JPH0614209A - Pincushion distortion correction circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In the correction of the pincushion distortion of the CRT display device, the pincushion distortion is corrected accurately and stably in response to the shortening of the blanking period. [Structure] A current mirror circuit 21 composed of a diode D1 and a transistor Q2, and a current switching circuit 2 composed of a constant current source S2 and switching transistors Q3 and Q4.
2 is provided. The current output from these circuits charges and discharges the capacitor 13. Two voltage comparison circuits 14 and 15 having a threshold V _L, V _H the terminal voltage of the capacitor 13
Give to. The output of the voltage comparison circuits 14 and 15 causes FF
18 is set and reset, and a switching signal is output to the current switching circuit 22. The triangular wave generated by the capacitor 13 is applied to the waveform conversion circuit to form a substantially parabolic waveform, and pincushion distortion of the CRT is corrected with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pincushion distortion correction circuit for a scanning display device using a cathode ray tube (hereinafter abbreviated as CRT).

[0002]

2. Description of the Related Art In recent years, a display device using a CRT has been widely used as a display device for not only a television receiver but also a computer. Particularly, a display device used for a computer needs to display without distortion of the screen. Further, as the screen display density is improved, it is required that the correction waveform of the pincushion distortion be stable during a very short blanking period. Therefore, a pincushion distortion correction circuit that corrects a pincushion distortion around the screen peculiar to a CRT is required to generate a precise correction waveform.

FIG. 4 is a block diagram showing a configuration example of a conventional pincushion distortion correction circuit, and FIG. 5 is a signal waveform diagram showing its operation. The sawtooth wave generation circuit 1 in FIG.
It is a circuit for generating a sawtooth wave synchronized with the vertical synchronizing signal of the image shown in (a). FIG. 6 is a circuit diagram showing a configuration example of the sawtooth wave generation circuit 1.

In FIG. 6, a power source Vcc, a constant current source S1,
The switching transistors Q1 are connected in series. A capacitor C1 is connected between the collector and emitter of the transistor Q1. When the vertical synchronizing signal is input to the base of the transistor Q1 at time t _{0 as} shown in FIG. 5A, the charge of the capacitor C1 is rapidly discharged via the transistor Q1. When the vertical synchronizing signal is turned off, the capacitor C1 is charged from the power source Vcc by the constant current source S1. Therefore, as shown in FIG. 5B, the voltage of the capacitor C1 rises until the next vertical synchronizing signal is input, and the sawtooth wave signal is output from both ends thereof. This sawtooth signal is applied to the absolute value circuit 2 of FIG.
(B) The waveform below the midpoint voltage V _M shown by the alternate long and short dash line is folded back. Next, the signal converted into the triangular wave by the absolute value circuit 2 is output to the waveform conversion circuit 3.

The waveform conversion circuit 3 is a circuit for converting an input triangular wave into a substantially parabolic waveform (parabolic waveform), and is composed of, for example, a polygonal line approximation circuit or a multiplication circuit using a plurality of diodes. The output of the waveform conversion circuit 3 has a parabolic waveform as shown in FIG. The horizontal deflection circuit 4 is a circuit that applies a sawtooth wave current to the horizontal deflection coil 5 in synchronization with the horizontal synchronization signal. Since the horizontal deflection circuit 4 corrects the pincushion distortion on the left and right of the CRT, the parabolic signal output from the waveform conversion circuit 3 modulates the amplitude of the deflection current. FIG. 5E shows a sawtooth-shaped deflection current waveform thus modulated, and this current is applied to the horizontal deflection coil 5. This corrects the left and right pincushion distortions in which the horizontal scanning width is reduced at the center of the CRT 6.

[0006]

However, in such a configuration, the discharge time of the capacitor C1 has a finite value because of the internal resistance of the sawtooth wave generating circuit 1 when the transistor Q1 is conductive. That is, at time t ₀ in FIG.
Therefore, even if the vertical synchronizing signal is input to the transistor Q1, a transient time t _r is required to discharge the electric charge of the capacitor C1 to a predetermined voltage level as shown in FIG. 5B.
Therefore, when the sawtooth wave shown in FIG. 5 (b) is folded back at the midpoint voltage V _M , as shown in FIG. 5 (c), V is generated at the apex of the triangular wave.
A character-shaped break occurs. When this signal is output to the waveform conversion circuit 3, a parabolic signal as shown in FIG. 5D is generated. Therefore, when this parabolic signal is given to the horizontal deflection circuit 4, the amplitude of the deflection current is deformed into a convex shape at the time when the vertical synchronizing signal is generated, as shown in FIG.

In recent years, the frequency of horizontal and vertical synchronization has increased in display devices with variable scan rates.
Therefore, when a convex distortion is generated in the correction waveform within such a blanking period, there arises a problem that the deflection operation of the display device becomes unstable.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a stable pincushion distortion correction circuit in which transient distortion does not occur in response to shortening of the blanking period. To do.

[0009]

The invention according to claim 1 of the present application comprises a triangular wave generating circuit for generating a triangular wave synchronized with a scanning cycle of a display screen, and a waveform converting circuit for converting the triangular wave into a substantially parabolic waveform. , A pincushion distortion correction circuit of a cathode ray tube display device that corrects pincushion distortion of a display screen by amplitude-modulating a deflection current using a substantially parabolic waveform, wherein a triangular wave generation circuit outputs a voltage signal to a waveform conversion circuit. A capacitor, a constant current charging / discharging circuit that alternately switches charging / discharging of the capacitor, a terminal voltage of the capacitor, a first reference power source, and a second reference voltage higher than this are compared, and the terminal voltages are the first and second. And a voltage comparison circuit that outputs a control signal for charging and discharging to the constant current charging / discharging circuit when the reference voltage is reached.

The invention according to claim 2 of the present application comprises a triangular wave generating circuit for generating a triangular wave in synchronization with the scanning cycle of the display screen, and a waveform converting circuit for converting the triangular wave into a substantially parabolic waveform. This is a pincushion distortion correction circuit for a cathode ray tube display device that corrects pincushion distortion on the display screen by amplitude-modulating the deflection current by means of an on / off signal to charge or cut off a constant current from the power supply to the load. Constant current charging circuit, a constant current charging circuit connected in series with the constant current charging circuit, which discharges or cuts off a constant current from the load by an ON / OFF signal, and a common connection terminal of the constant current charging circuit and the constant current discharging circuit. Connected to one terminal and the other end grounded; a first voltage comparison circuit that outputs a signal when the voltage of the capacitor reaches the voltage of the first reference power supply; A second voltage comparison circuit that outputs a signal when the voltage exceeds a second reference voltage higher than the first reference power supply, and is set by the output of the first voltage comparison circuit. The output is reset and its Q
And a flip-flop that supplies the Q-bar output to the control terminals of the constant current charging circuit and the constant current discharging circuit, respectively.

The invention according to claim 3 of the present application comprises a triangular wave generating circuit for generating a triangular wave synchronized with the scanning cycle of the display screen, and a waveform converting circuit for converting the triangular wave into a substantially parabolic waveform. A pincushion distortion correction circuit of a cathode ray tube display device that corrects pincushion distortion of a display screen by amplitude-modulating a deflection current by using a triangular wave generation circuit, a capacitor that outputs a voltage signal to a waveform conversion circuit, and a load side The transistor has a current mirror circuit connected to one end of the capacitor, and a switching element and a constant current source that switch the operations of the current mirror circuit connected to the reference current source side and the load side, and alternately switches the charge and discharge of the capacitor. The current switching circuit is compared with the terminal voltage of the capacitor, the first reference power supply, and the second reference voltage higher than the first reference power supply.
And a voltage comparison circuit for outputting charge and discharge control signals to the current switching circuit when the second reference voltage is reached, respectively.

The invention according to claim 4 of the present application comprises a triangular wave generating circuit for generating a triangular wave in synchronization with the scanning cycle of the display screen, and a waveform converting circuit for converting the triangular wave into a substantially parabolic waveform. A pincushion distortion correction circuit of a cathode ray tube display device that corrects pincushion distortion of a display screen by amplitude-modulating a deflection current by means of a modulation method, wherein a triangular wave generation circuit includes a constant current source and the constant current source commonly connected to an emitter. A current mirror circuit including a current switching circuit having first and second transistors, and a current control transistor that uses a current flowing into the collector of the first transistor as a reference current and applies a load current equal to the reference current to a capacitor. And the second
The collector of the transistor and the output of the current mirror circuit are commonly connected to one terminal, and the other terminal outputs a signal when the capacitor voltage reaches the voltage of the first reference power source A first voltage comparison circuit,
The voltage of the capacitor is higher than that of the first reference power source.
Is set by the output of the first voltage comparison circuit and the second voltage comparison circuit that outputs a signal when the reference voltage of the second voltage comparison circuit is exceeded, and is reset by the output of the second voltage comparison circuit.
And a flip-flop that supplies the bar output to the bases of the first and second transistors.

[0013]

According to the inventions of claims 1 and 2 having the above characteristics, when the control signal for charging is applied to the constant current charging / discharging circuit by the voltage comparison circuit, the charging current flows through the capacitor. Then, the charging voltage of the capacitor rises in proportion to time. Next, when the voltage comparison circuit detects that the charging voltage becomes higher than the second reference voltage, it outputs a signal to the constant current charging / discharging circuit and switches to the discharging side to discharge the accumulated charge in the capacitor. Therefore, the voltage of the capacitor drops in proportion to time. Then, when the triangular wave output from the capacitor is applied to the waveform conversion circuit, a substantially parabolic waveform is generated. Further, if the envelope of the deflection current is amplitude-modulated by this waveform, the deflection current will not be distorted even if the blanking period of the cathode ray tube display device is shortened.

According to the third and fourth aspects of the present invention, when the control signal for charging is applied to the current switching circuit by the voltage comparison circuit, the charging current flows through the capacitor by the operation of the current mirror circuit. Then, the charging voltage of the capacitor rises in proportion to time. Next, when the voltage comparison circuit detects that the charging voltage becomes higher than the second reference voltage, the voltage switching circuit switches the current switching circuit to the discharging side and discharges the electric charge accumulated in the capacitor. Therefore, the voltage of the capacitor drops in proportion to time. Then, when the triangular wave output from the capacitor is applied to the waveform conversion circuit, a substantially parabolic waveform is generated.
Further, if the envelope of the deflection current is amplitude-modulated by this waveform, the deflection current will not be distorted even if the blanking period of the cathode ray tube display device is shortened.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pincushion distortion correction circuit according to a first embodiment of the present invention will be described with reference to FIG. In this figure, the pincushion distortion correction circuit has the same waveform conversion circuit 3 as that of the conventional example, and the output thereof is a horizontal deflection circuit 4, a horizontal deflection coil 5, and a CRT 6.
The same is given to the conventional example and its detailed description is omitted.

In the pincushion distortion correction circuit of FIG. 1, the constant current charging circuit 11 is a circuit for outputting a constant load current from the power supply Vcc, and has a control terminal for connecting and disconnecting the load current.
On the other hand, the constant current discharging circuit 12 is a circuit that discharges a constant load current from the constant current charging circuit 11 or an external load, and has a control terminal that connects and disconnects the load current. The charging circuit 11 and the discharging circuit 12 are connected in series between the power source Vcc and the ground.

Next, the capacitor 13 is connected between the common connection end of the charging circuit 11 and the discharging circuit 12 and the ground. The terminal voltages of the capacitors 13 are respectively the first voltage comparison circuit 14
To the non-inverting input terminal of the second comparison circuit 15. The non-inverting input terminal of the voltage comparison circuit 14 is connected to the first reference power source 16 of the voltage V _L , and the voltage comparison circuit 1
The inverting input terminal of 5 is connected to the second reference power supply 17 having the voltage V _H (> V _L ).

The outputs of the voltage comparison circuits 14 and 15 are connected to the set (S) and reset (R) terminals of a flip-flop (FF) 18, respectively. The Q terminal of the FF 18 is connected to the control terminal of the charging circuit 11, and the Q bar terminal is connected to the control terminal of the discharging circuit 12. The FF 18 is a voltage comparison circuit 14, 1
A switching signal is output to the charging / discharging circuits 11 and 12 according to the signal output from the circuit 5.

The terminal voltage of the capacitor 13 is also given to the waveform conversion circuit 3. The waveform conversion circuit 3 is a circuit that converts an input triangular wave signal into a parabolic waveform signal. Similar to the conventional example, the horizontal deflection circuit 4 is a circuit that generates a sawtooth current signal in synchronization with the horizontal deflection synchronization pulse and modulates the amplitude of the sawtooth wave with the parabolic waveform output from the waveform conversion circuit 3. .

The pincushion distortion correction circuit 10 thus configured
The operation of will be described. 2A to 2F are waveform diagrams of the portions indicated by a to f in FIG. As shown in FIG. 2A, it is assumed that the terminal voltage of the capacitor 13 is slightly higher than the voltage V _H of the reference power supply 17 at the time t ₀ in the initial state. At this time, the voltage comparison circuit 14 is shown in FIG.
As shown in (c), the voltage comparison circuit 1 outputs no pulse.
5 outputs a pulse as shown in FIG. Therefore, the FF 18 is in the reset state from time t _{0 as} shown in FIG.

Next, an L level signal is input to the control terminal of the charging circuit 11, and an H level signal is input to the control terminal of the discharging circuit 12. Therefore, the capacitor 13 is discharged with a constant current by the discharge circuit 12, and the period T of FIG.
As indicated by 1, the terminal voltage drops in proportion to time.

At time t ₁ when the terminal voltage of the capacitor 13 reaches the reference voltage V _L , the voltage comparison circuit 14 outputs a pulse and sets the FF 18. Therefore, Q of FF18
The H and L level signals are output from the Q and Q bar terminals, respectively, and the charging circuit 11 is turned on and the discharging circuit 12 is turned off. Therefore, the capacitor 13 is charged through the charging circuit 11, and its voltage rises in proportion to time as shown in the period T2 of FIG.

When the charging voltage of the capacitor 13 exceeds the voltage V _H at time t ₂ , the voltage comparison circuit 15 outputs a pulse and resets the FF 18. Therefore, Q of FF18
And the Q-bar output is inverted, the charging circuit 11 is turned off,
The discharge circuit 12 is turned on. After that, the capacitor 13 is discharged and charged similarly to the operation from the time t ₀ .

Thus, unlike the conventional pincushion distortion correction circuit, the voltage of the capacitor 13 becomes a complete triangular wave without voltage drop at the apex of the triangular wave. This triangular wave is given to the waveform conversion circuit 3 and converted into a parabolic signal as shown in FIG. When this parabolic signal is applied to the horizontal deflection circuit 4, a deflection current modulated by the parabolic signal flows through the horizontal deflection coil 5 as shown in FIG. By such an operation, the pincushion distortion on the left and right of the screen in the CRT 6 is corrected, and the distortion does not occur in the deflection current in the portion where the vertical synchronizing signal is generated even when the blanking period is short.

Next, a pincushion distortion correction circuit according to a second embodiment of the present invention will be described with reference to FIG. Second in this figure
The pincushion distortion correction circuit 20 of the embodiment is provided with the same waveform conversion circuit 3 as that of the first embodiment, and the output thereof is the same as being applied to the horizontal deflection circuit 4, the horizontal deflection coil 5, and the CRT 6, The description is omitted. The pincushion distortion correction circuit 20 is also provided with a capacitor 13 for generating a voltage signal, voltage comparison circuits 14 and 15, reference power supplies 16 and 17, and an FF 18, as in the first embodiment.

Unlike the first embodiment, a current mirror circuit 21 and a current switching circuit 22 are connected to the capacitor 13. The current mirror circuit 21 has a power supply Vcc and a transistor Q.
2, composed of a diode D1. The anode of the diode D1 and the emitter of the transistor Q2 are connected to one end of the power source Vcc. The cathode of the diode D1 is connected to the base of the transistor Q2 and the collector of the transistor Q3. The transistor Q2 is a current control transistor that causes a load current equal to the reference current flowing through the diode D1 to flow out from the power supply Vcc.

The collectors of the transistors Q3 and Q4 are respectively the cathode of the diode D1 and the transistor Q2.
Connected to the collector. The emitters of the transistors Q3 and Q4 are both connected to the constant current source S2, and the bases thereof are connected to the Q and Q bar terminals of the FF 18, respectively. Here, the transistors Q3 and Q4 and the constant current source S2 form a current switching circuit 22.

The pincushion distortion correction circuit 20 configured as described above
Only the part of the operation that is different from the first embodiment will be described. First, the operation of the current switching circuit 22 will be described. If the FF 18 is set in the period T2 as shown in FIG. 2 and the Q output is at the H level, the transistor Q3
Is on. Therefore, the reference current regulated by the constant current source S2 flows through the diode D1, and the same current also flows through the transistor Q2 as the load current due to the current mirror effect. Further, since the Q-bar output of the FF 18 is at L level, the transistor Q4 is turned off, the load current of the transistor Q2 does not pass through the transistor Q4, and the capacitor 13
Flow to. As a result, the capacitor 13 is charged, its charge rises in proportion to time, and approaches the reference voltage V _H at time t _{2 as} shown in FIG.

When the charging voltage of the capacitor 13 exceeds the voltage V _H at time t ₂ , the voltage comparison circuit 15 outputs a signal and resets the FF 18. Therefore, the Q and Q bar outputs of the FF 18 are inverted, and the transistor Q4 of the current switching circuit 22 is turned on. At this time, the transistor Q3 is turned off, so that the reference current of the diode D1 becomes 0 and the load current of the transistor Q2 also becomes 0. Therefore, from the capacitor 13 via the transistor Q4 to the constant current source S2
A constant current flows in, and the charge of the capacitor 13 is discharged. Therefore, as shown in the period T3 of FIG.
The terminal voltage of 3 drops in proportion to time.

Eventually, the voltage of the capacitor 13 becomes the reference voltage V
_L or less voltage compared to the time t ₃ when made in the circuit 14 outputs a signal to set the FF18 again.

The triangular wave signal thus generated is output to the waveform conversion circuit 3. Since the operation after this is the same as that of the first embodiment, its explanation is omitted. Although the charging and discharging of the capacitor 13 is directly switched by the output signal of the FF 18, for example, the phase difference between the vertical synchronizing signal input from the outside and the pulse output from the FF 18 is detected and the charging is performed based on this phase difference signal. By performing on / off control of the circuit 11 and the discharge circuit 12, the phase of the triangular wave can be synchronized with the vertical synchronizing signal of the image.

[0032]

As described above in detail, according to the inventions of claims 1 and 2 of the present application, the constant current charging / discharging circuit is connected to the capacitor, so that the voltage sharply drops at the apex potential of the triangular wave. Disappears. Therefore, by generating a parabolic waveform from this triangular wave, a horizontal deflection signal for pincushion distortion correction whose envelope is switched without being discontinuous can be obtained. Therefore, even when the blanking period of the CRT display device is short, stable image display can be performed without causing distortion in the deflection current.

Further, according to the inventions of claims 3 and 4 of the present application,
In addition to the effects of the inventions of claims 1 and 2, the current mirror circuit and the current switching circuit are connected to the capacitor for generating the voltage signal so that the time constants at the time of discharging and charging the capacitor are controlled to be the same. it can. Therefore, it is possible to realize a deflection operation with less pincushion distortion.

[Brief description of drawings]

FIG. 1 is a block diagram of a pincushion distortion correction circuit according to a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram showing the operation of the pincushion distortion correction circuit of the first embodiment.

FIG. 3 is a block diagram of a pincushion distortion correction circuit according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration example of a conventional pincushion distortion correction circuit.

FIG. 5 is a circuit diagram of a sawtooth wave generation circuit used in a conventional pincushion distortion correction circuit.

FIG. 6 is a signal waveform diagram showing an operation of a conventional pincushion distortion correction circuit.

[Explanation of symbols]

 3 waveform conversion circuit 4 horizontal deflection circuit 5 horizontal deflection coil 6 CRT 10, 20 pincushion distortion correction circuit 11 constant current charging circuit 12 constant current discharge circuit 13 capacitor 14 first voltage comparison circuit 15 second voltage comparison circuit 16, 17 Reference power supply 18 FF 21 Current mirror circuit 22 Current switching circuit Q2-Q4 Transistor D1 Diode S2 Constant current source

Claims (4)

[Claims] 1. A triangular wave generation circuit for generating a triangular wave synchronized with a scanning cycle of a display screen, and a waveform conversion circuit for converting the triangular wave into a substantially parabolic waveform, wherein a deflection current is amplitude using the substantially parabolic waveform. A pincushion distortion correction circuit for a cathode ray tube display device that corrects pincushion distortion of a display screen by modulating, wherein the triangular wave generation circuit includes a capacitor that outputs a voltage signal to the waveform conversion circuit, and charge and discharge of the capacitor. A constant current charging / discharging circuit that switches alternately, a terminal voltage of the capacitor, a first reference power source, and a second reference voltage higher than this are compared, and the terminal voltages are first and second.
And a voltage comparison circuit which outputs charge and discharge control signals to the constant current charge / discharge circuit when the reference voltage is reached. 2. A triangular wave generation circuit for generating a triangular wave synchronized with a scanning cycle of a display screen, and a waveform conversion circuit for converting the triangular wave into a substantially parabolic waveform, wherein the deflection current is amplitude using the substantially parabolic waveform. A pincushion distortion correction circuit of a cathode ray tube display device that corrects pincushion distortion of a display screen by modulating, wherein the triangular wave generation circuit is a constant current charge for charging or blocking a constant current from a power source to a load by an on / off signal. A circuit, a constant current discharge circuit that is connected in series with the constant current charge circuit and discharges or blocks a constant current from the load by an on / off signal, and a common connection end of the constant current charge circuit and the constant current discharge circuit. A capacitor connected to one terminal and grounded at the other end; a first voltage comparison circuit that outputs a signal when the voltage of the capacitor reaches the voltage of the first reference power supply; A second voltage comparison circuit that outputs a signal when the voltage of the capacitor exceeds a second reference voltage higher than the first reference power supply; and a second voltage comparison circuit set by the output of the first voltage comparison circuit,
And a flip-flop that is reset by the output of the voltage comparison circuit and supplies the Q and Q bar outputs to the control terminals of the constant current charging circuit and the constant current discharging circuit, respectively. . 3. A triangular wave generating circuit for generating a triangular wave synchronized with a scanning cycle of a display screen, and a waveform converting circuit for converting the triangular wave into a substantially parabolic waveform, wherein the deflection current is amplitude using the substantially parabolic waveform. A pincushion distortion correction circuit for a cathode ray tube display device that corrects pincushion distortion of a display screen by modulating, wherein the triangular wave generation circuit includes a capacitor that outputs a voltage signal to the waveform conversion circuit, and a load side transistor. It has a current mirror circuit connected to one end of a capacitor and a switching element and a constant current source for switching the operation of the current mirror circuit connected to the reference current source side and the load side, and alternately switches the charging and discharging of the capacitor. The current switching circuit, the terminal voltage of the capacitor is compared with the first reference power supply and the second reference voltage higher than the first reference power supply, and the terminal voltages are the first and second.
And a voltage comparison circuit which outputs control signals for charging and discharging to the current switching circuit when the reference voltage is reached, respectively. 4. A triangular wave generation circuit for generating a triangular wave synchronized with a scanning cycle of a display screen, and a waveform conversion circuit for converting the triangular wave into a substantially parabolic waveform, wherein the deflection current is amplitude using the substantially parabolic waveform. A pincushion distortion correction circuit of a cathode ray tube display device for correcting pincushion distortion of a display screen by modulating, wherein the triangular wave generating circuit includes a constant current source, and a first and a constant current source commonly connected to an emitter. A current switching circuit having a second transistor; a current mirror circuit including a current control transistor which uses a current flowing into the collector of the first transistor as a reference current and applies a load current equal to the reference current to the capacitor; A collector in which the collector of the second transistor and the output of the current mirror circuit are commonly connected to one terminal and the other terminal is grounded; A first voltage comparison circuit that outputs a signal when the voltage of the capacitor reaches the voltage of the first reference power supply; and the voltage of the capacitor exceeds a second reference voltage higher than the first reference power supply. And a second voltage comparison circuit that outputs a signal, and a second voltage comparison circuit that is set by the output of the first voltage comparison circuit.
And a flip-flop that is reset by the output of the voltage comparator circuit and supplies the Q and Q bar outputs to the bases of the first and second transistors.