| 摘要 |
A frequency of an original clock signal is spread based on a spread spectrum width thereby generating a real clock signal, and a timing signal is generated based on the real clock signal. Noise in the timing signal is reduced in a plurality of harmonic noise reduction stages to thereby obtain a noise-reduced timing signal. An optical image obtained by scanning a document is converted into an electric signal based on the noise-reduced timing signal. The spread spectrum width to be used when spreading frequency of an original clock signal, and number of the harmonic noise reduction stages to be used when reducing noise in the timing signal are changed depending on an operation mode.
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