| 摘要 |
PURPOSE:To provide a variable filter circuit small in circuitry, low in cost and capable of controlling pass band width in accordance with a receiving state. CONSTITUTION:In this variable filter circuit, the center frequecy f0 of a receiving signal is shifted upward only by f1 through the 1st shifting means to limit the upper limit pass band of the receiving signal by the 1st filter circuit 5, the center frequency of the hand-limited receiving signal is shifted upward only by f2 through the 2nd shifting means to limit the lower limit pass band of the receiving signal by a filter circuit 8 and to make frequencies f1 and f2 variable, thereby a receiving signal with required band width is obtained from the circuit 8. The circuit is provided with a multiplier 3 for multiplying the receiving signal by a signal of frequency f1 oscillated from a voltage control oscillator 4 as the 1st shifting means and a multiplier 6 for multiplying the receiving signal by a signal of frequency f2 oscillated from a voltage control oscillator 7 as the 2nd shifting means.
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