detection circuit for a rotation type color wheel irrelevantly to the performance of a reflection type photointerrupter of the rotating speed detection circuit, the quantity of external incident light, etc. SOLUTION: The reflection type photointerrupter 19a of the rotating speed detection circuit 19 detects the rotation of the rotation type color wheel 12. A comparator 19b converts the analog output of the reflection type photointerrupter 19a into a digital signal by using a reference signal. The reference signal of the comparator 19a is generated by smoothing output pulses of the reflection type photointerrupter 19a by a low-pass filter 19c. The reference signal of the comparator 19b follows up variation of the output pulses of the reflection type photointerrupter 19a even when the external light greatly varies. As a result, the output of a rotating speed detection circuit can be obtained irrelevantly to the quantity of external incident light or the performance of a reflection type photointerrupter. COPYRIGHT: (C)2006,JPO&NCIPI
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