JPS5927508B2 - contour compensation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for performing contour compensation using scan velocity modulation.

It is generally well known that contour compensation can be performed by modulating the scanning speed.

This principle will be briefly explained using the waveform diagram in FIG. Now, when a video signal as shown in Fig. 1a is received, it is first differentiated to create the signal shown in Fig. 1b. This linearly differentiated signal current is added to the main deflection current A to form a scanning signal as shown in FIG. 1c. Although this adding means may actually send this first-order differential signal to the main deflection yoke, it is more practical to provide it separately in the auxiliary yoke. This is because a large flyback pulse is generated in the main deflection yoke, and this pulse flows back into the speed modulation circuit, requiring the transistors in that circuit to have extremely high withstand voltages. This is due to the fact that it is difficult for the current to flow. In this way, when the main deflection current is modulated by the first-order differential waveform of the video signal, the steepest part of the deflection current waveform, that is, the first
In the part of Figure c (7) B, the scanning speed becomes faster, so the image becomes darker, and in the part where the slope of the deflection current waveform is gentler, that is, the part of Figure 1 c (1) C, the scanning speed becomes slower, so the image becomes brighter. As a result, an image with emphasized outlines is displayed as shown in Fig. 1(d). FIG. 2 shows a conventional circuit system for obtaining a scanning speed modulation signal using a lumped constant delay line.

In FIG. 2, an input terminal 1 is supplied with an intermediate frequency amplifier output signal of a television. 2 is a detection circuit, 3 is a video amplification circuit, 4 is a video signal output circuit, 5 is a synchronous separation/separation circuit, 6 is a horizontal and vertical deflection circuit, and the output of 3 is also supplied to an emitter follower composed of a transistor T. .

8 is a matching resistor whose value matches the characteristic impedance Ro of the delay line 9.

The delay line 9 is composed of LC, and its characteristic impedance is Ro) and the delay time is τ. The terminal end of 9 is shorted.

The signal from the input end of the delay line 9 is supplied to a transistor 10 constituting an amplifier.

The output signal 10 is further amplified by an amplifier 11 for driving the auxiliary deflection yoke.

12 is a high frequency blocking coil, 513 is a damping resistor, 1
4 is an auxiliary deflection yoke, 15 is a horizontal and vertical main deflection yoke, 16 is a cathode of a cathode ray tube, and 17 is a cathode ray tube.

The operation shown in FIG. 2 will be explained below. The input signal from 1 is 2
The wave is detected by

This detected signal is separated into a video signal and a synchronization signal by 3 and 5, respectively. The synchronization signal is separated in the synchronization separation circuit 5, and guided to the main deflection yoke 15 via the deflection circuit 6, where horizontal and vertical deflection is performed. One of the outputs of the video amplification circuit 3 is amplified by the video output circuit 4, and is supplied to the cathode 16 of the cathode ray tube 17 to display a video signal. The other one of the outputs of No. 3 is supplied to the emitter follower 7.

7 is an emitter follower that drives the delay line 9.

9 is short-circuited, the input video signal is reflected at the end and returns to the input end again with a delay of 2τ with the opposite polarity.

Therefore, when the input signal Ein is now , the voltage ET at the input end of the delay line is . --1v're1--l
ノ＼←【ノ(1′).

The absolute value of the frequency characteristic is as shown in FIG. It can be seen from this that when τ=100 ns, 2.5 MHz is most emphasized. Emphasizing high frequencies in this way is equivalent to performing first-order differentiation. The waveform thus first differentiated is amplified by 10 and further amplified by auxiliary yoke drive amplifier 11.

Reference numeral 12 is a coil that passes only direct current and blocks high frequencies, and is used to efficiently flow high frequency signals to the auxiliary yoke 14.

13 is a damping resistor for preventing ringing occurring in the auxiliary yoke.

To show the correspondence with FIG. 1, when the waveform of FIG. becomes like c. From the video signal input to the cathode ray tube 16 and the c-polarized wave, the brightness on the cathode ray tube becomes d. Generally, such 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. Since the signal waveform needs to be delayed by τ from the timing relationship with the speed modulation signal, the signal waveform is ACOSω(t
−τ). The deflection waveform WD generated by the main deflection yoke and the auxiliary deflection yoke can be calculated using equation (1).Since the brightness on the surface is proportional to the video signal and inversely proportional to the deflection speed, the brightness L is calculated using the equation (1). It becomes a DC bias.

Generally holds, so taking the linear term of the Taylor expansion of equation (2), we get the luminance change on the screen [Lmax-L
min] increases in proportion to K.

In other words, the brighter the screen brightness, the more speed modulation is applied. However, as the brightness increases, blooming generally increases and the spot diameter increases, so the above-mentioned effects are further weakened. In other words, if the configuration shown in FIG. 2 is used as is, the advantage of speed modulation, which is that the higher the brightness is, the higher the contour enhancement effect is, which is unique to velocity modulation, will be lost due to blooming when the signal has a very high brightness. In the present invention, in order to solve this problem, the amplitude of velocity modulation is increased when the brightness is high, and the emphasis frequency is also increased in order to further enhance the effect.

Hereinafter, details of the present invention will be explained with reference to the drawings.

In FIG. 4, numerals 1 to 7 and 11 to 17 are exactly the same as in FIG. 2, so their explanation will be omitted. Reference numerals 20 to 22 constitute a clamp circuit, in which 20 is a capacitor for holding the clamp potential, 21 is a switching diode, and 22 is a volume for setting the clamp potential.

23 is a transistor constituting a nonlinear amplifier; 24 is a diode for providing nonlinear characteristics; 26 is a potential setting volume; 25 is a volume for adjusting the degree of nonlinearity;
7 is a delay line constituted by a variable capacitance diode, 28 is a variable capacitance diode, and 29 and 30 are resistors and capacitors for taking out the average value of the video signal.

Next, the operation of portions 20 to 28 in FIG. 4 will be explained. Now, assuming that the set potential of 22 is Vc, the diode 21 becomes conductive only when the leading edge of the synchronizing signal shown in FIG. This clamped signal is guided to the base of transistor 23. When the set potential of 26 is set to VA, when the video signal exceeds the level of VA, the diode 24 becomes conductive, the emitter impedance of 23 decreases, and the gain of 23 increases.

Therefore, the waveform shown in FIG. 4b is obtained at the collector. However, a delay line 27 with a terminal short circuit is attached to the collector 23, and the actual waveform at the collector is a first-order differential waveform of b. At this time, the delay time τ of the delay line is given by:

C is a variable capacitance diode 28, and since the average value of the video signal is given to the cathode side of 28 by 29 and 30, the collector potential of 23 decreases as the image becomes brighter, so it is stored in 30. The average voltage generated will also be lower,
The potential difference between both ends of 28 increases, and the value of C decreases. This is based on the fact that in a variable capacitance diode, the larger the potential difference, the smaller the capacitance value. In this way, the higher the brightness level of the signal, the shorter the delay time and the more emphasized high frequencies will be. Therefore, the waveform at the collector becomes as shown in FIG. 5c. As described above, according to the circuit shown in FIG. 4, the brighter the luminance, the larger the amount of correction by speed modulation, and the correction that emphasizes the high frequency range is performed, making it possible to correct the influence of blooming. That is, as the luminance signal level increases and the diameter of the beam current of the cathode ray tube increases, the spatial frequency characteristics on the screen deteriorate.
Since the characteristics of the contour portion deteriorate, the amplitude of the contour compensation signal is increased, but this alone is insufficient to compensate for the deterioration of resolution characteristics due to the increase in beam diameter.

This is because the contour compensation is performed while the beam diameter is still large, so contour compensation is performed while the beam is on the low spatial frequency side, resulting in a long modulation time. If, as in this embodiment, the signal for contour compensation is moved to the high frequency side and contour compensation is performed on the high frequency side, the modulation time becomes shorter and the beam spot diameter becomes thicker, resulting in characteristic deterioration. can be adequately compensated for. The above example is an example of obtaining a first-order differential signal using a variable delay line, but the same thing can be done with a variable differential constant circuit purchased using a variable impedance element such as a variable capacitance diode. Needless to say.

In the above embodiment, the delay time of the delay line is changed by the average brightness of the screen, but if this delay time is further changed by the video signal itself, the waveform of FIG. 5b on the higher side of the brightness signal level is The waveform characteristics of the contour part become a signal with the high frequency side emphasized, and the rise and fall characteristics become sharp, so the differential output signal obtained by differentiating this signal becomes larger as it goes to the higher side of the luminance signal level. The waveform becomes as shown in Figure 5 d, and the width of the differential output signal can be narrowed, speed modulation can be applied with an area N smaller than the area M in Figure 5 c, and power can be saved. It is also possible to obtain the same effect.

As described above, by using the present invention, it is possible to obtain a contour compensation device that very well corrects the effects of blooming in high-brightness areas.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing contour compensation by velocity modulation, Fig. 2 is a configuration diagram of a conventional contour compensation device according to an embodiment, Fig. 3 is a frequency emphasis explanatory diagram of Fig. 2, and Fig. 4 is a diagram of the present invention. FIG. 5 is a diagram illustrating the configuration of a contour compensating device according to an embodiment of the present invention, and FIG. 5 is an explanatory waveform diagram of FIG. 20... Capacitor, 21... Diode, 22... Resistor, 23... Nonlinear amplifier, 24... Diode, 25...・・・
・Nonlinear control volume, 26...Volume for potential setting, 27...Delay line, 28...
Variable capacitance diode, 29... Resistor, 30...
...Capacitor.

Claims (1)

[Scope of Claims] 1. means for clamping an image signal to a constant potential, amplifying means for increasing the degree of amplification of a luminance signal portion above a certain level of the clamped image signal, and the amplified signal. means for differentiating, means for changing the differential characteristic of the differentiating means in accordance with the luminance level of the image signal, and scanning speed modulation means for modulating the scanning speed of the cathode ray tube using the differentiated signal. A contour compensation device characterized by the following features. 2. The device according to claim 1, wherein the means for changing the differential characteristic according to the brightness level of the image signal changes the differential characteristic using an average level of the brightness level of the image signal. Contour compensation device.