KR830002655B1 - Signal Processing Circuit with Nonlinear Transfer Function - Google Patents

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Description

Signal Processing Circuit with Nonlinear Transfer Function

1 is a block diagram of a color television receiver using a nonlinear signal processor according to the present invention.

2 illustrates one embodiment of a non-linear signal processor in accordance with the present invention.

3 shows a modified form of the circuit shown in FIG.

4 and 6 show amplitude response characteristics useful for understanding circuit operation according to the present invention.

7 shows another embodiment of a circuit according to the invention;

FIELD OF THE INVENTION The present invention relates to electrical circuits characterized by nonlinear amplitude lines, in particular attenuation of image vertical detail information in color television receivers comprising a comb-like filter or similar circuitry in order to disadvantage the luminance and chromaticity components of the color television signal. And circuitry for selectively providing amplitude recovery and peaking.

In the United States, in color television devices, such as the developed device, the luminance and chromaticities of the color television signal are the chromatic component at the even multiples of half the line scan frequency and the luminance component at the integer multiples of the horizontal line scan frequency. And are placed in the video frequency spectrum in the interpolated frequency relationship. Various comb-shaped filter devices are known for separating the intervening luminance and chromatic components of a video signal, for example, US Pat. No. 4,143,397 (D. D. Holmes) and US Pat. No. 4,096,516 (D. H. Fritchard) and references cited here.

The comb filtered luminance signal appearing in the luminance output of the comb filter is summarized as a "comb filter" effect over the entire band. This “comb filter” action across the high frequency receiver region divided into chromatic signal components has the desirable effect of planting chromatic signal components. However, synthesizing this comb-like filter action into a low frequency band subdivision that is not divided into chromatic signal components is not necessary for the desired removal of the chromatic signal components, but only to plant unnecessary luminance signal components. The components at the bottom end of the undivided band for this purpose are represented by a "vertical detail" luminance signal. This preservation of the vertical details is necessary to prevent the loss of vertical sharpness in the luminance component of the screened image.

One device for preserving vertical detail information uses a lowpass filter connected to the output of a comb filter that exhibits a comb filtered color component. The upper cutoff frequency of such a filter is below the band occupied by the chroma signal component (ie the choice to be located just below 2 MHz). Such a filter causes the sub-chromatic luminous signals to be selectively coupled to the summing network from the chromatic output of the comb filter, where the selectively combined signals are summed with the comb-filtered luminance output signal from the comb filter. The summed signal is composed of the "comb-filtered" high-frequency portion from which the chroma signal components have been removed and the assisted non-filtered (ie "flat") low-frequency portion of all luminance signal components (including the frequency band above the filter cutoff frequency). Include.

Occasionally, it is necessary to emphasize or peak vertical detail of a projected image by adding a greater amount of vertical detail signal to the luminance signal than is required to restore the luminance signal to its original form (i.e., " flat " amplitude characteristic). desirable. The additional vertical detail signal is then driven to emphasize vertical detail information to emphasize image detail sharpness. However, this emphasis on low level luminance signal components may provide a poor visibility effect when noise interference is present or when there is an undesirable emphasis upon vertical detail of the luminance signal.

This will also be unnecessarily emphasized if there are alternating line set-up variations (ALSUV) in the video signal. This ALSUV phenomenon is a form of low-level signal interference formed by line-to-line video signal fluctuations or fluctuations in the level, and may also be due to misalignment of the signal processing apparatus in a broadcast transmitter. This ALSUV interference is especially detected for low level video signals of approximately 5% maximum required video signal amplitude and provides poor visibility effects in unnecessarily amplified and reproduced images with vertical detail emphasis.

Techniques for minimizing the adverse effects of noise and other undesirable components of a video signal include processing referred to as a coring signal as described in US Pat. No. 3,715,477 to eliminate small amplitude deviations of the signal (including noise). Use technology.

A convenient device that is particularly concerned with low-level detail signal information that restores the luminance signal and that completes the "coating" of the vertical detail signal in a way that does not compromise the vertical detail information is a US patent of "Video Image Vertical Restoration and Emphasis". US Pat. No. 038,202 (applicants, Deuldeu A. Lagoni and J. S. Purrer).

The device described in the patent application also provides emphasis of vertical detail signal information without simultaneously emphasizing noise and interfering signal components such as ALSUV.

Devices that are planted to prevent kinescope "blooming" where large amplitude vertical detail signals distort or obscure detail are well known in the art and are well known in the art. The nonlinear processing technique is a signal processing circuit having a nonlinear amplitude transfer function for selectively providing paring, emphasis (peaking) and reconstruction for small paring medium and large amplitude video signals according to the principles of the present invention. Consists of

The circuit according to the invention comprises an amplifier having one input and output terminal each comprising an amplifier device having input and output. A first feedback passage comprising a first impedance is coupled between the input and the output of the amplifier device. In addition, a second feedback passage comprising a second impedance and a critical switching network are connected between the input and the output of the amplifier device. The switching network has one input connected to the output of the amplifier device and one output connected to the output terminal of the circuit. The switching network exhibits one conducting state in response to the signal amplitude of the first magnitude in the first region and another conducting state in response to the signal amplitude of the second magnitude greater than the first magnitude in the second region.

According to a feature of the circuit according to the invention, the third feedback passage is provided between the input and the output of the amplifier device. The third feedback passage has an additional threshold switching network having an input coupled to the third impedance and to the output of the switching network in the second feedback passage. The additional switching network exhibits one conducting state in response to signal amplitudes of the first and second magnitudes and another conducting state in response to a third signal amplitude greater than the first and second magnitudes in the third region. . The second feedback passage also includes an additional impedance. The switching network in the second passage is connected to the additional impedance to control switching of the current conduction through the additional impedance.

According to another aspect of the present invention, a circuit according to the principles of the present invention may be used in a color television receiver or similar device to convey a vertical image detail signal having a nonlinear transition function over defined areas of vertical detail signal amplitude. Can be used.

The present invention will be described in more detail with reference to the accompanying drawings.

In FIG. 1, a source of synthetic color video signals 10 comprising luminance and chromaticity components comprises a comb-shaped filter using a charge transfer device (CCD) as shown in US Pat. No. 4,096,156. It is supplied to the input of the same well-known comb-shaped filter 15 of national tone. These luminance and chromatic components are arranged in the video signal main frequency spectrum in a frequency interleaved relationship. This luminance component has a relatively wide bandwidth. (Extended to about 4 MHz at D.C or 0 frequency). The upper frequency region of the luminance component is divided into chroma components including phase modulated with color information and subcarrier signals of 3.58 MHz amplitude. The amplitude frequency response of the comb filter 15 for light comb filter operation represents the peak amplitude response at an integer multiple of the horizontal line scan frequency (approximately 15.734 Hz) extending from DC or 0, and the 3.58 MHz chroma subcarrier. Amplitude 0 is shown in multiples of the line scan frequency of 1/2 including the frequency. The amplitude frequency response of the comb-shaped filter 15 for the color comb filter shows a magnitude-to- amplitude response at even multiples of the half tin frequency, including 3.58 MHz, and an amplitude zero at integer multiples of the line frequency. Indicates.

The "comb-filtered" luminance signal Y from the luminance output of the comb-type filter 15 is applied to an input of the signal synthesis network 30 through the all-pass filter 22. The filter 22 is configured to pass all luminance signals below a cutoff frequency of about 4 MHz, and filters the noise and clock frequency components of the switching signals associated with the switching operation of the comb filter 15 in the case of a CCD comb filter. Works to remove

From the chromaticity output of the comb filter 15, the "comb filtered" chroma signal C is applied to the chroma signal processor 64 to generate the RY, BY, and GY color difference signals and is lowpass vertical. Is applied to the input of the detail filter 35. Apparatus 64 has a filter suitable to pass only signal frequencies from comb-shaped filter 15 occupying a band of chromatic signal frequencies. The filter 35 has a cutoff frequency of about 1.8 MHz, and selectively passes a signal frequency within the comb-filtered chromaticity signal output of the comb-shaped filter 15 that is below this cutoff frequency. The signal frequencies in this region are not in the combed luminance signal, and represent vertical detail luminance information that must be restored to prevent the loss of vertical sharpness in the chromaticity component of the screened image. This vertical restoration and vertical detail emphasis and paring are achieved as follows.

The vertical detail signals from the output of the filter 35 are applied to the nonlinear signal processor 50 described later. The amplitude transfer characteristic of the signal processor 50 is shown in FIG. The following indications about the response of the positive polarity signal also apply to the negative polarity signal.

The signal processing circuits in the signal processor 50 provide the signal amplitude transfer (gain) characteristics as shown in FIG. 5 for the three regions I, II and III for the three predetermined regions of the vertical detail signal amplitude. to provide. The defined gain response is provided in the reconstruction region I for low level signals (i.e. signal amplitudes of about 5% of the maximum expected amplitude), so that low level detail signals due to noise and other unwanted components are emphasized in region I. Is processed without. The peak amplitude of the vertical detail signals of medium amplitude (signal amplitude between 5% and 40% of the side maximum expected amplitude) is emphasized in region II with about three times the gain, thus highlighting the vertical detail and emphasis image definition. . For example, the maximum amplitude of a relatively large vertical detail signal (i.e., the amplitude between the maximum amplitude and the maximum expected amplitude) corresponding to a high contrast image, such as a character, prevents overcontrast It is "cut" or reduced in amplitude as indicated by the frequency response in region III to prevent kinescope "blooming" of distorting the image details.

In region I (vertical detail reconstruction), the low level vertical detail signal information is reconstructed in an amount sufficient to maintain the low level vertical reconstruction of the earth within the luminance component of the screened image. In this example, and as will be seen later, about twice the defined recovery gain is divided by the small signal amplitudes processed within region I. Since the area I and gain are the amount of signal gain required to restore a small amplitude excursion of the vertical detail signal to the luminance signal in a given device, the reconstructed luminance signal is clearly "flat" for small amplitude details. "Amplitude Response. In this process, the amplitude of the recovery gain is determined by the signal transition characteristics of the network connected between the comb-shaped filter 15 and the outputs of the luminance processor 32 and the comb-shaped filler 15 that process the reconstructed luminance signals. It is a function of several factors, including the relative amplitudes of the signal appearing at the output.

The choice of reconstruction gain as provided by the amplitude transfer response of region I is also a choice taking into account which results are acceptable in a given video signal processing apparatus. For example, if the gain is excessive, the low level ALSUV signal interference will be visible.

If the gain here is not sufficient, significant comb-like filter effects (ie signal peaks and signals at other frequencies) appear in the vertical detail frequency region below 2 MHz and thus low level vertical detail information will be lost. Therefore, the slope of the amplitude transfer characteristic in the region I corresponds to the amount of signal gain necessary to provide a predetermined response (i.e., flatness response) without exhibiting unnecessary side effects. The signal amplitude response in the region I has a fixed relationship with the response of the signal path applying the comb-shaped filtered luminance signal Y to the synthesizer 30 from the output of the comb-shaped filter 15.

In region II (vertical detail emphasis), the appropriate amount of vertical detail emphasis is provided by adding an additional gain to the signals of medium amplitude with the technique considered to benefit the vertical sharpness of the image being shown. As will be seen later, although the peak amplitude deviations of the emphasized intermediate amplitude signals are amplified with a gain greater than the recovery gain in this example, their small amplitude departures are treated as a recovery gain.

(Ie without emphasis). Also, small amplitude signals that are not emphasized are treated as reconstruction gains. Therefore, emphasis on undesirable low-level signal components, including noise and ALSUV interference, is reduced or eliminated to an acceptable minimum, and image "smear" of low-level vertical detail information is prevented.

The vertical detail signal processed from the processor 50 is summed in the network 30 together with the comb-filtered luminance signal Y supplied through the filter 22. The output signal from synthesizer 30 corresponds to the reconstructed luminance component of the video signal with recovered (area II), highlighted (area I) and canceled (area III) vertical detail information. The reconstructed comb component is applied to the luminance signal processor 32. The amplified luminance signal Y from the device 32 and the color difference signals from the chromaticity signal processor 64 are synthesized in the metrology 68 to provide R, B and G color image output signals. . Thereafter, these signals are appropriately applied to the image intensity control electrodes of the color kinescope 70.

2, one circuit embodiment of a non-linear signal processor 50 is shown. The output signal from the detailed filter 35 is supplied to the conversion input of the associative amplifier 35 included in the processor 50 through the coupling capacitor 72 and the input resistor 73 as the input signal S ₁ . . The unconverted input of the amplifier 75 is connected to a reference potential point (ie ground).

The first feedback network connected between the output of the amplifier 75 and the conversion input comprises a feedback resistor 6.

The second feedback passage includes a parallel configuration of center diodes 81 and 82 having a resistor 87, a feedback resistor 78, and a coupling capacitor 77. That is, diodes 81 and 82 are mutually arranged to conduct in response to opposite polarities of the signal generated at the output of amplifier 75, as described. The third feedback network is arranged in parallel so that the diodes 83 and 84 coupled in parallel are conductive in response to the opposite polarities of the applied signal as described later. The output signal S ₀ from the processor 50 is applied to the second input of the synthesizer 30 (FIG. 1) via the coupling capacitor 140.

First disregarding the capacitors 90, 91, and 92, the signal processor circuit 50 may vary the signal gain to signals having amplitudes in the three regions indicated by I, II, and III as shown in FIG. In order to apply different amounts, the nonlinear cry amplitude transfer function is shown. Since the value of the capacitor 77 is selected sufficiently large, the DC voltage across the capacitor 77 becomes the initial setting time, and then the DC level at the output of the amplifier 75 is equal to the DC voltage across the capacitor 77. Generally the same.

It is important that the details associated with the small amplitude signal, as mentioned above and already known in the prior art apparatus, are restored to prevent "smearing" of the vertical details of the luminance signal. This function is provided by the resistor 87 in the circuit of FIG.

Diodes 81 and 82 are nonconductive for small signal amplitudes. The resistor 87 in the circuit 50 is in a linear manner,

This allows for small amplitude detail signals that have been processed with a defined recovery gain (see FIG. 4) in region I as shown by the amplitude transfer characteristic of FIG. The recovery signal gain A ₁ (approximately 2), which has been processed in the region I and then distributed to the output signal S ₀ , is given by the given expression, where R ₇₃ , R ₇₈ and R ₈₇ are each of the resistors 73, 78 and 87. R ₉₃ corresponds to the series sum of resistors 78 and 87 and the parallel combination of resistor 76.

Resistor 87 gives no area to divide the signal gain into intermediate and large amplitude signals processed in areas II and III as described. This is because resistors 87 are bypassed or short-circuited when diodes 81 and 82 are conductive in response to application of medium and large amplitude signals.

By increasing the amplitude of the signal appearing at the output of amplifier 75 above the threshold conduction levels of diodes 81 and 82 by an intermediate amount (corresponding to the signal processed in region II), diodes 81 and 82 become conductive. do. The signal gain for signal processor 50 in region II (A ₁₁ ) is then determined to be approximately 3 or greater than the recovery gain, according to the expression given below, where R ₉₁ is equal to the value of the parallel combination of resistors 76 and 78. And R ₇₃ corresponds to the value of resistor 73.

The gain divided by the intermediate amplitude signal is shown by the amplitude transfer function for region II in FIG.

In this connection, a small amplitude deviation of the intermediate amplitude signal is transferred to the recovery gain, since the peak amplitude deviation is amplified as indicated above. The region I width for both signal polarities is a function of the ratio of the value of resistor 76 to the value of resistor 73.

The amplitude transfer function associated with the large amplitude detail signal corresponding to those signals associated with region III in FIG. 5 is determined by the feedback network comprising resistors 79 and reducing diodes 83 and 84, which are large amplitude signals. It becomes conductive in response to the deviation of the peak amplitude. Diodes 81 and 82 are also conductive at this time. This network makes it possible to reduce the peak amplitude deviation of the large amplitude detail signal in the region III by this peak deviation processed less than the recovery gain. Where the signal gain of region III (A ₁₁₁ ) is given by the given expression, where R ₉₂ corresponds to the value of the parallel combination of resistors 76, 78 and 79, and R ₇₃ matches the value of resistor 73 do.

In this connection, the small amplitude deviation of the large amplitude signal is transferred to the restoration gain, the intermediate amplitude deviation is processed larger than the restoration gain, and the peak amplitude deviation is processed smaller than the restoration gain. Thus, as shown in FIG. 5, the composite amplitude transfer function of the signal processor 50 shows three gain regions for three selected levels of signal amplitudes of both the positive and negative signal polarities. . The frequency response of the signal processed in any of the three areas can be applied by using filter capacitors such as capacitors 90, 91 and 92 in parallel with the appropriate feedback resistors as shown. In this example, the small amplitude signal processed frequency bandwidth (region I) is inversely proportional to the value of the capacitor 90. The frequency bandwidth (region II) subjected to the intermediate amplitude signal is inversely proportional to the sum of the values of the capacitors 90 and 91. The large amplitude signal processed frequency bandwidth (region III) is inversely proportional to the sum of the values of capacitors 90,91 and 92.

The third diagram circuit is the same circuit as the second diagram except that the resistor 87 is removed in FIG. The amplitude transfer function for the circuit of FIG. 3 is given by FIG. 6, which transmits a " cored " or " cored ")"do. This response corresponds to the zero gain response in region I, so that small amplitude signals do not appear as output signal S ₀ . The small amplitude signal does not appear as an output signal S ₀ because the diodes 81, 82 and 83, 84 are nonconductive at this time, and the conversion input (-) of the amplifier 75 represents a virtual ground point. Does not flow through the resistors 78 and 79 or capacitors 77,91 and 92 to the circuit output under these conditions.

7 shows another circuit embodiment of the nonlinear signal processor 50, which is similar to the circuit configuration of FIG. Corresponding elements in the circuits of FIGS. 2 and 7 have the same reference numerals.

In this embodiment the common emitter amplifier transistor 75 has a base input electrode that matches the collector output electrode connected to the operating supply voltage source (+ 16V) via the conversion input, grounded emitter electrode and collector load impedance 112. Have The open loop gain for transistor 75 is first determined by the value of the load impedance 112 and is high enough to approach the open loop gain of the amplifier (eg, amplifier 75 in the second diagram).

The vertical detail signal Si from the filter 35 is supplied to the base input of the transistor 75 via a network having an input resistor 73, a capacitor 105 and a resistor 106 as shown. The elements of the capacitor 105 and resistor 106 are used to compensate for the open loop frequency response of the transistor 75. The input signal Si represents a stable and expected D.C level as assumed for the case in this example, where the input signal is D.C applied to the base of the transistor 75. This D.C label, along with resistors 73, 76 and 114, sets a predetermined operating point for transistor 75.

As in the case of the circuit of FIG. 2, the resistance in FIG. 7 determines the width of the region I (i.e., the recovery gain region for both signal polarities) along with the threshold conductivity levels of resistor 73 and diodes 81 and 82. Do it. The feedback denser cone 77 exhibits a low DC leakage current and assists in maintaining properly biased diodes 81-84 to yield a symmetric transfer function. The output signal S ₀ is AC coupled through the condenser 140 to prevent DC current conduction which may upset the desired symmetry of the synthesis transfer function (FIG. 5). The frequency response of the processed signal in any of the three gain regions can be applied by using capacitive feedback as described with the second degree.

For either of the circuit configurations of FIG. 2 or FIG. 7, the complex transfer function shown in FIG. 5 can be modified to meet the needs of a given device. For example, the response in region I can be deleted by removing resistor 78 and short circuit diodes 81 and 82 and resistor 87. Low-level signal recovery in region I can be eliminated by removing resistor 87 as indicated in the third and sixth degrees. The reduced large signal amplitude signal in region III can be deleted by removing diodes 83 and 84 and resistor 79.

The vertical detail signal processing apparatus described is not affected by the change in the D.C level of the luminance component. The comb-shaped filtered chromaticity signal represents the D.C component due to the radix that the comb-shaped filter derives the comb-shaped filtered chromaticity signal by using a negative signal combining process. Therefore, the D.C component of the comb chromaticity signal does not reject the D.C bias component generated at the comb filter chromaticity output. The processing of the vertical detail signal, such as derived from the comb filter chromaticity output, can be aggregated into approximately bias components when the comb filter chromaticity output is D.C coupled to the vertical detail signal processing network. Since the reference level on which the signal processing has been roughly fixed is fixed fixedly, a good restoration, emphasis and reduction area is achieved.

Claims (1)

An amplifier having an input and an output terminal and including an input and an output is provided, and a first feedback passage is provided between the input and the output of the amplifier, and includes a resistor 76 having a second impedance, and a second feedback passage. In the signal processing circuit provided between the input and the output of the amplifier to include a resistor (78) of the second impedance, the second feedback path is provided with a diode (81, 82), which is a bidirectional conductive switch network Two impedances 78 in series, with the switching network 81, 82 being coupled between the output terminal and the output of the amplifier, with a first magnitude signal deviation and first and second in the first region. Indicates a conduction state in response to any signal deviation in the polarity, and responds to a signal deviation of the second magnitude greater than the first magnitude in the second region and one of the first and second polarities. A non-linear transfer function that exhibits a signal processing circuit having a conductive state.

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