| 摘要 |
PROBLEM TO BE SOLVED: To provide an offset beat cancellation apparatus constituted of an A-D converter having generally practical operation speed and a digital circuit, by undersampling an IF signal by the A-D converter. SOLUTION: In the case of receiving television broadcasting signals of the same channel of which the frequency bands are slightly offset from each other from a plurality of transmission stations, an IF signal is undersampled and converted into a digital signal by the A-D converter 22. A digital orthogonal demodulation part 30 orthogonally demodulates a digital signal and outputs an in-phase component I(t) including a video signal and an offset beat component and an orthogonal component Q(t) of the offset beat component. The in-phase component I(t) is sent to a subtraction circuit 42 through a low-pass filter 41 and the orthogonal component Q(t) is sent to the subtraction circuit 42 through a low-pass filter 43 and aπ/2 phase shift circuit 44. The subtraction circuit 42 calculates a difference between both the inputs, removes the offset beat component and extracts the video signal. COPYRIGHT: (C)2006,JPO&NCIPI
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