| 摘要 |
PURPOSE:To eliminate the fluctuation of the center frequency caused by the deviation, etc., of the value of each parts, by determining the center frequency from the natural frequency of a frequency selecting element itself, such as ceramic vibrator, etc. CONSTITUTION:Oscillation in which the natural frequency of a ceramic vibrator X1 is used as the center frequency, is performed by a positive feedback circuit from the transistor (TR) Q7 of an oscillating circuit section to another TR Q6 through a node P3 and resistance R3. On the other hand, electric currents of the same and opposite polarities to the electric current flowing from the node P3 to a capacitor C3 are respectively produced in the collectors of TRs Q12 and Q13. Thereafter, each current is mixed in a ratio corresponding to a control voltage VCNT and outputted to TRs Q9 and Q11, and then, fed back to the TR Q13 through the node P3 and capacitor C3. Therefore, a positive and negative equivalent capacities are connected with the node P3 in accordance with the value of the control voltage VCNT. Accordingly, fluctuation of the center frequency caused by the deviation, etc., of the constant value of each parts can be eliminated. |
