Samsung DVD-VR320/COM, Manual

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Circuit Operating Descriptions
Samsung Electronics 14-29
(5) Drum Phase Error Detector
Drum phase control must start operating after the drum motor is brought to the correct rotational speed by the
speed control system . Drum speed control works as follows in record and playback.
- Record : Phase is controlled so that the vertical blanking intervals of the recorded video
signal will line up along the edge of the tape.
- Playback : Phase is controlled so as to trace the recorded tracks accurately.
A digital counter detects the phase deviation from a preset value. The phase error data is added to speed error
data in a digital filter. this filter controls a pulse-width modulated (PWM) output, which controls the rotation
phase and speed of the drum.When the error is zero, the PWM circuit outputs a waveform with a 50% duty cycle.
The phase counter error detector compares the phase of the DPG pulse (tach pulse),which contains video head
phase information, with a reference signal. In the actual circuit , the comparison is carried out by comparing the
head-switching (HSW) signal,which is delayed by a counter that is reseted by DPG, with a reference signal. The
reference signal is the REF 30Hz signal,which differs between record and playback as follows.
- Record : V sync signal extracted from the video signal to be recorded (frame rate signal, actually 1/2V sync).
- Playback : 30Hz signal divided from the system clock.