Television – Cathode-ray tube display automatic black level bias control
Reexamination Certificate
1998-12-30
2001-05-01
Eisenzopf, Reinhard (Department: 2614)
Television
Cathode-ray tube display automatic black level bias control
C348S379000, C348S380000, C348S678000, C348S691000, C348S695000, C348S696000, C315S381000, C315S382000, C315S383000, C315S388000, C315S370000
Reexamination Certificate
active
06226037
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to interface circuits for conditioning output signals of one or more integrated circuits (IC) for application to other circuits. The invention has particular application in display systems for interfacing signals provided by one or more kinescope driver integrated circuits for application to video signal processing circuits.
BACKGROUND OF THE INVENTION
In conventional television receiver/monitor applications a video signal may be displayed is processed for display by a signal processing integrated circuit and coupled to the cathodes of a kinescope by means of respective kinescope driver integrated circuit. For AKB (automatic kinescope bias) operation, the driver amplifiers may include cathode current sensing circuits for supplying cathode current indicating pulses back to an AKB input of the signal processing IC.
In certain applications, the output signals produced by the driver ICs may not be directly compatible with the particular signal processing IC and may require interface circuitry to properly condition and couple the current indicating signals from the driver ICs to the processing IC. An example of such an arrangement, described in detail hereinafter, employs a signal processing IC such as the Toshiba type TA1276N or the Philips type TDA4780 ICs and driver ICs such as the type TDA6120Q IC manufactured by Philips.
SUMMARY OF THE INVENTION
The present invention resides, in part, in the discovery that when interfacing processing and driver ICs, it would be particularly desirable to provide circuitry for correction kinescope leakaqe currents. It is an object of the present invention to provide an AKB interface circuit for conditioning AKB related output signals of one or more kinescope driver integrated circuits for application to a video signal processing integrated circuit and for additionally providing correction for kinescope leakage currents when interfacing the ICs.
Display apparatus in accordance with the invention comprises a video signal processing IC (
12
) having outputs coupled via respective kinescope driver ICs (
18
,
20
,
22
) to respective kinescope cathodes (K
1
,K
2
,K
3
) for display of a color image, said signal processing IC having an input
27
for receiving an AKB input signal, the driver ICs having respective outputs (
28
,
30
,
32
) providing respective cathode current indicating signals (RP,GP,BP). An interface circuit (
100
) is provided, for coupling the cathode current indicating signals to the AKB input of the signal processing IC. The interface circuit (
100
) comprises a load circuit (
110
) for generating a load voltage (Vo) in response to at least one of the cathode current indicating signals. A leakage correction circuit (
130
) is responsive to the load voltage (Vo) for applying a leakage correction current (Io) to the load circuit. The correction circuit comprises a keyed comparator (Q
5
,Q
6
,Q
7
) for comparing the output voltage of the load (
110
) with a reference potential during a vertical retrace pulse interval to provide a leakage indicating signal; and a controllable current source (Q
1
,Q
3
) is coupled to the keyed comparator and responsive to the leakage indicating signal for feeding back a leakage correction current to said load circuit (
110
).
In a desirable application of the principles of the invention, the cathode current indicating signals are first combined and then subjected to leakage compensation for application to the processing IC AKB input.
In another application of the principles of the invention, the cathode current indicating signals are individually leakage compensated and then combined for application to the processing IC.
REFERENCES:
patent: 4450476 (1984-05-01), Tallant, II
patent: 4482921 (1984-11-01), Filliman
patent: 4484229 (1984-11-01), Parker
patent: 4502073 (1985-02-01), Hinn et al.
patent: 4518986 (1985-05-01), Hinn et al.
patent: 4554578 (1985-11-01), Willis
patent: 4599642 (1986-07-01), Willis
patent: 4677491 (1987-06-01), Hinn et al.
patent: 4694350 (1987-09-01), Hinn et al.
patent: 5835161 (1998-11-01), Keller
patent: 5894327 (1999-04-01), Griepentrog
patent: 5994841 (1999-11-01), Allen et al.
Eisenzopf Reinhard
Natnael Paulos
Shedd Robert D.
Thomson Licensing S.A.
Tripoli Joseph S.
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