KR810001902B1 - Average beam current limiter - Google Patents

Abstract

An average beam current limiter for a kinescope responsive to video signals coupled via a signal transmission channel(STC) comprises a source of control signals representative of average current drawn by the kinescope. When average beam current exceeds a predetd. threshold level by an amt. within a first range beam current, a corresponding control signal is coupled to the STC to vary the DC content of the video signal in a direction to limit beam current above the threshold level within the first range. When beam current exceeds the threshold level by a relatively greater amt. within a second range of current, a corresponding control signal serves to current within the second range.

Description

Improved Average Beam Current Limiter

Figure is a schematic and circuit diagram of a color television receiver to which the apparatus devised by the present invention is applied.

The present invention relates to an apparatus for automatically controlling an electron beam current drawn by an image reproducing apparatus such as Kineskov of a television receiver in response to an average beam current requirement of the image reproducing apparatus.

The content of the image reproduced by the kinescope of the television receiver includes luminance information, and in the case of a color image in a color television device, chromaticity information is included. The luminance information includes the peak-to-peak amplitude of the video signal representing the image related to the image contrast, and the D.C. It depends on the content. Peak amplitude of the video signal and D.C. The content can cause the kinescope to draw excessive beam current.

Various automatic beam current controllers are known that work in conjunction with the brightness and contrast control of television sets. For example, the contrast and brightness control functions of US Pat.

Excessive average beam currents can be caused by the content of the video signal, or by the viewer adjusting the passive brightness control circuitry contained in the brightness signal processing channel of the receiver, or both. However, since the video signal is unlikely to be delivered with a brightness level indicating excessive brightness, excessive average beam currents are more frequently generated by misadjusting the passive brightness control circuit in the direction of increasing brightness.

Excessive beam current can cause an unclear image on the receiver. In particular, excessive beam current degrades the performance of the receiver's deflection device, does not connect the electron beam and breaks the image. These high beam currents also exceed the kinescope safe operating current limit, which can cause damage to the kinescope and associated circuit components.

The latter problem is caused by the new developments, namely the higher beam currents required in high luminance kinescopes.

Since excessive average beam currents are mainly due to excessive brightness levels, it is desirable for the average beam current limiter to limit or suppress an increase in the average beam current demand that exceeds the threshold level of the beam current demand by a reduction in image brightness. It is also desirable that the average beam current limiter be provided with means for suppressing an increase in the beam current above the second threshold level by a reduction in image contrast. In this way, the relationship between image brightness and contrast will not be unduly upset, so the behavior of the beam current limiter in response to the increase in beam current will not be felt by the viewer. Otherwise, the reproduced image may appear with excessive contrast while limiting the beam.

Since the beam current may be generated in response to the chroma signals and the brightness signals, it is preferable that the beam current limiter used for the color television receiver interlock with the brightness and chroma signal processing circuits to limit the excessive beam current. For example, excessive beam current may result from solid color reproduction of one color, which does not necessarily involve excessive brightness signals, or may occur due to high luminance white image portions represented by high level brightness signals. have. Since the amplitudes of each of the brightness and chroma signals are maintained in a desirable relationship, it is believed that the amplitude adjustment of the chroma signals accompanying the amplitude adjustment of the brightness signals to limit excessive beam currents is advantageous. This adjustment provides very good color images to the viewer because the effects of beam limiting operation are not felt very much.

According to the present invention, the peak amplitude and the image brightness, which determine the image contrast, determine the D.C. An apparatus for processing a video reproduction video signal having a level includes a video signal transmission channel and an apparatus for reproducing an image in response to signals transmitted through the channel. The current drawn by the video reproducing device is the D.C. Responds to level and peak amplitude.

Also included is a device for deriving a control signal representing the magnitude of the average current drawn by the image reproducing apparatus. If the current exceeds a predetermined threshold level by the amount of current in the first region, then the D.C. To change the level, the control signal is connected to the video signal transmission channel. The control signal is also connected to the video signal channel in order to change the peak amplitude of the video signal in the direction of limiting the current above the threshold level when the current exceeds the threshold level by a relatively larger amount of second region current.

According to another feature of the invention, in an apparatus comprising a chromaticity channel for processing color signal components, the currents in the second region change the gain of the chromaticity channel, change the peak amplitude of the color signal components, and simultaneously It is limited by varying the amplitude of the video signals.

Video signal source 10 supplies detected composite video signals that make up the brightness, chroma, sound, and sync signal components. The chromaticity component is connected to the chromaticity signal processing unit 24 of the chromaticity channel of the receiver via the frequency selection unit 20. For example, the chromaticity processing unit 24 includes signal amplification stages, automatic color control (ACC) and automatic phase control (APC) stages. The signals processed in unit 24 are further amplified by chroma amplifier 35 and fed to chroma demodulator 30 to derive R-Y, B-Y, and G-Y chrominance signals. The chrominance signals are combined with the brightness signal Y in the matrix network 40 to produce R, B and G color reproduction signals. The R, B and G signals are connected to kinescope 41 via an appropriate kinescope driver stage (not shown).

The brightness signal processing unit 42 of the brightness channel of the receiver contributes to amplifying the brightness components of the composite video signal from the source 10 and performing other processing. The processed brightness signals are supplied to a brightness amplifier 44 consisting of a pair of transistors 45,46 arranged in differential amplifier form and a current source comprising a transistor 47 and a resistor 48 for supplying operating currents to the transistors 45 and 46. do. The load circuit for amplifier 44 consists of a common collector bias transistor 85 and a load resistor 49 disposed in the collector circuit of transistor 46. The amplified brightness signals Y appear at the collector electrode of transistor 46 and are connected to matrix unit 40.

Manual adjustment of the contrast of the brightness signals is made by adjustment of the contrast adjustment potentiometer 95. For example, the contrast is increased by adjusting the wiper of potentiometer 95 to the uppermost position. The increased contrast increases the bias on the base electrode of the PNP type transistor 92 so that the conductivity of the transistor 92 is reduced.

At this time, since the bias on the emitter voltage of transistor 92 and the base electrode of emitter follower transistor 90 increases, the bias on the base electrode of transistor 47 increases.

Thus, transistor 47 is more heavily challenged, resulting in an increase in the gain of amplifier 44 and the peak amplitude of the brightness signals appearing at the collector of transistor 46. In contrast, the reduction in contrast is achieved by adjusting the potentiometer 95 to the lowest position. In this case, the conductivity of transistor 47 is lowered, so that the peak amplitude of the brightness signals is reduced, so that the contrast is reduced.

It should also be noted that the contrast regulation voltage, which appears at point A on the emitter side of transistor 90, is connected to the regulation input of chroma amplifier 35. Therefore, this voltage is supplied to adjust the gain of the chroma amplifier 35 in proportion to the amount by which the gain of the brightness amplifier 44 is adjusted. Therefore, the amplitudes of each of the brightness and chroma signals are kept in a desirable relationship as the contrast is adjusted.

Manual adjustment of the brightness level of the brightness signals is made via the brightness adjustment potentiometer 80. For example, the increase in brightness is achieved by adjusting the mover of potentiometer 80 to the top.

This increased luminance increases the bias on the base electrode of the PNP type transistor 79 to reduce the conductivity of the transistor 79.

The increased voltage present at the emitter side of transistor 79 is then connected to the base electrode of transistor 85 via resistor 82, junction D and point E, increasing the potential at the emitter of transistor 85 and the collector of transistor 46. The increased potential raises the D.C level of the brightness signal appearing at the collector side of transistor 46, thereby increasing the luminance of the reproduced image proportionally. In contrast, when the potentiometer 80 is adjusted to the lowest level, the D.C. The level and image brightness are reduced.

The high voltage source (i.e. voltage triple) generates high operating voltages for the kinescope's ultor and focusing electrodes. Periodic horizontal flyback pulses generated at the time of horizontal image return are supplied from the deflection circuit (not shown) of the receiver to the input terminal of the high voltage source 50. The current source comprising the operational supply voltage B + and the current crystal resistance 52 is D.C. It is connected to the input terminal. D.C. of Source 50 The currents flowing into the input stage represent the kinescope's beam current demand.

The voltage representing the average beam current demand is supplied via a sense circuit 54, an average sensitive filter capacitor 63 and a prepotentiometer 62. Sensing circuit 54 is applied to D.C. Any circuit arrangement suitable for detecting the magnitude of the beam current demand exhibited by the current supplied to the input stage may be any.

For example, the sensing circuit 54 may include the D.C. A suitably biased common emitter transistor having a base electrode connected to the connection point of the input stage, and an output collector load network connected to the capacitor 63 and the potentiometer 62.

In such a case, source 50 D.C. The increasing beam current represented by the current supplied to the input reduces the base bias of the transistor, thus raising the collector voltage of the transistor and the voltage across the potentiometer 62.

The beam current display voltage appearing at the pre-operator of the potentiometer 62 is connected to the input point B of the voltage divider 70 consisting of series connection resistors 71 and 73 via the base-emitter junction of the common collector transistor 65 and the resistor 67.

Point B is connected to the base input electrode of the auto-brightness transistor 75 via a resistor 74. The collector output electrode of the transistor 75 is connected to the base electrode of the transistor 85 via a current determining resistor 78 and a resistor 82.

The midpoint C of the voltage divider 70 is connected to the base input electrode of the automatic contrast control transistor 87.

The collector output of transistor 87 is connected to circuit point A and the base of current source transistor 47 through a resistor 89 and a base-emitter junction of transistor 90.

Potentiometer 62 is displaced to a normal operating state, so that when the beam current demand is sufficiently low that no beam current limit is required, the regulated voltage appearing at point B of voltage divider 70 is insufficient for the bias transistor 75 or 87 to conduct.

The voltage divider 70 causes the conduction of the transistor 87 to be delayed with respect to the conduction of the transistor 75 when there are excessive beam currents.

When the non-critical current demand exceeds the first threshold level and generates a voltage at the mover of potentiometer 62 representing the first area beam currents, a proportional regulating voltage appears at point B of voltage divider 70.

This voltage is the magnitude that makes transistor 75 conductive. However, the proportional voltage at point C due to the voltage dividing of resistors 71 and 73 is still insufficient for transistor 87 to be conductive.

The increased conductivity of transistor 75 causes the collector voltage of transistor 75 to decrease in response to the voltage present at point B. This collector voltage causes the corresponding decay voltage to appear at the base and emitter sides of transistor 85 via resistors 78 and 82.

The collector current of transistor 46 is still unchanged because it is determined by the current supplied from source transistor 47, and the later current still does not change. Thus, because the collector current of transistor 46 does not change the voltage across resistor 49, the collector voltage of transistor 46 is reduced by the amount by which the base and emitter voltages of transistor 85 are reduced.

Thus, the D.C. The level is reduced by the same amount.

D.C. This reduction in level suppresses excessive beam current levels in the first area to reduce the brightness of the playback image.

When the non-critical current requirement is greater than the first threshold level and exceeds the second threshold level far beyond the first zone, the proportional voltage present at point C of the voltage divider 70 is large enough to bias the bias transistor 87 to conduct. . At this time transistor 75 is still conductive. However, at this time transistor 75 is operated in a conductive region that is saturated such that an increase in base bias does not cause a corresponding decrease in the collector regulation voltage of transistor 75. The saturation level of transistor 75 is determined by the values of current crystal resistance 78 and resistors 82 and 84.

Thus in this example transistor 87 no longer adjusts the luminance beyond the second critical level at which it is challenged. In this regard, it should be noted that the resistor 74 contributes to limiting the base electrode of transistor 75 in saturation, in order to prevent the base current of transistor 75 from disrupting the action of voltage divider 70 and transistor 87.

The increased conduction of transistor 87 in the second regulation region above the second threshold level causes the collector voltage of transistor 87 to decrease in response to the voltage at point C. This collector voltage causes the corresponding decreasing voltage to appear across the base-emitter junction of resistor 89 and transistor 90. Therefore, the current conduction of transistor 47 is reduced, which reduces the signal gain of brightness amplifier 44 and reduces the peak amplitude of the brightness signals appearing at the collector output of transistor 46. The amplitude reduction of the brightness signals suppresses excessive beam current levels in the second region above the second threshold level to reduce the contrast of the reproduced image.

Note that at this time, in response to the reduced collector voltage of transistor 87, the reduced voltage at point A is connected to the control input of chromatic amplifier 35. This voltage reduces the gain of amplifier 35, thereby reducing the peak amplitude of the chromaticity signals processed by amplifier 35.

The reduction in image contrast in response to beam current levels in the second region allows for an additional limit of beam current limiting without making the viewer feel much of the beam limiting action.

If only the image luminance is adjusted through the first region and the second region, the reproduced image appears with excessive contrast in the beam limiting action in the second adjusting region. Also in color television receivers, simultaneously adjusting the brightness and chroma signal amplitudes during the second control region makes the beam limiting action less visible and less unpleasant during this period since the brightness and chroma signal amplitudes remain in a desirable relationship. to be.

In the embodiment, it should be noted that the brightness is described as being directly adjusted in response to the voltage generated at the emitter of transistor 79 and the proportional voltage at junction D. The brightness may also be controlled in accordance with the method discussed in the co-pending US patent specification filed with the present specification and entitled to the same assignee as the present invention under the heading “luminance control circuit using a closed control loop”.

More specifically, the method uses a keyed differential comparator (not shown) connected between points D and E. This comparator supplies the signal generated at point D to the first input, as discussed, and a color reproduction signal (e.g., B) from the matrix 40 to the second input. Detect the "back porch" level (approximately black level) of the sync section of the video signal (e.g. with a burst gate) that generates an output control signal determined by the input signals applied to this comparator. This comparator is keyed to ON. The output signal is the D.C. It is applied to the base of transistor 85 via point E to control the level.

Claims (1)

As described in the text and as shown in the figure, D.C. A video signal transmission channel for processing an image reproduction video signal having a level, and a video reproduction device for reproducing an image in response to video signals transmitted through the channel; Current is equal to the peak amplitude of the video signal and the DC An average beam current limiter responsive to a level, comprising: a device for inducing a control signal indicative of the magnitude of the average current drawn by the image reproducing apparatus, and wherein the current exceeds a predetermined threshold level by the amount of current in the first region; The DC in a direction to limit the current above the threshold level To change the peak amplitude and to change the peak amplitude in a direction to limit the current above the threshold level when the current exceeds the threshold level by a relatively large amount of current in the second region. An improved average beam current limiter, characterized in that it is equipped with a device for coupling said regulation signal to a channel.

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