KR800001023B1 - Switching arrangement for flesh tone correction and chrominance overload control circuit - Google Patents

Abstract

Switching apparatus is included in a color television receiver for changing the threshold of a saturation overload detector and simultaneously changing the gain characteristics of an associated chrominance signal amplifier. The overload detector is operative to limit chrominance signals at a lower level when noisy signals are present and at a higher level when relatively noise-free signals are present. The switching apparatus is arranged to avoid annoying large shifts in picture saturation upon its operation.

Description

Switching device for bright tone correction and chromatic overload control circuit

Figure is a circuit diagram of a chromaticity signal processing apparatus according to the present invention

The present invention relates to a color television signal processing apparatus, and more particularly, to an apparatus for operating and deactivating automatic tone tone correction and chromatic signal overload protection circuits in such apparatus. Differential chroma signal gain control device is L. a. It is described in U.S. Patent No. 3,740,462, issued June 19, 1973 to Aoud, which includes a burst amplitude detector that provides a chroma gain control signal and a peak chromaticity signal that provides an additional gain control signal. It includes a level detector. The latter gain control signal is responsive to noise and image information and drives to prevent over saturation during reception of the noise color signal. This type of device is sometimes called chromatic overload protection. Conventional automatic chromatic signal gain control devices provide corrections for undesirable deviations from a predetermined amplitude relationship between the coloration burst and the maximum chromaticity signal. The deviation of the burst to chromaticity ratio appears as an error result in the transmission of the color television signal.

The additional transmission error that may appear is related to the relative phase of the color burst as compared to the chroma signal. This phase error is discernible by the viewer, particularly when observing vivid tones and color reproduction, which is more easily perceived within the image than most others. Many sharpness correction circuits propose to minimize the phase deviation of the color near the orange tone that is perceived as fresh (ie, substantially coincident with the ″ + I ″ axis in color television terminology). A particularly advantageous dynamic vivid color tone corrector is described in US Pat. No. 3,663,744, issued May 16, 1972 to L. A. Howard.

In the case where the transmitted signal is maintained in a proper phase and amplitude relationship and the received signal intensity is a relatively noiseless chroma signal, it is desirable to disable the chromaticity overload and sharp tone correction circuit to the viewer. The highlighted areas of chromatic signal amplitude (saturation) and phase angle (hue) are useful for optimal color reproduction.

According to the present invention, an apparatus for changing the operating characteristics of an included chromaticity signal processing apparatus is provided in a color television receiver. The signal processing apparatus includes at least one gain control chromaticity amplifier and an image period signal detector. The detector responds to the peak of the chroma signal in excess of the selected level and provides the amplifier with the resulting gain control signal.

A static DC gain control voltage source is also connected to the amplifier to set its normal gain. The switching device is connected to a detector and connected to a static gain control voltage source to vary the peak detection level and static gain control voltage in the city, increasing the allowable peak deviation of the chroma signal while increasing the relative level of the other parts of the chroma signal. To avoid sudden changes in chromaticity level when the switching device is operated.

According to another aspect of the present invention, a vivid color tone correcting apparatus is included in the signal processing apparatus for compressing the entire area of the color in the vicinity of the ″ + I ″ axis or orange. The switching device is arranged such that the sharp tone corrector does not operate when the threshold level for the gain control device is increased.

Hereinafter will be described in detail with reference to the accompanying drawings an embodiment of the present invention.

According to the figure, the synthesized chroma signal is popular in the first chroma amplifier 20. The short-color chromaticity signal constitutes an amplitude modulated suppressed subcarrier signal. The phase information is related to the color tone of an image line segment within the subcarrier signal, and the amplitude information is related to saturation. This composite chromatic signal contains a color reference burst (e.g. at 3.58 MHz), which is repeated for each line retrace period. This color burst provides a reference phase for the reproduction of modulated information on the suppressed subcarriers as is known.

The amplified push-full chroma signal output from the first chroma amplifier 20 is applied to a second chroma amplifier 22 constituting differentially coupled transistors 24 and 26. Current source transistor 28 is associated with transistors 24, 26. As described later, the gain control signal is applied to the base of the transistor 28.

The erase signal response transistors 30, 32 are connected across the collector-emitter passages of transistors 24 and 26 and operate to remove the burst component from the amplified chromaticity signal reproduced across the load resistor 34, respectively. The erase pulses are sourced from the line scan generator as described and known in Howard's Patent No. 3,740,462 described above. The resulting video-period chromaticity signal across resistor 34 is applied to terminal 15 through emitter follower transistor 36, which is the chromatic signal processing integrated circuit CA-produced by RCA Corporation. Corresponds to the 3216 type terminal.

A coupling circuit 38 is provided between the terminal 15 and the saturation control amplifier 40, which is located, for example, on the second integrated circuit of the color demodulator type. The gain of amplifier 40 is controlled by potentiometer 42. Such a good amplifier is December 6, 1974. a. Howard and Lee. second. US patent application 530,405, filed by Whitman.

The video period chromaticity signal provided at terminal 15 is connected via input condenser 44 to input terminal 13 associated with peak detector circuit 46. In the peak detector circuit 46, the low voltage divider 48 biases the base of the common emitter transistor 58 and couples the chroma signal to it. The collector of transistor 58 is connected via a terminal 16 to a time constant circuit which constitutes separate elements comprising capacitor 60, resistor 62 and voltage divider resistors 64,66. The gain control voltage generated by the capacitor 60 is connected to the base of the transistor 86, the collector of the transistor is connected to the power supply, and the emitter is connected to the base of the current source transistor 28 through the resistor 88. Resistor 90 and diode 92 are connected in series between the base of transistor 28 and the reference potential (ground) point.

Burst-response auto-color gain control and color cancellation are provided by the device in circuit elements 68-84 for the chroma amplifier. The circuit elements shown and their functions are described in detail in Mr. Howard's Patent No. 3,740,462, the description of which is hereby incorporated by reference.

According to the present invention, the switching device 100 is provided for changing the operation state of the peak detector 46 and for operating and deactivating the vibrating tone correcting device 112. The switching device 100 constitutes a bipolar switch, for example, in which each of the two center contacts in the bipolar switch is returned to the reference potential (ground).

One additional contact is connected to the voltage divider 48 via a threshold ring resistor 102 and terminal 13 which operates to set the limit bias for the peak detector transistor 58.

Bypass capacitor 104 is connected between one end of resistor 102 and ground, which is remote from terminal 13.

The second additional contact of the switching device 100 is connected to the contacts of the bottoms 64 and 66 via a gain reduction resistor 98.

The second contact is connected to the current supply circuit 106 associated with the vibrating color corrector 112 via the isolation diode 114 and terminal 15 '. Bypass capacitor 116 is connected to ground from terminal 15 '.

The current supply circuit 106 provides an operating current to the " I " phase detector 108 and the chroma signal limiting circuit 100, the chroma signal limiting circuit being operated to provide an operation signal to the vibrating color calibrator 112. The general form of the vibrating color corrector 112 shown is described in Mr. Howard's Patent No. 3,663, 744 described above, the contents of which are described herein by reference. A detailed description of the improved sharpening correction circuit is given in a. It is described in Howard, US Pat. No. 580,681, and is suitable for use in the present invention.

In the operation of the device shown, the chroma signal is amplified by the differential transistors 24, 26 and the resulting output signal is provided by terminal 15. The burst component is suppressed from the output signal by the conduction of transistors 330 and 32 during each line retrace period. The gain of amplifier 22 is canceled in response to the peak of the picture period chromaticity signal provided at terminal 15. The circuit reduces the gain of amplifier 22 when this peak is unnecessarily large and tends to cause blurring and supersaturation of the displayed image. This result occurs, for example, when there is a catch signal ″ spike ″ having a relatively high amplitude. To prevent this poor result, the capacitor 44 couples the chromaticity signal to the peak detector transistor 58. Transistor 58 is normally nonconductive. Resistive voltage divider 48 provides a portion of V _be (forward base-emitter conduction voltage) to the base of transistor 58 to determine the limit for conduction of transistor 58. That is, a static bias potential of about 450 to 500 millivolts is applied to the base at transistor 58 when switch 100 is in the position shown (sharpening and overload ″ on ″). This bias potential is about 200 millivolts, which is insufficient to bring transistor 58 into a conductive state. Therefore, it is necessary to conduct a positive chromatic signal peak detector detector 58 of about 200 millivolts or more.

Signals or noise above this predetermined limit conduct the transistor 58 and thus discharge the capacitor 60.

The voltage across capacitor 60 determines the gain of amplifier 22. The static voltage across capacitor 60 is set by voltage divider resistors 64 and 66. Depending on the component values shown, this static voltage will be about +3.8 volts when switch 100 is in the position shown. The voltage across capacitor 60 is applied to the base of transistor 86 and sets the static operating current of transistor 28 in association with resistors 88 and 90 and diode 92.

When the circuit value shown in the figure is used, the chromaticity output signal is provided to terminal 15 having a peak-to-peak value of about 400 millivolts when the switch 100 is in the " on " state.

It can be seen that the color erased portions of circuit elements 70-84 do not adversely affect the voltage across capacitor 60 during normal reception of the color signal. That is, transistor 82 is biased off except when the associated autochromatic signal gain control detects the received burst at a very low level. In such a case, transistor 82 conducts to discharge capacitor 60 and thus shuts off current source transistor 29. Then the chroma processing circuit is not operated and the associated receiver receives only black and white images as is known.

When switch 100 is in the shown position (on), sharp tone corrector 112 is operated to provide a certain suppression in the full color region near sharp tone as described in Mr. Howard's patent described above. In this case, diode 114 is reverse biased, the bias voltage being the voltage provided by resistors 64 and 66 more positively than the base bias voltage associated with the transistor of current source 106 connected to the anode of diode 114.

The above-described operation mode is usually used when the received signal is considered to contain a burst which is not suitable for chromatic phase noise and chroma noise components are inadequate. However, if the received signal is relatively noisy and stable, the viewer may not operate the sharpener 112 and turn the conversion switch 100 ″ off ″ simultaneously with the maximum peak-to-peak of the chromaticity output signal. You can increase your level.

In the latter case, the color tone calibrator 112 will not operate because the cathode of the diode 114 is returned to ground while a constant voltage is applied to the anode. Thus diode 114 conducts and applies a voltage that is not sufficient to conduct them to the base of the transistors in current source 106. Next, the associated circuits in detector 108, limiter 100 and sharpening calibrator 112 do not operate.

At the same time, resistor 102 is connected between terminal 13 and ground to reduce the static voltage on the base of peak detector transistor 58 by 300-4350 millivolts. Complementary increments that maximize the peak-to-peak chromaticity output signal at terminal 15 are made next. The overload detector 46 will continue to operate to prevent oversaturation of the noise spikes only at higher (saturated) levels.

When the limit of the peak detector 58 is changed in the above-described manner, the chromaticity signal level at the output terminal 15 is also expected to increase. To prevent a sudden change in saturation level in the regenerated image, resistor 98 can be connected across resistor 66 by placing switch 100 in the " off " state. In this way, the static voltage across capacitor 60 is reduced, thus reducing the gain of amplifier 22 to maintain the chromaticity signal at the same relative level as it occurs when the switch is turned ″ on ″. Those skilled in the art will appreciate that many modifications can be made to the illustrated circuits without departing from the object of the invention.

Claims (1)

As described in the text and illustrated in the drawings, in a color television receiver including a chromatic signal processing apparatus, at least one chromatic signal amplifier 22 having control gain characteristics, for providing a gain control signal to the signal amplifier, A signal detector 46, a static DC gain control voltage source 64,66, coupled to the signal amplifier, responsive to the departure of an image period chromaticity signal having an amplitude exceeding a level, a gain control signal and a gain control voltage to the amplifier; An apparatus 86 for coupling the power supply, to simultaneously change the static gain control voltage and a predetermined level to increase the allowable peak deviation of the chroma signal while maintaining the level of the other portion of the chroma signal relatively. It is characterized by consisting of a gain control voltage source and a switching device 100 connected to the detection device. Switching device for color tone correction and chromaticity overload control circuit.

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