JPH0134503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Video signals for satisfactory image reproduction in television receivers typically have a video bandwidth of approximately 5 MHz. In reality, the video signal is, for example,
With poor film scanning, simple cameras, playback of recording devices with reduced bandwidth or in band-limited transmission sections, it can occur to have a reduced bandwidth of 2-3 MHz. This type of reduced bandwidth results in reduced sharpness during reproduction, especially at the side edges of the image.

It is known to improve image sharpness in this type of signal by processing the video signal. In the differential equalizer used for this purpose, a correction signal obtained by twice differentiating the video signal is added to the video signal. As a result, during the video signal,
Due to the band limitation, the flat side edges become steeper.

This type of circuit has the following disadvantages: When the amplitude of the modification signal is optimally determined for small signal step changes in the video signal, for relatively large signal step changes, e.g. black/white steps in the modified video signal,
Extremely high voltage peaks occur at these steps. Moreover, such high voltage peaks, which can occur asymmetrically with respect to the original value of the video signal, also have a visible image deterioration effect. This type of voltage peak may also exceed the sync base level of the horizontal sync pulse in the black-to-black direction, causing deflection disturbances in the horizontal sync deflection circuit. This disadvantage is avoided by choosing the amplitude of the correction signal relatively small, but on the other hand, if the signal step changes in the video signal are small, the image improvement will again be small or hardly noticeable. .

The object of the present invention is to provide a circuit of the type described so far with an optimal image improvement effect in the case of small signal step changes in the video signal, without the generation of voltages in the video signal that would interfere with relatively large step changes. It is an object of the present invention to provide a circuit in which this is carried out.

This problem is solved in claim 1 or 7.
The problem is solved by the features described in section 9 or section 9.

The present invention is based on the following considerations. For visual image improvement, the sharpening of the edges in the video signal is particularly important for small signal step changes. Moreover, statistically speaking, small signal step changes occur frequently in images. In the case of relatively small signal step changes, it is neither necessary nor effective to add a correspondingly proportional relatively large correction signal. Rather, it is advantageous to limit the amplitude of the correction signal. That is, the action of the modification circuit of the present invention is advantageously adaptively matched to the amplitude of signal step changes in the video signal, allowing for a visible image improvement to occur.

In video recorders, the inventive modification of the video signal advantageously takes place in the recording path.
In this case, if a not very good video signal arrives for recording, for example due to a disturbed broadcast, the video signal is improved already before recording. This is important. This is because the recording of the poor video signal and the further deterioration added by the video recorder can no longer be improved satisfactorily. Modifying the video signal during recording has the advantage that a video signal is recorded that is improved with respect to image sharpness. Therefore, when this tape is played again on any other video recorder, the advantage is that an image with improved sharpness is obtained. In video recorders, the video signal is usually degraded to some extent during recording by the recording circuit. This deterioration of the video signal can be compensated for during recording as well by the circuit of the invention, so that the quality of the video signal recorded on the tape does not differ from the quality of the video signal supplied to the recorder.

Due to the double differentiation, the modified signal contains significant noise components at high frequencies, which itself can again degrade the image reproduction. According to an advantageous embodiment of the invention, therefore, a low-pass filter is inserted in the modified video signal path, which has a passband approximately equal to the bandwidth of the original video signal. The cut-off frequency of the low-pass filter can be, for example, 3MHz, 4MHz or 5MHz depending on the bandwidth of the incoming video signal. Image reproduction is significantly improved by this low-pass filter, which removes all noise components above the high band limit of the video signal.

Next, the present invention will be explained in detail using illustrated embodiments.

In FIG. 1, unmodified video signal 1
reaches the summing stage 7 from the terminal 2 via the amplifier 3, the delay element 4 and the amplifier 5. From there, the video signal passes through an amplifier 8 and a low-pass filter 9 with a cutoff frequency of 3.0 MHz to an output terminal 10.
A modified video signal 1' is taken off at this output terminal.

From the output of the amplifier 3, the video signal 1 further reaches a differentiation stage 12 via an amplifier 11. Differential stage 12
An amplitude limiter 13 is connected to the output side of the differential signal, which limits the signal amplitude of the differentiated signal in the positive and negative directions. The thus differentiated and amplitude limited signal reaches a second differentiation stage 17 via an amplifier 16. A limiter 18, which acts in the same way as limiter 13, is also connected downstream of the second differentiation stage. This results in a modified signal 21 in the line 20, which is obtained by two differentiations and an amplitude limitation following the differentiation in each case. This signal is added to the video signal in a summing stage 7 to modify it, ie to make the side edges steeper. The amplitude of the correction signal 21 and the limit values of the limiters 13, 18 are selected as follows. That is, when the signal step change in the video signal 1 is small, the amplitude limiters 13, 1
8 does not actually take effect, the correction signal 21 is not limited and the desired steepening of the side edges in the video signal 1 occurs, but if the signal step changes in the video signal 1 are relatively large, the image reproduction or synchronization The voltage peaks were chosen to avoid significantly large voltage peaks that could cause damage.

FIG. 2 shows the unmodified video signal 1 applied to terminal 2. FIG. This video signal has a relatively wide black/white jump, a so-called 20T-pulse, and a 5T-pulse.
has two small signal step changes. The circuit particularly sharpens these small signal step changes.

FIG. 3 shows the modified video signal produced at terminal 10 in a known manner by the circuit of FIG. 1 (but without the limiter). Five small signal step changes were made to provide the desired steepening effect to produce the visually improved image reproduction.
However, if the step changes in the signal are relatively large, very high voltage peaks 33 occur. This voltage peak reaches three times the value of the signal step change contained in the video signal itself. This extremely high signal step change results in visible image degradation. Since this deterioration exceeds the synchronization base level of the horizontal synchronization pulse, it may also damage the horizontal synchronization deflection circuit that operates depending on the amplitude during image reproduction.

FIG. 4 shows the modified video signal 1' appearing at terminal 10 when the limiters 13, 18 of FIG. 1 are used. The five small signal step changes are
The slope is steepened in almost the same way as in Figure 3. This is because limiters 13 and 18 do not act on such amplitude step changes, but the undesired signal step change 33 in FIG. 3 is significantly reduced by limiters 13 and 14. It is from.

A combination of germanium and silicon diodes can be used in the restrictor. Germanium diodes have lower resistance than silicon diodes in the conducting state, but become disadvantageously large at high currents.
It has a dynamic internal resistance in the forward region. Silicon diodes, although not as low resistance as germanium diodes, maintain approximately constant dynamic internal resistance in the forward region even at large signal currents. The advantages of two different types of diodes are thus advantageously combined. Overall, this combination results in a particularly low internal resistance in the conduction region, which is effective both for small signal currents and for relatively large signal currents. This significantly improves the switching characteristics of the diode at the threshold determined by the forward voltage and thus the action of the limiter.

In a specific example, the following model names were used for the semiconductor device shown in FIG.

Transistors 11, 16: Model name 2N2218 All other transistors: Model name BC237B Silicon diodes 13, 14, 18, 19: Model name BAY95 Germanium diodes 13', 14', 18',
19': Type name AAZ10 In practice, it has been found that diodes with the desired characteristics are not always available in sufficient numbers. In order to ensure satisfactory functioning of the circuit, it is then necessary to search among a large number of diodes that have certain properties. However, such methods are unsuitable for mass production. The desired switching characteristics of the diode are not optimal for amplitude limiting when the diode does not have the desired characteristics.

According to an embodiment of the invention, the necessary limitation is therefore achieved without diodes as follows. That is, a diode is formed across the collector-emitter of two oppositely polarized transistors of the same type, the collectors of these transistors each being connected to the base.

By using transistors as limiting diodes, a wide variety of semiconductor components can be used. The transistor can be connected in a manner known per se in such a way that it fulfills the role of a diode. A further advantage here is that the transistor connected as a diode has a lower resistance than a diode in the forward region. controlling the forward resistance of a transistor operating as a diode by means of a special circuit of the transistor according to an embodiment of the invention;
For example, it can be intentionally made larger. This is advantageous in order to ensure that the entire circuit is not unduly heavily loaded and damped by transistors which are controlled to have very low resistance.

An embodiment improved in this way will be explained based on FIGS. 5 and 6.

In FIG. 5, the video signal 1 is connected to the capacitor 60.
The signal is supplied to transistor 11 via. The base-bias voltage of the transistor is determined by the voltage divider 61, 6.
It is determined by 2. The emitter of the transistor 11 is grounded via an RC element having a capacitor 63 and a resistor 64, and a resistor 65. According to the circuit of FIG.
A once differentiated correction signal appears which is fed to the differentiation stage of . Differentiation is performed by an inductance 12 in the collector circuit of transistor 11. Two silicon transistors 13 and 14 are connected in antiparallel to the inductance 12, and the collector is connected to the base. Transistors 13, 14 in this circuit act like two anti-parallel connected diodes. However, the forward resistance of this circuit is significantly reduced as desired. When designing the overall circuit for processing video signals, the circuit of FIG. 1 results in an undesirably low forward resistance of transistors 13, 14 and an undesirably significant attenuation of the amplifier comprising transistor 11. Sometimes.

In the alternative embodiment circuit of FIG. 6, the forward resistance of transistors 13, 14 is intentionally increased by connecting the collectors to the bases via diodes 67-68, respectively. Transistor 13, by diodes 67, 68
The switch characteristics of 14 are weakened and the forward resistance is advantageously increased. As a result, transistor 1
The load and attenuation of the amplifier with 1 can be reduced. In the case of silicon transistors 13, 14 germanium diodes 67, 68 are advantageously used.
is used. This is because germanium diodes have lower forward resistance than silicon diodes at small signal amplitudes.
At large signal amplitudes, the dynamic internal resistance of germanium diodes increases, while the dynamic internal resistance remains approximately constant for silicon diodes. The combination of germanium diodes 67, 68 and silicon transistors 13, 14 is therefore advantageous in order to obtain a switch-like limiter with a predetermined internal resistance.

In a specific example, the elements had the following values:

Transistor 11: Model name 2N2218 TR13, 14: Model name BC237B R61: 10KΩ R62: 10KΩ C63: 50μF R64: 100Ω R65: 10Ω Diode 67, 68: AA143 As is well known in video recorders, recording of video signals is performed using video signals. Therefore, it is carried out in the form of an FM modulated carrier wave. The overall transmission characteristic curve is limited by the frequency characteristics of the recording head and magnetic tape and decreases with higher frequencies. However, high frequency linear signal components have relatively small amplitudes from a statistical perspective. Therefore, in order to improve the reproduction of fine image denier, it is known to carry out so-called pre-emphasis on the video signal before the FM modulator to emphasize the amplitude of high frequencies. During playback, the high frequencies are again correspondingly weakened in the de-emphasis circuit. This also improves the noise-to-signal spacing for this high frequency component. When using a pre-emphasis circuit in the circuit shown in Figure 1 during recording in a video recorder,
Two circuits are provided in the video signal path that have approximately the same effect, ie, enhance the high frequency components. The cooperation of these two circuits can result in undesirably high amplitudes of the video signal at signal step changes. Since the maximum amplitude of the video signal is limited by the operating voltage, this can lead to distortions in the course of the video signal. This deteriorates the quality of the reproduced image. However, on the other hand, the above-mentioned pre-emphasis circuit is not necessary for performing FM modulation.

In the present invention, the signal distortion caused by pre-emphasis is avoided by means of a simple circuit arrangement. This can be done as follows. In other words, FM in the recording path of the recorder
In front of the modulator, an amplifier provided for pre-emphasis of the video signal is provided with a negative feedback network whose degree of negative feedback increases as the frequency increases.

This solution is based on the following recognition. In known pre-emphasis circuits, the degree of emphasis increases continuously as the frequency increases. Moreover, this is advantageous for providing a satisfactory signal transmission for video signals which are not processed according to the circuit of FIG. However, when a video signal is processed according to the circuit of FIG. 1, it is disadvantageous that the higher the frequency, the greater the degree of emphasis acting in the pre-emphasis circuit. This is because signal step changes involving high frequencies are then overemphasized. According to the invention, this disadvantage is avoided by providing the pre-emphasis circuit with a predetermined degree of negative feedback that increases with increasing frequency. This results in
It's in the pre-emphasis circuit itself. Advantageously, an effect counteracts the increased emphasis with increasing frequency. That is, the pre-emphasis circuit has two mutually independent frequency-dependent circuitry. One network is still used in the direction of pre-emphasis to increase the emphasis as the frequency increases. The other network is used to reduce the emphasis in a predetermined frequency range in a predetermined manner.

An embodiment of this solution will be described on the basis of FIGS. 7 and 8.

FIG. 7 shows the video signal 1 applied to the terminal 2, the amplifier 3, the delay element 4, the amplifier 5, the summing stage 5, the amplifier 8, the reduction filter 9 and the image signal corresponding to FIG. A terminal 10 is shown on which a video signal 1' processed to enhance sharpness appears. In addition stage 7, a correction signal 21 is added to the video signal. This means that the amplifier 11, the differential stage 12,
It is obtained from the video signal 1 in a branch having an amplitude limiter 13 , a second amplifier 16 , a second differentiation stage 17 and a second amplitude limiter 18 .

Video signal 1' is connected to line 30 and capacitor 31
The signal is supplied to the pre-emphasis circuit 32 via the pre-emphasis circuit 32. On its output side, this pre-emphasis circuit sends a video signal to an FM modulator 34 via a capacitor 33. The FM modulator generates a carrier wave that is FM modulated by the video signal, and this carrier wave is recorded on the magnetic tape 36 using a head. The circuit 32 includes resistors 37, 3 used to generate a base-bias voltage, as is known in the art.
8 and a transistor 3 having a collector actuation resistance.
9, an emitter resistor 41, and a frequency dependent negative feedback network having resistors 42, 43 and capacitors 44, 45. transistor 3
The signal from the output of circuit 32 reaches the output of circuit 32 via an emitter follower stage having transistor 46 and actuation resistor 47. Circuit network 42-4
5 performs a negative feedback effect that decreases as the frequency increases, and therefore performs a strengthening effect that increases the video signal 1' for pre-emphasis.

Circuit 32 additionally includes a negative feedback network having resistor 48 and capacitor 49. This network reduces the negative feedback effect, which increases as the frequency increases, and thus the amplification effect of transistor 39. The time constant of networks 48 and 49 is approximately
It is on the order of 200ns, corresponding to a cutoff frequency of 0.9MHz.

FIG. 8a shows that the processing of the video signal according to FIG.
3 illustrates a rectangular pulse resulting from the input signal of FIG. 2; This pulse has the required form for recording by FM. In the combination of the known pre-emphasis circuit and the circuit element 2-18 of FIG. 7, the pulse of FIG. 8c is generated at the output side of the pre-emphasis circuit. The voltage peaks shown are higher than shown due to the boosting effect at high frequencies themselves. The voltage peaks are amplitude limited by the operating voltage. This limitation results in the undesirable curve deformations of FIGS. 8a to 8c, regardless of the amplitude changes. If this signal is recorded, the 8th
The distorted pulse in figure d results.

Through the use of networks 48, 49 in circuit 32, the pulses of FIG. 8e are generated at the output of circuit 32. This pulse has approximately the same amplitude as the pulse of FIG. 8c, but in this case also has the same curve profile as FIG. 8a. During recording and subsequent demodulation and de-emphasis, the pulses of FIG. 8f result therefrom. This pulse also has the desired curve shape similar to that of FIG. 8b, but due to the use of circuit elements 2-18 of FIG.
with the desired over-emphasized portion of the step change as illustrated by . During image reproduction, this overemphasized portion performs an image improvement effect that further sharpens the display of fine image details at high frequencies.

The circuit 32 is supplied at the input side from the terminal 10 with a processed video signal 1' having a peak-to-peak amplitude of approximately 1V.

In FIG. 7, a frequency-dependent negative feedback according to the invention is implemented in the same amplifier stage with pre-emphasis and transistor 39. Pre-emphasis and negative feedback described above can also be separated and performed in successive stages in the signal path.

In a specific embodiment, the elements of circuit 32 had the following values.

C31: 47μF C33: 47μF R37: 15KΩ R38: 10KΩ Tr39: Model name BC237B R40: 1KΩ R41: 1KΩ R42: 470Ω R43: 1KΩ C44: 580pF C45: 1.2nF Tr46: BC237B R47: 1KΩ R48: 2.2KΩ C49: 82p F book When using the circuit of the invention in a television receiver, the following problems may occur. When the receiver is not optimally tuned, the reproduced image using the circuit of the present invention may be impaired by plastic effects and noise. Under certain conditions, the image reproduction may then be visually worse than without the circuit of FIG.

According to the invention, the above-mentioned disturbances in the case of non-optimal tuning are reduced by increasing the amplitude of the modified signal by increasing the amplitude of the signal components in the higher frequency range of the unmodified video signal. , avoided.

This solution is based on the following recognition. The visually non-optimal tuning is done in the direction of increasing the high frequency components of the video signal. This is often visually perceived as a sharpened image and is commonly referred to as "peaking." However, the circuit of the embodiment shown in FIG. 1 similarly operates in such a way that high frequency components are enhanced. The combination of misadjustment in the direction of peaking and the action of the circuit of FIG. 1 results overall in a very strong enhancement of the high frequency components, which makes positive effects and noise noticeable. In the present invention, non-optimal tuning is automatically detected by frequency selectivity evaluation of the video signal and the effect of the circuit of FIG. 1 is automatically reduced accordingly. For this purpose, the correction voltage can be reduced continuously as the amplitude of the high frequency signal components in the video signal increases. In another embodiment, relatively high frequency signal components in the video signal are completely blocked when they exceed a predetermined threshold. Moreover, in the event of a misadjustment, the circuit of FIG. 1 does not work and therefore does not work for image improvement. However, in case of misadjustment, the circuit of FIG. 1 is prevented from undesirably degrading the image quality.

Examples of this solution are shown in Figures 9 and 10.
This will be explained based on the diagram.

In FIG. 9, a video signal 1 passes from a terminal 2 through an amplifier 3, a delay element 4, an amplifier 5, a summing stage 7, an amplifier 8 and a low-pass filter 9 to a terminal 10, where the image signal according to the embodiment of FIG. A video signal 1' appears which has been processed to enhance the sharpness of the image.
A correction signal 21 is added to the video signal in the addition stage 7. The correction signal is sent to the amplifier 11 and the differential stage 1.
2, obtained from the video signal 1 in a shunt having an amplitude limiter 13, a second amplifier 16, a second differentiation stage 17 and a second amplitude limiter 18. The illustrated circuit, together with terminals 2 and 10, is incorporated into the luminance signal path of a color television receiver.

In addition, a gate 70 is inserted into the signal path leading from the output of the limiter 18 to the summing stage 7 in which the correction voltage 21 occurs, which is conductive in an optimally tuned television receiver.

The signal from the output side of amplifier 5 is approximately 2 to 3 MHz.
reaches a filter 1 which has a passage area at . If the receiver is mistuned, the signal content in this frequency range will be significantly enhanced, resulting in filter 71
An excessively high voltage occurs on the output side of the . This voltage is rectified in rectifier 72. When the rectified voltage exceeds a predetermined threshold value, a switching voltage 73 occurs in a threshold circuit, which is not shown in detail. This switching voltage controls the gate 70 to be non-conductive,
As a result, the modified signal 21 no longer reaches the summing stage 7. At that time, the correction circuits 11-13, 16-18 are
It doesn't work in your favor either. When the receiver is properly tuned again, the amplitude of the signal component in the higher frequency range of the video signal at the output of amplifier 5 decreases again. Switching voltage 73 then disappears and gate 70 is switched on again. The corrected voltage 21 then advantageously reaches the summing stage 7 again.

In FIG. 10, the video signal is passed from the output side of the amplifier 5 to the transistor 75 via the capacitor 74.
reach the base of. The base bias voltage of the transistor is generated by a voltage divider 76, 77 and its emitter is grounded via a resistor 78. The collector circuit of the transistor 75 includes two to
A filter 71 tuned to 3MHz is provided and is attenuated by a resistor 79. By means of a coil 80 coupled by the inductance of the filter 71, signal components in the frequency range of 2 to 3 MHz are coupled out and fed via a rectifier 72 to the base of a transistor 81. The collector is connected to the base of transistor 16a. This transistor corresponds to amplifier 16 of FIG. transistor 16
The base bias voltage for a is the resistor 83, 8
Caused by 4. The emitter of transistor 16a is grounded via resistor 85 and capacitor 86. The differential stage has an inductance 17a
The amplitude limiter 18 is formed by two anti-parallel connected diodes 18a. The video signal reaches the base of transistor 16a from limiter 13 via capacitor 87.

In an optimally tuned television receiver, the signal component present in the filter 71 and the resulting DC voltage at the base of the transistor 81 remains in the cut-off state of the transistor 81 and does not affect the action of the transistor 16a. It's fairly slight. A correction voltage 21 then reaches the input of the summing stage 7 in order to increase the sharpness.

In non-optimal tuning, the DC voltage developed at the base of transistor 81 is large enough that transistor 81 is conducting and the base of transistor 16a is at ground. As a result, no correction voltage 21 is applied to the input side of the summing stage 7. That is, transistor 81 serves as an amplitude threshold circuit, and transistor 1
6a acts as gate 70 in FIG.

Low-pass filter 9 advantageously has a cut-off frequency of 3.5 MHz in a color television receiver.
A low-pass filter with the same cut-off frequency is preferably arranged in series with amplifier 8.

In a specific embodiment, the elements of FIG. 10 have the following values.

Rectifier 72: Diode/AA143 Tr75R76: Model name 22KΩ R77: 10KΩ R78: 47Ω R79: 2.2KΩ Tr81: Model name BC237B R82: 10KΩ R83: 22KΩ R84: 10KΩ R85: 390Ω C86: 4.7μF C87: 10nF C74: 10nF 1st 1 The figures show concrete circuits of the invention, corresponding parts being provided with the same reference symbols. A path for the video signal 1 is provided with a transistor 30, a low-pass filter 31 having a cutoff frequency of 30 MHz, a transistor 32, and a transistor 3 operating as an emik follower. The circuit point at the base of transistor 7 is
This is the point where the video signal and the modified signal 21 are added. Coil 12 in the collector circuit of transistor 11 acts as a differential element. Silicon diodes 13 and 14 are provided in parallel with this coil 12 and connected in antiparallel. The diodes 13, 14 create a limiting effect at voltages around 0.2V. The transistor 16 is
forming a second amplifier stage, and coil 17 forms a second amplifier stage;
form a differential element. The diodes 18 and 19 also have an amplitude limiting effect in this case. From the collector of the transistor 16, the correction signal reaches a circuit 15 which passes only signals above a predetermined threshold and thereby suppresses noise below this threshold. The correction signal appearing at the output of circuit 15 is then 2
two limiters 90 and 91 are reached. This limiter additionally limits the modified signal in the positive and negative directions, so that the modified signal 21 at circuit point 6
has the optimum maximum amplitude relative to the video signal 1. Note that the unmarked transistor in FIG. 11 is BC237B.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of an unmodified video signal, and FIG.
FIG. 4 is a waveform diagram of a video signal with significantly high voltage peaks modified by a known method; FIG. 4 is a waveform diagram of a video signal modified by the circuit of the present invention; and FIG. 5 is a waveform diagram of a video signal used in the present invention. FIG. 6 is a partial circuit diagram of an alternative embodiment of FIG. 5; FIG. 7 is a block diagram of a circuit with a pre-emphasis circuit according to the invention; FIG. 8a ~f is a signal waveform diagram for explaining the operation and effect of the circuit of FIG. 7, FIG. 9 is a basic block circuit diagram of the present invention, FIG. 10 is a circuit diagram of an embodiment of the circuit of FIG. 9, and FIG. The figure is a circuit diagram of a specific embodiment. 1... Uncorrected video signal, 1'... Modified video signal, 7... Addition stage, 12, 17... Differential stage (inductance), 13, 18... Amplitude limiter (diode), 14, 19, 67, 68... Diode, 21... Correction signal, 32... Pre-emphasis circuit, 34... Frequency modulator, 48, 49... Negative feedback network.

Claims (1)

[Scope of Claims] 1. A video signal is differentiated in first and second differentiation stages, and the differentiated signal is added as a correction signal to the video signal in an addition stage to steepen the side edges of the video signal. In the circuit, a first amplitude limiter 13 is connected downstream to the first differential stage 12, a second differential stage 17 is connected downstream to the first amplitude limiter 13, and the second differential stage A second amplitude limiter 18 is connected downstream, and the output of the second amplitude limiter 18 is converted into a correction signal 21.
is added to the video signal 1 in the summing stage 7, and the two amplitude limiters 13, 18 add the modified video signal 1' appearing at the output 10 of the summing stage 7 in the case of large signal step changes in the video signal 1.
1. A circuit for sharpening side edges of a video signal, characterized in that the circuit is configured so that pulse peaks that degrade image reproduction or that disturb synchronization do not occur in the circuit. 2. Diodes 13, 14, connected in parallel and antiparallel to the differentiating stages 12, 17 leading to the correction signal 21.
Claim No. 18 and 19 are provided.
The circuit described in section. 3 Diodes 13, 1 connected in parallel and antiparallel to the differential stage 12, 17 having inductance.
4, 18, 19 are provided. 4. A circuit according to claim 1, wherein the path of the modified video signal 1' is provided with a low-pass filter 9 having a passband width corresponding to the bandwidth of the video signal 1'. 5. The circuit according to claim 1, wherein two silicon diodes connected in anti-parallel and two germanium diodes connected in anti-parallel are connected in parallel to the differentiating stages 12 and 17. 6. A diode used in the amplitude limiter is formed between the collectors and emitters of two oppositely polarized transistors 13, 14 of the same type (npn), the collectors of which are connected to the bases of each transistor. The circuit according to claim 2, which is connected to. 7. In a circuit for steepening the side edges of a video signal, the video signal is differentiated in the first and second differentiation stages, and the differentiated signal is added as a correction signal to the video signal in the addition stage. A first amplitude limiter 13 is connected downstream to the stage 12, a second differentiation stage 17 is connected downstream to the first amplitude limiter 13, and a second amplitude limiter is connected to the second differentiation stage. 18 is connected afterward, and the output of the second amplitude limiter 18 is converted into a correction signal 21.
is added to the video signal 1 in the summing stage 7, and the two amplitude limiters 13, 18 add the modified video signal 1' appearing at the output 10 of the summing stage 7 in the case of large signal step changes in the video signal 1.
The circuit is constructed so that there are no pulse peaks that degrade image reproduction or that disturb synchronization, and when the circuit is used in the recording path of a video recorder, it is connected upstream of the frequency modulator 34 in the recording path of the recorder. Also, video signal 1'
Amplifier 3 used for pre-emphasis of
2. A circuit for making the side edges of a video signal steeper, characterized by comprising negative feedback circuit networks 48 and 49 whose degree of negative feedback increases as the frequency increases. (FIGS. 7 and 8) 8 The circuit network connects the RC between the collector and base of the transistor 39 provided in the amplifier 32.
8. A circuit according to claim 7, which is formed by series circuits 48, 49. 9. In a circuit for steepening the side edges of a video signal, the video signal is differentiated in the first and second differentiation stages, and the differentiated signal is added as a correction signal to the video signal in the addition stage. A first amplitude limiter 13 is connected downstream to the stage 12, a second differentiation stage 17 is connected downstream to the first amplitude limiter 13, and a second amplitude limiter is connected to the second differentiation stage. 18 is connected afterward, and the output of the second amplitude limiter 18 is converted into a correction signal 21.
is added to the video signal 1 in the summing stage 7, and the two amplitude limiters 13, 18 add the modified video signal 1' appearing at the output 10 of the summing stage 7 in the case of large signal step changes in the video signal 1.
The modified signal 21 is configured so that no pulse peaks that degrade image reproduction or that disturb synchronization occur, and the amplitude of the modified signal 21 is equal to the amplitude of the signal component in the higher frequency region of the unmodified video signal 1. A circuit for making a side edge of a video signal steeper, characterized in that the side edge of a video signal is reduced as the edge of the video signal increases. (Figures 9 and 10)