JPS5951796B2 - Scan speed modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scanning speed modulation circuit that performs contour correction by scanning speed modulation in a television receiver, and controls the amount of contour enhancement by scanning speed modulation in accordance with changes in the DC level for brightness adjustment. The purpose is to perform more appropriate contour compensation.

For example, when a television receiver receives a black and white pattern as shown in Figure 1 and displays it on a CRT,
If the video signal has steep rises and falls in the brightness changing part as shown in Figure 2A, the image quality will be good, but in general, the video signal will depend on the frequency characteristics of the receiver, etc. Therefore, as shown in FIG. 5B, the brightness changes have slow rises and falls, and are not sharp and do not have clear outlines. Therefore, as a method of compensating for the decrease in sharpness, there is a contour compensation amount adjustment circuit (hereinafter referred to as an image quality adjustment circuit). This circuit performs second-order differentiation on the video signal shown in B in the same figure to create a signal shown in C in the same figure, and then superimposes this signal C on the original video signal B to produce a rise as shown in D in the same figure. A video signal with a steep fall is obtained and supplied to a CRT. However, in this method, the beam current increases further at the peak of the signal, resulting in a larger beam spot size, causing a so-called blooming phenomenon, and the sharpness is not improved much.
On the other hand, there is a scanning speed modulation method as a method of compensating for the decrease in sharpness without directly correcting the waveform of the video signal. Figure 3 shows the principle of scanning speed modulation.

By firstly differentiating the original video signal 5 shown in FIG. 3A, a signal 50 as shown in FIG. Then, as shown by curve 1 in Figure C, the horizontal deflection magnetic field is corrected at the times corresponding to the rising and falling edges of signal 5, thereby changing the scanning speed of the beam on the screen as shown by curve 2 in Figure D. A modulation method has been proposed as shown.

According to the above scanning speed modulation method, the scanning speed of the beam on the screen becomes slow at the position immediately after the signal 5 starts falling, so the amount of light emitted at the corresponding point on the screen increases rapidly. However, since the scanning speed of the beam becomes faster thereafter, the amount of light emitted at the corresponding point on the screen can be suppressed to a small level. On the other hand, signal S
Since the rising side of , has a symmetrical shape, the amount of light emitted in the horizontal direction on the five screens changes as shown in FIG. 5E, and the sharpness in the horizontal direction can be improved. However, a relatively large amount of power is required to generate the magnetic field for scanning speed modulation. A possible method is to use both of the above two sharpness improvement methods to effectively perform contour compensation.

An example of the block diagram is shown in FIG.

In the figure, 1 is a high frequency amplification circuit, 2 is a frequency conversion circuit,
3 is a video intermediate frequency amplification circuit, 4 is a video detection circuit, 5 is a video amplification circuit, 6 is a scanning speed modulation circuit, 7 is an auxiliary deflection yoke, and 8 is a CRT. However, since the normal deflection circuit is not particularly relevant, illustration thereof is omitted. Here, the video signal from the video detection circuit 4 is applied to the scanning speed modulation circuit 6, the video signal added by the scanning speed modulation circuit 6 is first differentiated and amplified, and a scanning speed modulation current is passed through the auxiliary deflection yoke to perform scanning. Performs contour compensation using velocity modulation. In general, such scanning speed modulation exhibits a characteristic that the brighter the luminance, the more effective it is.

The reason for this will be explained below using a mathematical formula. When the terminal end of the delay line is short-circuited and the reflection is used for first-order differentiation, the input video signal is reflected at the terminal end and is sent back to the input terminal with the opposite polarity.
It will come back τ late.

Therefore, now the input signal Ein is Ein=AcOsωt
(A: amplitude, ω = 2πF, f: input signal frequency), the voltage ET at the input end of the delay line is ET = AcOsω
t −AcOsω (t−2τ)=2A sinωτ・
Sinω (τ− t) ・・・・・・・・・・・・・・・
・・・・・・・・・・・・(1)

The signal waveform is τ due to the timing relationship with the scanning speed modulation current.
It is necessary to make the signal delayed by the same amount of time.

Therefore, the signal waveform is AcOsω (t-τ).
The deflection waveform Wd generated by the main deflection yoke and the auxiliary deflection yoke is calculated using equation (1) as follows: Wd=αt +2A sin
It is expressed as τ·Sinω (τ−t), where α is the horizontal deflection velocity.

The brightness on the screen is proportional to the video signal and inversely proportional to the deflection speed, so the brightness L is L=[K+AcOsω (t-τ)]
/d/DtWd=[K+AcOsω (t-τ)]/[
α−2AωSlnωτ ・COsω (t−τ)]・・
・・・・・・・・・・・・・・・・・・・・・・・・
(2) However, K is the DC bias of the signal.

In general, α>Ac=)Sinωτ holds, so equation (2
) by taking the linear term of the Taylor expansion of L=-[K+AcO
sω (t−τ)]・[α+2AωSlnωτ . C
Osω (t-τ)], and since -l≦COsω (t-τ)≦l, L
maX=(K+A) (α+2AωSinωτ)Lmi
n=(K-A) (α-2AωSinωτ)LmaX-
Lmin=4KAωSinωτ・・・・・・・・・(3
), and the brightness change on the screen [LmaX-Lmin
] increases in proportion to K.

In other words, scanning speed modulation is more effective at higher luminance. However, in reality, as the brightness increases, pluming generally increases and the beam spot size increases, which impairs the above-mentioned effect.

As a means to solve this problem, the present invention attempts to prevent deterioration due to blooming by increasing the amount of contour compensation by scanning speed modulation as the brightness increases.

In other words, in the circuit configuration shown in FIG. 4, when the signal has a very high brightness, the advantage of having a contour compensation effect as the brightness increases due to scanning speed modulation alone is lost due to blooming. In order to solve this problem, the amount of contour compensation by scanning speed modulation is increased when the brightness is high, and the emphasis frequency is also increased to further enhance the effect. An embodiment of the present invention will be described below with reference to FIG. In the figure, 9 is an input terminal to which a detected video signal is added, 10 is a video amplification circuit, 11 is an image quality adjustment circuit, and 1
2 is a clamp circuit, 13 is a video output circuit, 15 is a gain control circuit, 6 is a scanning speed modulation circuit, 6-1 is a first-order differential amplifier circuit, 6-2 is an output circuit, 7 is an auxiliary deflection yoke, and 8 is a CRT, 16 is a contrast adjustment variable resistor (hereinafter referred to as contrast adjustment VR), and 14 is a brightness adjustment variable resistor (brightness adjustment VR). Here, a video signal is applied to the input terminal 9 from the video detection stage, amplified by the video amplification circuit 10, and then contrast adjustment (adjustment of the amplitude of the video signal) is performed by the contrast adjustment VR16. Then, the image quality adjustment circuit 11 performs image quality adjustment (adjustment of the amount of edge enhancement of the video signal), and the signal is sent to the clamp circuit 12 for brightness adjustment VR14 (
The DC level of the video signal is adjusted by adjusting the clamp potential (hereinafter referred to as clamp potential adjustment VR), and the signal is led to the video output circuit 13 and further applied to the cathode electrode of the CRT 8. Further, the clamp voltage from the clamp adjustment VRl4 is applied to the gain control circuit 15 to control the gain of the video signal from the input terminal 9, and is applied to the scanning speed modulation circuit 6. In the scanning speed modulation circuit 6, a first-order differential amplification circuit 6-1 performs first-order differentiation and amplification, an output circuit 6-2 drives the auxiliary deflection yoke 7, and a scanning speed modulation current is passed through the auxiliary deflection yoke 7 to perform scanning. Contour compensation is performed using velocity modulation. As described above, in the scanning speed modulation circuit of the present invention, the gain control circuit controls the amount of the video signal input to the scanning speed modulation circuit in accordance with the change in the clamp potential of the clamp adjustment VRl4, that is, the change in the DC level of the video signal. 15, it provides a scanning speed modulation circuit that can control the amount of contour compensation using scanning speed modulation according to brightness.

FIG. 6 shows an example of a specific circuit of the main part of the present invention.

In the figure, 9 is an input terminal, 14 is a clamp adjustment VR,
15 is a gain control circuit, and 6 is a scanning speed modulation circuit. Here, the clamp potential is controlled by clamp adjustment VRl4.

That is, the clamp voltage is applied to the clamp circuit 12 in FIG. 5 to control the clamp level, while the gain control circuit 1
5 is applied to the base of the transistor Trl, and is compared with the voltage obtained by dividing the voltage between the resistors R1 and R2 (hereinafter referred to as reference voltage EO) to control the conduction state of the transistor Trl, and is applied to the scanning speed modulation circuit 6. The gain of the detected video signal from the input terminal 9 is controlled. In other words, when the clamp potential is low and the brightness is low, that is, the transistor Tr
When the clamp potential applied to the base of the transistor Trl is lower than the reference potential EO, the impedance between C and E of the transistor Trl becomes low, so that a considerable portion of the video signal is bypassed through the transistor Trl. Therefore, since the video signal guided to the scanning speed modulation circuit 6 is a small signal, the amount of contour compensation due to scanning speed modulation is also relatively small. On the other hand, when the clamp potential is high and the brightness is high, that is, when the clamp potential applied to the base of the transistor Trl is higher than the reference voltage EO, the C-E of the transistor Trl
Since there is a high impedance between them, the video signal is guided to the scanning speed modulation circuit 6 without much attenuation. Therefore, the amount of contour compensation due to scanning speed modulation also increases. As mentioned above, the higher the clamp potential, that is, the higher the brightness, the
By gradually increasing the contour compensation amount by scanning speed modulation, it is possible to effectively correct the effects of blooming at high brightness times.

Next, a second embodiment of the present invention will be described using FIG. 7.
Since the operation and circuit configuration are similar to those of the first embodiment, detailed explanations will be omitted. The clamp potential controlled by the clamp adjustment VRl4 is applied to the gain control circuit 14, and the video signal (that is, the signal with the amplitude and edge enhancement amount of the video signal adjusted) that has passed through the contrast adjustment VRl6 and the image quality adjustment circuit 11 is applied to the gain control circuit 14. In addition to the control circuit 15, the gain of a gain control circuit 15 is controlled in accordance with changes in the clamp potential and is applied to the scanning speed modulation circuit 6.

Therefore, by increasing the amount of contour compensation by scanning speed modulation during high brightness, it is possible to correct the deterioration of the contour compensation effect due to blooming. Furthermore, in this embodiment, since the video signal that has undergone contrast adjustment and image quality adjustment is added to the gain control circuit 15 for gain control, the amount of contour compensation by scanning speed modulation can also be controlled according to the contrast and image quality conditions. .

As a means of increasing the amount of contour compensation by scanning speed modulation as the brightness increases, as in the embodiment shown in FIG.
By operating the scanning speed modulation circuit 6 in addition to the scanning speed modulation circuit 6 having a speed of -3, blooming correction can be performed by increasing the amount of contour compensation due to scanning speed modulation as the brightness increases. As described above, the scanning speed modulation circuit of the present invention adjusts the brightness by changing the clamp potential using the clamp adjustment variable resistor, and increases the amount of video signal input to the scanning speed modulation circuit according to the clamp potential. , a gain control circuit that controls the gain to decrease at low brightness, and the amount of contour compensation by scanning speed modulation can be controlled by brightness, and as the brightness increases, the amount of contour compensation by scanning speed modulation increases,
It is possible to improve the sharpness at high brightness by correcting blooming in which the beam spot size increases and the sharpness decreases due to an increase in the beam current in a high brightness area.

In addition, an output signal that has undergone contrast adjustment and image quality adjustment is added as a video signal to the gain control circuit, and according to the detection signal, the amount of video signal input to the scanning speed modulation circuit is controlled, and contour compensation is performed by scanning speed modulation. By controlling the amount, contour compensation by scanning speed modulation can also be controlled in accordance with changes in the amplitude of the video signal and the amount of contour enhancement due to contrast adjustment and image quality adjustment.

In this way, the present invention controls the amount of contour compensation by scanning speed modulation according to the image quality conditions (contrast, amount of edge enhancement, brightness) of the receiver, so that a sharp image with excellent image quality can be produced on a CRT. can be displayed.

[Brief explanation of drawings]

Figure 1 shows an example of an image displayed on a CRT, Figure 2 shows an example of an image displayed on a CRT.
Figures A, B, C, and D are waveform diagrams showing the operation of the contour compensation amount adjustment circuit, Figure 3 A, B, C, D, and E are waveform diagrams showing the operation of scanning speed modulation, and Figure 4 is the waveform diagram of the conventional FIG. 5 is a block diagram showing the circuit configuration of the scanning speed modulation circuit in an embodiment of the present invention, FIG. 6 is an electrical wiring diagram of the same part, and FIGS. FIG. 8 is a block diagram showing another embodiment of the present invention. 10... Image amplification circuit, 11... Image quality adjustment circuit, 12... Clamp circuit, 15...
...Gain control circuit, 6...Scanning speed modulation circuit.

Claims (1)

[Claims] 1 means for clamping a video signal; means for controlling the clamp level of the video signal to adjust the brightness; and in response to the clamp level of the video signal, the gain of the scanning speed modulation signal is increased for high brightness and high for low brightness. A scanning speed modulation circuit comprising: means for controlling the gain to be small; and means for guiding the gain-controlled signal to an auxiliary deflection yoke for performing scanning speed modulation.