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Wavy Video Compensation Method With Phase-Locked Loop

IP.com Disclosure Number: IPCOM000101231D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Matsubara, K: AUTHOR [+2]

Abstract

Disclosed is a technique to compensate Wavy Video of the CRT display by PLL (Phase-Locked Loop). The vertical frequency of the CRT display is changed by PLL in accordance with power line input frequency. The technique is widely applicable to all CRT displays.

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Wavy Video Compensation Method With Phase-Locked Loop

       Disclosed is a technique to compensate Wavy Video of the
CRT display by PLL (Phase-Locked Loop).  The vertical frequency of
the CRT display is changed by PLL in accordance with power line input
frequency.  The technique is widely applicable to all CRT displays.

      As a most popular method of CRT display interface, the video,
horizontal and vertical signals are input to the video circuits to
the display screen.  These signals are generated from the fixed
frequency oscillator, as shown in Fig. 1.

      When any objects which generate a strong magnetic field, such
as a fluorescent light or generator, are located close to the CRT
display, the display screen is moved (jittering) in accordance with
the beat frequency between its vertical frequency and external
magnetic one, that is 60 Hz (or 50 Hz).

      To cancel this movement, the CRT display has a capability to
function with two vertical frequencies, that is the original high one
and 60 Hz.  When there is any wavy video observed at the environment
of machine installation, its frequency can be switched to 60 Hz.

      However, there are generally  0.5 Hz variation for power
line frequency.  Due to this variation, there is wavy video observed
if the display frequency is fixed and power line frequency is changed
to 60.5 Hz or 59.5 Hz.

      The technique will be well understood with reference to the
drawing which schematically is...