JPS638674B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiver that projects an image on a cathode ray tube by internally generating vertical and horizontal blanking signals and combining them with an image signal. It is an object of the present invention to provide a device that can maintain a constant screen outline and display an image that is easy to see when using an underscan scanning method for an effective visible screen.

Conventionally, many television receivers use an image scanning method that overscans the effective visible screen area of a cathode ray tube. However, recently, there have been many television receivers using cathode ray tubes using an underscan scanning method for applications such as displaying text or graphic information, or projection television.

FIG. 1 shows how an image is projected on the visible screen area of a conventional overscan scanning type cathode ray tube. Here, the image being sent is of the area indicated by 1, but it is blocked by the effective visible screen area 2 of the cathode ray tube, so the image is from area 3.
is actually an invisible part. In this case, the vertical and horizontal deflections are each scanned over the effective visible screen area 2 of the cathode ray tube (overscan scanning method).

Figure 2 shows the state of image projection on the cathode ray tube in the case of the underscan scanning method. are all located inside the effective visible screen area 2 of the cathode ray tube, so in this case all signal information content can be displayed. However, in general, waveform distortion is likely to occur near the scan start point and scan end point of vertical and horizontal deflection currents, and the image on the screen is also likely to be distorted.Furthermore, the retrace period between various video signals is not necessarily different. Since it is not constant, it is desirable to blank the upper and lower, right and left peripheral areas 3 of the projected image so that they are not visible, and to display only the area 4. In this way,
Compared to the one shown in FIG. 1, the amount of information transmitted during video projection, that is, the actually visible image area 4 can be made almost the same or more.

In order to blank the peripheral area 3 in the case of the underscan scanning method as described above, it is necessary to control the time widths of the vertical and horizontal blanking pulses. Conventionally, vertical and horizontal blanking pulses used for such purposes are created from vertical and horizontal deflection output pulses, respectively. However, as shown in FIGS. 3A and 3B, the vertical deflection output voltage A is modulated by the voltage from the horizontal deflection circuit to correct the vertical pincushion distortion, and the horizontal deflection output voltage B is modulated by the voltage from the horizontal deflection circuit to correct the vertical pincushion distortion. It is modulated by the voltage from the vertical deflection circuit for distortion correction, and the vertical and horizontal deflection output pulses are also susceptible to fluctuations due to high voltage fluctuations, etc., and are also susceptible to signal content. For these reasons, the position and time width of the blanking pulse created from these inevitably fluctuate.
Therefore, there is an inconvenience that fluctuations and flickers occur at the upper, lower, left and right edges of the image area 4 within the effective visible screen area 2 of the cathode ray tube.

Therefore, the present invention solves these conventional drawbacks, stabilizes the edge of the image when projecting an image using the underscan scanning method, makes the screen outline constant, and makes it possible to project an image that is easy to see. Another object of the present invention is to provide a television receiver in which a blanking period can be arbitrarily selected.

Therefore, in the present invention, the oscillation output of the vertical and horizontal oscillation circuits, which is not affected by pincushion distortion correction or high voltage fluctuations, is used as a blanking pulse for blanking the peripheral area of the projected image using the underscan scanning method. It is unique in that it uses voltage.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment thereof.

FIG. 4 shows an example of the overall configuration, FIG. 5 shows a specific circuit example of the horizontal blanking pulse generating part, and FIG. 6 shows waveform diagrams of each part. First, 5 is a synchronization separation circuit which separates horizontal and vertical synchronization signals from the input composite video signal A and supplies them to a horizontal oscillation circuit 6 and a vertical oscillation circuit 7, respectively. The horizontal oscillation circuit 6 and the vertical oscillation circuit 7 generate oscillation pulses of a predetermined phase in synchronization with the horizontal synchronization signal and the vertical synchronization signal, and supply them to the horizontal deflection circuit 8 and the vertical deflection circuit 9. On the other hand, in this device, this horizontal oscillation circuit 6
The horizontal oscillation pulse and the vertical oscillation pulse from the vertical oscillation circuit 7 are respectively added to waveform shaping circuits 10 and 11, where the pulse phase and pulse width are controlled to predetermined values to create horizontal and vertical blanking pulses. Then, by adding the blanking terminal of the video output circuit 13 after combining in the combining circuit 12, blanking of the peripheral area 3 of the projected image is performed.

To explain the creation part of the horizontal blanking pulse with reference to FIG. 5, the horizontal oscillation circuit 6 has a general circuit configuration and outputs a comparison between the horizontal synchronizing signal separated from the composite video signal A and the horizontal flyback pulse. A horizontal AFC signal is applied to the terminal 14, and a stable horizontal oscillation pulse with a constant phase synchronized with the horizontal synchronizing signal as shown in B is outputted from the collector of the transistor 15 and supplied to the horizontal deflection circuit 8. On the other hand, this horizontal oscillation pulse B is taken out and applied to the waveform shaping circuit 10, first integrated as shown in C by a resistor 16 and a capacitor 17, and then by a transistor 1.
At steps 8 and 19, the signal is slid to the level indicated by the broken line to obtain a delayed pulse delayed by a predetermined time as shown at D. Furthermore, this is differentiated by a capacitor 20 and a resistor 21 as E, and is sliced at the level indicated by the broken line by transistors 22 and 23 to obtain a horizontal blanking pulse F having a predetermined phase and a predetermined pulse width.

In this way, the horizontal blanking pulse F whose waveform is shaped based on the horizontal oscillation pulse B always has a constant and stable phase with respect to the video signal A, and its pulse width is also constant and stable. If this is used to blank the image projected on the cathode ray tube, the left and right edges can be straightened without wavering, and the flickering caused by left and right fluctuations can be avoided. can do.

Note that the same applies to the creation part of the vertical blanking pulse.

Furthermore, in the circuit shown in FIG. 5, the blanking position and blanking width can be changed by changing the time constants of the integrating circuit made up of the resistor 16 and capacitor 17 and the differentiating circuit made up of the capacitor 20 and resistor 21. For example, as shown in FIG. 7, a horizontally long screen can be created by significantly blanking the top and bottom.

In the above embodiment, an integrating circuit, a differentiating circuit, and a slicing circuit are used as a means for waveform-shaping the horizontal and vertical oscillation output pulses to create horizontal and vertical blanking pulses. It goes without saying that a monostable multivibrator or a digital circuit such as a counter may also be used.

As described above, according to the present invention, when projecting a television image on a cathode ray tube using the underscan scanning method, the horizontal and vertical oscillation output pulses synchronized with the horizontal and vertical synchronizing signals are waveform-shaped and created. Since the peripheral area of the projected image is blanked using blanking pulses, the peripheral edges of the image are not affected by pincushion distortion correction or high voltage fluctuations, and the edges are stabilized and the screen contour is can be displayed in a constant and easy-to-see manner.

[Brief explanation of the drawing]

1 and 2 are front views showing the state of image projection, FIG. 3 is a waveform diagram for explaining the operation of a conventional television receiver, and FIG. 4 is a television according to an embodiment of the present invention. Figure 5 is a block diagram of the main parts of the television receiver, Figure 5 is a specific circuit diagram of a part of it, Figure 6 is a waveform diagram to explain its operation, Figure 7 is a front view showing the projection state of another image. It is a diagram. 2... Active visible screen area, 3... Peripheral area, 4... Image area, 5... Synchronization separation circuit, 6... Horizontal oscillation circuit,
7... Vertical oscillation circuit, 10, 11... Waveform shaping circuit,
12...Composition circuit, 13...Video output circuit.

Claims (1)

[Claims] 1 A television image is projected within the effective visible screen area using an underscan scanning method, and a blanking pulse is created by waveform-shaping the oscillation output pulse of an oscillation circuit that oscillates in synchronization with the synchronization signal of the television signal. A television receiver characterized in that the peripheral area of the displayed television image is blanked by the blanking pulse.