| 摘要 |
PURPOSE:To perform switching between high-sensitivity reception and high-selectivity reception through a simple circuit, by cascading high-frequency tuning circuits having channel selecting varactors through coupling varactors, and switching the capacities of coupling varactors. CONSTITUTION:When switches 17 and 18 are placed at sides (a), the output of a voltage supply circuit 16 is passed through a bias resistance 15 and supplied to varactors 3 and 8 and even a voltage correcting circuit 20 through a varactor 14 for determining the frequency of local oscillation 13 and bias resistances 4 and 7. Its output is supplied to a varactor 5 through a bias resistance 6, thus constituting a multiple tuning circuit 24 which allows variation in the coupling capacity between the 1st and 2nd high-frequency tuning circuits 22 and 23. When the switches 17 and 18 are on sides (b), on the other hand, the output of a voltage correcting circuit 21 is supplied to the varactor 5 to decide on the coupling index of the multiple tuning circuit 24. A voltage correcting circuit 19 controls the varactors 3 and 8 to track the tuning frequencies of the tuning circuits 22 and 23 to the local oscillation frequency. |
