JPS6086473A - Focus correction circuit - Google Patents

Abstract

PURPOSE:To change automatically and suitably a focus voltage at the change of luminance by detecting a cathode current corresponding to a luminance adjusting grid voltage by an impedance element, and controlling the focus voltage by a cathode reference voltage through an amplifier. CONSTITUTION:If the luminance of a CRT1 is increased by increasing the grid voltage Ed, the cathode current is increased and the voltage drop is generated by the impedance element 5 connected to a cathode 3. The voltage drop is applied to one terminal of an amplifier 6 of which other terminal receives driving voltage, so that the output of the amplifier 6 is dropped. The potential between the impedance elements 7, 9 and a focus electrode 4 is changed on the basis of the cathode voltage to be changed in accordance with the luminance. Thus, the focus voltage is changed automatically and suitably at the change of the luminance and the change of the focus voltage can be easily observed without focus adjusting operation or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a focus correction circuit for a CRT.

(゛Sensitive technology and its problems) In devices using CRTs such as oscilloscopes, the purpose is to easily observe 2 display signals each time they change.

Adjust brightness. The brightness changes depending on the control grid (hereinafter referred to as grid) voltage of the CRT. On the other hand, the relationship between the grid drive voltage and the optimal focus voltage is not constant, as shown in FIG. 1, for example.

There is an inconvenience in that the focus voltage must be adjusted to the optimum focus voltage when adjusting the brightness. In the figure, the horizontal axis Ed represents the optical drive voltage, and the vertical axis Eb represents the optimum focus voltage.

(Objective) In order to improve these drawbacks, the present invention is designed to automatically change the focus force when the brightness changes.

(Embodiments) A comprehensive embodiment of the present invention will be described below in detail with reference to FIGS. 2 and 3, and a specific embodiment will be explained in detail with reference to FIGS. 1, 2, and 4.

Figure 2 shows grid drive voltage Ed and cathode current Ik.
This is an example. As is clear from the figure, the grid drive voltage Ed and cathode current Ik are:

There is a direct proportional relationship.

In FIG. 3, reference numeral 1 is a model diagram of a CRT, in which only a focus electrode 4, a cathode electrode 3, and a control grid electrode 17 are depicted. 2 is a negative power supply for the cathode. 5 is a first impedance element, and 6 is an amplifier.

7 is a second impedance element, 8 is ground, and 9 is a third impedance element.

Now, if the control grid electrode 17 is increased in the positive direction, the brightness becomes brighter, but at that time the grid drive voltage Ed
If the relationship between the optimum focus voltage Eb of the focus electrode 4 and the optimum focus voltage Eb of the focus electrode 4 is as shown in Fig. 1, when the luminance increases, the focus voltage Eb based on the cathode potential decreases as shown in Fig. 1, and becomes Eb. Therefore, the focus on the tube surface will not change.

Now, if the grid drive voltage Ed is increased to raise the brightness, the cathode current Ik will increase as shown in FIG. 2, a voltage drop will occur in the impedance element 5, and the input voltage of the amplifier 6 will increase. Since the output of the amplifier 6 decreases, the potential of the focus electrode 4 decreases depending on the ratio of the impedance elements 7 and 9.

The above process is accomplished. In addition.

FIG. 3 shows the basic configuration of the present invention, and without departing from this configuration, an optimal embodiment can be easily constructed for a particular CRT.

FIG. 4 shows one of the more specific embodiments of the present invention.

In FIG. 4, numerals 1 to 9 indicate the same parts as in FIG. 3. 10
C is a resistance and corresponds to the impedance element 5 in FIG. 1
1 is a transistor forming an amplifier 6;

12.13 is a capacitor to speed up the response speed, 14
゜15.18 is a resistor, 16 is a variable resistor for focus initial setting, and resistors 1.5, 18. Focus bias when variable resistor 16 and transistor 11 are off? Determine the pressure.

Approximately deciphering the characteristic example in Figure 1, Ed=50V
The focus voltage is constant up to 50V, and decreases linearly from 50V. On the other hand, in FIG. 2, the cathode current Ik is 100 μA when the grid drive voltage Ed=50V. Therefore, in FIG. 4, if the value of the resistor 10 is selected so that the value of 100 μA of the resistor 10 becomes the 'base-emitter saturation voltage VBE of the transistor 1j, this resistance value x 10
0μA is the base-emitter saturation voltage V of transistor 11
The transistor 11 is off until the value of BE is reached, and the focus voltage Eb does not change even if the brightness is changed. Ed=
When the voltage exceeds 50V, the cathode current Ik further increases, so the transistor 11 whose voltage drop due to the resistor 10 is not large becomes active, and the focus voltage Eb begins to drop. How is this descent?

If the resistor network is appropriately selected, characteristics approximately as shown in FIG. 1 can be achieved. Normally, if the deviation from this characteristic curve is kept within the number 7, it can be judged that the optimum focus is almost maintained when visually observed, so this circuit network is determined by
It's not that difficult.

In FIG. 4, 15 is a resistor for determining the focus bias voltage when the transistor 11 is off, together with resistors 18 and 16, and 16 is a variable resistor for focus initial setting. Note that capacitors 13 and 12 are provided to speed up the response speed.

(Effects) As explained above, according to the present invention, the focus is automatically maintained optimally when the yH degree changes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the relationship between grid drive voltage and optimal focus voltage, FIG. 2 is a diagram showing an example of the relationship between grid drive voltage and cathode current, and FIG. 3 is a comprehensive block diagram of the present invention. FIG. 4 is a circuit diagram of a specific embodiment of the present invention. ]: CRT, l focus electrode, 6: amplifier. 5.7, 9: Impedance element, 10, 14, 15
, 18: Resistance. 1 transistor, 16: variable resistor.

Claims (1)

[Claims] A first impedance element is connected between the cathode power source and the cathode electrode of the CRT, and the human power of one of the amplifying means is connected to this impedance element. The other power supply of this amplifying means is connected to the power source for the cathode, and the output of this amplifying means is connected to a second power source and a focus electrode connected to an impedance element via a second impedance element. Featured focus correction circuit.