JPS5834843Y2 - Sharpness improvement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sharpness improvement circuit that modulates the scanning speed of an electron beam.

When displaying an image on a television receiver, the beam current of the cathode ray tube increases in areas with high brightness, which increases the beam spot size and reduces the sharpness of the image.

In particular, the original video signal changes sharply between the black level and the white level in horizontal contour areas and line areas, but the high frequency components are attenuated due to the frequency characteristics of the receiver's transmission system, so the signal It becomes dull and the sharpness in the horizontal direction further deteriorates.

Therefore, various methods have been proposed to compensate for this decrease in sharpness.

First, a conventional example of this type of sharpness improvement circuit will be explained with reference to FIG.

In FIG. 1, 1 is an input terminal to which a video signal voltage from a video detection circuit is supplied.

This terminal 1 is connected to the input end of the differentiating circuit 2 and directly to the cathode 26 of the cathode ray tube 22.

5 is a first class A amplifier composed of transistors 4 and the like;
3 is a polarity inversion circuit, and 7 is a second class A amplifier composed of a transistor 6 and the like.

The output terminal of the differentiating circuit 2 is connected to the input side of the first amplifier 5 and also to the input side of the second amplifier T via the polarity inverting circuit 3.

The output side of the first amplifier 5, ie, the collector of the transistor 4, is connected to one speed modulation electrode 25 through a series circuit of a discharge protection resistor 10 and a DC blocking capacitor 11 of the cathode ray tube 22.

Similarly, the output side of the second amplifier 7, that is, the collector of the transistor 6, is connected to the other speed modulation electrode 24 through a series circuit of a discharge protection resistor 20 and a DC blocking capacitor 21 of the cathode ray tube 22. Ru.

The secondary electrodes 24 and 25 are provided integrally with the focusing electrode, as will be described later.

Furthermore, 14 is a power source for supplying focus voltage to the cathode ray tube 22, and the voltage thereof can be changed.

The positive electrode of power supply 14 is connected to electrode 25 through resistor 12.13.
．． 24.

Note that the resistance value of the resistor 12.13 is selected to be considerably large compared to the impedance of the stray capacitance between the electrode 25.24 and ground.

Note that by specially configuring, for example, a focusing electrode of the electron gun in the neck portion of the cathode ray tube 22, an electrode for modulating the scanning speed of the electron beam can be configured.

FIG. 6 shows an example, in which a cathode 50, a control electrode 51, an accelerating electrode 52, a first anode 53, a focusing electrode 54, and a second anode 55 are arranged in sequence on the same axis.

Then, the focusing electrode 54 is divided into two electrode parts 54A and 54B having a shape similar to that of a single cylindrical body cut by a plane that is perpendicular to the horizontal plane but diagonal to the tube axis. A focused voltage of zero to several kV is supplied to the electrodes 54A and 54B, respectively, and a focused voltage of zero to several kV is supplied to the electrodes 54A and 54B, superimposed on this.
(corresponding to 24.25 in FIG. 1), the above-mentioned scanning speed modulation signal is supplied.

In this way, the signal generates a horizontal electric field at the location of the focusing electrode 54, which deflects the beam 56 horizontally, thereby modulating the scanning speed of the beam on the screen as described above. .

Next, the operation of the sharpness improvement circuit shown in FIG. 1 will be explained with reference to the waveform diagram shown in FIG. 2.

FIG. 2A shows the video signal voltage Ec(
t) shows an example of the waveform, in which the lower end is the black level and the upper end is the white level.

Video signal voltage E. (1) is then supplied to the differentiating circuit 2, resulting in the waveform shown in FIG. 2B of the differentiating table.

This is supplied to an amplifying circuit 5 consisting of a class B transistor 4, etc., where it is amplified and given a waveform as shown in FIG. 2C. The signal is supplied to the speed modulation electrode 25 of the cathode ray tube 22 via a large DC blocking capacitor 11.

On the other hand, the differentiated output of the differentiating circuit 2 is further supplied to the inverting amplifier 3 and its polarity is inverted, resulting in a waveform shown in the second diagram.

This is supplied to an amplification circuit 7 consisting of a transistor 6 etc. that operates in class B, and is amplified as shown in FIG. 2E. The other speed modulation electrode 2 of the cathode ray tube 22
4.

Therefore, the speed modulation electrode 25 and the other speed modulation electrode 2
For example, when looking from the electrode 25 to the electrode 24 side, an effective output voltage having a peak-to-peak value of 200 cm is applied as shown in FIG. 2F.

In addition, the voltage indicated by the broken line in FIG.
It is assumed that the output voltage is directly supplied to the velocity modulation electrodes 25 and 24, and the peak-to-peak value is 400V.

However, in reality, the discharge resistor 1 of the cathode ray tube 22
0 and 20, the output voltage drops by, for example, 50%, as shown by the solid line, and the amplitude of the maximum output voltage is considerably limited.

Therefore, if you set the power supply voltage high in an attempt to increase the amplitude of the maximum output voltage, a very high voltage will be applied to the transistors 4 and 6 of the amplifier circuits 5 and 7, so the transistors 4 and 6 will have a withstand voltage. The one with the highest value must be selected.

In view of these points, the present invention simplifies the circuit configuration, does not increase the power supply voltage, and does not use a high-voltage transistor as an amplifying transistor. The purpose of this paper is to propose a sharpness improvement circuit that can supply a voltage of .

Hereinafter, one embodiment of the sharpness improvement circuit of the present invention will be described in detail with reference to FIG.

In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and redundant explanation thereof will be omitted.

In Fig. 3, the differentiating circuit 2 is omitted from Fig. 1, and the resistor 1 is
Connect coils 32 and 33 instead of 2.13, and connect resistor 10 and coil 32 and resistor 20 and coil 33.
A differentiating circuit 40 and 41 are configured.

Note that the video signal from the input terminal 1 is supplied to the cathode 26 through a delay circuit 23 for phase compensation.

Next, the operation of the embodiment of the present invention shown in FIG. 3 will be specifically explained with reference to the waveform diagram of FIG. 4.

The video signal shown in FIG. 4A supplied to the input terminal 1 is first supplied to the delay circuit 23 and then delayed as shown in FIG. 4B, and then supplied to the cathode 26 of the cathode ray tube 22.

Further, this video signal is supplied to the first amplifier 5 which performs class A operation and is amplified, and a voltage having the waveform shown in FIG. 4C is obtained at the collector of the transistor 4.

This voltage is further differentiated by a differentiating circuit 40 comprising a resistor 10 and a coil 32, as shown in the fourth diagram, and is supplied to the velocity modulating electrode 25 of the cathode ray tube 22.

The video signal shown in FIG. 4A is further supplied to the second amplifier 7 via the polarity inversion circuit 3 and amplified, and a voltage having the waveform shown in FIG. 4E is obtained at the collector of the transistor 6.

This voltage is further differentiated by a differentiating circuit 41 comprising a resistor 20 and a coil 33, as shown in FIG.

As a result, an effective output voltage with a peak-to-peak value of SOO■ is applied between the velocity modulation electrodes 25 and 24, for example, as shown in FIG. Ru.

Furthermore, if the resistance value of the discharge protection resistor 10°20 of the cathode ray tube 22 is RG, and the inductance value of the coils 32 and 33 is L, the smaller the differential constant -1, the larger the output voltage will be. The differential output voltage will no longer have the correct waveform.

If we ignore this now, the output voltage supplied to the velocity modulating electrode will increase significantly, e.g.
increase twice.

In other words, since the power supply voltage B can be lowered to a minimum, inexpensive transistors with low breakdown voltage can be used as the transistors 4 and 6.

Next, another embodiment of the present invention will be described with reference to FIG.

Figure 5 shows resistor 42.43 instead of coil 32.33.
Connect capacitor 11.21 and resistor 10, 20
and 42, 43 constitute a differentiating circuit 40, 41.

That is, this is the discharge protection resistor 10.2 of the cathode ray tube 22.
0 is also used as a resistor constituting the differential circuit, and its circuit operation is almost the same as in the case of Fig. 3, so the explanation is omitted, but in this case, the output voltage loss in resistor 10.20 can be kept quite low.

Thus, according to the sharpness improvement circuit of the present invention, a DC voltage for focusing is supplied to a pair of velocity modulating electrodes of a cathode ray tube having a pair of velocity modulating electrodes through a resistor or a coil, respectively. A first class A amplifier to which a video signal is directly supplied and a second class A amplifier to which the video signal is supplied via a polarity inversion circuit are provided, and these first and second class A amplifiers are provided.
The output ends of the class amplifiers are connected to a pair of speed control electrodes through a series circuit of a discharge protection resistor and a DC blocking capacitor, respectively, and the resistor and coil or resistor, discharge protection resistor and DC blocking capacitor are connected to a pair of speed control electrodes. A differentiating circuit is configured using any combination of capacitors for the purpose of supplying the delayed output of the video signal to the cathode of the cathode ray tube.The circuit configuration is therefore simplified and the output voltage for controlling the speed of the cathode ray tube can be greatly increased. I can do it.

In other words, if a predetermined voltage is to be applied to the speed control electrode of a cathode ray tube, it is not necessary to use amplifier transistors with very high withstand voltages, and the circuit can be constructed at low cost. can do.

In the above example, a pair of amplifiers, differentiating circuits, etc. are provided, but each is made into one piece, one of the pair of velocity modulation electrodes is grounded, and the differential output of the video signal is supplied to the other. You can do it like this.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an example of a conventional sharpness improvement circuit, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a circuit diagram of an embodiment of the sharpness improvement circuit of the present invention. Fig. 4 is a waveform diagram for explaining the operation of Fig. 3, Fig. 5 is a circuit diagram of another embodiment of the present invention, and Fig. 6 is a diagram of an electron gun section in which the concentration electrode used in the present invention is a scanning velocity modulation electrode. FIG. 3 is a polarity reversing circuit, 5 and 7 are amplifiers, 10°20 is a discharge protection resistor for the cathode ray tube 22, 11°21 is a DC blocking capacitor, and 24.25 is a speed installed in the cathode ray tube 22. The modulation electrode, 40° 41, is a differential circuit.

Claims (1)

[Scope of utility model registration request] A first class A amplifier to which a direct current voltage for focusing is supplied to the pair of velocity modulating electrodes of a cathode ray tube having a pair of velocity modulating electrodes through a resistor or a coil, respectively, and a video signal is directly supplied. An amplifier and a second class A amplifier to which the video signal is supplied via a polarity inversion circuit are provided, and the output terminals of the first and second class A amplifiers are connected to discharge protection resistors, respectively. and a DC blocking capacitor connected to the pair of speed modulating electrodes through a series circuit, and forming a differential circuit using either the resistor and coil or the resistor, discharge protection resistor, and DC blocking capacitor in combination. and supplying a delayed output of the video signal to the cathode of the cathode ray tube.