| 摘要 |
PROBLEM TO BE SOLVED: To provide an intermediate frequency selection circuit for a superheterodyne receiver, in which sensitivity suppression with respect to a received frequency is hard to take place. SOLUTION: This intermediate frequency selection circuit has a configuration similar to the conventional intermediate frequency selection circuit, except that an LC series parallel resonance circuit is provided in which an intermediate frequency transformer T is coupled with a series resonance circuit consisting of a capacitor C and a 2nd inductor L2 connected with the capacitor C in series. Thus, a low spurious intermediate frequency selection circuit, that shows satisfactory filter characteristic passing through only the intermediate frequency, is realized. When an LC circuit for series resonance is configured, since a parallel capacitor required for the intermediate frequency transformer is used, the intermediate frequency selection circuit is realized by adding only one inductor to a conventional circuit. Then the spurious characteristic of a low cost ceramic filter in the market can be improved without the need for an expensive high order ceramic filter.
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