PURPOSE: To solve the problems of the life time due to existence of the sliding part as well as occurrence of the sliding noise, by using the contactless air capacitor for the capacitance variable element.
CONSTITUTION: The charge of CV1 is stored at capacitor 12 when switch 11 is turned toward terminal 10. Then with switch 11 turned toward terminal 13, the charge amount flowing out toward terminal 13 features C(V1-V2). And when switch 11 is changed over with cycle T, the mean level is regarded as (V1-V2)C/T for the alternating current flowing between terminals 10 and 13. And thus coefficient C/T can be regarded equivalently as the admittance, and accordingly the impedance features T/C to be the function of capacitance C. Switch 11 is constituted with MOSFETS5 and 6 which are switched alternately, and then the two signals of the opposite phases to each other which are obtained by making the reference control signal pass through differential amplifying circuit 4 are supplied to the gate to perform the switching.
| JP2001257547 | SOUND VOLUME ADJUSTER |
SUGANO MASASHI
OKAMOTO MICHIO
