JP2993586B2 - Scan speed modulation circuit - Google Patents

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 to correct the contour of an image on a cathode ray tube (CRT).

[0002]

2. Description of the Related Art FIG. 3 is a schematic configuration diagram of a scanning speed modulation circuit of a conventional television receiver. In the figure, 1 is a modulation coil disposed on a CRT (not shown), 2 is a DC blocking capacitor, 3 and 4 are transistors of a push-pull circuit constituting an output stage of a scanning speed modulation circuit, 5 and 6
Is a transistor of the SEPP circuit constituting the drive stage,
Reference numeral 7 denotes an amplification circuit, and reference numeral 8 denotes a secondary differentiation circuit.

Next, the operation will be described. First, a video signal is input to the secondary differentiating circuit 8 to generate a contour signal. This contour signal is amplified by the amplifier circuit 7, and the SEP of the drive stage is
The final stage push-pull circuit is driven by the P circuit. The final stage push-pull circuit allows the primary differential current of the video signal to flow through the modulation coil 1. The operating principle is described in
It is described in, for example, Japanese Patent Application Laid-Open No. 0-53950 and is well-known, so that the description is omitted here.

FIG. 4 shows an ideal case of a cathode ray tube (CRT) signal (FIG. 4A), a current flowing through the modulation coil 1 (FIG. 4B), and a luminance output on the CRT display surface (FIG. 4B). 4 (c))
Shows the time relationship. 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 _A
During period _B, the brightness is dark because the scanning is performed early,
Since scanning is performed slowly during the period from t _{B to} t _C , the rise of the luminance output becomes sharp and bright. Moreover, contrary to the white → black transient portion of the video, t _D ~t period is scanned slowly luminance output of _E falls steeply, period t _E ~t _F is scanned earlier, the luminance becomes dark . By performing such an operation, the luminance output is apparently pre-shot, auto-
Burst is applied, and the rising and falling transition portions of the image on the CRT display surface become steep, and the sharpness of the image is increased. It should be noted that the video contour signal can be obtained by differentiating the video signal as described above, or by using the delay line DL.

[0005]

Since the conventional scanning speed modulation circuit has the above-described configuration and function, it can be seen from FIG. 4 that the circuit between t _A and t _{B and} between t _E and t _F. Since the image signal has an amplitude to the white side as a video signal, even if the scanning speed is increased, some luminance output is obtained. For this reason, a sharp outline is formed in the outline portion of the image, but the luminance has a tail before and after the outline, and there is a disadvantage that the image becomes unsightly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and both the transition portions of the rising edge from black to white and the falling edge from white to black are displayed as steep edges. It is intended to obtain such a scanning speed modulation circuit.

[0007]

A scanning speed modulation circuit according to the present invention includes 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, in response to rising and falling of the video signal. Then, a first-order differential signal obtained by first-order differentiating the video signal and a delayed signal obtained by delaying the first-order differential signal are selectively supplied.

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

[0009]

The scanning speed modulation circuit according to the present invention uses a first-order differential signal obtained by first-order differentiation of a video signal for a rising portion of an amplitude change of the video signal, and converts a delayed signal obtained by delaying the first-order differential signal into a video signal. By preparing the signals independently for the falling of the amplitude change of the signal, and selectively switching these two signals, the transient portion of the video amplitude change causes a current to flow through the modulation coil so as to slow down the scanning speed. . Also, 2
The operation of switching the two signals is performed so as to select a primary differential waveform that is not delayed only when the integrated output level is greater than 0 based on an integrated output obtained by integrating the primary differential waveform. Therefore, the switching operation is controlled by a switching signal wider than the primary differential signal.

[0010]

[Embodiment 1] FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 11 denotes a modulation coil disposed on a CRT (not shown), 12 denotes a DC blocking capacitor, 13 denotes an input terminal of a video signal (luminance signal), 14
Is a first-order differentiating circuit for performing a first-order differentiation of the video signal, and 15 is a delay line DL1, 1 that delays the first-order differential signal by a time corresponding to the rising and falling transient portions 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 has an integrating circuit for integrating the primary differential output. 18 is SW
An amplifier connected to the output side of 16 and 19 is a modulation coil 1
1 is a drive circuit for flowing current to 1, 20 is a color signal input terminal, 21 is a video signal processing circuit for performing color demodulation and amplification,
2, a CRT drive circuit; 23, a CRT; 24, a delay line DL2; 25, a delay line DL3 for adjusting the time of a luminance signal and a chrominance signal.

FIG. 2 shows the waveforms and timing of each part. 3A shows the waveform of an input video signal (luminance signal) at the input terminal 13, and FIG.
The second derivative signal waveform, (c) is 1
(D) a delayed signal waveform obtained by delaying the next differential signal by a time corresponding to the rising and falling transition portions of the video signal;
Is the output signal waveform after the switching operation of SW16, (e)
Is a signal waveform obtained by delaying the video signal by the delay line 16, (f) is a current waveform flowing through the speed modulation coil 11,
(G) is a luminance output waveform on the CRT display surface, and (h) is a SW switching signal output from the control device 17.

Next, the operation will be described. First, FIG.
A video signal (luminance signal) as shown in FIG.
4 to obtain the primary differential signal shown in FIG.
Further, a delay line 15 for delaying the primary differential signal
2 (c) is obtained. These two signals are input to a side and b side of SW16, respectively. The switching operation of the SW 16 is performed by the control device 10 including the integrating circuit.
Is controlled by The controller 17 receives the primary differential signal before the delay, integrates the primary differential signal, and switches SW only when the integrated output level is a positive output (except 0).
16 is switched to the a side, and at other times, it is switched to the b side. The differentiated signal after being switched by the SW 16 is a signal shown in FIG. This signal is amplified by an amplifier 18, and the speed modulation coil 11 is
2D, the signal shown in FIG. 2D is integrated, and a wider current signal flows. The signal is shown in FIG. In order to match the timing of the video signal of the CRT cathode with the modulated 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 supplied to the velocity modulation coil 11, the scanning is accelerated from t _A to t _B immediately before the rising of the video signal as shown in FIG. Goes down. Between all periods t _B ~t _C rising transient portion of the next video signal is scanned luminance output slower rises. Similarly, t _{D of the} falling transient portion of the video signal
During t _E, the scanning speed decreases and the luminance output rises, and between t _E and t _F after the fall, the scanning speed increases and the luminance output decreases. As a result, the luminance output of the CRT display surface as a whole is as shown in FIG. 2 (g), and both the rising and falling of the video signal, the transient portion of the amplitude change of the video signal has a low scanning speed, and the CRT has a low scanning speed. A sharp edge appears on the display. Further, the outline is further sharpened by pulling the black side before and after the white peak.

[0014]

As described above, according to the scanning speed modulation circuit of the present invention, both the rising and falling of the video signal
The scanning speed can be slowed down during all the transition periods of the video signal, and the time axis is compressed on the CRT display surface, so that the frequency appears to be higher, so that the sharpness of the video displayed on the CRT is improved. . Also, the CR that remains before and after the transient portion of the video signal
Compared with the conventional display showing the T display, the remaining display portion is small, and a border for pulling slightly to the black side can be provided, so that the outline can be further clarified.

[Brief description of the 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. 1;
It is.

FIG. 3 is a schematic configuration diagram illustrating 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: Speed modulation coil 12: DC blocking capacitor 13: Video signal input terminal 14: First-order differentiator circuit 15: Delay line DL1 16: Switch (SW) 17: Control device 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)

(57) [Claims] An image signal is supplied to a modulation coil which modulates a horizontal scanning speed of a cathode ray tube by a magnetic field, and a modulation current corresponding to the rise and fall of the video signal is supplied to sharpen an image on a cathode ray tube display surface. In a scanning speed modulation circuit for increasing the degree, a first-order differential signal obtained by first-order differentiation of the video signal and a delay signal obtained by delaying the first-order differential signal corresponding to the rising and falling of the video signal, A scanning speed modulation circuit characterized in that it is selectively supplied to a modulation coil. 2. A modulation current according to the rise and fall of the video signal is passed through a modulation coil that modulates the horizontal scanning speed of a cathode ray tube to which a video signal is supplied by a magnetic field, thereby sharpening an image on a cathode ray tube display surface. Means for first-differentiating the video signal and outputting the first-differential signal in a scanning speed modulation circuit for increasing the degree, and deriving the first-differential signal for a time corresponding to the rising and falling transient portions of the video signal Means for outputting a delayed signal delayed, and control means for integrating the primary differential signal, selectively switching the primary differential signal or the delay signal according to the integrated output level, and supplying the signal to the modulation coil And a scanning speed modulation circuit.