| 摘要 |
In a video disc system for recovering prerecorded signals from a disc record by a signal pickup including a turntable, turntable drive means, and turntable speed adjusting means, a turntable speed control system is provided for maintaining the rotation of the turntable at a predetermined speed. Means responsive to the rotation of the turntable generate sample pulses having a frequency which is a function of the actual speed of rotation of the turntable. The sample pulses occur at a predetermined frequency when the turntable is rotating at the predetermined speed. Means are employed for generating a sawtooth-shaped reference wave having a frequency which is a multiple of the predetermined frequency. A sample-and-hold circuit is coupled to the sample pulse generating means and reference wave generating means for determining the magnitude of the reference wave during the occurrence of each of the sample pulses for developing a speed error correction signal. The magnitude of the speed error correction signal is a function of the phase deviation between the sample pulse train and the reference wave. The adjusting means coupled to the sample-and-hold circuit and responsive to the speed error correction signal maintain the rotation of the turntable at the predetermined speed. |
