| 摘要 |
PURPOSE:To adjust resonance frequency of a resonance circuit and also to make a device small in size, by executing electromagnetic coarse coupling of an AFC loop to a resonance line. CONSTITUTION:A resonant line 11 of a lambda/4 distribution constant type, placed on an insulating substrate is made tangent to an electrostatic capacity variation detecting part 10 containing a needle for detecting recorded information and is resonated by resonance frequency f0. An AFC loop 23 executes electromagnetic coarse coupling to the resonant line 11, and also a resonance frequency variable circuit 25 is formed by a variable capacity diode 21 and a capacitor 22. In this case, by controlling DC voltage applied to the variable capacity diode 21, the resonance frequency f0 can be adjusted. Also, the resonant line 11 can be made small in size since a distributed constant resonant line of lambda/4 is used, and by using the AFC loop 23, etc. as a plane electric conductor on the insulating substrate, stabilization and mass production can be realized. |
