| 摘要 |
PURPOSE:To enable the prevention of erroneous calculation of frequency even when a signal with a larger amplitude is inputted, by comparing the amplitude of video signals at various channels with an omnivideo to judge the significance of the center channel. CONSTITUTION:Outputs of (n) band pass filters are inputted into an A/D converter 2 and in a specified time after the time at which a signal above a fixed level is detected a control circuit 3 operates PAU, PAO and PAL registers 4 to store output levels of own channel and both adjacent channels. A comparator circuit 13 validates an Fp signal indicating the center channel when the requirement of PAU<=PAO>=PAL is met. On the other hand, an omni comparator 11 outputs a channel validation signal 12 to a comparator circuit 13 when the video signal of a channel is larger than an output of a filter, the pass band of which covers the total pass band of the (n) filters. Then, a frequency computation circuit determines the frequency using the PAU, PAO and PAL at the center channel.
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