Servo arrangement for the recording tape drive in broadband signal reproducing systems

摘要

A servo arrangement for the drive motor of the recording tape of a color video recording and reproducing system, in which a phase detector is included in a tachometer loop for regulating the speed of the drive motor. Another phase detector and a voltage controlled oscillator are included in a tape lock loop for providing to the tachometer loop phase detector a reference derived from off-tape sync information. The voltage controlled oscillator is controlled by the error signal voltage of the tape lock phase detector, and the oscillator output is used as a reference for the tach loop. In one embodiment the oscillator is of the voltage controlled crystal type having a relatively high center frequency which is heterodyned down to a suitable frequency for controlling the tach loop phase detector. In this manner a servo reference of great stability is produced for the tach loop phase detector. Since the heterodyning frequency is derived from the signal carrier source present in the recorder no separate oscillator is required for generating the heterodyning frequency, and thus the costs for this highly stable servo arrangement are minimized. In all embodiments, the tape lock loop for providing the tach loop reference is independent of the feedback loop for the control of the variable delay line of the electronic time base error correction circuitry of the system, and the tape lock loop phase comparator sample pulse is disabled when a dropout is sensed so that the tach loop is substantially insensitive to signal dropouts.