| 摘要 |
PURPOSE:To enable always a most adequate detecting information for both a strong ghost or a weak ghost by providing a gain control circuit at the preceding stage of an A/D converter for the detection of the ghost and controlling it by a control signal that is formed by the output signal of the A/D converter. CONSTITUTION:The digital output of an AD converter 4 is stored once at a RAM 6 by a DMA controller 8 and a microcomputer 5 judges the suitability of the size of an input signal that is AD-converted from that data, and the result is feedbacked to a control voltage generating circuit 14 and the gain of a gain control circuit 13 which is provided at the preceding stage of the AD converter 4 is controlled by the output voltage of the control voltage generating circuit 14. A proper detection can be performed as shown at figure (d) by thus controlled input signal level shown at figure (c). Furthermore, the control of the input signal level of the AD converter by the microcomputer 5 is made possible by keeping the maximum value of the data within a specified range.
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