KR920000980B1 - Video signal peaking apparatus - Google Patents

Abstract

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Description

Video signal picking device

1 is a partial schematic block diagram of a luminance channel portion of a color television receiver incorporating a picking system according to a specific embodiment of the present invention.

FIG. 2 is a schematic circuit diagram that can be used for generating a cooring level control voltage in the picking system of FIG.

* Explanation of symbols for the main parts of the drawings

17 luminance signal amplifier 18 signal generator

19: translator 20: signal combiner

The present invention relates to a video picking system for improving the horizontal detail depiction of image reproduction, and more particularly to a coring level in which the picking signal formed in addition to the video signal introducing the desired detail enhancement does not interfere with the desired picking effect. A peaking system suitable for use in a television receiver that is cored to a furnace.

Coring of a signal (signal processing by a translator having a deadband propagation characteristic for the axial signal bypass to remove the "core" of the signal axis) is a known signal processing function and is usually a means for noise reduction purposes. For example, see pages 134-140 of the March 1978 issue of the SMPTE journal, entitled "Digital Techniques for Television Noise Reduction," by J.P.Rossi. In using a coring circuit, facilities are needed to adjust the resulting coring level. Such facilities can be adjusted by hand (e.g., SMPTE Journal March 1968, 221-228) (see page RHMcmann et al. In a paper entitled "Advanced Signal Processing Techniques for Color Television Broadcasting"). As can be) or to enable dynamic adjustment of the coring level (e.g., as described in Burrus, U.S. Patent No. 4,167,749), the coring level depends on the detected noise level as a function of the detected noise level. Is provided).

In television receivers, the horizontal peaking signal component can be formed in addition to the received luminance signal for the purpose of increasing detail, which signal peaking component can be used to reduce the possibility of unwanted background noise increase or decrease as the desired image detail is increased. It is preferable to ring. In L. Cochran's concurrent US patent application No. 373,750 entitled “Dynamic Coring Circuit”, a low-frequency component of a luminance signal whose peak variation is to be peaked between black and white limits by controlling the coring of horizontal peaking components. How to adjust the level is shown. The dynamic control proposed by Cochran means that the maximum co-ring is performed at the extreme black level and the minimum coring is performed at the extreme back level. It is based on the phenomenon of being lowered. Thus, using Cochran's system to control the coring depth of the peaking signal components, the maximum increase in noise in the viewing picture is suppressed, suppressing the noise increase and reducing the higher noise level.

If the coring level of the horizontal peaking signal is undesirably changed, the magnitude of the cored signal, that is, the magnitude of the residual signal remaining after core removal is also changed. Thus, for example, if the coring level is increased, the peaking component of the reduced magnitude is added to the luminance signal, thereby undesirably reducing the peaking effect.

In the system illustrated for variable coring of the horizontal peaking signal, the range of the coring level can be between 0% and 6% of the maximum peak to peak swing of the peaking signal. Adjusting the coring between the minimum and maximum levels only slightly changes the residual amplitude of the peaking peaking signal component, but such adjustment causes the residual amplitude of the low or medium peaking and other peaking signal components to vary much larger. . Since these other peaking signal components apply largely to the sharpness of the entire image given by the peaking system, the size indicated by the coring level adjustment can significantly interfere with the peaking effect on the residual signal.

The present invention relates to a horizontal peaking system employing coring of horizontal peaking signal components, wherein the level of coring can be varied without being impeded to achieve the desired peaking effect. The peaking signal generator coreably adjustable according to the principles of the present invention is arranged to supply an input to the automatic picking control system, wherein the automatic peaking control system is subjected to level fluctuations that are corrugated in such a way that it does not interfere with the desired picking effect. It automatically responds to changes in the residual signal magnitude.

According to an embodiment of the invention, the horizontal peaking signal formed in response to the video signal indicative of the brightness of the image is correlated to an adjustable level before being applied to the gain control peaking signal translator. The output of the translator is combined with the luminance signal to form a peak luminance signal. In response to the peak luminance component within the selected frequency range, the peak detector generates a control voltage to control the gain of the peaking signal transistor. The gain control means to contrast the change in the magnitude of the component delivered to the peak detector. When the coring level changes, the change in magnitude of the residual signal delivered to the input of the peaking signal translator is practically eliminated by compensating for the change in the transducer gain. Hereinafter, the present invention will be described in more detail with reference to the drawings.

1 shows a luminance channel portion of a color television receiver. The video signal indicative of the luminance of the image to be reproduced is derived from the composite color video signal received by a suitable comb filter device (e.g., as shown in Pritchard, US Pat. No. 4,096,516), appear.

The luminance signal at terminal I is coupled to the input terminal of the delay line 16 via a series connection of the blocking capacitor 14 and the resistor 15. Specifically, the resistance value of the resistor 15 is selected to terminate the input terminal of the delay line with an impedance that actually matches the characteristic impedance of the delay line 18. The luminance signal amplifier 17 responds to the delayed luminance signal at which the delay line 16 appears at the output terminal L '.

For the purpose of horizontal picking signal formation, the output end of delay line 16 is preferably mis-terminated to obtain a reflection effect. Therefore, the signal appearing at each end of the delay line 16 is as follows. That is, the sum signal of the luminance signal delayed once at (a) terminal L ', and the luminance signal which is not delayed at the terminal L and the luminance signal delayed twice is shown. As an illustration, delay line 16 is a broadband device that exhibits linear phase characteristics over a frequency band occupied by a luminance signal (e.g., extending to 4.0 MHz) and provides a signal delay of 140 nanoseconds.

The difference between each signal at terminals L and L 'corresponds to a suitable horizontal peaking signal to add to the luminance signal to improve horizontal detail by efficiently boosting the high frequency luminance component with the maximum boost occurring at about 3.5 MHz. An adjustable cored variant of this peaking signal is formed by an adjustable cored peaking signal generator 18 in response to inputs from terminals L and L '. The coring depth of the picking signal generated by the signal generator 18 varies from the output terminal cc of the variable coring level control voltage source 25 to the coring level voltage applied to the signal generator 18.

The adjustable cored horizontal peaking signal output of the signal generator 18 is supplied to a gain controlled horizontal peaking signal translator 19 in a push-pull manner. The magnitude of the horizontal peaking signal output of the translator 19 changes in accordance with the gain control input at terminal pc of the translator 19, which will be described later.

The peak luminance signal is formed by the signal combiner 20 in response to the push-pull output of the luminance signal amplifier 17 and the push-pull output of the horizontal peaking signal translator 19. The peak luminance signal amplifier 21 generates a single-ended output for delivering to the peak luminance signal output terminal PL in response to the push-pull deformation of the peak luminance signal generated by the signal combiner 20.

The peak luminance signal appearing at the terminal PL is applied to the input of the band pass amplifier 22 for the purpose of automatic peaking control. Since the band has a pass band of about 1 MHz around the frequency of about 2 MHz, the amplifier 22 transmits the peak luminance signal component in the pass band to the peak detector 23, which peak detector of the delivered component. Generate a control voltage proportional to the amplitude. This control voltage is applied to the gain control input terminal PC of the translator 19 to control the magnitude of the horizontal peaking signal supplied to the combiner 20 to the extent that it prevents a change in the transmitted component amplitude. Examples of advantageous circuits for the operation of such automatic picking control systems and for performing the functions of elements 17, 19, 20, 21, 22, and 23 are US patents filed Oct. 9, 1981. It is described in detail in the original 310,139 and related picking control operation is also described.

In the case where only manual control of the coring level of the peaking signal input at the translator 19 is desired, the variable coring level control voltage source 25 is simply composed of a potentiometer with a suitable direct current power source connected across a fixed end terminal. It may be composed of a control terminal (cc) connected to an adjustable tap of the potentiometer. When the tap adjustment changes the magnitude of the DC voltage applied to the control terminal cc, the magnitude of the signal “core” removed from the signal generator 18 is changed. While a change in the residual signal magnitude delivered to the input of the translator 19 occurs, in response to the transmitted peak signal component, the peak detector 23 is coupled to the translator 19 to rule out severe disturbances of the peaking effects that have been introduced. Appropriately change the gain control voltage supplied to the terminal PC which introduces the compensation gain variation.

If dynamic control of the peaking signal coring level is desired with the method presented in the above Cochran application, the variable coring level control voltage source 25 is now described as described in W. Harlan's simultaneous ongoing US patent application 373,531. It is preferable to take the form as schematically shown in FIG.

In FIG. 2, the signal appearing at terminal I (the luminance signal input terminal of the FIG. 1 system) includes a luminance signal, which is represented by a polarity in which the luminance signal (blacker than black) deflection synchronization pulse component extends in the negative direction. . The signal from the terminal I is amplified NPN transistor through a series coupling of the blocking capacitor 81 and the resistor 82 to the capacitor 81 and the resistor 82 connected between the base electrode of the NPN transistor 83 and the terminal I. 83). The emitter electrode of transistor 83 is directly grounded while the collector electrode of transistor 83 is connected to operating power supply terminal + Vcc via load resistor 84. Resistor 89 shunts the base-emitter path of transistor 83 directly.

The feedback between the collector and the base electrode of the transistor 83 includes a pair of resistors 85 and 86 connected in series between the collector and the base electrode, a capacitor 88 connected in series with a series coupling of resistors, and a series arrangement. Provided via a bridged T filter network formed of capacitor 87 connected between the junction of resistors 85 and 86 and ground.

The PNP transistor 90 having a feedback clamping action has an emitter electrode directly connected to the collector electrode of the amplifying transistor 83, and a collector electrode directly connected to the junction of the capacitor 81 and the resistor 82. A pair of series connected resistors 91 and 93 is connected between ground and the + Vcc terminal to form a voltage divider, which is applied directly to the base electrode of the clamping transistor 90. Generates a reference direct current potential at the junction.

The circuit described forms an inverted signal translator for an input luminance signal that exhibits low pass frequency response and provides a signal delay suitable for matching with the delay divided by the delay line 16. For an illustrative set of circuit parameters, the high frequency roll-off of the frequency response characteristic is stepped as a cutoff frequency (-3 dB point in characteristic) that falls at approximately 1.05 MHz.

In circuit operation for the power source 25, the capacitor 81 isolates the signal transistor from any DC level change that may occur at terminal I as a result of the input signal swing adjustment. The direct current recovery action is performed by the clamp transistor 90 which is usually driven in a conducting state periodically while the synchronization pulses appear. The charge on capacitor 81 is readjusted during the biceps conduction cycle, which tends to clamp (and then slightly offset) the synchronous pulse peak of the transistor output at a predetermined potential to the reference potential generated by voltage dividers 93 and 91. do.

The reference potential is selected so that the transistor output potential (at terminal cc) generated in response to the black level input introduces the desired coring depth (eg 6%). As determined by the ratio of the resistance of resistor 82 to the sum of resistors 85 and 86, the gain of the signal transistor is such that the black-to-white signal swing for the transducer output potential at terminal cc is within the desired range. It is selected to provide a change in the coring depth. Illustratively, the gain selection is such that the zero coring level reaches a back level of 70 to 80 IRE units or more.

A “soft” clamping action is provided to the clamp transistor 90 that keyes into the signal itself (ie, there is no external keying provided) in the described circuit. For some scene transitions, conduction by transistor 90 may be excluded for several line periods. However, these transition states are acceptable and thus the complexity and waste added by external keying can easily be avoided.

In using the FIG. 2 circuit, as the low frequency component of the luminance signal at terminal I changes, the effective level of coring in the peaking signal generator 18 of the FIG. 1 system is automatically controlled by a change in the control potential generated at terminal cc. Is adjusted. While such coring level adjustments cause unwanted amplitude changes in the residual signal delivered to the input by the newlywed transistor 19 of the FIG. 1 system, the adverse effects of these amplitude changes are caused by the control potential output of the peak detector 23. It is practically prevented by the gain compensation change of the generated signal transistor 19.

The above-mentioned application of W. Harlan also outlines the details of a circuit that can be advantageously used to perform the function of a properly cored horizontal signal peaking signal generator 18 of the FIG. 1 system. In such a configuration by reference, the peaking signal generator 18 includes a straight signal translating channel and a non-linear signal translating channel, providing a straight clipped peaking signal and a double clipped peaking signal forming a horizontal peaking signal. A nonlinear translating channel, the two channels respond to the difference between signals at each end of delay line 16.

Coring of the peaking signal is accomplished by combining the output of the channel to remove the core portion of the horizontal peaking signal. The nonlinear signal translating channel only takes the form of a limiting amplifier, and the gain distribution between the cascaded connecting stages of the limiting amplifier varies with the change in the coring control potential. The cascaded amplifier stages of the limiting amplifiers each include a differential amplifier, each amplifier inducing an operating current from the collector electrode of each current source transistor. The base-emitter path of each current source transistor is connected in series across a biased public source. The variation of the variable direct current impedance connected in parallel with the base emitter path of one of the current source transistors results in the desired coring level control with the variable direct current impedance including the collector-emitter path of the control transistor with a properly biased base-emitter junction. to provide. In order to bring the minimum coring level to zero, the other control transistor is in parallel between the first control transistor and in parallel with the first control transistor, the base of which is transferred to the base of the first control transistor. Respond to the same level of coring.

Claims (3)

A video signal picking system of a video playback system comprising a video signal source (I) representing the brightness of a video being reproduced, the video signal picking system comprising: a coarse level control that forms an adjustable cored horizontal picking signal output in response to the video signal Means 18 for forming a horizontal peaking signal output having a terminal cc, means 25 for generating a variable coring level control potential supplied to said control terminal, and said adjustable core of said forming means Means 20 for combining a gain controlled peaking signal translator 19 responsive to a horizontal peaking signal output and a video signal derived from said video signal source forming a peak luminance signal with the output of said gain controlled peaking signal translator And a passband having an input responsive to the peak luminance signal and surrounding a portion of the frequency band occupied by the video signal. Feedback means for controlling the gain of the peaking signal translator with a variation in contrast to the magnitude so that a variation in the coring level does not interfere with the peaking in response to an output magnitude of the frequency selective amplifier (23), wherein the coring depth of the horizontal peaking signal caused by the forming means is in accordance with the potential level appearing at the control terminal. A signal line according to claim 1, further comprising a delay line (16) having a terminated input terminal (L) to which a video signal from the video signal source (I) is applied and a misterminated output (L '). And a means (18) for responding to a signal appearing at said input / output terminal of said delay line. The video signal picking apparatus according to claim 1, wherein said control potential generating means (25) responds to a video signal from a video signal source (I).

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