JPH0324829B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a correction device for correcting screen distortion of a vertical image that appears in a video portion when a screen of a white peak portion is received in a television receiver. Conventionally, as a means to correct such screen distortion,
Something like the one shown in FIG. 1 has been proposed. That is, the input coil 1 of the flyback transformer 11
1A and the ground, the collector-emitter of the horizontal output transistor 2 for switching is connected, and the first damper diode 3 and the second damper diode 4, which are connected in series with the same polarity, are connected. The resonant capacitor 5 and the second resonant capacitor 6 are connected, and the midpoint of their connection is connected to the midpoint of the connection between the first and second damper diodes 3 and 4. The first coil 7 is a horizontal deflection coil and is connected in series with the first scanning capacitor 8. These also include a second coil 9 and a second scanning capacitor 10 connected in series.
connected in series with the transistor 2, and both ends of the transistor 2
The first scanning capacitor 8 and the second coil 9 are connected to the midpoint between the first and second resonance capacitors 5 and 6. Here, it can be seen that if point B is grounded, the circuit becomes equivalent to the conventional horizontal deflection circuit. Then, a horizontal pulse is supplied to the base of the transistor 2 from the horizontal oscillation circuit 1. Furthermore, a high voltage is applied from the output coil 11B of the flyback transformer 11 to a cathode ray tube (not shown) through a rectifier diode 12. In addition, a focus voltage and a screen voltage are obtained from the intermediate tap of the output coil 11B of the flyback transformer 11 through a circuit consisting of a resistor 15, a variable resistor 16, a variable resistor 17, and a resistor 18.
The midpoint between the resistor 7 and the resistor 18 is connected to the modulation circuit 19.
The output of this modulation circuit 19 is connected to the base of a transistor 20, its emitter is grounded, and its collector is connected to the second coil 9 and the second scanning capacitor 10.
Connect to the intersection with . Next, the operation of this first one will be explained. first,
Considering a screen that changes vertically from black to white to black as shown in Figure 2, the CRT anode voltage EHT is
It is high in the black part, and low in the white part because a large amount of beam current flows. This state is the third
As shown in the figure. In other words, the change in the vertical image (vertical line) that appears on the screen at this time is that in the black part, the CRT
Because the anode voltage is high (the accelerating voltage for the beam is high), it does not receive much lateral deflection, but the white area is deflected more horizontally than the black area because the CRT anode voltage is lower (the accelerating voltage for the beam is lower). As a result, as shown in FIG. 2, the vertical lines of the screen appear to be bent outward in the white area. This becomes more noticeable as the white peak becomes higher in the screen. As shown in Fig. 3, if we look at the change in high voltage at this time in terms of the vertical period, the high voltage is lower on the white screen than on the black screen. Therefore, in the circuit shown in FIG. 1, this high voltage fluctuation is transferred to the output coil 11B of the flyback transformer 11.
It is detected from between resistors 17 and 18 connected between the middle tap point C and ground. It is clear that the detected high voltage load variation changes in the same way as the anode voltage in the output coil 11B. Therefore, this high voltage load fluctuation is amplified and polarized by the modulation circuit 19 and the output transistor 20, and is applied between the second coil 9 and the second scanning capacitor 10 of the horizontal deflection circuit. The high voltage load fluctuation at this time becomes a screen distortion correction wave, which is made up of the sum voltage of the DC voltage and the correction signal voltage. Also, the basic operation of the horizontal deflection circuit is 3, 5, 7,
a first horizontal resonant circuit consisting of a section 8;
The resonant frequencies in the second horizontal resonant direction consisting of parts 6, 9, and 10 are made to match. That is, it is a necessary condition that the pulse widths of the retrace pulses generated in each circuit are made to match to keep the circuits in a balanced state. Under such conditions, when the above correction wave is applied between the second coil 9 of the second horizontal resonant circuit and the second scanning capacitor 10, the voltage Vm across the second scanning capacitor 10 becomes As shown in Figure 4a, it is modulated by the content of the correction wave. Moreover, the power supply voltage Vb is the sum of the voltage Vt across the first scanning capacitor 8 and the voltage Vm across the second scanning capacitor 10 as shown in FIG. 4c, and if there is no fluctuation in the power supply voltage,
Vb = Vt + Vm = a certain relationship holds true.
Therefore, when the voltage Vm is modulated by the correction wave, the voltage Vt changes to the opposite polarity to Vm modulated by the correction wave so that the power supply voltage Vb is always constant. Therefore, since the voltage Vt is the scanning voltage of the first horizontal resonant circuit, the current flowing through the deflection coil 7 has the opposite polarity to the correction wave as shown in FIG. It will be subject to modulation depending on the content. FIG. 4 shows the voltage and current waveforms at each part at this time. b is the current Im flowing through the second capacitor 10
It is. The current flowing through the deflection coil 7 decreases in the white screen portion in the vertical period, as shown in d of the figure. This means that in the white screen area, the anode voltage decreases as shown in Figure 3, and the electron beam becomes more susceptible to deflection, so if the deflection current in this area is kept small, the vertical The lines appear almost straight. The above is an explanation of the operation of the conventional circuit example. According to this method, the resonant frequencies of the first horizontal resonant circuit and the second horizontal resonant circuit must be matched, and the second scanning capacitor It is necessary to switch the voltage across the terminal 10 using the output transistor 20, and a procedure is required to detect the high voltage load fluctuation, which increases the number of circuit parts and is expensive. . Therefore, it is an object of the present invention to provide a new screen distortion correction device that eliminates such conventional drawbacks. In the screen distortion correction device of the present invention, the Q of the first horizontal resonant circuit and the Q of the second horizontal resonant circuit are
The deflection current of the first horizontal resonant circuit is different from the resonant frequency of the second horizontal resonant circuit.
The deflection current is controlled by changing the resonant frequency of the deflection current, and the deflection current is controlled by an impedance element such as a fixed resistor without using a controllable switch. Next, the basic circuit and basic operation of the present invention will be explained. FIG. 5 shows a circuit configuration of an embodiment of the present invention, in which a horizontal pulse is applied from a horizontal oscillation circuit 21 to the base of a horizontal output transistor 22. In FIG.
The first horizontal resonant circuit includes a first resonant capacitor 2
3, a first damper diode 25, a first coil (deflection coil) 27, and a first scanning capacitor (S-shaped correction capacitor) 28.
The second horizontal resonant circuit includes a second resonant capacitor 2
4, a second damper diode 26, a second coil (modulation coil) 29, and a second scanning capacitor (modulation capacitor) 30. The first horizontal resonant circuit and the second horizontal resonant circuit are connected in series between the collector and emitter of the horizontal output transistor 22. Further, an input coil 32A of a flyback transformer 32 is connected to the collector of the horizontal output transistor 22, and the other end of the input coil 32A is connected to the power supply voltage +Vb. A fixed resistor 31 is connected between the second coil (modulation coil) 29 of the second horizontal resonant circuit and the second scanning capacitor (modulation capacitor) 30 and between ground. The anode voltage EHT is applied to the cathode ray tube (not shown) from the output coil 32B of the flyback transformer 32 via the rectifier diode 33, and the other end of the output coil 32B is connected to the resistor 34 and the capacitor 3.
Connect to the ABL circuit via 5. FIG. 6 is an equivalent circuit of FIG. 5 to show the basic operation. In addition, the internal resistance [Ry] of the first coil (deflection coil) 27, the internal resistance [Rm] of the second coil (modulation coil) 29, and the internal resistance [Rp] of the input coil 32A of the flyback transformer 32 are shown. There is. Here, on the screen as shown in Fig. 2, the anode voltage fluctuates as shown in Fig. 3, but if the degree of coupling between the windings of the input coil 32A and output coil 32B of the flyback transformer 32 is kept tight, , Fluctuation in anode voltage - Fluctuation in pulse voltage of output coil 32B -
The relationship between fluctuations in the pulse voltage of the input coil 32A occurs within a vertical period. Therefore, load fluctuations in the anode voltage appear as fluctuations in the pulse voltage of the input coil 32A. Therefore, if the inductance of the input coil 32A of the flyback transformer 32 is Lp, the stray capacitance is Cp, and the internal resistance of the coil is Rp, then
The resonant frequency determined by these constants is

It is represented by [Formula]. Here, if there is a load fluctuation on the output coil 32B side, Rp will equivalently increase in the fluctuation part (white peak part), the resonance frequency will shift to the lower side, and the horizontal collector pulse width will become wider. I will be working like this. Therefore, in the high voltage fluctuation part (white peak part), the first coil (deflection coil) 27 [Ly]
The pulses at both ends of the second coil (modulation coil) 29 [Lm] are similarly modulated, the pulse width becomes wider, and the resonant frequency becomes lower in each circuit. Next, the first coil (deflection coil) 27 and the second
The internal resistance Ry of the coil (modulation coil) 29,
When Rm is considered, the equivalent circuit at the time of resonance becomes the equivalent circuit shown in FIG. 7 by setting the Q of each coil to Q ₁ and Q ₂ and selecting such that Q ₁ and Q ₂ >10. Now, let the admittances of the first coil (deflection coil) Ly side and the second coil (modulation coil) Lm side be Y〓 ₁ and Y〓 ₂ , respectively, and the first coil (deflection coil) Ly
Considering the resonance operation on the side, the admittance Y〓 ₁ becomes Y ₁ = 1/RyQ ₁ ² +jωC ₁ + 1/jωLy, and if the resonance frequency is ωo and the impedance is Z ₁₀ ,

[Formula] Z〓 ₁₀ = 1/Y ₁ = RyQ ₁ ² = ωoLyQ ₁ . Here, the first coil (deflection coil) in Fig. 7
The branch currents at resonance on the Ly side are respectively I _Ry , I _Ly , I _C1
Then, I _Ry =V/ωoLyQ ₁ , I _Ly =V/jωoLy=−Q ₁ I _Ry , I _C1 =jωoC ₁ V=Q ₁ I _Ry . That is, at the time of parallel resonance, the current in the entire circuit is minimum, and I _Ry flows, and a current Q ₁ times I _Ry flows in the closed circuit of Ly and C ₁ . Therefore, the closed circuit current depends on Q ₁ and I _Ry . Furthermore, the same result as above is obtained for the second coil (modulation coil) Lm. Therefore, Q ₁ of the first coil (deflection coil) Ly
If is selected to be larger than Q ₂ of the second coil (modulation coil) Lm, the resonance frequency will be greater than ωo in the high voltage fluctuation (white peak) part (the frequency deviation at this time is △ω), The rate of change of current is
Since Q ₁ >Q ₂ , the change in the first coil (deflection coil) Ly is △I _Ly > the change in the second coil (modulation coil) Lm is △I _Ln . Therefore, the closed circuit current is smaller on the first coil (deflection coil) side than on the second coil (modulation coil) side, and the change in this current appears between points A and B in Figure 6. This will control the deflection current. FIG. 8 shows changes in resonance frequency versus current due to differences in Q value. Also, the changes in the current flowing between point A and point B in Figure 6 are shown in Figure 9: (a) the first half of the blanking period, (b) the second half of the blanking period, (c) the first half of the scanning period, and (d) It is shown separately in the second half of the scanning period. In other words, from Fig. 9, the current in the second coil (modulating coil) Lm is higher than the current in the first half of the retrace period in (a).
Since the current flows more than the coil (deflection coil) Ly,
More charge is stored in the resonant capacitor C ₂ than in C ₁ , and in the latter half of the retrace period in (b), C ₁ ,
The charge stored in C ₂ is transferred to Ly and Lm, but since there is more charge stored in C ₂ than C ₁ , the charge transferred to Lm is greater than Ly. It turns out. Next, in the first half of the scanning period (c),
Damper diodes D ₁ and D ₂ are conductive, respectively.
The charges stored in Ly and Lm are transferred to the first scanning capacitor Cs and the second scanning capacitor Cm, but since the charge stored in Lm is larger than Ly, the second scanning capacitor Cs More charges are transferred to Cm than to Cs. Therefore, in the second half of the scanning period (d), part of the charge stored in the second scanning capacitor Cm flows to the horizontal output transistor ₂₂ through the first damper diode D1. Therefore, due to high voltage load fluctuations, a modulated current is generated between points A and B in Figure 6, and the current flowing through the first coil (deflection coil) Ly is modulated with the same polarity as the load fluctuations. Become. In the screen shown in Figure 2, when the high voltage drops within one vertical period, the deflection current decreases,
At a special price, changes in horizontal amplitude due to high voltage will not appear on the screen. Further, FIG. 10 shows the modulation current flowing during each period of FIG. 9 in comparison with the flyback pulse. Figure 11 shows (a) the collector pulse that appears on the screen in Figure 2 in one vertical period, (b) the voltage across the first scanning capacitor Cs, and (c) the second scanning capacitor Cm. shows the combined waveform of the voltage across both ends. That is, since the input coil and output coil of the flyback transformer are tightly coupled when there is a high voltage load fluctuation, it is necessary to make the Q of the first horizontal resonant circuit and the Q of the second horizontal resonant circuit different. According to
The voltage across the first scanning capacitor Cs is modulated with the same polarity as the high voltage load fluctuation, and the voltage across the second scanning capacitor Cm is modulated with the opposite polarity. Next, set the resonant frequency of the second horizontal resonant circuit to the first
A description will be given of changing the resonant frequency of the horizontal resonant circuit and controlling the deflection current by connecting both ends of the second scanning capacitor Cm with an impedance element, such as a fixed resistance element. This is because the deflection current determined by the voltage waveforms b and c shown in FIG. 11 is small and the horizontal amplitude is narrow, so it is necessary to correct this. That is, in FIG. 5, when the second resonant capacitor 24 is made larger, the flyback pulse width T ₂ of the second horizontal resonant circuit is given by T ₂ =π√・₂ , and the flyback pulse width of the first horizontal resonant circuit is given by T 2 =π√・2. It becomes wider than the back pulse width T ₁ (T ₁ =π√・₁ ). The relationship between this pulse width is shown in FIG. The fact that the pulse width T ₂ of the second horizontal resonant circuit is greater than T ₁ means that
The retrace period in the first horizontal resonant circuit is as shown in Fig. 12a.
The first half of the scanning period (damper diode 25 is on) ends at time t ₁ , but the retrace period has not yet been completed in the second horizontal resonant circuit, and the charge stored in the second resonant capacitor 24 are all second
The first damper diode (on) 25 is not transferred to the first damper diode (modulating coil) 29.
It then moves to the first coil (deflection coil) 27 through the deflection coil. Thereafter, the second horizontal resonant circuit ends the blanking period at time _t2 in FIG. 12b, and enters the first half of the scanning period (damper diode 26 is on). This can be achieved by increasing the size of the second resonant capacitor 24 and increasing the size of the second scanning capacitor 30.
The voltage transferred to the first scanning capacitor 28 becomes smaller, and the voltage transferred to the first scanning capacitor 28 becomes larger. In other words, the deflection current determined by the voltage across the first scanning capacitor 28 increases. Also, since the voltage across the first and second scanning capacitors 28 and 30 at this time increases or decreases only by the DC component, the high voltage load fluctuation (AC component) explained earlier becomes relatively large. . The current flow from the second half of the retrace period to the first half of the scanning period when the second resonant capacitor 24 is increased is
Shown in Figure 3. Further, FIG. 14 shows the voltage waveforms across the first scanning capacitor 28 and the voltage waveforms across the second scanning capacitor 30 with dotted lines when the second resonant capacitor 24 is increased in size. FIG. 15 shows the screen correction state when the second resonant capacitor 24 is increased by the present device when the screen of FIG. 2 is received. Figures 14 and 15
As can be seen from the figure, as the second resonant capacitor 24 is increased, the correction state of the screen becomes over-corrected, and the horizontal amplitude of the portions a and b in FIG. 15 becomes narrower than that of a normal screen. . That is, this means that when the power supply voltage is constant, the power supply voltage is a combination of the voltage across the first scanning capacitor 28 and the voltage across the second scanning capacitor 30, and the voltage across the first scanning capacitor 28 is Since the deflection current is determined by , the horizontal amplitude is narrowed because the voltage across this terminal is lower than normal (conventional circuit). Therefore, as a method of widening the horizontal amplitude, it is sufficient to lower the voltage across the second scanning capacitor 30. In FIG. 5, by connecting a fixed resistance element 31 selected to a certain value between the second coil (tuning coil) 29 and the second scanning capacitor 30 and between the ground, the second scanning capacitor 30
can lower the voltage across the first
The voltage across the scanning capacitor 28 increases, the deflection current increases, and the horizontal amplitude also widens. The appropriate screen correction state at this time is shown in FIG. Note that as a method of making the pulse width of the first horizontal resonant circuit and the pulse width of the second horizontal resonant circuit different in advance, which is a feature of this device, the second resonant capacitor 24
Although we explained how to change the
It is clear that similar results can be obtained by changing the inductance of 29. Also, resistor 3 in Figure 5
It goes without saying that the control effect can be further improved by using a voltage- or current-controlled impedance element (thermistor, varistor, etc.) instead of the impedance element. Furthermore, according to the present invention, there is no need for a conventional high-voltage load fluctuation detection circuit for screen distortion correction, and the voltage across the scanning capacitor can be controlled simply by an impedance element without using a controllable switching element. This has the effect of significantly reducing the number of circuit components and reducing costs.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a screen distortion correction circuit equipped with a conventional high-voltage load fluctuation detection circuit, Figures 2, 3, and 4.
The figure is a front view of the screen and a waveform diagram for explaining the device, FIG. 5 is a circuit diagram of the screen correction device in an embodiment of the present invention, and FIGS. 6 and 7 are for explaining its basic operation. The equivalent circuit diagram, Figure 8 is a characteristic diagram for explaining its operation, Figures 9 and 13 are circuit diagrams showing how the current flows, Figures 10, 11, 12, and 14. The figure is a waveform diagram for explaining the operation, and FIGS. 15 and 16 are front views of the screen. 21... Horizontal oscillation circuit, 22... Horizontal output transistor, 23... First resonant capacitor, 24
...Second resonance capacitor, 25...First damper diode, 26...Second damper diode, 27...First coil, 28...First scanning capacitor, 29...Second damper diode Coil, 30...
...Second scanning capacitor, 31...Resistance element,
32...Flyback transformer.

Claims (1)

[Claims] 1. Disposed between the input coil of the flyback transformer and the horizontal output transistor in order to correct screen distortion that appears in the video portion when a white peak portion of the screen is received in a television receiver. This screen distortion correction device comprises first and second deflection capacitors 23 and 24 connected in series between the collector and emitter of a horizontal output transistor, a cathode connected to the collector of the horizontal output transistor 22, and an anode connected to the collector of the horizontal output transistor 22. a first damper diode 25 connected to a common connection point of the first and second resonant capacitors 23 and 24, and a cathode connected to the first and second resonant capacitors 2;
3 and 24, a second damper diode 26 whose anode is connected to the emitter of the horizontal output transistor 22, and one end connected to the cathode of the first damper diode 25 and the input coil of the flyback transformer. a first scanning capacitor 28 connected between the other end of the horizontal deflection coil 27 and the anode of the first damper diode 25; and a cathode of the second damper diode 26. a second scanning capacitor 30 connected between the other end of the modulation coil 29 and the anode of the second damper diode 26; and the horizontal deflection coil 27. and the first scanning capacitor 28 or the modulation coil 2
9 and the second scanning capacitor 30, and an impedance element 31 that discharges the charge of the first or second scanning capacitor 28, 30 connected between one of the connection points of the scanning capacitor 9 and the second scanning capacitor 30 and the ground. Screen distortion correction device.