JPS62188568A - Focus adjusting circuit - Google Patents

Abstract

PURPOSE:To adjust suitably a focus by connecting a variable current source in series to a potential dividing circuit to which a high voltage is impressed and operating this variable current source correspondingly to the level of a compensation voltage signal. CONSTITUTION:The control input end of a variable current source Iv is made a silence input state or a prescribed direct current bias state and the impedance of resistances R10, R11 and the variable current source Iv is suitably set and the potential dividing output voltage is set to the suitable voltage for a static focus adjustment. Then, the level of the direct current bias component supplied to the variable current source Iv from a level adjustment circuit 2 is adjusted to perform the static focus adjustment. The compensation voltage signals such as the signals proportional to a parabola shape voltage signal, a video correction signal and the fluctuation in a plate voltage of a CRT are supplied in the suitable level, thereby, focus control voltage corresponding to both of a direct current signal component and an alternating signal component is obtained, and a dynamic focus adjustment is performed. Thereby, the proper focus adjustment can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION 1.1 The present invention provides a cathode ray tube (hereinafter referred to as CRT) that displays a two-dimensional screen.
The present invention relates to a focus adjustment circuit (referred to as ``1'').

Focus control means for appropriately electrostatically or electromagnetically focusing the electron beam flow by controlling the voltage of a focus plate provided in the electron gun portion of the CRT or the current of a focusing coil provided in the neck portion of the CRT. The electron beam is focused on the fluorescent surface of the CRT face plate. A conventional example of a focus adjustment circuit that obtains a focus control voltage for operating such a focus control means will be explained with reference to FIG.

In the conventional circuit shown in FIG. 4, a resistor R11, a variable resistor VR+, and a resistor R2 are connected in series to form a resistive voltage divider circuit. A voltage source (not shown) that supplies a high voltage of about 15 to 30 kilovolts obtained by rectifying and smoothing the output of a flyback transformer, for example, is connected to both ends of this resistive voltage divider circuit. A DC divided voltage is obtained at the sliding end of the variable resistor VR+, and this is applied as a focus control voltage to the focus control means 1 via the current limiting resistor R3. Then, by appropriately setting the value of the variable resistor VR1, the focal length of the so-called electrostatic lens is adjusted, and the area of the electron beam spot on the fluorescent surface is set to a required size, thereby performing static focus adjustment. It will be done. By the way, since the face plate of a CRT is formed flat, the distance from the change start position of the electron beam to the fluorescent surface is different between the central part and the peripheral part of the screen. Therefore, the area of the electron beam spot tends to change as it moves from the center to the periphery. Furthermore, when the brightness of the screen becomes high, the area of the beam spot changes due to an increase in the area of the beam spot due to an increase in the flow of electron beams or a change in the beam focusing position due to a change in plate voltage. Such a variation in the area of the beam spot becomes more noticeable as the CRT has a larger screen. In order to suppress this, a compensation voltage signal is superimposed on the focus series control voltage via the signal relay means 3 and the DC element capacitor C1. Furthermore, dynamic focus adjustment is performed. This compensation voltage signal includes a parabolic voltage signal that compensates for the horizontal and vertical modifiers of the CRT, and an anode level signal that is proportional to the variation of the CRT's anode voltage.
An RT drive correction signal or a video correction signal proportional to the brightness level of the video signal is used.

In this way, in the conventional focus adjustment circuit, static focus adjustment is performed by operating the variable resistor VR+ to set the DC voltage, and an AC voltage valve is superimposed on this DC voltage via the DC blocking capacitor C1. It is configured to perform dynamic focus adjustment. However, in such a configuration, it is not necessarily easy to automate static and dynamic focus adjustment. Furthermore, a signal including both an AC signal component and a DC signal component, such as the movie correction signal mentioned above, is
The DC signal component is removed by the DC blocking capacitor C1. Therefore, depending on the type of image, for example, when an image is formed in a low-brightness or high-brightness area of the screen, it is difficult to properly adjust the focus. Furthermore, it is also conceivable that the cutoff frequency of the time constant including the DC blocking capacitor C1 influences the AC signal component.

+111(7)11 Therefore, an object of the present invention is to provide a focus adjustment circuit that can automatically change the DC voltage component and the AC voltage component of the focus control voltage separately.

In order to achieve the above object, in the focus adjustment circuit of the present invention, a variable current source is connected in series with a voltage divider circuit to which a high voltage is applied, and this variable current source is adjusted in accordance with the level of a compensation voltage signal. It is configured to operate.

*k　J Embodiments of the present invention will be described below with reference to FIG.

In the block circuit diagram shown in FIG. 1, voltage dividing resistors R10 and R++ and variable current source lv are connected in series to form a voltage dividing circuit.

A high DC voltage is applied to both ends of this voltage divider circuit, and a resistor R
The connection point between +o and Ru becomes a partial voltage output. This divided voltage output is applied as a focus control voltage to the focus control means 1 of the CRT via a current limiting resistor R12. The aforementioned compensation voltage signal is applied to the control end of the variable current source 1v via the level adjustment circuit 2. In response to this compensation voltage signal, the variable current source IV changes the current level of the voltage divider circuit, producing a voltage signal component in the focus control voltage m that is proportional to the compensation voltage signal. Here, the compensation voltage signal is a combination of a plurality of signals such as a parabolic voltage signal and an image correction signal.

By the way, the above-mentioned parabolic voltage signal is usually obtained from a boost capacitor of a linearity control circuit of a horizontal change circuit. In such a case, the level of the parabolic voltage signal 9 may be higher than the level of the video correction signal, and it may not be easy to combine the signals.

In such a case, as shown in the circuit example of FIG. 2, a parabolic voltage is separately applied to the divided output voltage of the resistor voltage divider circuit at the required level via the signal relay means 3 and the DC capacitor C2. A focus control voltage can be obtained as a configuration superimposed on the .

The above-mentioned parabolic voltage is only an alternating current signal component and its frequency is lower than that of the video signal, so it is not affected by the cutoff frequency of the capacitor C2 or the like. It is obvious that a signal proportional to the plate voltage described above may be superimposed on the parabolic voltage signal.

An example of the configuration of the variable current source 1v will be explained with reference to the circuit shown in FIG. A current bypass resistor R13 is connected between the other end of the aforementioned resistor Ru and ground. Further, the collector of the output transistor Q1 is connected to the other end of the resistor Ru, and its emitter is grounded via the resistor R14.

Resistors R13 and RI4 reduce the voltage applied to transistor Q+.

This transistor Q1 represents a variable current circuit,
A DC bias current and a current proportional to the complementary ffl voltage signal are supplied from the level adjustment circuit 2 to the base corresponding to the control input terminal of the circuit. Here, resistors R13 and R1
4 is used because the withstand voltage of currently available transistors is about 3 kilovolts, so it is necessary to prevent voltages higher than that from being applied to the variable current circuit made up of transistors, etc., and to prevent the voltage of the variable power supply from being applied. This is to reduce burden current.

Next, the operation of the circuit will be explained. First, the control input terminal of the variable current source Iv is set to a no-signal input state or a predetermined DC bias state, and the resistors Rho, Rn and the variable current source iv
The impedance is set appropriately and the divided output voltage is set to a voltage suitable for static focus adjustment. Next, static focus adjustment is performed by adjusting the level of the DC bias component supplied from the level adjustment circuit 2 to the variable current source 1v.

Then, the above-mentioned parabolic voltage signal is applied to the control input terminal.
By supplying a video correction signal and a compensation voltage signal, such as a signal proportional to the CRT plate voltage variation, at appropriate levels, a focus control voltage corresponding to both the DC signal component and the AC signal component is set to 1q, and dynamic focus is achieved. Adjustments are made. Since the level of each signal supplied to this control input terminal may be at a sufficiently low level, this circuit has the advantage that signal processing such as signal synthesis is easier to perform than conventional circuits. Further, it is preferable as an automatic adjustment circuit that automatically adjusts each of the DC signal component and AC signal component of the focus control voltage.

As explained above, in the focus adjustment circuit of the present invention, a variable current source is provided in the current path of the voltage dividing circuit, and the current value of the current path is changed in accordance with the compensation voltage signal. This is preferable because focus control voltages corresponding to the levels of the DC and AC components of the compensation voltage signal can be obtained, and appropriate focus adjustment can be performed at all times.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit showing an example of the configuration of a variable current source 1v. Figure 4 is
FIG. 2 is a block circuit diagram showing a conventional example. Explanation of symbols of main parts R+, R2, Rho, Rn -... Voltage dividing resistor C+, Cz... DC blocking capacitor 1...
...Variable' current source 1 ... Focus control means 2 ... Level adjustment circuit 3 ... Signal relay means

Claims (1)

[Claims] A focus adjustment circuit that supplies a focus control voltage to a focus control means of a screen display cathode ray tube according to a compensation signal, the voltage dividing circuit having a divided voltage output as the focus control voltage, and a current value according to the compensation signal. 1. A focus adjustment circuit comprising: a direct circuit formed by connecting variable current sources in series with each other, and a constant voltage source supplying a constant voltage to both ends of the series circuit.