Circuit arrangement for controlling a picture display tube

Details Circuit arrangement for controlling a picture display tube Circuit arrangement for controlling a picture display tube

1996-05-13

1998-11-24

Chin, Tommy P.

Television

Image signal processing circuitry specific to television

Gray scale transformation

348805, H04N 5202, H04N 520, H04N 969

Patent

active

058414878

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION



Field of the Invention

The invention relates to a circuit arrangement for controlling a picture display tube having a non-linear voltage/current characteristic by means of a picture signal which is precorrected or linear for compensating the non-linear characteristic of the picture display tube.
The known prior-art circuit arrangements for controlling picture display tubes employ a voltage control, i.e., the beam current of the picture display tube is generated by a voltage between cathode and grid 1 of the picture display tube. For this reason, a precorrection of the signal is necessary because the beam current, and hence the luminance, is non-linearly related to the control voltage. The main drawback of these circuit arrangements is that they must operate in a voltage range of approximately 100 V at the cathode with a bandwidth of, for example, 8 MHz for a 50 Hz receiver with a 4:3 format. For a 100 Hz television receiver, a bandwidth of 16 MHz is required and a further increase of the bandwidth is required for apparatuses having a 16:9 aspect ratio. Voltage control of picture display tubes involves the further drawback that the output voltage range to be used for the RGB processor must be large. This renders these control circuits very elaborate. A further drawback of these circuits is that, for reasons of the non-linear relationship between beam current and control voltage, they cannot present linear RGB signals without correction, which signals are supplied, for example, by a computer, a D/A converter or are suitable for displaying a menu generated in the television receiver.


SUMMARY OF THE INVENTION

It is an object of the invention to provide a circuit arrangement having a simple structure for controlling picture display tubes, which can process picture signals with a large bandwidth.
For a first embodiment of the invention, this object is solved in that the picture signal is applied to a non-linear compensation circuit which cancels the precorrection of the picture signal and controls a controlled current source at the output end, the output of said current source being coupled to the cathode of the picture display tube, and in that a differentiator is provided which differentiates the picture signal and controls a voltage-controlled compensation current source which is coupled to the cathode of the picture display tube for a picture signal-dependent reversal of the charge of the parasitic input capacitance of said picture display tube.
As already stated in the opening paragraph, the television signals nowadays transmitted by television stations are generally non-linearly precorrected. This precorrection is carried out in such a way that it just compensates the non-linear proportion between the applied voltage and the beam current upon a voltage control of the picture display tube, so that a linear behavior of the luminance results when the picture is displayed on the picture display tube.
For picture signals which are precorrected in this way, the precorrection is cancelled by means of a non-linear compensation circuit in the circuit arrangement according to the invention which employs a current control of the picture display tube. The non-linear characteristic curve of this compensation circuit is then exactly opposite to that of the precorrection performed at the transmitter end. A linear picture signal is then again present at the output of this compensation circuit. By means of this linear picture signal, a controlled current source is controlled which couples a corresponding current to the cathode of the picture display tube at the output end in dependence upon this signal (linear dependence). Since a current is directly supplied in this case, the luminance is also linear because the luminance is directly dependent on the current in a linear way.
However, it should be noted that the picture display tube has a parasitic input capacitance which may be produced by the picture display tube itself, but possibly also by external circuit connections between the pict

REFERENCES:
patent: 4547797 (1985-10-01), Mick
patent: 4672452 (1987-06-01), Corbel et al.
patent: 5103145 (1992-04-01), Doran
patent: 5335068 (1994-08-01), Hanajima
patent: 5410223 (1995-04-01), Van Amesfoort

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