| 摘要 |
<p>A video disc player, employing a stylus electrode to form a variable capacitance with a conductive disc coating, as geometry variations in the disc groove pass beneath the stylus, has a conductive stylus support arm which forms a transmission line with a surrounding arm housing of conductive material. The transmission line is capacity end loaded at the arm end remote from the stylus by a series combination of capacitances which include an air dielectric capacitor and a voltage variable capacitor. The air dielectric capacitor has a first set of plates suspended from the movable stylus support arm, and a second set of plates fixedly mounted on the housing and interleaved with the first set. The transmission line and associated capacitances form a tuned circuit with a resonant frequency subject to variation as the stylus-disc capacitance varies. The tuned circuit is excited with UHF oscillations from a fixed frequency oscillator operating at a frequency within an ISM-allocated band. As the resonant frequency of the tuned circuit varies, the resultant UHF oscillation amplitude variations are detected to recover the recorded information. A tuning control circuit responsive to the detector output adjusts the voltage variable capacitance to maintain a desired spacing between the oscillator output and the tuning range of the transmission line resonant circuit. The stylus support arm is subject to replacement in the housing without wiring disconnection or connection.</p> |
