The present invention relates to a deflection system and a deflection method of a horizontal reciprocating deflection mode scanning an electron beam in a reciprocating manner.
A deflection system of a horizontal reciprocating deflection mode scanning an electron beam in a reciprocating manner is recently proposed in the field of a display unit for a television set or the like, in order to make display of a high resolution. In the deflection system of the horizontal reciprocating deflection mode, a forward scanning line and a backward scanning line must be parallelized with each other.
FIGS. 4(a) to 4(d) are waveform diagrams for illustrating a vertical deflection current and a horizontal deflection current employed in the horizontal reciprocating deflection mode for parallelizing forward and backward scanning lines with each other. FIG. 4(a) shows a first sawtooth wave current SI1 for generating a vertical deflection magnetic field moving an electron beam from the top to the bottom of a screen of a television set or the like and thereafter returning the electron beam to the top of the screen again. When performing reciprocating scanning with the first sawtooth wave current SI1 shown in FIG. 4(a), the forward and backward scanning lines are not parallelized with each other. Therefore, inclination of a vertical deflection current must be nulled in forward scanning and backward scanning in order to parallelize the forward and backward scanning lines with each other.
Therefore, a second sawtooth wave current SI2 shown in FIG. 4(b) is added to the first sawtooth wave current SI1 shown in FIG. 4(a), for generating a vertical deflection current VI shown in FIG. 4(c). The second sawtooth wave current SI2 shown in FIG. 4(b) has the same frequency as a horizontal scanning frequency, and the inclination of the second sawtooth wave current SI2 in forward scanning and backward scanning is so set that inclination of the composited vertical deflection current VI in forward scanning and backward scanning is nulled.
A horizontal deflection current HI shown in FIG. 4(d) has the waveform of a frequency half the horizontal scanning frequency for performing reciprocating scanning.
FIGS. 5(a) and 5(b) are conceptual diagrams showing parallelized reciprocating deflection scanning. When performing reciprocating scanning with the vertical deflection current VI shown in FIG. 4(c) and the horizontal deflection current HI shown in FIG. 4(d), such ideal reciprocating scanning that a scanning line 21 performs reciprocating scanning in parallel on a screen 20 is implemented as shown in FIG. 5(a). When supplying the vertical deflection current VI shown in FIG. 4(c) to a vertical deflection coil while supplying the horizontal deflection current HI shown in FIG. 4(d) to a horizontal deflection coil, however, the scanning line maybe distorted. When a current component resulting from the horizontal deflection current HI is induced from the horizontal deflection coil to the vertical deflection coil and superposed on the vertical deflection current VI shown in FIG. 4(c), a scanning line 22 is distorted as shown in FIG. 5(b), to distort a displayed image.
In a conventional deflection system, the following method, for example, is carried out in order to cancel a current component induced to flow in a vertical deflection coil from a horizontal deflection coil by a horizontal deflection current: A transformer is serially connected to the vertical deflection coil for supplying the vertical deflection coil with a current 180xc2x0 out of phase with the horizontal deflection current flowing in the horizontal deflection coil through the transformer. Thus, the current component induced to the vertical deflection coil is canceled. In this case, the transformer serially connected to the vertical deflection coil must be of a standard suitable to the large vertical deflection current, and hence the manufacturing cost is increased. Further, power consumed in a driving circuit for driving the transformer is disadvantageously increased.
An object of the present invention is to provide a deflection system and a deflection method capable of performing reciprocating deflection without distorting a scanning line and reducing the cost as well as power consumption.
A deflection system according to an aspect of the present invention, performing reciprocating scanning by horizontally deflecting an electron beam in a reciprocating manner in response to a vertical synchronizing signal and a horizontal synchronizing signal, comprises a vertical deflection coil, a horizontal deflection coil, a horizontal deflection current supply circuit supplying a horizontal deflection current for horizontally deflecting the electron beam in a reciprocating manner, an induced current detection circuit detecting a current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil, a sawtooth wave voltage generation circuit generating a sawtooth wave voltage synchronous with the vertical synchronizing signal, a first current supply circuit receiving the sawtooth wave voltage generated by the sawtooth wave voltage generation circuit and supplying a first sawtooth wave current for vertically deflecting the electron beam to the vertical deflection coil, a second current supply circuit supplying a second sawtooth wave current for parallelizing forward and backward scanning lines with each other to the vertical deflection coil, and a correction voltage addition circuit adding a correction voltage for canceling the current component detected by the induced current detection circuit to the sawtooth wave voltage generated by the sawtooth wave voltage generation circuit.
In the deflection system, the induced current detection circuit detects the current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil. The correction voltage addition circuit adds the correction voltage to the sawtooth wave voltage on the basis of the detected current component, and the first current supply circuit supplies the current component responsive to the correction voltage to the vertical deflection coil.
Thus, the current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil can be canceled. Therefore, reciprocating deflection can be performed without distorting the scanning lines. In this case, no transformer may be serially connected to the vertical deflection coil for supplying a current component for canceling the current component induced to the vertical deflection coil. Therefore, the cost for the deflection system as well as power consumption can be reduced.
The induced current detection circuit may generate an output voltage responsive to the current component, and the correction voltage addition circuit may include a regulating circuit regulating the amplitude and the phase of the output voltage from the induced current detection circuit and outputting the regulated output voltage as the correction voltage and an addition circuit adding the correction voltage output from the regulating circuit to the sawtooth wave voltage generated by the sawtooth wave voltage generation circuit.
In this case, the induced current detection circuit generates the output voltage responsive to the current component induced to the vertical deflection coil, while the regulating circuit regulates the amplitude and the phase of the output voltage and outputs the correction voltage having proper relation to the phase of the current component induced to the vertical deflection coil. Further, the addition circuit adds the correction voltage to the sawtooth wave voltage generated by the sawtooth wave voltage generation circuit. Thus, the first current supply circuit supplies a current component of opposite polarity to the current component induced to the vertical deflection coil to the vertical deflection coil in response to the correction voltage. Consequently, the current component induced to the vertical deflection coil can be canceled by the current component supplied from the first current supply circuit.
The induced current detection circuit may include a horizontal deflection current detection circuit detecting the current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil from the horizontal deflection current.
In this case, the horizontal deflection current detection circuit detects the current component induced to the vertical deflection coil from the horizontal deflection current. Thus, the induced current component can be more readily detected as compared with the case of extracting the induced current component from the vertical deflection current.
The horizontal deflection current detection circuit may include a first transformer having a primary winding serially connected to the horizontal deflection coil and a secondary winding connected to the correction voltage addition circuit.
In this case, the horizontal deflection current is smaller than the vertical deflection current and hence the current component induced to the vertical deflection coil can be detected with a smaller transformer as compared with the case of inserting a transformer serially to the vertical deflection coil. Thus, the cost can be further reduced.
The correction voltage addition circuit may include a regulating circuit regulating the amplitude and the phase of an output voltage from the secondary winding of the first transformer and outputting the regulated output voltage as the correction voltage and an addition circuit adding the correction voltage output from the regulating circuit to the sawtooth wave voltage generated by the sawtooth wave voltage generation circuit.
In this case, the regulating circuit regulates the amplitude and the phase of the output voltage from the secondary winding of the first transformer and outputs the regulated voltage as the correction voltage, while the addition circuit adds the correction voltage to the sawtooth wave voltage.
The second current supply circuit may include a second transformer having a primary winding and a secondary winding serially connected to the vertical deflection coil and a sawtooth wave current supply circuit supplying a sawtooth wave current synchronous with the horizontal synchronizing signal to the primary winding of the second transformer.
In this case, the primary winding of the second transformer is supplied with the sawtooth wave current synchronous with the horizontal synchronizing signal, and the secondary winding supplies the second sawtooth wave current to the vertical deflection coil.
The deflection system may further comprise a feedback circuit negatively feeding back a voltage on an end of the second winding of the second transformer to the correction voltage addition circuit, and the addition circuit may add the voltage negatively fed back by the feedback circuit to the correction voltage and the sawtooth wave voltage.
In this case, the voltage on the end of the secondary winding of the second transformer is negatively fed back to the correction voltage addition circuit, while the addition circuit adds the negatively fed-back voltage to the correction voltage and the sawtooth wave voltage.
The induced current detection circuit may include a resonance circuit resonating at a frequency substantially half a horizontal scanning frequency and a resonance current detection circuit detecting a current flowing in the resonance circuit by resonance.
The frequency of the current component induced to the vertical deflection coil by the horizontal deflection current is half the horizontal scanning frequency. Therefore, the current component induced to the vertical deflection coil by the horizontal deflection current can be directly detected by detecting the current flowing in the resonance circuit resonating at the frequency substantially half the horizontal scanning frequency.
The induced current detection circuit may include a capacitor and a first transformer having a primary winding serially connected to the capacitor and a secondary winding connected to the correction voltage addition circuit, the resonance circuit may be formed by the primary winding of the first transformer, the capacitor and the vertical deflection coil, and the resonance current detection circuit may be formed by the secondary winding of the first transformer.
In this case, the primary winding of the first transformer, the capacitor and the vertical deflection coil form the resonance circuit, and the resonance current detection circuit formed by the secondary winding of the first transformer detects the current flowing in the resonance circuit. The current flowing in the resonance circuit is smaller than the vertical deflection current, and hence the current component induced to the vertical deflection coil can be detected with a smaller transformer as compared with the case of inserting a transformer serially to the vertical deflection coil. Thus, the cost can be further reduced.
The correction voltage addition circuit may include a regulating circuit regulating the amplitude and the phase of an output voltage from the secondary winding of the first transformer and outputting the regulated output voltage as the correction voltage and an addition circuit adding the correction voltage output from the regulating circuit to the sawtooth wave voltage generated by the sawtooth wave voltage generation circuit.
In this case, the regulating circuit regulates the amplitude and the phase of the output voltage from the secondary winding of the first transformer and outputs the regulated voltage as the correction voltage, while the addition circuit adds the correction voltage to the sawtooth wave voltage.
The second current supply circuit may include a second transformer having a primary winding and a secondary winding serially connected to the vertical deflection coil and a sawtooth wave current supply circuit supplying a sawtooth wave current synchronous with the horizontal synchronizing signal to the secondary winding of the second transformer, and the resonance circuit may be formed by the primary winding of the first transformer, the capacitor, the vertical deflection coil and the secondary winding of the second transformer.
In this case, the primary winding of the first transformer, the capacitor, the vertical deflection coil and the secondary winding of the second transformer form the resonance circuit, and the resonance current detection circuit formed by the secondary winding of the first transformer detects the current flowing in the resonance circuit. The current flowing in the resonance circuit is smaller than the vertical deflection current, and hence the current component induced to the vertical deflection coil can be detected with a smaller transformer as compared the case of inserting a transformer serially to the vertical deflection coil. Thus, the cost can be further reduced.
The deflection system may further comprise a feedback circuit negatively feeding back a voltage on an end of the secondary winding of the second transformer to the correction voltage addition circuit, and the addition circuit may add the voltage negatively fed back by the feedback circuit to the correction voltage and the sawtooth wave voltage.
In this case, the voltage on the end of the secondary winding of the second transformer is negatively fed back to the correction voltage addition circuit, and the addition circuit adds the negatively fed-back voltage to the correction voltage and the sawtooth wave voltage.
The first current supply circuit may include an amplifier. In this case, a current based on the sawtooth wave voltage and the correction voltage added to each other by the addition circuit is supplied to the vertical deflection coil.
A deflection method according to another aspect of the present invention, performing reciprocating scanning by horizontally deflecting an electron beam in a reciprocating manner in response to a vertical synchronizing signal and a horizontal synchronizing signal in a deflection system comprising a vertical deflection coil and a horizontal deflection coil, comprises steps of supplying a horizontal deflection current for horizontally deflecting the electron beam in a reciprocating manner to the horizontal deflection coil, detecting a current component induced to the vertical deflection coil by a horizontal deflection current flowing in the horizontal deflection coil, generating a sawtooth wave voltage synchronous with the vertical synchronizing signal, receiving the sawtooth wave voltage and supplying a first sawtooth wave current for vertically deflecting the electron beam to the vertical deflection coil, supplying a second sawtooth wave current for parallelizing forward and backward scanning lines with each other to the vertical deflection coil and adding a correction voltage for canceling the detected current component to the generated sawtooth wave voltage.
According to this deflection method, the current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil is detected. The correction voltage is added to the sawtooth wave voltage on the basis of the detected current component, and the current component responsive to the correction voltage is supplied to the vertical deflection coil.
Thus, the current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil can be canceled. Therefore, reciprocating deflection can be performed without distorting the scanning lines. In this case, no transformer may be serially connected to the vertical deflection coil in order to supply a current component for canceling the current component induced to the vertical deflection coil. Therefore, the cost for the deflection system as well as power consumption can be reduced.
The step of detecting the current component may include a step of detecting the current component induced to the vertical deflection coil by the horizontal deflection current flowing in the horizontal deflection coil from the horizontal deflection current.
In this case, the current component induced to the vertical deflection coil is detected from the horizontal deflection current. Thus, the induced current component can be more readily detected as compared with the case of extracting the induced current component from the vertical deflection current.
The step of detecting the current component may include steps of generating a current resonating at a frequency substantially half a horizontal scanning frequency and detecting the resonating current.
The frequency of the current component induced to the vertical deflection coil by the horizontal deflection current is half the horizontal scanning frequency. Therefore, the current component induced to the vertical deflection coil by the horizontal deflection current can be directly detected by detecting the current resonating at a frequency substantially half the horizontal scanning frequency.