| 摘要 |
A tuning circuit is so constructed that it is possible to set Q of the tuning circuit to a high desired value by using a negative resistance value. The tuning circuit is made to oscillate weakly by using a negative resistance circuit, a voltage-resistance converter and a digital-analog converter and a negative resistance of said negative resistance circuit is scanned by a counter, so that two negative resistance values corresponding to an oscillation amplitude and another oscillation amplitude of half of it are obtained by analog comparators COMP1 and COMP2. A negative resistance value to be set is operated by an adder/subtracter from a series resistance value corresponding to a desired Q and these value. Said scanning is stopped when said negative resistance value is obtained. The tuning circuit can be constituted small and simple by small size digital ICs.
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