Television – Receiver circuitry – Power supply
Reexamination Certificate
2000-04-20
2004-07-27
Lee, Michael H. (Department: 2614)
Television
Receiver circuitry
Power supply
C348S739000, C345S060000
Reexamination Certificate
active
06768520
ABSTRACT:
The invention is based on a method for regulating the picture power in a television receiver.
BACKGROUND OF THE INVENTION
In computer monitors having a picture tube, it may be seen that a small white picture area is displayed with the same white value as a large white picture area. If it were intended to achieve the same result for a television receiver with a picture tube, a voltage supply is necessary in which the power is permitted to fluctuate between 60 and 300 watts given a stable output voltage.
For televisions with picture tubes there is a solution in that the average value of the beam current is measured. The larger this average value is, the more the contrast and the brightness of the picture are reduced. If separately regulated high-voltage generators are used, this regulating principle can no longer be used satisfactorily.
In television receivers with plasma screens, on account of the lower luminous efficiency, this effect would have considerably more severe repercussions on the power consumption. In addition, the known solutions cannot be transferred to television receivers with plasma screens.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a simplified method for regulating the picture power in a television receiver. This object is achieved by means of the features of the invention which are specified in the claims. Advantageous developments of the invention are specified in the subclaims.
The inventive method for regulating the picture power in a television receiver having a video processor which has a control input which receives an input signal and which emits an output signal, having a converter circuit, having a control unit and having a comparator circuit, is characterized in that the converter circuit monitors the output signal of the video processor and converts it into a picture power signal, in that the picture power signal is fed to the comparator circuit via the control unit, in that the comparator circuit performs a comparison with a predetermined desired value, and, in the event of deviations from the desired value the picture power is changed by way of the control input.
It is advantageous in this case that the power consumption of the picture power is obtained using the video voltages R, G, B. The video voltages are converted into an information item which is then a measure of the picture power. This information item is preferably a voltage value. This information item is subsequently fed to two regulating loops. In the fast loop, as dynamic regulation, the value of the picture power is determined during a short time period, for example one millisecond. The fast loop, that is to say the fast regulation, ensures fast falling of the amplitude of the picture power for the case where a large number of lines are displayed completely white. This serves to ensure that the maximum power consumption, which is defined beforehand, is not exceeded.
In the slow loop, as static regulation, the picture power is determined during a relatively long time period, for example a few milliseconds. The slow loop does not react to the dynamic range of the picture as such, but rather is intended to control the total white value and thus the total picture power of the pictures to be displayed. In other words the fast loop is for dynamic, horizontal rate regulation and the slow loop is for static, vertical rate regulation. It is possible additionally to use a further slower loop in order to form protection for the electronic components against overtemperature and/or ageing effects. On account of these loops, the regulating principle according to the invention permits a high dynamic range of the picture and reduces the outlays which would otherwise be necessary in order to provide a voltage supply with similar criteria.
A desired value is predetermined for the picture power in the circuit for the regulation. This desired value can be set by the manufacturer and/or by the user, there being a maximum value which is not supposed to be exceeded.
In the simplest case, the solution of the invention is such that only the fast loop is used, which loop can also be referred to as control unit.
One advantage of the solution according to the invention is the fact that the picture power and thus the peak luminance value can be reduced during a field. A reduction can be performed to an extent such that the critical region for the maximum power consumption is not reached. That is to say that if the fast loop detects that the picture power rises excessively greatly or assumes an excessively high value during a plurality of lines, a regulating signal passes from this fast loop via a comparator to the contrast control input of the video processor, which then reduces the video voltage R, G, B, thereby rapidly decreasing the picture power.
If the slow loop detects that the picture power is too high during a plurality of fields, the regulation is effected, as in the case of the fast loop, via a linear comparator, which then forwards a signal to the contrast control input of the video processor where, once again, the video voltage R, G, B is decreased, with the result that the picture power slowly decreases.
The instances of regulation can also be used to enable the picture powers to be increased. If, for example, only a small picture excerpt is displayed white, then the maximum white value of this picture can be set by the instances of regulation in that the picture power is only reduced when a relatively large picture excerpt is displayed. The user consequently sees a picture having the maximum white value, since it is now possible to permit the maximum picture power for this small area of the small picture excerpt. The new solution has the advantage that a better dynamic range of the picture and no overloading of the voltage-supplying circuits are ensured.
The following considerations may be summarized once again at this point: on the one hand, the regulating loop must be stable enough and must not change significantly when the picture contents are the same. On the other hand, the present status and the alteration of the contrast and of the power consumption must not be visible on the screen. For this reason, a maximum deviation of the peak white value of 10% during a frame is designed in order to obtain an acceptable delimitation of the value. During a change from a full-black to a full-white picture, it is not necessary to keep to this rule. In this case, it is possible to reduce the peak white value by factors of 2 to 4. However, this should apply in each case only to the first picture, in order that the viewer does not notice it. The maximal 10% increase in the peak white value should be maintained for the subsequent fields. The system then monitors whether the picture has the same content. In this case, it is necessary to correct the 10% increase for each field. If the picture becomes darker, the 10% increase field by field again leads to the maximum picture power consumption.
In order to acquire a simple solution for the stability criteria, the following solution has been worked out. During the frame flyback, the level of the picture power can rise slightly if the picture remains the same and if the picture power is reduced during the subsequent field. However, if the picture becomes less bright, that is to say that the picture power slowly rises, then the peak white value can slowly be decreased from field to field. This fast increasing by a maximum of 10% during a field is not visible since the increasing from field to field takes place when no picture is being displayed. If the extreme case is assumed, that is to say a full-black to a full-white picture, an increase can then be effected in 10% steps during the transition from a white to a black picture.
The number of grey-scale values in plasma is limited by the use of 8 bits on 256 level steps. The level steps are to be equated with the grey-scale values. In a plasma display, the video luminance is given by the video code which corresponds to the number of plasma cell discharges per field. This number of
Ahmari Hossein
Bicheler Hans Guenter
Kimmelmann Stefan
Rilly Gerard
Davenport Franceis A.
Fried Harvey D.
Lee Michael H.
Thomson Licensing S.A.
Tran Trang U.
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