JP3569818B2 - Horizontal deflection circuit for CRT - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a horizontal deflection circuit for a CRT, and more particularly, to a horizontal deflection circuit for a CRT improved so that the horizontal direction (linearity) of a displayed image in the horizontal direction can be sufficiently increased even when the horizontal deflection frequency is low. . In particular, it is useful for a multi-scan display device in which the horizontal deflection frequency changes in the range of about 30 kHz to 110 kHz.
[0002]
[Prior art]
FIG. 5 is a configuration diagram showing an example of a conventional CRT horizontal deflection circuit.
The CRT horizontal deflection circuit 500 includes a horizontal position control circuit 1 that delays an input horizontal synchronization signal HD according to a horizontal position control signal CH ′ to generate a delayed horizontal synchronization signal HD ′, A horizontal oscillation circuit 2 for generating a horizontal deflection pulse voltage Vp whose frequency and phase match HD ′, a horizontal drive circuit 3 for amplifying the horizontal deflection pulse voltage Vp and shaping the waveform, a switching operation and resonance of a transistor Q1 A horizontal output circuit 4 for supplying a horizontal deflection current i 'to the horizontal deflection coil 41 and the linearity coil 42 by the operation of the circuit, and a flyback pulse generated by the horizontal output circuit 4 is boosted to raise an anode electrode of a CRT (not shown). Transformer 5 for generating a high voltage applied to the screen and a horizontal position control so that the image display position is at the center of the screen. And a microcomputer 50 for outputting a control signal CH '.
[0003]
Next, the operation of the CRT horizontal deflection circuit 500 will be described.
FIG. 6 shows a case where the horizontal deflection frequency fh is 110 kHz. As shown in FIG. 6A, the delay synchronization signal HD ′ (solid line) has a waveform obtained by delaying the horizontal synchronization signal HD (dotted line) by a delay time τ corresponding to the horizontal position control signal CH ′.
The cycle T1 is 9.09 μs. The image display position in the horizontal direction is determined by the time difference between the delay synchronization signal HD 'shown in FIG. 6A and the display signal shown in FIG. As shown in FIG. 6C, a sawtooth horizontal deflection current i ′ synchronized with the delay synchronization signal HD ′ flows through the horizontal deflection coil 41. When the horizontal deflection frequency fh is high, the linearity of the waveform of the horizontal deflection current i ′ in the horizontal scanning period L is high, and the linearity of the display image in the horizontal direction is good.
FIG. 7 shows a case where the horizontal deflection frequency fh is 30 kHz. As shown in FIG. 7A, the delay synchronization signal HD ′ (solid line) is a waveform obtained by delaying the horizontal synchronization signal HD (dotted line) by the delay time τ. The period T is 33 μs. As shown in FIG. 7C, a sawtooth-shaped horizontal deflection current i ′ flows through the horizontal deflection coil 41 in synchronization with the delay synchronization signal HD ′. If the horizontal deflection frequency fh is low, the waveform of the horizontal deflection current i ′ is dull in the period D due to the influence of the characteristics of the flyback transformer 5 and the like, and the linearity is lowered, and the linearity of the displayed image in the horizontal direction is deteriorated. That is, as shown in FIG. 8, the low linearity area (left-upward shaded area) DF corresponding to the period D in FIG. 7C overlaps the image display area (right-upward shaded area) G, and Causes distortion in the image. In the figure, W is the screen width. LF is a horizontal scanning range (horizontal raster area). F is the screen width of the CRT.
[0004]
[Problems to be solved by the invention]
In the conventional horizontal deflection circuit 500 for CRT, when the horizontal deflection frequency is low, there is a problem that the linearity of the displayed image is reduced.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a CRT horizontal deflection circuit that can sufficiently increase the horizontal linearity of a displayed image even when the horizontal deflection frequency is low.
[0005]
[Means for Solving the Problems]
According to a first aspect, the present invention is a horizontal deflection circuit for a CRT that scans an electron beam in a horizontal direction by flowing a sawtooth-shaped horizontal deflection current through a horizontal deflection coil of the CRT, the timing of the horizontal deflection current being delayed. An image display area moving means for moving the image display area to the left, and a direct current for superimposing a direct current on the horizontal deflection current so as to move the horizontal scanning range to the right to offset the movement of the image display area. A horizontal deflection circuit for a CRT, comprising: current superimposing means.
In the horizontal deflection circuit for CRT according to the first aspect, the timing of the horizontal deflection current is delayed and the image display area is moved to the left, so that the linearity of the waveform of the horizontal scanning current corresponds to the scanning period in which the linearity is low. It is possible to prevent the region from overlapping the image display region. Then, since the DC current is superimposed on the horizontal deflection current and the horizontal scanning range is moved rightward, the movement of the image display area can be canceled and the display position of the image can be returned to the original position. In general, when the horizontal deflection frequency decreases, the width of the image display area with respect to the horizontal scanning range of the screen tends to be narrowed. Therefore, the image display area can be sufficiently contained only in the scanning area having high linearity. As a result, even when the horizontal deflection frequency is low, the horizontal linearity of the displayed image can be sufficiently increased.
[0006]
In a second aspect, the present invention is characterized in that the horizontal deflection circuit for a CRT having the above-mentioned configuration includes control means for controlling the movement of the image display area and the DC current based on a horizontal scanning frequency. A horizontal deflection circuit for a CRT is provided.
In the horizontal deflection circuit for CRT according to the second aspect, when the horizontal deflection frequency is a low frequency at which the linearity of the waveform of the horizontal deflection current is deteriorated, the image display area is moved by the image display area moving means or the DC current superimposing means is used. , The DC current can be appropriately superimposed.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited to this.
FIG. 1 is a configuration diagram showing a horizontal deflection circuit for a CRT according to an embodiment of the present invention.
The CRT horizontal deflection circuit 100 includes a horizontal position control circuit 1 that delays the input horizontal synchronization signal HD according to a horizontal position control signal CH to generate a delayed horizontal synchronization signal HD ′, and the delayed horizontal synchronization signal HD. ′, A horizontal oscillation circuit 2 for generating a horizontal deflection pulse voltage Vp having the same frequency and phase, a horizontal drive circuit 3 for amplifying the horizontal deflection pulse voltage Vp and shaping the waveform, a switching operation and a resonance circuit for the transistor Q1. , A horizontal output circuit 4 for supplying a horizontal deflection current i to the horizontal deflection coil 41 and the linearity coil 42, and a flyback pulse generated by the horizontal output circuit 4 is boosted and applied to an anode electrode of a CRT (not shown). And a flyback transformer 5 for generating a high voltage, and a horizontal deflection current waveform corresponding to the horizontal deflection frequency fh. A microcomputer 10 for outputting a horizontal position control signal CH for moving an image display position so as to use only a scan period having a high nearness and outputting a DC current control signal CI so that the image display position is at the center of the screen; It comprises a DC current superimposing circuit 11 for superimposing a DC current id according to the current control signal CI on the horizontal deflection current i.
[0009]
Next, the operation of the CRT horizontal deflection circuit 100 will be described.
When the horizontal deflection frequency fh is 40 to 110 kHz, the operation of the CRT horizontal deflection circuit 100 is basically the same as the operation of the conventional CRT horizontal deflection circuit 500 (see FIG. 5). The microcomputer 10 outputs the same horizontal position control signal CH = CH ′ as before, and does not output the DC current control signal CI.
When the horizontal deflection frequency fh is 30 kHz, the microcomputer 10 outputs a horizontal position control signal CH = CH '+ cd for moving the image display position to the left from the center of the screen. As shown in FIG. 2A, the delay synchronization signal HD ′ (solid line) is obtained by converting the horizontal synchronization signal HD (dotted line) into the conventional delay time τ (see FIG. 7) and the delay time τcd corresponding to the cd. This is a waveform delayed by the added delay time {τ + τcd}.
The period T is 33 μs. The image display position in the horizontal direction is determined by the time difference between the delay synchronization signal HD 'shown in FIG. 2A and the display signal shown in FIG. 2B. As shown in FIG. 2 (c), the horizontal deflection coil 41 has a sawtooth shape which is delayed by the delay time τcd more than the conventional horizontal deflection current i ′ (dashed line) and synchronized with the delay synchronization signal HD ′. The horizontal deflection current i (solid line) flows. As a result, as shown in FIG. 3, the image display area G (upward diagonal oblique line) moves leftward by the cd from the center of the screen, and the low linearity area corresponding to the period D of FIG. The overlap with the DF is eliminated. The cd is, for example, about 10% of the screen width W. To facilitate understanding of the moving state, an image display area located at the center of the screen is indicated by a dotted line. In the drawing, LF is a horizontal scanning range. F is the screen width of the CRT.
The microcomputer 10 outputs a DC current control signal CI for superimposing a DC current id on the horizontal deflection current i in order to move the horizontal scanning range so as to cancel the movement of the image display area G. As shown in FIG. 2D, a current {i + id} flows through the horizontal deflection coil 41. Thereby, as shown in FIG. 4, the horizontal scanning range LF (solid line) moves rightward by the cd, and the image display area G is located at the center of the screen. The horizontal scanning range before the DC current id is superimposed is indicated by a dotted line.
In the above operation, for the sake of explanation, a time difference is provided between the output of the horizontal position control signal CH and the output of the DC current control signal CI, but the horizontal position control signal CH and the DC current control signal CI are output simultaneously. You may.
[0010]
According to the horizontal deflection circuit 100 for CRT, when the horizontal deflection frequency fh is low, the image display area G is moved leftward from the center of the screen by the horizontal position control circuit 1 and the horizontal deflection is performed by the DC current superposition circuit 11. Since the DC current id is superimposed on the horizontal deflection current i flowing through the coil 41 and the image display area G is returned to the center of the screen, an image can be displayed using only the scanning period in which the waveform of the horizontal deflection current i has high linearity. I can do it.
[0011]
【The invention's effect】
According to the horizontal deflection circuit for CRT of the present invention, when the linearity of the waveform of the horizontal deflection current is low (the waveform becomes dull in a part of the horizontal scanning period), only the scanning period in which the linearity of the waveform of the horizontal deflection current is high is used. Since the image can be displayed using the image, the distortion of the displayed image in the horizontal direction can be sufficiently reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a horizontal deflection circuit for a CRT according to an embodiment of the present invention.
FIG. 2 is a waveform chart of each part in the horizontal deflection circuit for CRT in FIG. 1;
FIG. 3 is an explanatory diagram showing a state of a screen scanned by the CRT horizontal deflection circuit of FIG. 1;
FIG. 4 is another explanatory diagram showing a state of a screen scanned by the horizontal deflection circuit for CRT in FIG. 1;
FIG. 5 is a circuit diagram showing an example of a conventional horizontal deflection circuit for CRT.
6 is a waveform chart of each part in the horizontal deflection circuit for CRT in FIG. 5;
FIG. 7 is an explanatory diagram showing a state of a screen scanned by the CRT horizontal deflection circuit of FIG. 5;
8 is another explanatory diagram showing a state of a screen scanned by the horizontal deflection circuit for CRT in FIG. 5;
[Explanation of symbols]
100 Horizontal deflection circuit for CRT 1 Horizontal position control circuit 2 Horizontal oscillation circuit 3 Horizontal drive circuit 4 Horizontal output circuit 5 Flyback transformer 10 Microcomputer 11 DC current superposition circuit 41 Horizontal deflection coil 42 Linearity coil CH Horizontal position control signal CI DC current Control signal HD Horizontal synchronization signal HD 'Delayed horizontal synchronization signal i Horizontal deflection current id DC current Vp Horizontal deflection pulse voltage

Claims (2)

A horizontal deflection circuit for a CRT which scans an electron beam in a horizontal direction by flowing a sawtooth-shaped horizontal deflection current to a horizontal deflection coil of the CRT,
Image display area moving means for moving the image display area to the left by delaying the timing of the horizontal deflection current; and moving the horizontal deflection area to the right to offset the movement of the image display area by moving the horizontal scanning range to the right. A horizontal deflection circuit for a CRT, comprising: DC current superimposing means for superimposing a DC current on a current. 2. The horizontal deflection circuit for a CRT according to claim 1, further comprising control means for controlling the movement of the image display area and the DC current based on a horizontal scanning frequency.

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