JPH06303451A - Scanning speed modulating circuit - Google Patents

Abstract

PURPOSE:To display the rising and falling transient parts as the sharp edges by supplying selectively the primary differential signal acquired by applying the primary differentiation to a video signal and the signal acquired by delaying the primary differential signal to a modulating coil. CONSTITUTION:A video signal is supplied to a primary differentiating circuit 14 and a primary differential signal is acquired. A delay signal is acquired through a delay line 15 which delays the primary differential signal. These differential and delay signals are supplied to the sides (a) and (b) of an SW 16 respectively. The undelayed primary differential signal is supplied to a controller 17. Then the controller 17 integrates the primary differential signal to switch the SW 16 to the side (a) only when the level of integration output is equal to the positive output (excluding 0) and otherwise switches the SW 16 to the side (b). Then integrated differential signal is amplified by an amplifier 18, and a current is supplied to a speed modulating coil 11 through a drive circuit 19. Thus it is possible to delay the scanning speed in the periods of both rising and falling transient parts of the video signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning speed modulation circuit used in a television receiver for contour correction of an image on a cathode ray tube (CRT).

[0002]

2. Description of the Related Art FIG. 3 is a schematic block diagram of a scanning speed modulation circuit of a conventional television receiver. In the figure, 1 is a modulation coil arranged in a CRT (not shown), 2 is a DC blocking capacitor, 3 and 4 are transistors of a push-pull circuit which constitute an output stage of a scanning speed modulation circuit, and 5 and 6
Is the transistor of the SEPP circuit that constitutes the drive stage,
Reference numeral 7 is an amplifier circuit, and 8 is a secondary differentiating circuit.

Next, the operation will be described. First, the video signal is input to the secondary differentiating circuit 8 to create a contour signal. This contour signal is amplified by the amplifier circuit 7, and the SEP of the drive stage is amplified.
The final push-pull circuit is driven by the P circuit. The push-pull circuit at the final stage sends a primary differential current of the video signal to the modulation coil 1. For the operating principle, see
It is described in JP-A No. 0-53950, etc., and is known, so that it is omitted here.

FIG. 4 shows a CRT cathode signal (FIG. 4A), a current flowing through the modulation coil 1 (FIG. 4B), and a luminance output on the CRT display surface (FIG. 4) in an ideal case. 4 (c))
Shows the time relationship of. The magnetic field generated by the current flowing through the modulation coil 1 and the magnetic field generated by the current flowing through the horizontal deflection coil (not shown) of the CRT are added, and t _{A to} t
_Since the period of _B is scanned early, the brightness becomes dark,
Since the scanning is performed late during the period from t _{B to} t _C , the rise of the luminance output becomes steep and bright. On the contrary, in the white → black transient portion of the image, conversely, the scanning is performed late during the period t _D to t _E and the luminance output steeply falls, and the period during the period t _{E to} t _F is scanned early and the luminance becomes dark. . By performing such an operation, the luminance output is apparently pre-shot and open.
The sharpness of the image rises because the transient portion of the rise and fall of the image on the CRT display surface is sharpened due to the burst shooting. The contour signal of the image can be obtained by differentiating the image signal as described above, or can be obtained by using the delay line DL.

[0005]

Since the conventional scanning speed modulation circuit has the above-mentioned structure and function, as can be seen from FIG. 4, it is between t _A and t _{B and} between t _E and t _F. Since the video signal has an amplitude toward the white side, some luminance output appears even if the scanning speed is increased. For this reason, a sharp contour is formed in the contour portion of the image, but there is a drawback in that the luminance is tailed before and after the contour, which makes it unsightly.

The present invention has been made to solve the above problems, and both the transient portion of the rising edge from the black to the white and the falling edge from the white to the black of the image are displayed as sharp edges. The object is to obtain a scanning speed modulation circuit as described above.

[0007]

A scanning speed modulation circuit according to the present invention uses a modulation coil for modulating a horizontal scanning speed of a cathode ray tube to which a video signal is supplied by a magnetic field, and corresponds to rising and falling of the video signal. Then, the first-order differential signal obtained by first-order differentiating the video signal and the delayed signal obtained by delaying the first-order differential signal are selectively supplied.

Further, the scanning speed modulation circuit according to the present invention outputs means for first-order differentiating the video signal and outputting the first-order differential signal, and a delay signal obtained by delaying the first-order differential signal for a predetermined time. And a control means for integrating the primary differential signal and selectively switching the primary differential signal or the delayed signal according to the integrated output level to supply the modulated coil to the modulation coil.

[0009]

In the scanning velocity modulation circuit according to the present invention, the primary differential signal obtained by first-order differentiating the video signal is used for the rising portion of the amplitude change of the video signal, and the delayed signal obtained by delaying the primary differential signal is imaged. Separately prepared for the falling edge of the amplitude change of the signal, and selectively switching between these two signals, the transient part of the image amplitude change applies a current to the modulation coil so as to slow down the scanning speed. . Also, 2
The operation of switching between the two signals is performed based on the integrated output obtained by integrating the primary differential waveform so as to select the primary differential waveform that is not delayed only when the integrated output level is greater than zero. Therefore, the switching operation is controlled by the switching signal wider than the primary differential signal.

[0010]

EXAMPLES Example 1. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 11 is a modulation coil arranged in a CRT (not shown), 12 is a DC blocking capacitor, 13 is an input terminal for a video signal (luminance signal), 14
Is a primary differentiating circuit for primary differentiating the video signal, 15 is a delay line DL1, 1 for delaying the primary differential signal by a time corresponding to the rising and falling transient parts of the video signal.
A switch (SW) 6 is connected to switch between the primary differentiating circuit 14 and the delay line 15. 17
Is a control device for controlling the switching operation of the SW 16 and is provided with an integrating circuit for integrating the primary differential output. 18 is SW
An amplifier connected to the output side of 16 and a modulation coil 1
1 is a drive circuit for supplying a current, 20 is a color signal input terminal, 21 is a video signal processing circuit for performing color demodulation and amplification, 2
Reference numeral 2 is a CRT drive circuit, 23 is a CRT, 24 is a delay line DL2, and 25 is a delay line DL3 for time adjustment of a luminance signal and a color signal.

FIG. 2 shows the waveform and timing of each part. In the figure, (a) is the waveform of the input video signal (luminance signal) of the input terminal 13, and (b) is the output 1 from the primary differentiating circuit 14.
Second derivative signal waveform, (c) is 1 by delay line 15
Delayed signal waveform obtained by delaying the second derivative signal by the time corresponding to the rising and falling transient parts of the video signal, (d)
Is the output signal waveform after the switching operation of SW16, (e)
Is a signal waveform in which the video signal is delayed by the delay line 16, (f) is a current waveform flowing in the velocity modulation coil 11,
(G) is a luminance output waveform on the CRT display surface, and (h) is a SW switching signal output from the controller 17.

Next, the operation will be described. First, Figure 2
The video signal (luminance signal) as shown in FIG.
4 and the first-order differential signal of FIG. 2B is obtained.
Further, the delay line 15 for delaying the first-order differential signal
Through, the signal of FIG. 2 (c) is obtained. These two signals are input to the a side and the b side of the SW 16, respectively. The switching operation of the SW16 is performed by the control device 10 including the integration circuit.
Controlled by. The control device 17 receives the primary differential signal before delay, integrates the primary differential signal, and switches only when the integrated output level is a positive output (except 0).
It works to switch 16 to the a side, and to switch to the b side at other times. The differential signal after being switched by the SW16 becomes the signal shown in FIG. This signal is amplified by the amplifier 18, and the drive circuit 19 amplifies the speed modulation coil 11.
When a current is passed through, the signal shown in FIG. 2D is integrated and a current signal having a wider width than that is flowed. The signal is shown in FIG. In order to match the timing of the video signal of the CRT cathode with this modulation signal, the video signal is delayed by the delay line 24, as shown in FIG.

When a current as shown in FIG. 2 (f) is passed through the velocity modulation coil 11, as shown in FIG. 2 (g), the scanning is accelerated during t _A -t _B immediately before the rise of the video signal, and the luminance output. Goes down. During all the periods t _{B to} t _C of the rising transient portion of the next video signal, the scanning is delayed and the luminance output is increased. Similarly, t _{D of the} falling transient part of the video signal
During t _E, the scanning speed becomes slow and the luminance output rises, and between t _E and t _F after the fall, the scanning speed becomes fast and the luminance output falls. As a result, the luminance output of the CRT display surface becomes as shown in FIG. 2 (g) as a whole, and the scanning speed is slowed at both the rising and falling edges of the video signal and the transient portion of the amplitude change of the video signal, resulting in a CRT. A sharp edge appears on the display. Further, by pulling the front and rear of the peak on the white side to the black side, the contour becomes sharper.

[0014]

As described above, according to the scanning speed modulation circuit of the present invention, both the rising edge and the falling edge of the video signal,
The scanning speed can be all delayed during the transient portion of the video signal, and it seems that the frequency is increased due to the time axis compression on the CRT display surface, which has the effect of improving the sharpness of the video displayed on the CRT. . Also, the crooked CR remaining before and after the transient part of the video signal
Compared with the conventional display that shows the T display, the remaining display portion is small, and rather it is possible to attach an edge that pulls slightly to the black side, and it is possible to further clarify the contour.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of FIG.
It is

FIG. 3 is a schematic configuration diagram showing an example of a conventional scanning speed modulation circuit.

FIG. 4 is a timing chart for explaining the operation of the conventional circuit.

[Explanation of symbols]

 11: Velocity modulation coil 12: DC blocking capacitor 13: Video signal input terminal 14: Primary differentiation circuit 15: Delay line DL1 16: Switch (SW) 17: Controller 18: Amplifier 19: Drive circuit 20: Color signal input terminal 21: video signal processing circuit 22: CRT drive circuit 23: CRT 24: delay line DL2 25: delay line DL3

Claims (2)

[Claims] 1. A sharpening of an image on a display surface of a cathode ray tube by applying a modulation current according to rising and falling of the image signal to a modulation coil which modulates a horizontal scanning speed of the cathode ray tube to which the image signal is supplied by a magnetic field. In the scanning speed modulation circuit for increasing the frequency, a first-order differential signal obtained by first-order differentiating the above-mentioned video signal and a delayed signal obtained by delaying the first-order differentiating signal are provided in accordance with the rising and falling of the above-mentioned video signal A scanning speed modulation circuit characterized by being selectively supplied to a modulation coil. 2. A sharpening of an image on the display surface of the cathode ray tube by applying a modulation current according to rising and falling of the image signal to a modulation coil for modulating the horizontal scanning speed of the cathode ray tube to which the image signal is supplied by a magnetic field. In the scanning speed modulation circuit for increasing the frequency, a means for first-order differentiating the video signal and outputting the first-order differential signal, and a means for outputting the first-order differential signal for the time corresponding to the rising and falling transient parts of the video signal. A means for outputting a delayed delay signal and a control means for integrating the primary differential signal and selectively switching the primary differential signal or the delayed signal according to the integrated output level and supplying the primary differential signal to the modulation coil. And a scanning speed modulation circuit.