JPH0631809Y2 - Speed modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a velocity modulation circuit suitable for application to a deflection circuit system of a television receiver.

[Prior Art] A television receiver is usually provided with a speed modulation circuit in order to correct the contour of a reproduced image.

In this velocity modulation circuit, a predetermined velocity modulation signal is supplied to a correction coil (auxiliary deflection coil) attached to the cathode ray tube to modulate the scanning velocity of the electron beam so that the contour portion of the reproduced image is emphasized. I have to.

FIG. 4 shows a conventional example of the speed modulation circuit 10.

In the figure, the video signal supplied to the terminal 1 is supplied to a differentiating circuit, which is a secondary differentiating circuit 2 in this example, and a contour signal corresponding to the contour portion is extracted.

The extracted contour signal is supplied as a velocity modulation signal to the deflection correction circuit 5 composed of a correction coil via the amplifier 3 and the output circuit 4 for current amplification, so that the electron beam becomes the velocity modulation signal. The velocity is modulated accordingly.

An example of the velocity modulation signal is shown in FIG. Each of the velocity modulation signals is a signal related to the contour portion of the video signal.

[Problems to be Solved by the Invention] By the way, the conventional velocity modulation circuit 1 configured as described above is used.
At 0, the contour correction amount was determined only by the contrast ratio of the video signal, and as shown in FIG. 5, the amplification degree of the velocity modulation signal was always constant regardless of the deflection position of the screen.

On the other hand, the focus of the cathode ray tube deteriorates significantly as it goes away from the center of the screen. That is, the four corners of the screen are most deteriorated.

Since the conventional contour correction performs velocity modulation regardless of the deflection position of the screen, the amount of contour correction is not sufficient especially at the deflection position where the focus is poor, and as a result, the sharpness of the entire screen is effectively improved. I couldn't.

Therefore, the present invention proposes a speed modulation circuit which solves such a conventional problem and is capable of improving the sharpness even when the focus is poor, especially at the deflection positions at the four corners of the screen.

[Technical Means for Solving Problems] In order to solve the above-mentioned problems, in the present invention, the contour signal is extracted from the video signal, and the contour signal is a correction value signal of the horizontal cycle and the vertical cycle. A modulated velocity modulation signal is formed, and the scanning beam is velocity-modulated by driving the scanning velocity correction coil provided in the cathode ray tube with this velocity modulation signal.

[Operation] Parabolic wave signals are used as the correction signals Sb and Sc of the horizontal period and the vertical period, respectively.

The contour signal is simultaneously modulated by these correction signals Sb and Sc. At that time, the modulation is performed so that the minimum amplitude values of the horizontal and vertical parabolic wave signals come to the center of deflection in the horizontal and vertical directions, respectively.

This maximizes its amplification at the four corners of the screen,
A velocity modulation signal is formed such that the velocity modulation signal is minimized toward the center of the screen.

The modulated contour signal is supplied to the correction coil (scanning speed correction auxiliary deflection coil) as a speed modulation signal. As a result, the degree of amplification of the velocity modulation signal in the poor focus portion is increased, and focus deterioration is compensated. This can improve the sharpness of the entire screen.

[Embodiment] Next, a case where an example of the velocity modulation circuit according to the present invention is applied to the deflection system of the television receiver described above will be described in detail with reference to FIG.

FIG. 1 shows an example of a speed modulation circuit 10 according to the present invention, in which a video signal supplied to a terminal 1 is differentiated by a differentiation circuit 2 so that a contour signal Sa ( FIG. 3F) is extracted.

The extracted contour signal Sa is supplied to the modulation circuit 20,
The amplitude is modulated by the correction signals Sb and Sc of the horizontal period and the vertical period.

As the correction signals Sb and Sc, parabolic wave signals formed from the sawtooth-shaped horizontal and vertical deflection signals Sh and Sv shown in FIGS. 3A and 3C are used (see FIGS. 3B and D).

When the amplitude-modulated contour signal is hereinafter referred to as a velocity modulation signal (contour correction signal) Sd (FIG. 3E), this velocity modulation signal Sd passes through the output circuit 4 for current amplification to the deflection correction circuit 5, It will be supplied as a velocity modulation signal of the electron beam.

FIG. 2 shows a specific example of the modulation circuit 20 and the output circuit 4.

The contour signal Sa is supplied to the input terminal 23 of the modulation circuit 20, which is amplified to a predetermined amplitude value by the amplifying transistor Q1 and the speed modulation signal Sd is obtained from the load resistor 24 provided on the collector side thereof. .

The transistor Q1 is provided with an amplification degree control means 25 for modulating the amplification degree of the contour signal Sa.

The control means 25 includes three control transistors as shown in the figure.
The first transistor Q2, which is composed of Q2 to Q4, is connected in parallel to the collector-emitter current path of the transistor Q1.

The second and third control transistors Q3 and Q4 are connected in parallel as shown. The second control transistor Q3 is for horizontal modulation, and the horizontal correction signal Sb formed from the horizontal deflection signal Sh (FIG. 3A) is supplied to the base terminal 21 as a horizontal period modulation signal.

Similarly, the third control transistor Q4 is for vertical modulation, and the vertical correction signal Sc formed from the vertical deflection signal Sv (FIG. 3C) is supplied to its base terminal 22 as a vertical period modulation signal. It

Therefore, the horizontal correction signal Sb is modulated by the vertical correction signal Sc, and this horizontal correction signal Sb further controls the first control transistor Q2. Therefore, the collector current flowing through the load resistor 24 is controlled based on the combined signal of the horizontal and vertical correction signals Sb and Sc.

Consider the case where the correction signals Sb and Sc having the polarities shown in FIGS. 3B and 3D are input.

A signal obtained by combining the phase inversion signals of the horizontal and vertical correction signals Sb and Sc is input to the base of the first control transistor Q2. Therefore, a combined collector current having the same polarity as the horizontal and vertical correction signals Sb and Sc flows through the collector of the first control transistor Q2.

As a result, the amplification degree of the velocity modulation signal Sd is modulated by both the horizontal period and the vertical period. That is, the collector current of the control transistor Q2 is minimized at the beginning and the end of one horizontal cycle, and is maximized at the middle of the horizontal cycle.

Similarly, the collector current of the control transistor Q2 is minimized at the beginning and end of one vertical cycle, and is maximized at the middle of the vertical cycle.

Contrary to the above, the collector current flowing through the load resistor 24 has the maximum at the beginning and the end of the horizontal and vertical periods, and the minimum at the intermediate portion, and the signal thus modulated is further modulated in the vertical period.

Therefore, the amplification degree of the modulation circuit 20, that is, the amplitude value is also modulated accordingly, and the amplitude of the speed modulation signal Sd after modulation is
The result is as shown in FIG. 3E.

The speed modulation signal Sd is supplied to the output circuit 4 for current amplification.

In this example, a push-pull amplifier composed of a pair of complementary-connected transistors Q5 and Q6 is used.

The speed modulation signal Sd is amplified by the output circuit 4 to a predetermined current value.

As shown in the figure, the deflection correction circuit 5 is composed of a correction coil (scanning speed correction auxiliary deflection coil) 6 and a charging / discharging capacitor 7 connected in series thereto.

If the scanning speed of the electron beam is modulated with respect to each of the horizontal and vertical directions by the speed modulation signal Sd having such a polarity and amplitude value, the contour correction is performed with the center of the screen as the center toward the four corners of the screen. This will offset the focus degradation as the amount will increase.

[Effect of the Invention] As described above, in the present invention, the velocity modulation signal Sd that is applied to the correction coil for scanning velocity modulation of the electron beam is similarly modulated by the correction signals of the horizontal and vertical periods. It is the one.

According to this, since the contour correction amount increases as it goes to the four corners of the screen, it is possible to effectively remove the deterioration of the contour due to the deterioration of the focus, particularly the deterioration at the four corners of the screen. As a result, the sharpness can be improved over the entire screen.

Further, the modulation circuit is realized by an extremely simple transistor circuit, and the configuration is extremely simple, which is practical.

Therefore, the velocity modulation circuit according to the present invention is extremely suitable when applied to the deflection system of the television receiver described above.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a velocity modulation circuit according to the present invention, FIG. 2 is a connection diagram showing a concrete example thereof, FIG. 3 is a waveform diagram used for explaining the operation thereof, and FIG. 4 is a conventional velocity modulation. A system diagram of the circuit, FIG. 5 is a waveform diagram of a velocity modulation signal used for velocity modulation. 2 ... Differentiation circuit 4 ... Output circuit 5 ... Deflection correction circuit 10 ... Velocity modulation circuit 20 ... Modulation circuit 25 ... Amplification degree control means Sa ... Contour signal Sb ... Horizontal correction signal Sc ... Vertical correction Signal Sd: speed modulation signal

Claims (1)

[Scope of utility model registration request] 1. A contour signal is extracted from a video signal, the extracted contour signal is supplied to a modulation circuit, and the contour signal is modulated by a correction signal of a horizontal period and a vertical period to form a velocity modulation signal. A speed modulation circuit, wherein the modulation circuit is connected to the first transistor for amplifying the contour signal to a predetermined amplitude value, and is connected to the first transistor, and modulates the amplification degree of the contour signal. Therefore, an amplification degree control circuit is provided, and the amplification degree control circuit is composed of second to fourth control transistors, and the second transistor is connected in parallel to the erector-emitter current path of the first transistor. The bases of the second transistors are connected to the collectors of the third and fourth control transistors, and the horizontal modulation signal is supplied to the bases of the third control transistors. Velocity modulation circuit of the vertical modulation signal to the base of the fourth control transistor is characterized in that each is supplied is connected in parallel.