JPH0123036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a deflection circuit for an image pickup tube that eliminates scanning distortion.

In image pickup tubes used in television cameras,
As shown in FIG. 1, the inner area of the frame 2, shown as a solid line with center q in the target plane 1, is
The beam scans horizontally and vertically. In this case, if there is a charged charge on the outer periphery of the frame 2, the beam will be bent by the electric field of this charge, which may cause image curvature at the periphery of the reproduced screen. In order to eliminate such scanning distortion, an imaging tube has been proposed in which the beam overscans the peripheral portion of the frame 2 of the target surface 1 to the area indicated by the dotted line. Through this overscan, the charges in the peripheral area can be discharged, and the potential difference between this peripheral area and the effective scanning area (inner area of frame 2) can be eliminated, thereby eliminating the scanning distortion described above. .

When performing this overscan, the beam scanning speed in the overscan area between frame 2 and the dotted line in FIG. This allows for overscanning. Increasing the beam scanning speed increases the signal current obtained from the image pickup tube. For example, doubling the scanning speed also doubles the signal current. Therefore, in the overscan area, the amount of the beam cannot fully follow the increase in signal, and the beam is more likely to be saturated than in the effective scan area. Once the beam is saturated, the charge in the overscan area cannot be sufficiently discharged, thus defeating the purpose of overscan.

The present invention is intended to solve the above problems,
Embodiments of the present invention will be described below with reference to the drawings.

First, a second embodiment of a horizontal deflection circuit that generates a horizontal deflection voltage for performing the above-mentioned overscan will be described.
The diagram will be explained. The circuit shown in Figure 2 is
It is particularly applicable to electrostatic deflection type image pickup tubes.

In this horizontal deflection circuit, pulse 1, which is an inverted image blanking pulse P ₁ as shown in FIG. 3A, is applied to terminal 3, and _a third pulse is applied to terminal 4.
Beam blanking pulse P ₂ as shown in Figure B
By applying a pulse P ₃ as shown in FIG.
An attempt is made to obtain a horizontal deflection voltage V _H+ as shown in Figure D. At the same time, the above pulse P ₁ is applied to terminal 7, and pulse ₂ , which is an inversion of the above pulse P ₂ , is applied to terminal 8, and the above pulse is applied to terminal 9.
By adding pulse ₃ , which is the inversion of P ₃ ,
A horizontal deflection voltage V _H- is obtained at the output terminal 10 as shown in FIG. 3E. Above horizontal deflection voltage
V _H+ and V _H- are applied to the horizontal deflection plates 11 and 12 of the image pickup tube, respectively, as shown in FIG. Note that vertical deflection voltages V _V+ and V _V- are applied to the vertical deflection plates 13 and 14, respectively.

In Figure 3, T ₄ of the horizontal deflection voltages V _H+ and V _H-
The period is an effective scanning period within frame 2 of FIG. 1, and is, for example, T ₄ =53 μsec. Also, the T ₂ period is the retrace period of the beam, for example, T ₂ = 4μsec
It is. Further, the T ₁ period and the T ₃ period are overscan periods, for example, T ₁ = 3 μsec, T ₃ = 2 μsec
It is. The voltages during the overscan period T ₁ , T ₃ and the retrace period T ₂ are as shown in the figure during the effective scan period T _{4 .}
The voltage slope is set to be steeper than that of the voltage.
This increases the scanning speed of the beam,
It is possible to overscan a sufficiently long distance in the short time of T ₁ and T ₃ . Therefore, it is possible to discharge charges in the peripheral portion of the frame 2 within a range necessary to eliminate scanning distortion. Together with this, the beam can be returned to the track in a short time T ₂ . In addition, the scan start potential V ₁ , effective scan start potential V ₂ and peak potential of the horizontal deflection voltages V _H+ , V _H-
V ₃ is specified respectively.

In FIG. 2, the horizontal deflection voltage V _H+ is obtained at the output terminal 6 provided at the connection point of complementary connected transistors Q ₁ and Q ₂ . That is, capacitor C ₁
is the current source transistor Q ₃ to the diodes D ₁ , D ₂
According to the charging voltage of the capacitor C ₁ , the voltage of the horizontal deflection voltage V _H+ during the scanning period T ₃ , T ₄ , and T ₁ is obtained at the output terminal 6. Furthermore, when this voltage reaches the peak value V ₃ , the pulse P ₂ causes the transistor Q ₄ to conduct, causing the capacitor C ₁ to discharge through this transistor Q ₄ , thereby obtaining the voltage for the period T ₂ . Furthermore, the conduction of the transistor Q ₄ charges the capacitor C ₂ , thereby defining the overscan starting potential V ₁ .
When transistor Q ₄ then becomes non-conductive, capacitor C ₁ is charged again and the deflection voltage rises from V ₁ . By applying the pulse P ₃ during this rise, the transistor Q ₅ becomes conductive, and the capacitor C ₃ is charged by this conduction. This defines the effective scan start potential _V2 . By defining the effective scan start potential V ₂ in this way,
The influence of variations in the overscan starting potential V ₁ can be removed. If the voltage V ₂ is not set and the voltage V ₁ changes, the DC voltage during the T ₄ period will change, and the center q of the frame 2 on the target surface 1 will change. That is, a centering error occurs. In order to prevent this, the potential V ₂ is temporarily reduced at the starting point of effective scanning.
is specified so that the voltage slope during the _T4 period is always constant. Note that the difference between the potentials V ₁ and V ₂ is obtained by the resistor R ₁ .

The steep slope of the voltage during the T ₁ , T ₂ , and T ₃ periods described above is obtained by making the transistor Q ₆ connected to the transistor Q ₃ conductive with the pulse ₁ . The conduction of this transistor _Q6 connects the resistor _R2 , so the transistor
The current flowing from Q ₃ to capacitor C ₁ is pulse ₁
increases during the applied time (10 μsec), thereby causing the output voltage to rise rapidly during the T ₁ and T ₃ periods. Furthermore, the transistor Q ₇ ,
Q ₈ and diode D ₃ are provided for temperature compensation.

The above is a description of the configuration and operation of the circuit for obtaining the horizontal deflection voltage V _H+ , but the circuit for obtaining the horizontal deflection voltage V _H- is also configured in substantially the same manner as described above. That is, transistors _Q9 to _Q16 are provided corresponding to transistors _Q1 to _Q8 , respectively, and diodes are provided.
Diodes D _{4 ,} D ₅ , D ₆ are provided corresponding to D 1 to D ₃ , respectively, capacitors C ₄ , C ₅ , C ₆ are provided to correspond to capacitors C ₁ to _{C 3} , and resistors R ₁ ,
Resistors R ₃ and R ₄ are provided corresponding to R ₂ , respectively.
By applying the pulses P ₁ , ₂ and ₃ , substantially the same operation as described above is performed, thereby obtaining the horizontal deflection voltage V _H- at the output terminal 10.

Further, this deflection circuit is provided with a variable resistor _R5 for centering adjustment and a variable resistor _R6 for size adjustment. By adjusting the variable resistor R ₅ , the emitter voltages of the transistors Q ₇ , Q ₈ , Q ₁₅ , and Q ₁₆ are adjusted to move the center q of the frame 2 in the horizontal direction, thereby changing the position of the frame 2. Can be adjusted horizontally. Further, by adjusting the variable resistor R ₆ and adjusting the current flowing through the transistors Q ₃ and Q ₁₁ , the horizontal size of the frame 2 can be adjusted.

The above describes the deflection circuit that obtains the horizontal deflection voltages V _H+ and V _H- , but the vertical deflection plates 13 and 1 shown in FIG.
The vertical deflection circuit for obtaining the vertical deflection voltages V _V+ and V _V- applied to 4 is also a circuit having substantially the same configuration as the circuit shown in FIG. Also, the vertical deflection voltage V _V+ , V _V-
The waveform of is similar to the waveform of the horizontal deflection voltages V _H+ and V _H- in Fig. 3, but the length of the T4 period is approximately 17 to 18 times that of _T4 in Fig. ₃ , and T The lengths of ₁ , T ₂ , and T ₃ can also be changed. Also, the vertical deflection voltage V _V+ , V _V-
In the circuit for obtaining this, the center q of the frame 2 is moved in the vertical direction by the centering adjustment, and the vertical size of the frame 2 is adjusted by the size adjustment. However, it is technically difficult to perform overscan using an electromagnetic deflection type image pickup tube.
Therefore, the deflection circuit shown in FIG. 2 is particularly effective when used in an electrostatic deflection type image pickup tube.

Next, an embodiment of the present invention to which the above-described horizontal and vertical deflection circuits can be applied will be described.

FIG. 5 shows a first embodiment. This embodiment uses the image pickup tube during horizontal and vertical overscan periods.
By increasing the voltage of the _G1 electrode (first grid), the beam amount during this period is forcibly increased. For this purpose, a horizontal overscan pulse shown in FIG. 7 is applied to terminal 20.
In addition to applying P _H , a vertical overscan pulse P _V shown in FIG. 7 is applied to the terminal 21. These pulses P _H and P _V are passed through the OR gate 22
It is added to the _G1 electrode drive circuit 23. Note that the variable resistor 24 is for adjusting the beam amount. Pulse P _H is substantially equal to pulse P ₁ of FIG. 3A, and pulse P _V is substantially equal to the corresponding pulse P ₁ applied to the vertical deflection circuit described above.

According to the above, since the beam control signal is applied from the drive circuit 23 to the G ₁ electrode during the overscan period and the voltage of this G ₁ electrode increases,
The amount of beam can be increased. This prevents the beam from becoming saturated even when the beam scanning speed is increased, and therefore, it is possible to sufficiently discharge charges around the effective scanning area and eliminate beam scanning distortion.

FIG. 6 shows a second embodiment in which the present invention is applied to an image pickup tube equipped with an ABO (automatic beam adjustment) circuit. Note that the same parts as in FIG. 5 are given the same reference numerals.

In the ABO circuit, by positively feeding back a portion of the signal current obtained from the image pickup tube, the beam amount is automatically increased when the signal current increases. Therefore, if the signal current increases in the overscan area, the beam amount also increases, but in order to prevent the beam from becoming saturated,
ABO alone is not enough. Therefore, in this example,
The amount of beam is sufficiently increased by adding to the increase due to ABO.

For this reason, in FIG.
The above-mentioned pulses P _H and P _V are added to the OR gate 2.
The pulse shown in FIG. 7 obtained through 2 is applied to the AND gate 25, and the pulse shown in FIG.
A pulse P _C shown in FIG. 8A which is substantially equal to the _pulse P ₂ of
The inverted pulse _C is applied to the AND gate 25. As a result, and gate 25
As a result, the pulse train shown in FIG. 8B is obtained. on the other hand,
The terminal 28 is connected to the video signal S _V obtained from the image pickup tube.
is added, and this signal S _V and the pulse train are mixed in a mixing circuit 29. This mixed output is generated by the clamp pulse P _L applied from the terminal 31 in the cathode clamp circuit 30 to V ₁ in FIG. 3D.
The level is clamped to the cathode level. This clamped signal is processed by the ABO signal processing circuit 32 and applied to the drive circuit 23.

According to the above, the beam is controlled by the beam control signal obtained from the drive circuit 23 according to the level of the signal S _V. At the same time, the beam is further increased during the period when the pulse train in FIG. 8B is at a high level, that is, during the horizontal and vertical overscan periods (T ₁ and T ₃ in FIG. 3C).
Beam saturation can be eliminated.

In the embodiment shown in FIG. 5, a signal obtained by ANDing the pulses P _H and P _{V shown} in FIG. You may also do so. In the embodiment shown in FIG. 6, the output of the AND gate 25 may be applied directly to the drive circuit 23 as shown in FIG. In this case, it is possible to eliminate oscillation due to gain up of the ABO circuit during overscanning and beam landing errors in the peripheral area.

Since the present invention is as described above, it is possible to overscan the outer periphery of the effective scanning area on the target surface in a short time at a high scanning speed within the video blanking period, and also because the scanning speed is high. Since the beam is never saturated, scanning distortions such as beam bending can be effectively removed.

[Brief explanation of drawings]

FIG. 1 is a front view of the target surface of the image pickup tube to explain overscan, and FIG. 2 is a circuit diagram showing an embodiment of a horizontal deflection circuit applicable to the present invention.
3 is a signal waveform diagram of the main part of FIG. 2, FIG. 4 is a side view showing the arrangement of horizontal and vertical deflection plates, FIG. 5 is a circuit system diagram showing the first embodiment of the present invention, and FIG. FIG. 6 is a circuit diagram showing the second embodiment, and FIG. 7 is a circuit diagram showing the fifth embodiment.
Figure 6 and signal waveform diagram of the main part of Figure 6, Figure 8 is the signal waveform diagram of the main part of Figure 6.
It is a signal waveform diagram of the main part of a figure. In addition, in the symbols used in the drawings, 1...target surface, 2...frame, 23... _G1 electrode drive circuit, P _H , _PV ...overscan pulse,
It is.

Claims (1)

[Scope of Claims] 1. A sawtooth wave generation circuit that generates a sawtooth wave signal for deflecting an electron beam scanning a target surface of an image pickup tube, and a beam amount control circuit that controls the amount of the electron beam. The sawtooth wave generating circuit includes a first slope portion for deflecting an electron beam scanning an effective scan area on the target surface, and a first slope portion that is steeper than the first slope portion and that is in the effective scan area. and a second slope portion for deflecting an electron beam scanning the outer periphery within an image blanking period, and the beam amount control circuit is configured to generate the sawtooth wave signal, and the beam amount control circuit is configured to generate the sawtooth wave signal. A deflection circuit for an image pickup tube, characterized in that the deflection circuit for an image pickup tube is configured to make the amount of electron beam when scanning the effective scanning area larger than the amount of electron beam when scanning the effective scanning area.