JPS5931913B2 - television receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiver having a function of enlarging and displaying a part of the image receiving screen.In addition to controlling a deflection circuit for enlarging operation and controlling a video signal amplitude, By controlling the bias of the cathode ray tube and the video signal under a certain relationship, changes in the brightness level of the screen during enlargement operation are suppressed, thereby providing a television receiver that has the same performance as during normal operation. It is something to do.

Recently, there has been an attempt to view the image receiving screen of a television receiver by enlarging it from the normal screen A shown in FIG. 1 to an enlarged screen as shown at the top of the figure.

As a television receiver in which such an attempt was made,
Only the center part of the screen during normal operation has a screen area of 1.5 to 2
, there is a method that enlarges the image by approximately 0 times. The configuration of the main parts of this television receiver will be explained using FIG. 2.
In the figure, 1 is an input terminal for an input video signal, and 3 is a video signal processing circuit that separates and amplifies the input video signal into red, green, and blue signals.
Drive 0.

The bias voltage for the CRT 10 is supplied from a bias power source 4 via a first grid bias adjustment circuit 5 and a second grid bias adjustment circuit 6, respectively. T is a sync separation circuit, 8 is a horizontal deflection circuit driven by a horizontal sync pulse from the early sync separation circuit 7, and 9 is a vertical deflection circuit driven by a vertical sync pulse from the early sync separation circuit T.
In the above configuration, if you want to enlarge the screen,
The horizontal deflection circuit 8 is controlled by the control signal from the screen enlargement control section 2.
The screen size is expanded by changing the scanning speed (deflection current waveform) of the vertical deflection circuit 9 and the scanning speed (deflection current waveform) of the vertical deflection circuit 9.

When the screen is enlarged in this way, the time the image is displayed on the CRTIO becomes shorter than during normal operation (for example, considering the horizontal direction, the scanning line on the CRT during normal operation The display period for one piece is approximately 50 pages.
S, but when magnified by 1.3 times, the display period is about 50 pS
/1.3■38μS, and the table period becomes shorter. )
Therefore, the screen becomes darker by that amount. In order to compensate for this phenomenon in which the screen becomes dark, conventionally the video signal amplitude is increased using a control signal for expanding the screen size. However, with this method, almost sufficient performance can be obtained when the screen enlargement ratio is small, but when the screen size enlargement ratio increases, it is necessary to sufficiently compensate for the screen brightness due to enlargement. It has the disadvantage that it cannot be used, and its performance is insufficient.

The present invention eliminates the above-mentioned drawbacks of the conventional art.One embodiment of the present invention will be described in detail below with reference to FIGS. 3 and 4.

Here, circuits having the same functions as those in FIG. 2 are given the same numbers, and descriptions of parts with the same functions will be omitted. First, to explain the operation of the deflection unit during the screen size enlargement operation, in order to control the position of the enlarged portion of the image content, the phase of the horizontal synchronization pulse from the synchronization separation circuit 7 is controlled by the phase control circuit 12. The phase control circuit 13 controls the phase of the vertical synchronization pulse from the synchronization separation circuit 7 , and then supplies it to the vertical deflection circuit 9 .

As the screen size increases, the brightness of the screen becomes darker, and in particular, as the magnification rate is increased to enhance the effect of magnification, the brightness tends to decrease.

In order to compensate for this, in the conventional example, only the video amplitude is increased, but due to the relationship with the bias condition of the CRTIO, when the video amplitude exceeds a certain value, a blooming phenomenon occurs or a grid current flows. There are limits because of the For this reason, in this embodiment, the operating conditions of the CRTlO are changed between normal operation and enlarged operation to compensate for the decrease in brightness.

This will be explained using FIG. 4. Figure 4 shows CRT
It shows the relationship between the bias voltage of lO and the beam current of CRTlO, and the reference point of the 4-circle bias during normal operation (
Black level] is set as V1, and the video signal S is set using this as a reference.
3 move. On the other hand, during the enlargement operation, the reference point (black level) is set to V, and the drive is performed using the video signal S2 with reference to this point.In each operation, the beam current of the CRTlO during the white signal is I,,l2. The brightness of CRTlO is C
Since it is proportional to the beam current of the RTIO, even if the magnification increases as shown by the values of the beam currents 11 and 12, normal operation can be maintained by optimally setting the bias voltage of the CRTIO and the video signal amplitude. It is possible to obtain a brightness level equivalent to the screen brightness at the time of use. In Figure 4, the bias reference point is set to 2 during normal operation, and the video signal is
It is obvious that when driven with an amplitude equivalent to 1, the beam current of the CRTlO becomes smaller than 1 due to the difference in nonlinearity (difference in gamma characteristics) between the bias voltage and beam current of the CRTlO. be.

It is also commonly experienced that increasing the amplitude of the video signal until it becomes equal to 11 causes an increase in the power of the video amplification circuit and a deterioration of the frequency characteristics, which is inappropriate for operation. be. The aforementioned CRTlO
The method of switching the bias point between the normal operation and the enlarged operation is as shown in FIG. This output is selected by the switching circuit 10 using the control signal from the control circuit 2 to
Supply to the first grid of O.

On the other hand, in the second grid bias adjustment circuit of the CRTlO, a circuit 6-1 for normal operation and a circuit 6-1 for enlarged operation are used.
2 is selected by the switching circuit 11 using the control signal from the control circuit 2, and is supplied to the second grid of the CRTIO. By adjusting these adjustment circuits, the bias point of the CRTlO during normal operation and during enlarged operation can be set to the optimum value. As explained above, according to the present invention, when attempting to enlarge the screen size, by changing the scanning speed of the deflection section and simultaneously changing the operating conditions of the CRT and the video signal amplitude, it is possible to increase the screen size compared to the normal operation. As a result, it is possible to display a receiving screen of good image quality at the same brightness level and without the occurrence of a blooming phenomenon or the flow of grid current.

[Brief explanation of the drawing]

Fig. 1A shows an example of a normal screen and an enlarged screen; Fig. 2 is a block diagram of a conventional television receiver having a screen enlargement function; and Fig. 3 shows a screen enlargement function in an embodiment of the present invention. A configuration diagram of a television receiver having a CRT.
FIG. 3 is a diagram showing bias voltage, beam current of a CRT, and operating conditions thereof. 2... Control circuit, 4... Bias power supply, 5-1, 5-2... First grid bias adjustment circuit, 6-1, 6-2... ...Second grid bias adjustment circuit, 7...Synchronization separation circuit, 8, 9
... Deflection circuit, 10, 11 ... Switching circuit, 12, 13 ... Phase control circuit.

Claims (1)

[Claims] 1 means for switching the screen size of a television reception screen, means for changing the deflection speed of the deflection circuit by the operation of the switching means, means for changing the video signal level for driving the display element, and means for changing the video signal level for driving the display element. A television receiver comprising means for suppressing fluctuations in brightness level due to switching operating conditions by changing bias conditions for driving.