JPS6121892Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a deflection circuit for an electron beam of an image pickup tube that employs an electrostatic deflection method.

In the image pickup tube, as shown in FIG. 1, a transparent electrode 2 such as a Nesa film is deposited on the inner surface of a face plate (glass) 1, and a photoconductor 3 is further deposited on the top surface of the transparent electrode 2 to form a so-called target 4. By scanning an electron beam within a predetermined range 5 (indicated by a dotted line in FIG. 1) of the photoconductor 3 while applying a DC voltage of, for example, 20 V to 80 V to the NESA film 2, the NESA film 2 is I'm trying to get more signals. In this case, the charge on the target 4 is sequentially discharged by scanning the electron beam in accordance with the amount of light received, and the voltage at this discharged portion drops to about 0V, but is still about 5V at the highest point. The scanning range 5 of the electron beam mentioned above is selected to be substantially the same as the so-called effective imaging screen.

However, in general, the area where the target 4 receives light is sufficiently wider than the area of the above-mentioned effective imaging screen, that is, the scanning range 5 of the electron beam, and the electron beam does not scan an area wider than the effective imaging screen. , outside the above-mentioned effective imaging screen, that is, the scanning range 5 of the electron beam on the target 4, there is no time when the electron beam is discharged, and therefore the range 5
Outside, the charge voltage becomes extremely high, which causes the electron beam to bend as it attempts to reach the effective imaging screen, causing scanning distortion and a framing effect that tends to produce a bright frame around the screen. In addition, color image pickup tubes that identify hue using index signals have drawbacks such as distortion of the electron beam, which causes the phase relationship between the index signal and color signal to become abnormal, which tends to impede color demodulation. .

The present invention is intended to avoid such drawbacks, and will be described with reference to FIG. 2 and subsequent drawings.

6 is a DC power supply terminal, 7 is a video blanking signal
Input terminal for applying Sa (see Figure 3A), 8a
and 8b are switching pulses Sa and Sc, respectively.
(See Figures 3B and C) is an input terminal to which voltage is applied. These pulses Sa and Sc are the blanking signal Sa
It is allowed to be located approximately in the center (in terms of time) of

A PNP transistor 9 serving as a first switching element is provided, and its base is connected to the input terminal 7 described above.
Then, the emitter is connected to the power supply terminal 6, and the collector is connected to the movable contact of the variable resistor 11 through the variable resistor 10, respectively. This variable resistor 11 is connected to the power supply terminal 6
and ground. Furthermore, an NPN transistor 12 is provided, the base of which is connected to the movable contact of the variable resistor 11, the collector connected to the power supply terminal 6 through the resistor 13, and the emitter connected to the ground through the resistor 14.

15a and 15b are constant current circuits, and are configured symmetrically so that they operate in opposite phase relation to each other. Therefore, the constant current circuit 15a will be explained.
The constant current circuit 15b has a suffix a on the symmetrical part.
will be added instead of b and its explanation will be omitted.

That is, a transistor 16a is provided, its base is connected to the output terminal (collector or emitter) of the transistor 12, its emitter is connected to the DC power supply terminal (terminal 6 or ground) through the resistor 17a, and the collector is connected to the DC power supply terminal (terminal 6 or ground) through the diode 18a and capacitor 19a. Connect to the power terminal (ground or terminal 6). Note that a collector-emitter transistor 21 of the transistor 20a is connected between the power supply terminal 6 and the ground.
A series circuit consisting of the emitter and collector of transistors 20a and 21a is connected, and both transistors 20a and 21a
A so-called buffer circuit 22a is constructed by connecting the base of the diode 18a to the anode and cathode of the diode 18a, and an output terminal 23a is led out from the connection point of both transistors 20a and 21a. However, this buffer circuit 22a is not necessarily necessary;
Connection point between diode 18a and capacitor 19a
The output terminal 23a may be derived from Pa. Although these output terminals 23a and 23b are not shown, they are connected to a pair of deflection plates (electrodes) for horizontally deflecting the electron beam of the image pickup tube. Of course, the invention can also be used in the case of vertical deflection. Note that the diode 18a is for generating base bias of the transistors 20a and 21a.

Furthermore, in the present invention, a transistor 24a serving as a second switching element is provided, and its base is connected to the input terminal 8a of the pulse Sb, its collector is connected to the above-mentioned connection point Pa, and its emitter is connected to the bias power supply 25a.
are respectively connected to the DC power terminal (terminal 6 or ground) through the terminals. The constant current circuit 15a is similarly configured.

Next, the operation of the above-described configuration will be explained. Since the operation of the constant current circuit 15b side is in an opposite phase relationship with that of the constant current circuit 15a side, only the constant current circuit 15a side will be explained, and the explanation of the constant current circuit 15b side will be omitted.

During an unblanking period (denoted Ta) other than the period of the blanking signal Sa shown in FIG. 3A (blanking period Ts), the transistor 9
is in the off state, and the voltage determined by the variable resistor 11 determines the internal impedance of the transistor 12, and accordingly, the constant current circuit 15
The magnitude of the current flowing through the collector-emitter of transistor 16a of transistor 16a is determined. The voltage (charge voltage of capacitor 19a) obtained at point Pa due to the current flowing during this period Ta is shown as Va in FIG. Therefore, the magnitude of change (degree of slope) of this voltage Va can be changed by adjusting the variable resistor 11.

Next, when entering Tb in the first half of the Ts period (before pulse Sb), the blanking signal Sa supplied to terminal 7
As a result, the transistor 9 is turned on, and the current passing through the transistor 9 and the variable resistor 10 is also supplied to the base of the transistor 12, so that it becomes more conductive, and the current in the constant current circuit 15a continues during the Ta period mentioned above. The current increases.
Therefore, the voltage at point Pa becomes faster than the rate of increase during the above-mentioned Ta period. The voltage during this period is shown as Vb in FIG. 3D. Therefore, the slope in this case is steeper than that of Va, and variable resistor 1
Can be changed with 0. Therefore, the transistor 9 and the variable resistor 10 become a circuit that increases the current of the constant current circuit 15a.

Next, when the period Tc of the pulse Sb begins, the transistor 24a becomes conductive (turned on) by the pulse Sb, and the capacitor 19a is discharged, and the Pa
The voltage at the point drops rapidly. The voltage during this period is shown as Vc in FIG. Furthermore, the second half of the blanking period Ts, that is, the period after the pulse Sb
When the voltage reaches Td, the capacitor 19a starts charging again because the transistor 24a is turned off. Since the current passing through the collector of the transistor 16a at this time, that is, the charge current, is the same as that in the previous Tb period, the voltage change at point Pa (slope of the curve) at this time is the same as Vb, and this is
Indicated by Vd in Figure D. Then, when entering the next amplifier ranking period Ta, the transistor 9 is turned off, so the transistor 12 is connected to the variable resistor 11 again.
The impedance is determined by the settings of
Therefore, the voltage at point Pa is expressed as Va. In the illustrated example, the voltage shown at point Pa is supplied to the output terminal 23a through the buffer circuit 22a. In addition, the output terminal 23b is
As shown in FIG. 3D, signals with polarities opposite to those shown in FIG. 3D are obtained, and these signals are applied to a pair of deflection plates. FIG. 3C shows the pulses applied to terminal 8b.

According to the present invention explained above, FIGS. 3D and E
It is clear that the signal shown in is applied to the deflection plate, so that normal deflection is performed during the unblanking period Ta. Of course, during the Ta period, the electron beam is scanned within the range shown by the dotted line in FIG. 1 (this is determined by the _magnitude of the voltage Va shown in FIG. 3D).

Even when entering the next Tb period, the electron beam is not retraced, and therefore the electron beam is scanned beyond the range 5 mentioned above (which is the range of the effective imaging screen as mentioned at the beginning). That will happen. This scanning range corresponds to the voltage shown in Figure 3D.
It is determined by the size H _E that is the sum of Vd, Va and Vb, and in this case, in the present invention, when scanning beyond range 5, the speed of the electron beam is increased, so the above-mentioned H _E is The value becomes even larger, that is, the scanning range can be expanded by that length, and as a result, the electron beam can be scanned over a sufficiently wide area outside the effective imaging screen, that is, range 5, and the target radiation in this area can be Therefore, the above-mentioned drawbacks can be reliably avoided.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the target surface of the image pickup tube;
FIG. 2 is a circuit diagram for deflecting an electron beam of an image pickup tube according to the present invention, and FIG. 3 is a waveform diagram for explaining its operation. 15a and 15b are constant current circuits; 9 is a transistor for the circuit for increasing the current; 23a and 2
3b is a connection terminal to the deflection plate.

Claims (1)

[Scope of utility model registration request] A constant current circuit that can vary the amount of current, a capacitor that is charged by the constant current circuit, an output terminal for the voltage across the capacitor or a voltage related to this, and a constant current circuit that is turned on during the video blanking period and charged by the constant current circuit. a first switching element that makes the current larger than the amount of current flowing during the unblanking period;
At approximately the middle position within the video blanking period above,
An electron beam deflection circuit for an image pickup tube, comprising a second switching element that is turned on for a shorter period than the on period of the first switching element to discharge the charge in the capacitor.