General Electric Company

Brian P Moran

Edward W Andrews

Herbert E Daniels

Harold E Stehman

Stanford W Miller

In cases where the reference signal pulses supplied to one input of the phase detector of a phase-locked loop (PLL) may shift in phase significantly, the PLL may not be able to lock-in quickly enough to the apparent input pulse frequency change. In video monitor circuits where digital counters are clocked by the output frequency of the PLL, for example, the momentary loss of synchronism can cause horizontal scanning of the monitor screen to start too early or too late. A circuit is provided that lets the PLL make normal phase and frequency adjustments during a predetermined period during which counter reset is disabled. The circuit provides a window before and after this period during which counter reset is enabled. A reference pulse with a substantial phase error falls within the window. If three conditions are met, namely, the Reset Enable window exists, the reference pulse occurred within the window and the scan is near the bottom of the monitor screen, then a counter reset to zero signal is produced.

Instant phase correction in a phase-locked loop

A system for supplying a selected voltage between the anode and cathode of an x-ray tube independent of power source voltage variations couples the x-ray tube power supply to the source with a transformer whose output voltages are selectable with tap switches. Prevailing source voltage and selected applied voltage are sensed and represented by analog signals which are converted to binary digital codes that form addresses for a read-only memory. The read-only memory is programmed with data representative of the pattern in which the tap switches should be set for the transformer to supply the selected voltage at the prevailing source voltage. When addressed by combinations of code words representative of the selected and source voltages, the memory outputs a code word that is used to set the switches in the corresponding pattern.

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Mukwonago, WI, United States of America

Brian P Moran