Servo Waveforms

These waveforms show the motor control voltage and 400 Hz sawtooth waveform at the input to the pulse-width modulator op-amp.

The upper image is for the case of the disc advanced by one line, the center image for nominal framing, and the bottom image shows one line retardation. (Note that two waveforms were captured by the low shutter speed in the center image).

The asymmetry of the top and bottom waveforms is apparently not enough to pull the loop to the proper phasing. However, an initial offset of 2 lines or more causes the loop to unlock and then find one of the three cases shown here.

mechanical TV waveform - disk advanced mechanical TV waveform - disk nominalmechanical TV waveform - disk retarded

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