JPH10271420A - Heater bias circuit and picture size switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching circuit suitable for miniaturization by simplifying configuration and reducing the number of parts by performing switching while varying a blanking period superimposed on a heater bias. SOLUTION: As circuits for setting the blanking period, circuits 1 and 2 are respective composed of two monostably multivibrators, capacitors and variable resistors connected to the monostable multivibrators. Horizontal synchronizing signals inputted to the circuits 1 and 2 are oscillated as blanking signals and outputted as BLK1 and BLK2 by controlling two kinds of blanking periods and phases. The respective outputs are inputted to an analog multiplexer 4, selected by a switch 3 and outputted to an adder circuit 5. At the adder circuit 5, these outputs are superimposed with a heater bias voltage VHB and outputted to the heater of cathode-ray tube. The switching of picture size is facilitated and a correction circuit such as horizontal linearity correction or high voltage stabilizing circuit is unnecessitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cathode ray tube heater bias circuit and a screen size switching circuit.

[0002]

2. Description of the Related Art Conventionally, the aspect ratio of a television screen of the NTSC system was 4: 3 in the horizontal: vertical direction. With the development of high-definition television, an aspect ratio of 16: 9 was adopted to provide a sense of realism and power, but it is necessary to be able to view conventional 4: 3 and 16: 9 images with compatibility. occured.

When a 4: 3 signal is supplied to a 16: 9 screen, various screens can be considered, but the following three are mainly considered. 1. Match the length in the vertical direction and blacken both sides in the horizontal direction. (FIG. 1) Cut both sides (top and bottom) in the vertical direction by matching the horizontal direction. (FIG. 2) The vertical direction is matched and the horizontal direction is extended to match.
(Fig. 3)

There is no problem when a signal formed for 16: 9 is supplied to a 16: 9 screen.
In the case where the image photographed in step (1) is supplied as a 4: 3 signal, it is necessary to check the 4: 3 screen.

[0005]

In order to switch the screen size between 16: 9 and 4: 3, the power supply voltage input to the horizontal deflection circuit is switched to change the current flowing in the horizontal deflection circuit. When the current flowing through the horizontal deflection coil is controlled, a high-voltage stabilization circuit by correcting horizontal linearity distortion and switching the power supply voltage becomes complicated, and the component mounting area increases with the increase in circuit components, making it difficult to reduce the size.

For example, in a horizontal deflection circuit, 16: 9/4:
In the case of switching 3, the capacity of the S-shape correction capacitor needs to be reduced at 16: 9 and the capacity of the S-shape correction capacitor needs to be increased at 4: 3 to correct horizontal linearity distortion. The horizontal deflection size is switched by switching the voltage applied to the horizontal deflection coil. Therefore, the power supply voltage applied to the flyback transformer is also 16: 9.
And 4: 3, the voltage applied to the brightness adjustment circuit changes.

[0007] In order to perform 16: 9/4: 3 switching, a correction circuit for solving the above problem is required.
No. 34037, Japanese Patent Application No. 8-20449, Japanese Patent Application No. 8-5
No. 2397 and other correction circuits have been developed and filed. However, the number of circuit components increases due to the correction circuit, and the component mounting area increases. This is a serious problem in a device that is desired to be small and lightweight, such as a viewfinder of a video camera.

[0008]

The blanking period is changed without changing the horizontal deflection size.
Switch in 9/4: 3 mode. That is, when 4: 3 video is output to a video device having a screen size of 16: 9, switching is performed by switching a blanking period to be superimposed on a video signal, and switching by a deflection circuit is not performed.

In the heater bias circuit of the cathode ray tube, the blanking period superimposed on the heater bias is changed and switched.

The blanking period is set to a screen aspect ratio of 1.
When switching in the 6: 9/4: 3 mode, a blanking period superimposed on the heater bias is switched in synchronization with the blanking period.

[0011]

FIG. 4 shows an embodiment of a circuit for changing the blanking period and switching the blanking period. The circuit 1 and the circuit 2 are circuits for setting a blanking period, and are each composed of two monomultivibrators, a capacitor connected to the monomultivibrator, and a variable resistor. The horizontal synchronization signal input to the circuits 1 and 2 is oscillated as a blanking signal, and two types of blanking periods and phases are adjusted.
Output as Each output is input to the analog multiplexer 4, selected by the switch (SW 1) 3, and output to the adding circuit 5. In the adding circuit 5, the signal is superimposed on the heater bias voltage VHB and output to the heater of the cathode ray tube.

The horizontal synchronizing signal HD is supplied to the mono multivibrator M / M1 and the mono multivibrator M / M2 of the circuit 1.
To enter. A capacitor C1 and a variable resistor RV are used as constants for determining the output pulse of the mono-multivibrator M / M1.
1 is connected. Mono-multi vibrator M / M1
Is connected to a mono-multivibrator M / M2. The mono-multivibrator M / M2 is also connected to a capacitor C2 and a variable resistor RV2 as constants for determining an output pulse. The input horizontal synchronizing signal HD is output as a blanking signal BLK1 from the circuit 1 via mono-multivibrators M / M1 and M / M2. Similarly, from the circuit 2, a mono-multivibrator M / M3 in which a capacitor C3 and a variable resistor RV3 are connected, and a mono-multivibrator M in which a capacitor C4 and a variable resistor RV4 are connected.
A blanking signal BLK2 is output via / M4.
In the present embodiment, BLK1 is 16: 9 and BLK2 is 4: 3.
Is a blanking signal corresponding to the screen size. If any one of the circuit 1 and the circuit 2 is used, it is merely an adjustment of the blanking period, and if the number is further increased, the number of selections will be increased, so that the description is omitted.

In the present invention, the blanking signal selected by the analog multiplexer 4 is superimposed on the heater bias voltage VHB by the adding circuit 5, and the heater bias voltage VHB is blanked in synchronization with the blanking period of the video signal. ing.

FIG. 5 shows a horizontal synchronizing signal HD of the circuit of the present invention.
4 is a timing chart of BLK1, BLK2, video signal 1, and video signal 2.

Circuit 1 and circuit 2 for the horizontal synchronizing signal HD
The blanking pulses BLK1 and BLK2 generated in the above are as shown in the figure, and are cut off by controlling the cathode to perform blanking. Corresponding 16: 9 and 4:
The video signal No. 3 is superimposed on the video signal pedestal in synchronization with the horizontal synchronizing signal HD as shown in the figure, and is applied to the first grid. The black level changes due to the fluctuation of the pedestal voltage of the video signal if only the blanking of the video signal is used. it can.

[0016]

According to the present invention, the blanking can be reliably applied by applying the blanking to the heater bias, and the blanking period can be changed, so that the adjustment becomes easy.

Since the blanking period of the heater bias can be selected in accordance with the blanking period of the video signal,
The screen size can be easily switched, and a correction circuit such as horizontal linearity distortion correction and a high-voltage stabilization circuit is not required.

Since the structure of the switching circuit is simple, the number of parts is small, and it is suitable for miniaturization, it is most suitable for electronic viewfinders that require small size and light weight.

[Brief description of the drawings]

FIG. 1 Screen

FIG. 2 Screen

[FIG. 3] Screen

FIG. 4 is a circuit diagram of the present invention.

FIG. 5 is a timing chart of the circuit of the present invention.

[Explanation of symbols]

 Reference Signs List 1 circuit 2 circuit 3 switch SW1 4 analog multiplexer 5 addition circuit M / M1 to M / M4 mono multivibrator C1 to C4 capacitor RV1 to RV4 variable resistor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 3/27 H04N 3/27

Claims (3)

[Claims] 1. A heater bias circuit for a cathode ray tube, wherein a blanking period superimposed on the heater bias is varied. 2. A screen size switching circuit wherein a blanking period is switched in a screen aspect ratio of 16: 9/4: 3 mode. 3. A screen size characterized by switching a blanking period superimposed on a heater bias in synchronization with the blanking period in a 16: 9/4: 3 screen aspect ratio mode. Switching circuit.