JPH01198874A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain a good S/N even when the strengthening of a high frequency area component is executed by providing a perceivable circuit by approximately meeting a certain condition respectively by the output capacity of a pickup tube and the input capacity of a front end amplifier. CONSTITUTION:Plural numbers of electric field effect transistors FET1 and FET2 connected in parallel at the first step of the front end amplifier are used in an image pickup device constituted by providing a perceivable coil PC so that the output capacity Cv of the pickup tube and the input capacity Ci of the front end amplifier may approximately meet the condition of Ci=2Cv. Consequently, it is easier to constitute the first step of the front end amplifier in order to approximately meet the condition of Ci=2Cv. Thus, since the equivalence heat noise and the resistance value of the first step of the front end amplifier are reduced, the extent of the improvement of the S/N of a circuit is further increased in addition to the reduction of the noise by this and the color camera of good S/N can be easily obtained.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an imaging device, particularly an imaging device configured by providing a percival circuit between the output side of an image pickup tube and the input side of a preamplifier. Regarding.

(Prior Art) In order to obtain a high-resolution reproduced image with a video signal exhibiting a high signal-to-noise ratio, a percival circuit is installed between the output side of the image pickup tube and the input side of the preamplifier. It has been known in the past to provide a high frequency component of the output signal of the image pickup tube.

Then, a color separation striped filter is installed in the optical path up to the photoelectric conversion surface of the image pickup tube, and a striped color-separated image of the object to be imaged is provided onto the photoelectric conversion surface of the image pickup tube, and color multiplexing is performed from the image pickup tube. In a single-tube color imaging device that generates a signal, an optical image of the object to be imaged is applied to the photoelectric conversion section of the imaging tube via a color separation striped filter, and a DC component and a specific repetition frequency fO are
An output signal (color multiplexed signal) consisting of a modulated wave in which a color multiplexed carrier wave having a signal is amplitude-1 phase modulated by the signal is outputted from the image pickup tube, and the output signal from the image pickup tube is amplified by a preamplifier. and a low-pass filter and a bandpass filter to output a luminance signal from the low-pass filter and output a chrominance signal modulated by the color multiplexed signal from the bandpass filter, i.e. , the image pickup tube outputs an output signal (color multiplexed signal) containing a modulated wave whose amplitude and phase are modulated by a color multiplexed carrier wave having a specific repetition frequency.

Therefore, in particular, as mentioned above, the color signal band C (C in Fig. 2) is above the luminance signal band Y (Y in Fig. 2).
In order to obtain a color multiplexed signal with a good signal-to-noise ratio from a color imaging device configured to output a color multiplexed signal located at Attempts have also been made to provide a percival circuit between the input side of the stationary amplifier.

(Problems to be Solved by the Invention) Now, since the output signal of a photoconductive type image pickup tube contains almost no noise, the output signal of the photoconductive type image pickup tube is The S/N of the output signal is substantially determined by the noise of the preamplifier, and when the output capacitance of the image pickup tube is Cv and the input capacitance of the preamplifier is Ci.

An imaging device with the best S/N ratio can be obtained when the output capacitance Cv of the image pickup tube and the input capacitance Ci of the preamplifier are configured to approximately satisfy the condition of Ci = Cv, etc. Tetsuo Sakai's paper on technical matters was published in the Television Society magazine "Television", Vol. 29, No. 8 (1
975), pages 5o to 54, entitled "Low-output capacitive vidicon and preamplifier".

However, the present inventors conducted experiments on a single-tube color camera in which a percival circuit was installed between the output side of the image pickup tube and the input side of the preamplifier to enhance the high-frequency components of the output signal of the image pickup tube. As a result, we found that the conditions stated in the paper mentioned above are that the S/N of the output signal in an imaging device using a photoconductive type image pickup tube is the best, that is, the output capacitance of the image pickup tube is set to Cv. When the input capacitance of the preamplifier is Ci, the output capacitance C of the image pickup tube mentioned above is
It is clear that the condition of Ci=Cv between v and the input capacitance Ci of the preamplifier is not met when a percival circuit is constructed between the output side of the image pickup tube and the input side of the preamplifier. Therefore, even if a percival circuit is installed between the output side of the image pickup tube and the input side of the preamplifier to enhance the high-frequency components of the output signal of the image pickup tube, a good S/N ratio can be achieved.
The arrival of an imaging device that can show this is long awaited.

(Means for Solving the Problems) The present invention provides an imaging device configured by providing a percival circuit between the output side of an image pickup tube and the input side of a preamplifier, where the output capacitance of the image pickup tube is defined as Cv. , when the input capacitance of the preamplifier is Ci, the output capacitance Cv of the above-mentioned image pickup tube is
and an input capacitance Ci of a preamplifier substantially satisfy the condition Ci=2Cv.

(Example) Hereinafter, specific contents of the imaging device of the present invention will be explained in detail. First, as a condition for achieving the best S/N ratio of an output signal in an image pickup device using a photoconductive image pickup tube,
C i = Cv (however, Cv
is the output capacitance of the image pickup tube and Ci is the input capacitance of the preamplifier) indicates the condition when the electrical resistance that exists from the output side of the image pickup tube to the input side of the preamplifier is ignored. Therefore, a percival circuit equipped with a percival coil having a non-negligible electrical resistance between the output side of the image pickup tube and the input side of the preamplifier is connected between the output side of the image pickup tube and the input side of the preamplifier. In the case of an imaging device installed between the input side and the input side, the best S/
Even if an imaging device was configured to meet the conditions described as conditions for obtaining N, good results could not be obtained.

Therefore, the present inventors proposed that a percival circuit including a percival coil having a non-negligible electrical resistance between the output side of the image pickup tube and the input side of the preamplifier be installed between the output side of the image pickup tube and the input side of the preamplifier. Regarding the imaging device installed between the input side of the amplifier, when setting the conditions to obtain the best S/N, the electric resistance value that exists from the output side of the image pickup tube to the input side of the preamplifier is also considered. A percival circuit, which is used as a parameter for analysis and is equipped with a par-level coil having a non-negligible electrical resistance between the output side of the image pickup tube and the input side of the preamplifier, is connected to the output side of the image pickup tube. We determined the conditions under which a good S/N ratio could be obtained for the imaging device installed between the camera and the input side of the preamplifier, and found that the output capacitance of the imaging tube is Cv, and the input capacitance of the preamplifier is Cv. A good S/N can be achieved if the imaging device is configured such that the output capacitance Cv of the image pickup tube and the input capacitance Ci of the preamplifier approximately satisfy the condition of Ci = 2 Cv, where Ci is As shown in FIG. 1, an imaging device having the following characteristics can be obtained.

Part 1 (a) shows that the noise level in the luminance signal band Y indicated by the frequency range 0-fy in Fig. 2 is the input capacitance Ci of the preamplifier and the output capacitance Cv of the image pickup tube.
FIG. 1(b) is a chart showing how the chrominance signal band Ci above the luminance signal band Y, that is, the specific The noise level in a frequency band C in which a modulated wave exists in which a color multiplex carrier wave having a repetition frequency fo is amplitude- and phase-modulated by a signal is given by the input capacitance Ci of the preamplifier and the output capacitance cv of the image pickup tube. (In FIG. 2, the repetition frequency fO of the color multiplex carrier wave is the upper limit frequency fy of the luminance signal band Y.
).

The input capacitance C of the preamplifier shown in FIG. 1(a)
Looking at how the noise level changes in the luminance signal band Y, which changes according to the change in the ratio between i and the output capacitance Cv of the image pickup tube, the lowest point of the noise level in the luminance signal band Y is the input capacitance of the preamplifier. The ratio Ci/Cv between Ci and the output capacitance Cv of the image pickup tube is approximately 2, and the noise level in the color signal band C shown in FIG. Input capacitance Ci and output capacitance C of the image pickup tube
The lowest state occurs where the ratio Ci/Cv to V is approximately 2 or more.

From this, in the imaging device of the present invention, in which a percival circuit is provided between the output side of the image pickup tube and the input side of the preamplifier, the output capacitance of the image pickup tube is reduced to C.
v and the input capacitance of the preamplifier is Ci, the output capacitance Cv of the image pickup tube and the input capacitance C of the preamplifier described above are
By configuring the image pickup device so that i substantially satisfies the condition of Ci=2Cv, it was possible to easily provide an imaging device with a good S/N ratio.

Figure 3 shows an image pickup device configured with a percival circuit provided between the output side of the image pickup tube and the input side of the preamplifier as described above, with the output capacitance of the image pickup tube being Cv, and the output capacity of the preamplifier being Cv. When the input capacitance is Ci, the output capacitance Cv of the image pickup tube mentioned above and the input capacitance Ci of the preamplifier are Ci =
2 is a block diagram showing a configuration example of an imaging device configured using a plurality of field effect transistors connected in parallel in the first stage of a preamplifier so as to substantially satisfy the condition of 2 Cv.

In Figure 3, 0 is the object, TL is the imaging lens, PT is the imaging tube, PC is the Percival coil, RQ is the load resistance of the imaging tube, FETI, and FET2 are multiple field effect transistors that constitute the first stage of the preamplifier. , R1 and R2 are resistors, 1 is an amplifier downstream of the preamplifier, and 2 is an output terminal.

In Fig. 3, the output signal from the image pickup tube PT is supplied via the percival coil PC of the percival circuit to the gate electrodes of two parallel-connected field effect transistors FETI and FET2, which constitute the first stage of the preamplifier. be done.

In the circuit arrangement shown in Figure 3, as mentioned above, the first stage of the preamplifier consists of two field effect transistors F connected in parallel.
Since it is constituted by ETI and FET2, its input capacitance is larger than that in the case of one field effect transistor. Therefore, the output capacity of the image pickup tube PT is C
v and the input capacitance of the preamplifier is Ci, the output capacitance Cv of the image pickup tube and the input capacitance C of the preamplifier are
It becomes easy to configure the first stage of the preamplifier so that i substantially satisfies the condition of Ci=2Cv.

In the configuration example shown in FIG. 3, the first stage of the preamplifier is constructed by connecting two field effect transistors FETI and FET2 in parallel. When the input capacitance of the preamplifier is Ci, the first stage of the preamplifier is set to 3. A plurality of field effect transistors may be connected in parallel.

If the first stage of the preamplifier is composed of a plurality of field effect transistors connected in parallel as described above, the image pickup tube PT
Let Cv be the output capacitance of Cv, and Ci be the input capacitance of the preamplifier, so that the output capacitance Cv of the image pickup tube and the input capacitance Ci of the preamplifier approximately satisfy the condition of Ci=2Cv. In addition to making it easier to perform In addition to the resulting reduction in noise, the degree of improvement in the S/N ratio of the circuit further increases.

(Effects of the Invention) As is clear from the above detailed explanation, the imaging device of the present invention is configured by providing a percival circuit between the output side of the image pickup tube and the input side of the preamplifier. In the apparatus, when the output capacitance of the image pickup tube is Cv and the input capacitance of the preamplifier is Ci, the output capacitance Cv of the image pickup tube and the input capacitance Ci of the preamplifier described above are Ci = 2 C.
An imaging device configured to substantially satisfy the condition of v, in which a high-resolution reproduced image is obtained by a video signal exhibiting a high signal-to-noise ratio. In order to increase A color-separating striped filter is provided in the optical path to the conversion surface, and a striped color-separated image of the object to be imaged is applied to the photoelectric conversion surface of the image pickup tube, so that a color multiplexed signal is generated from the image pickup tube. In a single-tube color imaging device, a percival circuit is provided between the output side of the image pickup tube and the input side of the preamplifier to enhance the high-frequency components of the output signal of the image pickup tube. A percival circuit comprising a percival coil having a non-negligible electrical resistance between the output side of the image pickup tube and the input side of the preamplifier connects the output side of the image pickup tube and the input side of the preamplifier. Because of the distance between the two, the best S/N can be obtained in the paper mentioned above, which shows the case where the electrical resistance existing from the output side of the image pickup tube to the input side of the preamplifier is ignored. In order to improve the problem that good results could not be obtained even when configuring an imaging device that met the conditions, a percival circuit was installed between the output side of the image pickup tube and the input side of the preamplifier. The present invention is designed so that the best S/N ratio can be obtained even for an imaging device in which the high frequency range of the output signal is enhanced.

Therefore, according to the present invention, problems with conventional imaging devices can be satisfactorily solved. In addition, when the first stage of the preamplifier is configured with multiple field effect transistors connected in parallel, its input capacitance becomes larger than when only one field effect transistor is used, and the output capacitance of the image pickup tube PT increases. is Cv, and the input capacitance of the preamplifier is Cv.
i When closed, the output capacitance Cv of the image pickup tube mentioned above and the prefix increase.

It becomes easy to configure the first stage of the preamplifier so that the input capacitance Ci of the width amplifier approximately satisfies the condition of Ci=2Cv, and furthermore, the first stage of the preamplifier can be configured by using a plurality of field effect transistors. When configured with devices connected in parallel, the equal-side thermal noise resistance value of the first stage of the preamplifier naturally decreases, so the S/N of the circuit also decreases due to this noise reduction.
Since the degree of improvement in S/
N good color cameras can be easily provided.

[Brief explanation of the drawing]

Fig. 1 is a frequency distribution diagram of an output signal from a single-tube color camera, Fig. 2 is a side view of a characteristic curve for explaining the construction principle of the imaging device of the present invention, and Fig. 3 is an example of the imaging device of the present invention. FIG. 2 is a block diagram showing the configuration. Y: Luminance signal band, C: Color multiplexed signal band,
0...Subject, TL...Imaging lens, PT...Picture tube, PC...Percival coil, RQ...Load resistance of image pickup tube, FETI, FET2...Field effect transistor, R1, R2 ... Resistor, 1... Amplifier after the preamplifier, 2... Output terminal,

Claims (1)

[Claims] In an imaging device configured by providing a percival circuit between the output side of the image pickup tube and the input side of the preamplifier, the output capacitance of the image pickup tube is Cv, and the input capacitance of the preamplifier is Ci.
An imaging device configured such that the output capacitance Cv of the image pickup tube and the input capacitance Ci of the preamplifier substantially satisfy the condition Ci=2Cv when