Deflection distortion correcting circuit for television set

Abstract: In a vertical deflection distortion correction circuit, there are provided a vertical deflection output circuit, a damping circuit, a vertical deflection yoke and a resonance circuit. A current is resonated in the resonance circuit, and on the other hand, a vertical deflection current is derived from the vertical deflection output circuit and supplied to the vertical deflection yoke. Then, the resonated current is superimposed on the vertical deflection current. The superimposed vertical deflection current is finally supplied to the vertical deflection yoke. The resonance circuit is constructed of an LC parallel circuit and a switching element circuit. The switching element circuit is arranged by either FETs, or thyristors.

Description: The present invention generally relates to a deflection distortion correction circuit for a television receiver. More specifically, the present invention is directed to a high precision vertical deflection distortion correction circuit suitable for, for instance, a large-screen television receiver. Vertical (upper and lower) pincushion distortion is known as typical deflection distortion in a television receiver. Fig. 1 of the accompanying drawings represents an example of vertical pincushion distortion on a television screen. In Fig. 1, a screen 60 indicates a front screen of a television receiver, and a raster 61 shows a pincushion-distorted raster. Originally, the screen 60 must be positioned in parallel with the raster 61 and must be coincident with the raster 61. However, the raster 61 is distorted in such a pincushion as shown in Fig. 1, resulting in a distorted picture displayed on the screen 60. Conventionally, the vertical pincushion distortion is corrected by employing the vertical deflection distortion correction circuit as shown in Fig. 2. In Fig. 2, the vertical deflection output circuit 70 is connected to the vertical deflection yoke V-DY which is connected to a resonance circuit 71. The resonance circuit is constructed of a capacitor C, a phase controlling coil PAC and a secondary coil of a resonance transformer (saturable transformer) V.PCT. That is, this resonance circuit is made of a parallel circuit of the capacitor C and a series circuit of the phase controlling coil and the resonance transformer. To a primary coil of the resonance transformer V.PCT, a pulse with the horizontal deflection period is inputted, and then the resonance current (distortion correction current) I 2 flows through the resonance circuit 71. Then, this resonance current I 2 is superimposed with the sawtooth vertical deflection circuit I 1 produced from the vertical deflection output circuit 70. In operation, from the vertical deflection output circuit 70, a vertical deflection current I 1 is outputted which is changed in a sawtooth form at the vertical deflection period. Upon input of a pulse into the primary coil of the resonance transformer V.PCT, a sinewave resonance current (i.e., distortion correction current) I 2 flows into the resonance circuit 71 constructed of the secondary coil of the resonance transformer V.PCT, the phase controlling coil PAC and the capacitor C. Then, such a current that the distortion correction current I 2 has been superimposed on the sawtooth vertical deflection current I 1 , flows into the vertical deflection yoke V-DY. Fig. 3 represents a waveform of such a current flowing through the vertical defection coil V-DY. In Fig. 3, a sawtooth wave 80 corresponds to a waveform of the original vertical deflection current I 1 , and sinewaves 81 to 83 correspond to waveforms of the distortion correction current I 2 used for the upper portion of the screen 60 shown in Fig. 1 and the lower portion thereof. The vertical deflection current I 1 is varied at the vertical deflection period 84, whereas the distortion correction current I 2 is varied at the horizontal deflection period 85. As shown in fig. 3, a composite waveform of the vertical deflection current corresponds to such a waveform that the sinewaves have been superimposed on the sawtooth wave 80. The polarity of the sinewaves 81 to 83 correspond to that of the vertical deflection current waveform, and the levels of the sinewaves are directly proportional to the level of the vertical deflection current I 1 . The levels of the sinewaves 81 and 83 at the upper portion and the lower portion on the screen 60 shown in Fig. 1 become large, and to the contrary, the level of the sinewave 82 at the center portion of the screen 60 becomes small. The polarities of the sinewaves 81 and 83 at the upper portion and the lower portion on the screen 60 are opposite to each other. There is a problem in the conventional vertical deflection distortion correction circuit that a specific transformer such as a saturable transformer is required, and there is poor linearity with respect to the vertical deflection current and the horizontal deflection pulse. Also, it is difficult to achieve pincushion correction at high precision due to fluctuation in the phase. Moreover, since the sinewave is employed as the deflection distortion correction wave, it is impossible to correct the trapezoidal distortion. US-A-3,676,733 discloses a deflection distortion correction circuit according to the preamble of claim 1 but in which the switching element is a triac. US-A-4,118,656 discloses a pincushion distortion correction circuit. The present invention has been made in an attempt to solve the above-described problems of the conventional deflection distortion correction circuit, and therefore, has an object to provide a deflection distortion correction circuit having good linearity with respect to a vertical deflection current and a horizontal deflection pulse, having less phase fluctuation, and capable of realizing high-precision pincushion distortion correction. According to the present invention, there is provided a deflection distortion correction circuit wherein a current resonated in a resonance circuit is superimposed on a vertical deflection current and the superimposed current is supplied to a vertical deflection yoke in order to correct vertical deflection distortion, wherein a switching element circuit is employed in said resonance circuit; and said switching element circuit is turned ON/OFF at a horizontal deflection period, whereby the current resonated in said resonance circuit is superimposed on the vertical deflection current and the resultant current flows into the vertical deflection yoke so as to correct the vertical deflection distortion; characterised in that said switching element circuit comprises: a transformer having a primary winding for inputting a control signal, and a secondary winding for outputting said control signal; first and second FETs connected to said transformer in such a manner that sources of said first and second FETs are commonly connected to each other and also to one end of said secondary winding, gates of said first and second FETs are connected to the other end of said secondary winding, and drains of said first and second FETs are connected between said capacitor and said inductor; and first and second parasitic diodes connected between the sources and the drains of said first and second FETs in such a manner that while said first and second FETs are turned on in response to said control signal, said resonated current can flow through said first and second parasitic diodes and drain-to-source paths of said first and second FETs in both of a positive direction and a negative direction. In the deflection distortion correction circuit with the above-described circuit arrangement, the switching element employed in the resonance circuit is turned ON/OFF at the horizontal deflection period, the parabolic current which has been produced by the resonance occurred in the resonance circuit is superimposed on the deflection current, and the superimposed current is flown into the deflection yoke. As a result, the vertical deflection distortion can be corrected. The present invention will be further described by way of example in the following description with reference to the accompanying drawings, in which: Fig. 1 illustrates an example of the vertical pincushion distortion; Fig. 2 is a schematic circuit diagram of showing an arrangement of the conventional deflection distortion correction circuit; Fig. 3 is an explanatory diagram for explaining a vertical deflection current waveform of the conventional deflection distortion correction circuit shown in Fig. 2; Fig. 4 is a circuit diagram for representing an arrangement of a deflection distortion correction circuit according to a preferred embodiment of the present invention; Fig. 5 is an explanatory diagram for explaining current waveforms at various circuit portions of the deflection distortion correction circuit of Fig. 4; Fig. 6 is a circuit diagram of one example of the switch circuit SW shown in Fig. 4 which utilizes FETs; and Fig. 7 is an explanatory diagram for explaining horizontal trapezoidal distortion correction performed in the deflection distortion correction circuit of Fig. 4. Fig. 4 represents a circuit arrangement of a deflection distortion correction circuit according to one preferred embodiment of the present invention. In Fig. 4, a vertical deflection output circuit 1 including an amplifier "A" is connected to a vertical deflection yoke V-DY and a damping circuit 1. A resistor R1 is connected parallel to a capacitor C1, which constitute the damping circuit 2. A coil L 2 is connected parallel to a capacitor C 2 via a switch SW, which constitute a resonance circuit 3. The resonance circuit 3 is connected to the vertical deflection yoke V-DY and the damping circuit 2. Both of the damping circuit 2 and the resonance circuit 3 are grounded via a circuit detecting circuit R 2 . A vertical deflection circuit I 1 is a sawtooth-shaped current outputted from the vertical deflection output circuit 1, and a parabolic current I 2 is a correction circuit flowing through the damping circuit 2, vertical deflection yoke V-DY and resonance circuit 3. The switch SW is turned ON/OFF by a control signal. The control signal is varied at a horizontal deflection period 5,and becomes a logic "H" level during a flyback period 4 and also a logic "L" level during the remaining scanning period 6. Operation of the deflection distortion correction circuit shown in Fig. 4 according to the preferred embodiment will now be described. The sawtooth current I 1 derived from the vertical deflection output circuit 1 flows through a signal path of the vertical deflection yoke V-DY, the resonance circuit 3 and the resistor R2. At this time, energy is reserved in the capacitor C2, the switch SW is turned ON during the horizontal flyback period 4, and also electron charge stored in the capacitor C2 is discharged via the coil L2 during this flyback period 4. Thereafter, even after a voltage across the capacitor C 2 becomes 0 (zero), the current of the resonance circuit 3 is continued to be flown due to the resonance phenomenon by the coil L 2 and the capacitor C 2 . However, a circuit constant of this circuit is so designed that when the current of the coil L 2 becomes zero, the switch SW is turned OFF in response to the control signal. At this time, a pulse voltage produced between both ends of the capacitor C 2 is directly proportional to the vertical deflection current I 1 , and a polarity of which pulse voltage corresponds to that of the vertical deflection circuit I 1 . During the horizontal scanning period 6, the switch SW is turned OFF, and then the resonant parabolic current I 2 flows through the signal path of the vertical deflection yoke V-DY, the resonance circuit 3 (capacitor C 2 ), and the damping circuit 2. It should be noted that the damping circuit 2 bypasses the parabolic current I 2 having the horizontal deflection frequency component with respect to the vertical deflection output circuit 1. As a consequence, it is possible to avoid an oscillation and a ringing effect of the current flowing through the vertical deflection yoke V-DY. If there is no damping circuit 2, since a voltage approximate 160V is produced across the terminals of the vertical deflection yoke V-DY, the amplifier "A" of the vertical deflection output circuit 1 must withstand such a high voltage. However, if the damping circuit 2 is connected to this deflection distortion correction circuit, since the parabolic circuit I 2 is flown as represented in Fig. 4, a voltage, e.g., on the order of 50V is applied to the amplifier "A". In Fig. 5, there are shown waveforms of currents flowing through the vertical deflection yoke V-DY. As represented in Fig. 5, the sawtooth current I 1 is varied at the vertical deflection period. Then, the parabolic current I 2 is superimposed on this sawtooth current I 1 . A level of this parabolic current I 2 becomes high when a level of the sawtooth current I 1 becomes high, and conversely, when the level of the sawtooth current I 1 becomes low, the level of the parabolic current I 2 becomes low. Also, when the polarity of the sawtooth current I 1 becomes positive, the polarity of the parabolic current I 2 becomes similarly positive. When the polarity of the sawtooth current I 1 becomes negative, that of the parabolic current I 2 becomes negative. In this preferred embodiment, since it is so designed that the polarity of the sawtooth current I 1 becomes positive at an upper portion of a television screen and becomes negative at a lower portion of the screen, the polarity of the parabolic current I 2 becomes positive at the upper portion of the screen and negative at the lower portion of the screen. Then, the levels of the sawtooth and parabolic currents become substantially zero at a center portion of the screen. As apparent from Fig. 5, a pulsatory current IL 2 is flown through the coil L at the timing when the switch SW is turned ON during the horizontal flyback period. As previously explained, since the vertical deflection current having the sawtooth shape and varied at the vertical deflection period is flown on which the parabolic correction current changing at the horizontal deflection period is superimposed, the vertical pincushion distortion can be corrected. Now, a description will be made of a concrete circuit arrangement of the switch SW shown in Fig. 4. Fig. 6 represents an example of a circuit arrangement in which the switch SW is constructed by employing FETs. In this preferred embodiment, two FETs (power MOSFET) 30 and 31 are connected in such a manner that sources thereof are commonly connected to each other. Parasitic diodes 32 and 33 are connected between a gates and a drain of each FET. Each of gates of these FETs 30 and 31 is connected to one terminal of a secondary coil of a transformer 34, and each of the sources thereof is connected to the other terminal of the secondary coil of the transformer 34. Upon input of a pulse 35 having a logic "H" level into the primary coil of the transformer 34, both of the FETs 30 and 31 are turned ON. As a result, for instance, a positive-direction current is flown in a signal path of the drain-source of the FET 32 and the parasitic diode 33 of the FET 31, whereas a negative-direction current is flown in a signal path of the drain-source of the FET 31 and the parasitic diode 32. When the pulse supplied from the transformer 34 becomes a logic "L" level, both of these FETs 30 and 31 are turned OFF. At this time, since the parasitic diodes 32 and 33 are connected along the opposite directions with each other, the current flows in any directions can be completely blocked. To the contrary, for example, if only one power MOSFET is employed, even when this power MOSFET is turned OFF, the current is flown through the parasitic diode, so that the signal path cannot be completely cut off. Accordingly, as shown in this preferred embodiment, it is preferable to constitute the switch by connecting the two FETs in a series circuit. As previously stated, the parabolic correction current which is superimposed on the sawtooth current is produced by switching the switch SW. Thus, a horizontal trapezoidal distortion as indicated in Fig. 7 can be corrected by properly adjusting the switching timing of the switch SW. That is to say, as illustrated in Fig. 7, to correct such a raster 50 having horizontal trapezoidal distortion that the height of the righthand screen becomes high, and the height of the lefthand screen becomes low, as a correct raster 51, the generation timing of the parabolic wave at the horizontal scanning period is set to be fast. Conversely, to correct such a horizontal trapezoidal distortion that the height of the lefthand screen becomes high and the height of the righthand screen becomes low, the generation timing of the parabolic wave is delayed. It should be noted that although such a signal that a parabolic wave is superimposed on a sawtooth wave is previously produced, and then this superimposed signal may be supplied to the vertical deflection coil V-DY, such a signal generation may consume high power. However, in accordance with the arrangement of the present invention, since the resonance current is utilized, total power consumption becomes low. While the deflection distortion correction circuit according to the present invention has been described in detail, since the correction current is generated by switching the switching element, such a specific transformer as a saturable transformer is not required. Also, linearity can be improved with respect to the vertical deflection current and the horizontal deflection pulse. Then, since the phase fluctuation can be controlled, high-precision pincushion distortion correction can be realized. Furthermore, since the parabolic wave is produced, the horizontal trapezoidal distortion can be corrected.

Claims: A deflection distortion correction circuit wherein a current resonated in a resonance circuit (3) is superimposed on a vertical deflection current and the superimposed current is supplied to a vertical deflection yoke (V-DY) in order to correct vertical deflection distortion, wherein a switching element circuit (SW) is employed in said resonance circuit; and said switching element circuit (SW) is turned ON/OFF at a horizontal deflection period, whereby the current resonated in said resonance circuit is superimposed on the vertical deflection current and the resultant current flows into the vertical deflection yoke so as to correct the vertical deflection distortion; characterised in that said switching element circuit comprises: a transformer (34) having a primary winding for inputting a control signal, and a secondary winding for outputting said control signal; first and second FETs (30, 31) connected to said transformer in such a manner that sources of said first and second FETs are commonly connected to each other and also to one end of said secondary winding, gates of said first and second FETs are connected to the other end of said secondary winding, and drains of said first and second FETs are connected between said capacitor and said inductor; and first and second parasitic diodes (32, 33) connected between the sources and the drains of said first and second FETs in such a manner that while said first and second FETs are turned on in response to said control signal, said resonated current can flow through said first and second parasitic diodes and drain-to-source paths of said first and second FETs in both of a positive direction and a negative direction. A deflection distortion correction circuit as claimed in Claim 1, wherein said resonance circuit includes: a capacitor (C2); and an inductor (L2) parallel-connected via said switching element to the capacitor. A deflection distortion correction circuit as claimed in Claim 1 or 2, further comprising: a damping circuit (2) connected to said vertical deflection yoke. A television receiver including a deflection distortion circuit according to any one of the preceding claims.

Inventors: KAWABERI SEIJI, SHOJI TAKESHI, KAWABERI, SEIJI, SHOJI, TAKESHI, Kawaberi, Seiji, c/o Sony Corporation, Shoji, Takeshi, c/o Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: H04N3
IPC codes: H04N3