JP2001223951A - Digital output image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital output image pickup device capable of outputting a digital signal directly from an image pickup element without necessitating an expensive peripheral circuit such as a high-speed A/D converter. SOLUTION: The device is provided with a photoelectric conversion target part consisting of a transparent electrode transmitting incident light 107 and a photoelectric conversion film 111 for generating a signal electric charge with the incident light 107 to store it, a cold cathode array 112 having plural electronic discharging sources in the state of a matrix, an electric discharging source selecting means capable of selecting an optional electronic discharging source, an electric charge reading means for reading the signal electric charge stored in a pixel at the optional position of the photoelectric conversion target part as an electric signal, and a sampled digital signal converting and extracting means which converts the electric signal read by the electric charge reading means directly to the digital signal by varying (101-106, 112) and sampling (114-116) the cathode potential of the cold cathode array and takes out (117, 118) it to outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat-type imaging device for reading out signal charges generated and accumulated in a photoelectric conversion film in a spatial distribution by the incidence of photons as time-series electric signals by scanning with an electron beam. In particular, the present invention relates to an imaging apparatus that extracts the electric signal as a digital signal directly to the outside by sampling a scanning side surface potential of a photoelectric conversion film using a cathode potential.

[0002]

2. Description of the Related Art A photoelectric conversion film generates and accumulates signal charges in accordance with the amount of incident light, and reads out the charges in an external circuit in a time-series manner by scanning with an electron beam so as to correspond to the spatial distribution of the amount of incident light. A photoconductive imaging device is known as an imaging device that generates an analog electric signal, and a photoconductive imaging device using a cold cathode array is disclosed in JP-A-6-176704 as means for scanning the electron beam. It has been disclosed. FIG. 3 is a schematic perspective view showing the structure of the photoconductive imaging device described in the above-mentioned Japanese Patent Application Laid-Open Publication No. Hei.

The cold cathode array 300 has a cathode conductor 302 formed on a substrate 301. Cathode conductor 302
Is provided with an insulating layer 303. Insulating layer 303
A gate electrode 304 is further provided on the substrate. A hole 305 is formed in the insulating layer 303 and the gate electrode 304, and a cone-shaped emitter 306 is provided on the cathode conductor 302 exposed in the hole 305. The cathode conductor 302 and the gate 304 are both formed in a strip shape, and are arranged in directions orthogonal to each other to form an XY matrix. By driving both electrodes in a matrix, an emitter group at an arbitrary position at the intersection can be selected to emit electrons. A glass substrate 310 is provided facing the cold cathode array 300. On its inner surface, a light-transmitting conductive film 311 and a photoelectric conversion film 312 are sequentially laminated to form a photoelectric conversion target 313. Light 314 from outside is applied to the conductive film 31 from the outer surface side of the glass substrate 310.
1 and is incident on the photoelectric conversion film 312.

In the above configuration, the cold cathode array 300
Are driven in a matrix, and the photoelectric conversion film 312 is scanned with the electron beam 307 emitted from the emitter 306.
The electron beam scanning side of the photoelectric conversion film 312, that is, the scanning surface is 2
It is made of a material and / or a structure that hardly emits secondary electrons. When the electron beam 307 arrives, the potential of the scanning surface decreases, but when it becomes equal to the potential of the cathode conductor 302, the electron beam 307 can reach further. Therefore, the potential of the scanning surface immediately after the scanning of the electron beam 307 is
Equal potential. The cathode conductor 3 is formed on the light-transmitting conductive film 311.
Since a positive target voltage VT is applied to 02, an electric field is applied to the photoelectric conversion film 312 in such a manner that the light-transmitting conductive film 311 side is positive and the scanning surface side is negative.

In this state, when external incident light 314 is incident on the photoelectric conversion film 312, electron-hole pairs are generated in the photoelectric conversion film in accordance with the amount of the incident light. The holes on the membrane 311 side travel to the scanning surface side, and the scanning surface potential rises from the cathode conductor potential by the reached holes. When the electron beam 307 arrives again, the scanning surface potential is reset to the cathode conductor potential. At this time, a time-series analog electric signal corresponding to the space charge distribution of the incident light amount is obtained from the output terminal 315. In order to convert the output analog electric signal into a digital signal, the signal is amplified by an amplifier provided externally from the output terminal 315 and thereafter, and further converted by an external A / D converter.

[0006]

In the above-mentioned prior art, in order to obtain a digital electric signal, it is necessary to apply an externally provided amplifier and A / D converter to the output weak analog signal. For this reason, it is necessary to increase the frequency bandwidth of the amplifier as the number of pixels of the imaging device increases, and there has been a problem that the SN ratio deteriorates. In addition, although the processing function of the A / D converter is required to be fast,
Since the high speed and the number of bits of the D converter are in a reciprocal relationship, there is a problem that it is very difficult to obtain a necessary number of gradations (number of bits) or the device becomes expensive. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a digital output image pickup apparatus capable of directly outputting a digital signal from an image pickup device without requiring an expensive peripheral circuit.

[0007]

In order to achieve this object, a digital output imaging apparatus according to the present invention comprises a transparent electrode that transmits at least externally incident light, and a photoelectric conversion film that generates a signal charge by the incident light and stores the signal charge. And a cathode having a plurality of electron emission sources arranged in a matrix, an electron emission source selection means capable of selecting any of the electron emission sources, and a pixel at an arbitrary position of the target portion. It is characterized by comprising charge reading means for reading out the stored signal charges as electric signals, and digital signal converting and extracting means for directly converting the electric signals read by the charge reading means into digital signals and taking them out. It is assumed that.

According to the present invention, a cold cathode array is used as a cathode having a plurality of electron emission sources arranged in a matrix, and a signal charge stored in a unit pixel of the target portion is used as the digital signal conversion and extraction means. Is sampled by changing the cathode potential of the cold cathode array, thereby directly converting the electric signal read by the charge reading unit into a digital signal and extracting the digital signal to the outside. It may be a configuration. That is, as described later with reference to FIGS. 1 and 2, the cathode potential of the corresponding cold cathode is changed for each pixel per unit time based on the count value, and the cathode potential at that time is changed. Sampling is performed by comparing the potential with the scanning surface on the photoelectric conversion film. By using as a switch a current flowing to balance the scanning surface potential to the cathode potential when the scanning surface potential is higher than the cathode potential, the sampled scanning surface potential is directly extracted as a digital value as a counter value, The object of the present invention can be solved.

According to the present invention, when a signal charge stored in a unit pixel of the target portion is directly taken out as a digital signal, a current used as a switch is used as a surplus signal of the digital signal as an external signal as an external signal or as an external signal. The digital signal may be further converted into a digital signal, and the digital signal which is an upper bit may be used as a digital signal of a lower bit. Thus, the number of gradations can be dramatically increased. The present invention may further have a configuration in which the amount of change in the cathode potential that changes with time can be controlled from the outside, and thus γ correction generally performed in a so-called imaging device can be achieved. A structure in which a transparent electrode is divided into a plurality of parts, and divided reading means for reading out the stored signal charges from each of the divided areas, and simultaneously reading the signal charges stored in pixels at relatively the same position in each of the areas. The reading configuration may be used. Thus, the selection period of one pixel can be lengthened, so that the number of bits of the counter can be increased. As a result, the number of gradations can be increased, and the problem of the present invention can be more easily solved.

[0010]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of a digital output imaging apparatus according to a first embodiment of the present invention, and FIG. 2 is a view for explaining the operation principle thereof. The configuration of FIG. 1 is referred to as single signal readout in correspondence with the multiple simultaneous signal readout according to the second embodiment described later. The configuration of the image pickup device 113 shown in FIG. 1 is exactly the same as the structure of the image pickup device constituting the photoconductive imaging device of the above-mentioned Japanese Patent Application Laid-Open No. H11-26011 shown in FIG.

A positive charge (hole) corresponding to the intensity of the incident light 107 from the outside is generated in the photoelectric conversion film 111 and has a certain potential accumulated on the scanning surface side. As the photoelectric conversion film, for example, HARP (High-ga) having a size of 1 inch and a thickness of 8 μm is used.
When a reference signal amount for obtaining 100% white of the TV standard is set to, for example, 200 nA using an in-avalanche rushing amorphous photoconductor) film, the back potential of the photoelectric conversion film is about 3.2 V. On the other hand, a cold cathode array having an XY matrix structure is used as a means for reading out the electric charges accumulated in the photoelectric conversion film. A gate electrode (304 in FIG. 3) is used to select a line in the vertical (Y) direction, and a cathode electrode (3 in FIG. 3) is used to select a pixel in the horizontal (X) direction.
02, 112 in FIG. 1).

A selection period of an arbitrary line (horizontal direction) is set to, for example, 63.5 microseconds, and a voltage of, for example, about 80 V is applied to the gate electrode during this period. The selection period of a certain pixel on one selected line is set to, for example, 750 nanoseconds (1
The line becomes about 80 pixels), and a unit time, for example, 46.9 nanoseconds from 16 (2 ⁴ ) to 0, for example, 46.9 nanoseconds (original clock 1)
01 pulse), and the cathode potential previously set in the look-up table 103 is set to, for example, 4 V in accordance with the output value of the counter 102.
From 0 V to 0.2 V every 0.25 V and output from the cathode electrode potential setting circuit 104.

The potential of the photoelectric conversion film scanning surface is, for example, 3.2 V
In the case of (1), when the cathode potential is, for example, 3.0 V (counter value is, for example, 12) and lower than the membrane scanning surface potential (potential comparison 114 operates), an electron beam is emitted from the cold cathode (the switch 115 is turned on) and the scanning surface is turned on. A current flows to the outside 118 until the potential and the cathode potential are balanced. Outside 118
Is used as a switch 116, and a counter value corresponding to the scanning surface potential in an equilibrium state is output 117 to directly obtain a digital unit image signal. That is, the scanning surface potential of the unit pixel of the photoelectric conversion film is sampled by the cathode potential corresponding to the counter value, and a digital signal is output by using the current flowing outside as the switch 116 (sampled digital signal conversion and extraction means, (Corresponding to claim 2).

The external current 118 used as the switch 116 is equal to the amount of surplus accumulated charge with respect to the scanning plane potential in the equilibrium state. Therefore, smoother image information may be obtained by using this current as an analog signal. However, by further digitizing this analog output signal using, for example, a 4-bit A / D converter, the above-mentioned digital output signal can be obtained. It is more preferable to use them together as lower bit signals (corresponding to claim 3). Even after the digital output signal 117 is obtained, the accumulated electric charge still remains on the back surface of the photoelectric conversion film. Therefore, the cathode potential directly follows the counter value, and finally the counter value becomes 0, that is, until the cathode potential becomes 0 V. It is necessary to sequentially lower and sweep out all the charges on the scanning surface of the photoelectric conversion film as a current to reset the scanning surface potential. Next, the counter value is set to an initial state, for example, 16 in the case of 4-bit count, and the same operation is repeated on the adjacent pixel, thereby performing scanning as an image sensor, and directly obtaining a digital image signal.

Further, an additional counter 106 of, for example, about 4 bits, which can be controlled from the outside, is provided, and the maximum potential of the cathode electrode and the amount of potential change for each bit of the count value are changed (performed by the additional counter set signal 105), thereby equivalently. The gamma characteristic can be changed (corresponding to claim 4), and the dynamic range can be expanded. The counter 102 for changing the cathode potential, the additional counter 106, the look-up table 103, and the cathode electrode potential setting circuit 104 may be provided outside the image pickup device of the present invention. Preferably, it is provided close to the array, in which case the entire block diagram of the configuration shown in FIG. 1 will be the digital output imaging device of the present invention.

FIG. 2 is a diagram for explaining the operation of the apparatus of the present invention. FIG. 2 (a) shows the distribution of the surface potential of each pixel in one line (shown by a bold line. Case 1
The horizontal axis indicates the pixel order in the line direction, the vertical axis indicates the accumulated potential of each pixel, and the unit thereof is the digital signal output 11 of the counter 102.
2 (a), the digital signal output 11
The maximum value of 7 is 11. In FIG. 2A, counting from the left, the output of the first pixel is exactly 8 digital outputs, the output of the second pixel is exactly 10 digital outputs, but the output of the third pixel is 8 digital outputs and there is still a surplus output. .

This will be described below with reference to FIG. 2B. In FIG. 2B, the abscissa represents the entire time of one pixel potential comparison as a whole (11 unit time in total), and the ordinate represents the cathode potential to be compared with the accumulated potential of the pixel (indicated by a thick line). The unit is the same as that of FIG. The accumulation potential (A) of the third pixel is sequentially compared with the cathode electrode potential 112 that changes every period of the original clock pulse set by the cathode electrode potential setting circuit 104. 2B, the lower right shaded portion of the third pixel in FIG. 2B becomes the analog signal output 118. At the same time, this turns on the switch 116 and outputs the digital signal (the lower left shaded line of the third pixel). Part). Then, the analog signal output 118 is further converted into a digital signal of lower bits.

Next, a parallel signal reading device according to a second embodiment of the present invention will be described.
A plurality of transparent electrodes (ITO) for supplying an applied voltage to the photoelectric conversion film and extracting a current to the outside, for example, 100
The electric charge on the back surface of the photoelectric conversion film, which is divided and accumulated in the same place relative to the divided area, is to be simultaneously taken out (corresponding to claim 5). In this case, the number of pixels in one divided region is significantly reduced, so that the selection period of one pixel can be increased by, for example, 100 times, and the number of bits of the count can be, for example, 8 bits (256) or more. Can increase. As in the first embodiment, a current flowing to the outside used as a switch when outputting a counter value may be used as an analog output signal, or a digital output signal may be output using, for example, a 4-bit A / D converter. By using them together as lower bit signals of, it is possible to reproduce finer gradations. In the second embodiment, since signals are output simultaneously from a plurality of areas, it is necessary to separately provide an image synthesis processing circuit to synthesize the screen information, and then take out as a serial signal in accordance with the TV standard.

Although the embodiments of the present invention have been described in detail with reference to some examples, the present invention is not limited to these, and various modifications and changes are possible within the gist of the invention. It would be obvious.

[0020]

By applying the means described in the first embodiment, a digital signal can be directly output from the image pickup device without requiring an expensive circuit. Also, by controlling the additional counter from the outside or updating the contents of the lookup table, if necessary, any characteristic (for example, γ
Correction) can be created. By applying the means described in the second embodiment, the selection period of one pixel can be extended, so that the number of bits of the counter can be increased, and as a result, the number of gradations can be increased. Further, in the second embodiment, the selection period of one pixel can be extended, so that even if a high-luminance subject is imaged, the electric charge accumulated on the photoelectric conversion film scanning surface must be completely reset. Can be achieved, the afterimage characteristics can be significantly improved, and the dynamic range can be significantly expanded. Further, even when a current flowing to the outside when the scanning plane potential is balanced with the cathode potential is used as a lower bit via an amplifier and an A / D converter, the A / D converter does not need to be high-speed and requires a high frequency band. Because the area can be narrow,
Inexpensive and high S / N ratio can be maintained. For this reason, even if the number of pixels increases dramatically in the future, the same effect can be expected by increasing the number of divisions of the transparent electrode.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram according to a first embodiment of a digital output imaging apparatus of the present invention.

FIG. 2 is a diagram for explaining the operation of the first embodiment of the digital output device of the present invention.

FIG. 3 is a perspective view showing a basic configuration of a conventional imaging device.

[Explanation of symbols]

 Reference Signs List 101 original clock pulse 102 counter 103 lookup table 104 cathode electrode potential setting circuit 105 additional counter set signal 106 additional counter 107 external incident light 111 photoelectric conversion film 112 cathode electrode 113 image sensor 114 potential comparison 115 switch 116 switch 117 digital signal Output 118 Analog signal output 300 Cold cathode array 301 Substrate 302 Cathode conductor 303 Insulating layer 304 Gate electrode 305 Gate hole (gate opening) 306 Emitter (electron emission source) 307 Electron beam 310 Glass substrate 311 Translucent conductive film (transparent electrode) 312) photoelectric conversion film 313 photoelectric conversion target unit 314 external incident light 315 output terminal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Saburo Okazaki 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Research Institute (72) Inventor Katsugen Nagata 1-10 Kinuta, Setagaya-ku, Tokyo No. 11 Japan Broadcasting Corporation Broadcasting Research Institute (72) Inventor Norifumi Egami 1-10-11 Kinuta, Setagaya-ku Tokyo 10-10-11 Japan Broadcasting Corporation Japan Broadcasting Research Institute (72) Inventor Fumio Okano 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Broadcasting Research Institute F-term (reference) 5C024 AA01 CA15 CA21 DA07 FA03 GA04 HA14

Claims (5)

[Claims] 1. A photoelectric conversion target unit comprising: a transparent electrode that transmits at least incident light from the outside; and a photoelectric conversion film that generates a signal charge by the incident light and stores the signal charge.
A cathode having a plurality of electron emission sources arranged in a matrix; an electron emission source selection means capable of selecting any of the electron emission sources; and an electric signal for storing signal charges accumulated in pixels at arbitrary positions of the target portion. A digital readout imaging device comprising: a charge readout unit that reads out the data as a digital signal; and a digital signal conversion extraction unit that directly converts an electric signal read by the charge readout unit into a digital signal and takes out the digital signal to the outside. 2. A cold cathode array is used as a cathode having a plurality of electron emission sources arranged in a matrix,
By sampling the signal charges accumulated in the unit pixels of the target section by changing the cathode potential of the cold cathode array as the digital signal conversion and extraction means, the electric signal read by the charge reading means is directly output. 2. A sampling digital signal converting and extracting means for converting the digital signal into a digital signal and extracting the digital signal to the outside.
Digital output imaging device as described 3. The method according to claim 1, wherein when the signal charge stored in the unit pixel of the target section is directly taken out as a digital signal, a current used as a switch is used as a surplus signal of the digital signal as an external analog signal or externally as a digital signal. 3. The digital output imaging device according to claim 2, wherein the digital signal is used as a lower-order digital signal for the higher-order digital signal by signalization. 4. The digital output imaging apparatus according to claim 2, wherein the amount of change in the cathode potential that changes with time can be controlled from the outside. 5. A structure in which the transparent electrode is divided into a plurality of parts and divisional readout means for reading out the stored signal charges from each of the divided areas, and stores the signal charges in pixels at relatively the same position in each of the areas. The digital output imaging device according to any one of claims 2 to 4, wherein the read signal charges are simultaneously read.