JPS615690A - Electromagnetic focusing circuit of multitube type television camera - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a focus circuit for a multi-tube television camera. A three-tube type television camera that provides high-quality images is common. There are an electromagnetic focusing method and an electrostatic focusing method as scanning beam focusing methods of the image pickup tube used for this, and the present invention relates to the former electromagnetic focusing method.

[Background of the invention]

Conventionally, for television broadcasting and applications that require high quality images, each primary color (red, green, blue) as shown in Figure 1 is used.
The so-called 3-tube type force 2-
A camera is used.

In FIG. 1, 11 is a taking lens, 12 is a three-color separation optical system, and 13, 14, and 15 are red (R).

It is an image pickup tube that supports each primary color of green (G) and blue (B),
Each output signal from these image pickup tubes is amplified and subjected to signal processing to create the final television signal. In addition to the three-tube color camera mentioned above, there is also a two-tube color camera that takes out the luminance signal from one image pickup tube and the color signal from the other, and a two-tube color camera that takes out the luminance signal from one image pickup tube and the color signal from the other image pickup tube, and a red, green, and blue color camera. There is a four-tube color camera, etc., which is provided with a fourth image pickup tube for detecting a luminance signal in addition to each primary color signal. A technique common to these multi-tube color cameras is the operation of superimposing images from each image pickup tube, that is, registration adjustment. In the three-tube type (multi-tube type), registration affects performance such as resolution and color shift, and is an important element that affects image quality. In particular, high-definition television cameras, which have more scanning lines than the current 525, require high registration accuracy. - There are four types of image pickup tubes used in cameras: electromagnetic focusing, electromagnetic deflection, electromagnetic focusing, electrostatic deflection, electrostatic focusing, electromagnetic deflection, electrostatic focusing, and electrostatic deflection. becomes. This time, we will discuss the focusing method among the above four types, and in particular, it will be related to a camera using an electromagnetic flux imaging tube, which has excellent high-resolution characteristics. There are various factors that determine the registration accuracy, such as errors in taze, skew, linearity, centering, etc. caused by the deflection circuit, errors in height, etc. caused by voltage fluctuations in the high-voltage circuit, and errors in rotation, etc. caused by the electromagnetic focus circuit. Generally, there are two ways to adjust the electron beam focus of the three tubes: one is to use a common electromagnetic focus and adjust the electrostatic focus independently, and the other is to use a common electrostatic focus and adjust the electromagnetic focus independently. There is. Either of the two letters above are red.

In order to increase the stability of registration between the three green and blue tubes, the more common parts there are, the better.

Therefore, the purpose of the present invention is to increase the stability of registration by making the electrostatic focus (high voltage circuit) common and most of the electromagnetic focus current amount common, thereby improving the registration accuracy regarding electron beam focus. It's about doing.

First, we will discuss the stability of the conventional electromagnetic focusing method. Conventionally, electron beams have been focused by an independent system in which electromagnetic focusing circuits having the configuration shown in FIG. 2 are separately provided for each of the red, green, and blue channels. In FIG. 2, 21 is an electromagnetic focus coil, 22 is a differential amplifier,
23 is a current detection resistor, and 24 is a focus current control resistor, which is generally well known as a circuit for supplying a constant current to a load. In this circuit system, the main factors that determine the stability of registration are the temperature characteristics (drift) of the differential amplifier and the temperature characteristics of the current detection resistor. Although it depends on the performance of the element used, the latter generally has a greater influence on stability than the former. For example, when considering the temperature rise up to 500%, a resistance with excellent temperature characteristics (±50rP/
Even if C) is used for current detection, the performance of this resistor alone will cause a resistance error of up to 0.5 inches in the worst case, which will affect registration. Furthermore, when the stability (performance) of the differential amplifier is included, the stability of registration accuracy is even more adversely affected. In particular, high-definition cameras require higher registration accuracy and stability than conventional cameras, and conventional independent methods have problems in terms of registration stability.

[Purpose of the invention]

An object of the present invention is to make most of the focus circuits necessary for a plurality of image pickup tubes common, and to dramatically improve stability.

[Summary of the invention]

The present invention separates the electromagnetic focus coil into a main focus coil and a nub 7 orcus coil, connects the main focus coils of each channel in series to achieve common use, and supplies the same focus current to each channel to improve stability. Improve. In addition, separate focus current circuits are provided for the subfocus coils of each channel, and this corrects variations in characteristics among multiple tubes.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 3 and 4. First, as the structure of the electromagnetic focus coil used in the present invention, a focus coil housed in a coil assembly is separated into a main focus coil and a nub focus coil at an appropriate division ratio. In FIG. 3, 31 is a main focus coil, and 32 is a nap focus coil, which are housed in the same coil assembly as the deflection coil 33 and alignment coil 34, and control the electron beam 36 within the image pickup tube 35. A circuit is configured so that separate focus currents can be supplied to the main focus coil 31 and the nub focus coil 32, respectively.

The purpose of the present invention is to increase the common parts among the three tubes to increase stability, so among the focus coils used for the three tubes, each main focus coil is connected in series and the same focus current is passed through the main focus coils. By doing so, it is possible to create commonalities.

Further, in order to increase the ratio of common parts as much as possible, the ratio of the main focus coil 31 to the sub-focus coil 32 is set to 9:1 in this embodiment. In this case, the focus state of the image pickup tube for each channel is determined by the magnetic field of the main focus coil, which accounts for 90% of the field. Therefore, 10% of the remaining amount is shared by the nub focus coil, which mainly plays the role of correcting the variation in focus among the three tubes. Note that the main focus coil 31,
The focus magnetic field distribution created by the sub-focus coil 32 is designed to be the same.

The circuit of the present invention using the electromagnetic focus coil with the above structure includes a main focus current circuit that supplies a common focus current to each main focus coil, and an independent focus current circuit that supplies each sub-focus coil corresponding to the main focus coil. A long focus current circuit is required to supply the current. In Figure 4, 41,
42 and 43 are the main focus coils corresponding to the three tubes, and the same focus current tM is supplied from the main focus current circuit 44.The focus current is adjusted by the focus current control resistor 45. and set. If the main focus coils used in the three tubes have exactly the same characteristics, nub focusing is not necessary, but normally, the characteristics among the three tubes differ slightly due to manufacturing errors in the coil assembly and image pickup tube. Therefore,
The nub focus coils 51, 52, and 53 corresponding to each of the main 7 orcus coils have a focus current Item for correcting variations in characteristics among the three tubes.
, [Its, a, , Item] are provided. The subfocus circuit may have the same configuration as the conventional electromagnetic focus system.

In the electromagnetic focus circuit configured as above, the same focus current I'm is supplied to the main focus coils 41, 42, and 43 of each channel, so errors due to temperature changes between channels do not occur, and the resist ration accuracy is improved.

On the other hand, the magnetic field change by the sub-focus coil uses the same circuit format as the conventional method, but overall, the main focus coil accounts for 90% of the total magnetic field strength. While most of the tube focus state is determined, the nap focus coil accounts for only 10%.

Therefore, the influence of the nap focus coil on the stability is less than 1/10, and overall, it is possible to improve the stability by a factor of 10 compared to the conventional method.

Note that in this embodiment, the ratio of the main focus coils and the length focus coils is 9:1, but the stability improves as the number of common parts increases. For example, if there is little variation in the focus coils among the three tubes, it is possible to further increase the proportion occupied by the main focus, thereby further increasing stability. Furthermore, since the reverse is also possible, the ratio of main and nap must be set appropriately to take into account variations in the coils.

〔Effect of the invention〕

According to the present invention, since the same focus current flows through the main focus coil of each image pickup tube, it is possible to keep the registration error between channels extremely small even when ambient temperature changes, compared to the conventional method. Stability can be dramatically improved.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of a three-tube color camera, Figure 2 is an explanatory diagram of the operation of a conventional electromagnetic focus circuit, Figure 3 is a model diagram showing the layout structure of the focus coil used in the present invention, and Figure 4. FIG. 2 is a circuit diagram for explaining the operation of the electromagnetic focus circuit according to the embodiment of the present invention. DESCRIPTION OF SYMBOLS 11... Taking lens, 12... Three-color separation optical system, 13.14.15... Image pickup tube, 21... Electromagnetic focus coil, 22... Differential amplifier, 23... Current Detection resistor, 24... Focus current control resistor,
31... Main focus coil, 32... Nub focus coil, 33... Deflection coil, 34... Alignment coil, 35... Image pickup tube, 36... Electron beam, 41-43... main focus coil,
44...Main focus current circuit, 45...Focus current control resistor, 51-53...Sub focus coil, 1st figure scale 2nd figure

Claims (1)

[Claims] an electromagnetic focus coil separated into a main focus coil and a sub-focus coil, means for supplying the same focus current to the main focus coil of each channel among the main focus coil and the sub-focus coil, and the sub-focus coil of each channel. An electromagnetic focus circuit for a multi-tube television camera, comprising means for independently supplying focus currents to focus coils, and independently adjusting the focus of each image pickup tube.