JPS6041508B2 - Sharpness improvement circuit - Google Patents

Description

[Detailed Description of the Invention] In order to improve the sharpness of television images, there is a method of density modulating the electron beam of the picture tube based on the contour signal obtained from the video signal (luminance signal). Sharpness can be further improved if the scanning speed of the electron beam is also modulated.

As shown in FIG. 1, this sharpness improvement circuit has four delay lines IA to ID connected in series, and a video signal is supplied to a terminal 2. 3 indicates the signal source for convenience.

The delay amounts of delay lines IB and IC are both selected to be 7v, and the other delay lines IA and ID are each selected to be ↑s. Here, the rise time (or fall time) of the input video signal when the input video signal changes the most from the black level to the white level (or vice versa), and therefore the highest sharpness is required.
The above-mentioned delay time of 7v is selected so that the voltage becomes 27v.

In reality, dv is about 0.11 mountain seconds. Also, the delay amount is 7s
When the sum of and ↑v is expressed as ↑A, this 7^ is the signal delay amount involved in aperture correction, as described later, and is usually within the range of 0.25 to 0.5 mountain seconds. To be elected.
In this example, ↑^=0.294 French seconds is selected. Connect each connection point of the delay lines connected in series to 1, ~ as shown in the figure.
15, if the signal obtained at the connection point 13 is assumed to be E(t) and this signal B(t) is considered as the reference signal, then the connection point 1. In other words, the input video signal supplied to the terminal 2 is E(t+A), and the signal obtained at the connection point 15 is E(t-7^).

Therefore, the connection point 12 obtains a signal E(t+↑v), and the connection point 14 obtains a signal E(t-7v).
These signals are illustrated in FIGS. 2A to 2E. In this example, a rectangular waveform signal as shown in FIG. 2 is considered as the input video signal.

In addition to the reference signal E(t), the density modulation signal forming circuit 10
It is formed using three signals: the first and second signals E(t+7^) and E(t1cho^). After these signals are appropriately level controlled through level control circuits 5 to 7,
It is supplied to the synthesizer 8〉 to produce the final density modulated signal E^P(
t) is formed. When the level control amount in the level control circuits 5 to 7 is expressed as heat ~a2 as shown in the figure, in this example, ao is 1.25a, and -0.1
2F And a2 is chosen so that it becomes -0.125 like a.

Therefore, if the respective outputs of these level control circuits 5 to 7 are illustrated, they will be as shown in FIG. 2 G to 1, and by combining these signals, a density modulation signal for aperture correction as shown in FIG. 2 J is generated. E^P(t) is obtained. This density modulation signal E^P(t) is supplied to the picture tube as a luminance signal, and the electron beam is density-modulated.

However, in the case of primary color drive, as shown in FIG. Needless to say. On the other hand, the speed modulation forming circuit 2 consists of a pair of delay lines IB and IC and a synthesizer 11, and the third and fourth E(t10V) and E(t-
7v) to the combiner 11 with the polarity shown in the figure, the desired velocity modulation signal E Shukawa can be obtained.

That is, this speed modulation signal EvM(t) is EvM([):E
(t10v)1E(t17v) It can be expressed as (1).

The scanning speed of the electron beam is modulated by this speed modulation signal Evw(t). This signal EvM(t) is applied to the deflection means 1 for scanning velocity modulation, which is provided separately from the horizontal and vertical deflection means 14 provided in the picture tube 13, as shown in FIG.
5. As shown in the figure, the deflection means 15 is composed of a pair of electrostatic deflection plates 15a and 15b that face each other in the horizontal direction.

Since various methods of supplying the signal can be considered, explanation thereof will be omitted.
In this way, the aperture-corrected density modulation signal E^P
If the density of the electron beam is modulated by EvN(t) and the scanning speed of the electron beam is modulated by the velocity modulation signal EvN(t), the input video signal (contour signal) will rise. The amount of light emitted at the corresponding position on the screen changes rapidly during the falling edge and the falling edge, thereby improving the sharpness of the image.

By the way, the effect of such density and velocity modulation method,
In other words, let's consider the problem of sharpness of television images as the response of step signals.

Now, the step signal with the fastest rise of the signal that can pass through the video signal transmission band (0 to 4.8 MHZ) is sent to the picture tube I.
In addition to step 3, the brightness distribution of the step signal on the screen at that time is measured, and the sharpness of the image is considered by observing its rise time, overshoot, etc. In this example, the rise time of the step signal used is 0.12 French seconds. FIG. 4 shows the step response of the step signal, and the groove is graduated in distance (time) in the horizontal direction of the screen.

The vertical axis is the relative brightness level on the screen. curve 3
0a is the step response when the beam spot diameter of the fin beam is set to zero, and this curve 30a is the curve most similar to the fin beam. The step response when density and velocity modulation is applied to this ideal curve 30a is the solid curve 3.
It will look like 0b. The observation example shown in FIG. 4 is when the peak current of the step signal is 100 A, but when the peak current is increased to about 1 A, the step signal curve 30b becomes as shown in FIG. 5. . As is clear from the observation results in Figures 4 and 5, when the peak current of the step signal is in the low current region (1 A or less), the sharpness of the image can be improved based on overshoot, etc. However, as shown in the figure, the positional deviation with respect to the ideal curve 30a becomes noticeable.

This gives the impression that the rising and falling positions of the image have shifted. It goes without saying that this phenomenon is not limited to step signals, but also occurs when normal video signals are displayed. In this case, when observing the vicinity of the rise of the step signal, it is observed that "in each current region" with respect to the ideal curve 30a. Since the observation curve 30b is located on the right side, for example, when a white image is projected, this white image appears to be slightly thinner than the actual image.Therefore, density and velocity modulation is applied in this way. In some cases, image distortion appears.

Note that the peak current of the step signal is 1 mA, for example 2
When the curve increases to about A, the observed curve 30b is in a mirror direction shifted to the left with respect to the ideal curve 30a, and therefore, when viewed as an image, it appears thicker than the actual image. , such movement is not actually perceived as image distortion.

This shift in the position of the image in the low current region of the step signal is due to the velocity modulation signal B for the electron beam.
This means that the amount of vM(t) is excessive in the low current region.

Let's explain with reference to FIG.

This figure shows the deviation between the twill line when the speed modulation signal is supplied and the rope line based on the ideal step signal as △T, and illustrates the relationship between this △T and the step signal current. . As shown by curve 32, the displacement ΔT decreases as the signal current increases.

Therefore, the speed modulation signal should be controlled so that it is small in the low current region and large in the high current region, that is, it has an n-proposal characteristic (proposal 2 or plan 3) as shown by curve 33. Well, this speed modulation signal causes positional deviation △
It is possible to correct T. In view of these points, the present invention aims to improve freshness by providing a sufficient amount of overshoot, and completely eliminates image distortion caused by positional deviation. The group fishing degree improving circuit according to the present invention will be explained with reference to FIG. However, the same reference numerals are given to the parts corresponding to those in the previous figure, and the explanation thereof will be omitted. In the present invention, instead of always supplying a constant speed modulation signal EvN with respect to the magnitude of the signal current, the signal amount is kept low especially in the low current region, and as the signal current increases, the signal EvN The amount of (t) is increased. Therefore, in the present invention, as shown in FIG. 7, the speed modulation signal forming circuit 20 is configured as follows. In other words, the third and fourth signals E (t+7v) and B (t-7v) obtained at the connection points 12 and 14 are sent to the nonlinear circuit 2, respectively.
1 and 22, and then added to the combiner 11 to form a new velocity modulation signal EvMN river. As is well known, the nonlinear circuits 21 and 22 can be achieved by using elements having nonlinear characteristics such as diodes as transistors.

Here, if each linear constant of the nonlinear circuits 21 and 22 is KEn, the nonlinear output can be obtained as follows. EVMN(t)=k{En(t+7v)−En(
t1choV)}! Water 7V [ki En (t)] t = Small V - Fertilizer - 1 (t) - Ki E (t).・・・．・・'2'' Here・ 27V-Takashi E(t) 3E(tJuchoV)-E(t-7V)
= EvN(t) ``””[31, so the formula ■ is EVMN(t) = nkEn-1(t)
It can be expressed as Evw([)...[4}.

By interposing the nonlinear circuits 21 and 22 in this way, nonlinear characteristics can be imparted to each output, so that the amount of speed modulation signal does not become excessive in the low current region.
For example, the observation results when n is 3 are shown by a one-point purchase line curve 30c in FIGS. 4 and 5.

According to the observed curve 30c of the present invention, the ideal curve 30
It can be seen that the step is at approximately the same position as the step for a.
Moreover, a sufficient amount of overshoot is obtained. As explained above, in the present invention, the speed modulation signal 8vMN(t) is generated based on the outputs obtained via the nonlinear circuits 21 and 22.
Since the scanning speed of the electron beam is modulated by this signal, the peak current of the input video signal is low, that is, in the low current region, the amount of the speed modulation signal is small, and as a result, as mentioned above, It is possible to completely correct misalignment.

That is, in the present invention, sufficient sharpness can be obtained with the density and velocity modulation signals, and a correct image can always be reproduced. Therefore, sharp and natural images can always be obtained. Furthermore, in the present invention, a plurality of delay lines IA to IA provided in the speed modulation signal forming circuit 20
The ID can also be used as a delay line for obtaining a plurality of signals E(t+7v), E(t), and E(t1chov) having different delay times required for density modulation signal formation.

Therefore, the dual use of these delay lines has the practical effect of significantly simplifying the overall circuit configuration. In the above-mentioned embodiment, the freshness improvement circuit was constructed using four delay lines, but for example, two delay lines on the left and right sides of the connection point 13 may be configured with one delay line each. Of course, it is also possible to construct it by a line, derive the tap from its midpoint, and set this point to 12 and 14, respectively.

Further, as the nonlinear circuits 21 and 22, although circuits using diodes and the like are illustrated, other circuits may be used.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an example of a freshness improvement circuit used to explain the present invention, and FIG. 2 is a waveform diagram used to explain its operation.
FIG. 3 is a diagram showing an example of a picture tube suitable for applying the present invention, FIGS. 4 and 5 are characteristic diagrams showing the response of a step signal, FIG. 6 is a diagram for explaining the operation, and FIG. 1 is a system diagram showing an example of a freshness improving circuit according to the present invention. 10' is a density modulation signal forming circuit, 20' is a speed modulating signal forming circuit, IA to ID are delay lines, E(t) is a reference signal,
21 and 22 are nonlinear circuits, E^P(t) is a density modulation signal, E Shukawa and EvMN(t) are velocity modulation signals. Figure 1 Figure 3 Figure 6 Figure 2 Figure 4 Figure 5 Figure 7

Claims (1)

[Claims] 1 A video signal is supplied to a density modulation signal forming circuit having a predetermined delay line to obtain a density modulation signal for aperture correction, and the video signal obtained from the delay line is used to adjust the magnitude of the output signal in a region where the input signal is small. A velocity modulation signal is obtained by supplying the velocity modulation signal to a velocity modulation signal forming circuit via a nonlinear circuit having suppressed input/output characteristics, density modulation of the electron beam is performed using the density modulation signal, and the electron beam is A sharpness improvement circuit that improves image sharpness by performing speed modulation.