Video signal processor for controlling the brightness and contrast of a display device

• US 5,504,538 A
• Filed: 12/27/1994
• Issued: 04/02/1996
• Est. Priority Date: 09/01/1992
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Inoue, Ikunori, Tsujihara, Susumu
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): Miller, John W.
• Application Number:
  US08/364,853
• Time in Patent Office: 462 Days
• Field of Search: 348/673, 348/678, 348/679, 348/682-685, 348/687, 348/689-697
• US Class Current: 348/673
• CPC Class Codes: H04N 5/59 in dependence upon beam current of cathode ray tube

Abstract

A video signal processor for controlling a displayed image on a CRT having a cathode electrode and a grid electrode includes a generator for generating a brightness reference signal, an adder for adding the brightness reference signal to a black level in a blanking period of an input video signal. The added brightness reference signal is applied to the cathode electrode though a current detector for detecting a current of the added brightness reference signal. A current level signal produced from the current detector is used for determining and clamping the peak of a control voltage applied to the grid electrode such that a voltage difference between a peak of the added brightness reference signal and the peak of the control voltage is maintained constant.

Claims

1. A video signal processor for receiving an input video signal and for controlling a display device having a first electrode and a second electrode, comprising:

generation means for generating, based on a brightness control signal, a brightness reference signal in a range from a positive voltage level to a negative voltage level including a zero voltage level;

adding means for adding the brightness reference signal, which is any one of a positive voltage level, a zero voltage level or a negative voltage level, to a pedestal level in a vertical blanking period of the input video signal, said added brightness reference signal being applied to said first electrode;

detection means for detecting a current of said added brightness reference signal, and for producing a current level signal commensurate with the detected current;

DC potential setting means for setting a DC potential based on said current level signal;

voltage supplying means for supplying a control voltage to said second electrode; and

clamping means for clamping a peak of said control voltage to a voltage determined by said DC potential setting means such that a voltage difference between a peak of said added brightness reference signal and said peak of the control voltage is maintained constant.

2. A video signal processor for controlling a display device having a first electrode and a second electrode, comprising:

generation means for generating a brightness reference signal, a contrast reference signal and a black level reference signal and subjecting the contrast and black level reference signals to a blanking process to reach a pedestal potential in a horizontal flyback period;

adding means for adding to an input video signal said brightness reference signal during a vertical blanking period and said contrast reference signal and black level reference signal simultaneously during a horizontal flyback period of the input video signal;

variable gain control means for controlling a level of said added contrast reference signal;

extraction means for extracting said added contrast reference signal;

contrast feedback control means for comparing said extracted contrast reference signal with a predetermined reference potential and feeding back a compared result to said variable gain control means to maintain said added contrast reference signal at predetermined level, said added brightness reference signal and said added contrast reference signal being applied to said first electrode;

detection means for detecting a current of said added brightness reference signal, and for producing a current level signal commensurate with the detected current;

DC potential setting means for setting a DC potential based on said current level signal;

voltage supplying means for supplying a control voltage to said second electrode; and

clamping means for clamping a peak of said control voltage to a voltage determined by said DC potential setting means such that a voltage difference between a peak of said added brightness reference signal and said peak of the control voltage is maintained constant.

3. A video signal processor for receiving an input video signal and for controlling a display device having a first electrode and a second electrode, comprising:

generation means for generating, based on a brightness control signal, a brightness reference signal in a range from a positive voltage level to a negative voltage level including a zero voltage level;

adding means for adding the brightness reference signal, which is any one of a positive voltage level, a zero voltage level or a negative voltage level, to a pedestal level in a vertical blanking period of the input video signal, said added brightness reference signal being applied to said first electrode;

correction means for effecting gamma correction applied to said video signal with the added brightness reference signal;

detection means for detecting a current of said added brightness reference signal from said correction means, and for producing a current level signal commensurate with the detected current;

DC potential setting means for setting a DC potential based on said current level signal;

voltage supplying means for supplying a control voltage to said second electrode; and

clamping means for clamping a peak of said control voltage to a voltage determined by said DC potential setting means such that a voltage difference between a peak of said added brightness reference signal and said peak of the control voltage is maintained constant.