CA1278621C - Image sensing apparatus - Google Patents

Abstract

ABSTRACT

An image sensing apparatus includes a photoelectric conversion device with photoelectric conversion elements arranged in rows and columns for non-destructive read out to generate an image line using a set of signals from several rows of conversion elements. A control circuit simultaneously reads out the signals from a group of three adjacent rows to produce a horizontal scan line, each line corresponding to a different group of rows. The groups of rows belonging to consecutive lines in an image field partially overlap with each other. The apparatus also includes a signal processing circuit for processing the signals from the group of rows to generate a double differentiation correction signal.

Description

1~78~

The present invention relates to an image sensing apparatus using a photoelectric conversion element having a photoelectric charge storage region in which a potential is controlled by a capacitor.
An image sensing apparatus according to the present invention is applicable to image input devices, workstations, digital copying machines, wordprocessors, bar code readers, and automatic focusing photoelectric conversion object detection devices for cameras, video cameras, 8-mm movie cameras, and the like.
Research on photoelectric conversion devices and in particular on solid state sensors is concentrated on CCD and MOS devices.
In a CCD sensor, a potential well is formed below a MOS capacitor electrode. A charge generated upon reception of light is stored in the well. During readout, the potential wells are sequentially operated by pulses applied to the electrodes, and the stored charges are transferred to an output amplifier.- The CCD sensor therefore has a relatively simple structure, generates low noise, and allows image sensing at low luminances.
The operation principle of a MOS sensor is as follows. Upon reception of light, charges are stored in photodiodes of p-n junctions constituting light-receiving sections. During readout, MOS switching transistors connected to the respective diodes are sequentially read out ~ yr ~278~

to an output amplifier. Therefore, a MOS sensor has a more complex structure than a CC~ sensor. However, a MOS sensor can have a high storage capacity and wide dynamic range.
Of the two types oE conventional sensors described ahove, a CCD sensor has the following drawbacks.
1) Since a MOS amplifier is formed on a chip as an output amplifier, l/f noise is generated from the interface between the si and the silicon oxide film, thus interfering with normal display.

2) When the number of cells is increased and cells are integrated at a high speed in order to provide high resolution, the maximum charge amount which can be stored in a single potential well is reduced and a wide dynamic range cannot be obtained.

3) Since a CCD sensor has a structure wherein stored charges are transferred, if even a single cell fails the transferred charges stop at the failed cell. Thus manufacturing yield is low.
An MOS sensor has the following drawbacks.
1) Since a wiring capacitance is connected to each photodiode, a large signal voltage drop occurs when a signal is read out.
2) Wiring capacitance is large, and random noise is easily generated.
3) Fixed pattern noise tends to become mixed in due to variations in the parasitic capacitance of a scanning MOS
switching transistor. Hence, image sensing at low luminances cannot be performed. When cells are reduced in size in order to allow high resolution, stored charges are reduced.
However, since the wiring capacitance is not decreased very much, the S/N ratio is reduced.
Neither CCD nor MOS sensors, therefore, can provide high resolution. As a result, a semiconductor image sensing apparatus of a new type has been proposed (Japanese Laid-Open 35 Patent Gazettes Nos. 150878/1981, 157073/1981 and 165473/1981). In an apparatus of this type, a charge 1278~

generated upon liqht reception is stored in a control electrode (e.g., the base of a bipolar transistor, or the gate of an electrostatic induction transistor SIT or a MOS
transistor). The stored charge is read out by charge amplification using the amplifying function of each cell.
With this apparatus, high output, wide dynamic range, low noise, non-destructive read out, and high resolution can be provided .
However, this apparatus is based on an X-Y address lo system. In addition, each cell has a basic structure wherein an amplification element such as a bipolar transistor or an SIT transistor is coupled to a conventional MOS cell. These factors have limited improvements in resolution.
In an image sensing element capable of non-destructive read out, the width of a wiring for X-Y
addressing must be minimized in order to guarantee a certain operating rate of the element. For this reason, the wiring capacitance is low, and the gain of the image sensing element is limited.
It is an object of the present invention to provide an image sensing apparatus which can alleviate the drawbacks of conventional image sensing apparatuses.
It is another object of the present invention to provide an image sensing apparatus which can form an image of high ~uality with a simple configuration.
According to the invention, an image input device comprises:
a photoelectric conversion device comprising a plurality of photoelectric conversion elements which are arranged in row and column directions, said elements being capable of non-destructive read out; and signal processing means, for operating upon signals of three adjacent rows which are read out simultaneously to generate a double di~ferentiation correction signal.
Further features of the invention will be apparent from the following description of preferred embodiments 12'786~L

thereof with reference to the accompanying drawings, in which:
Fig. lA is a plan view of a photosensor cell according to an embodiment of the present invention;
Fig. 1~ is a sectional view of the cell;
Fig. 2 is an equivalent circuit diagram of the cell;
Fig. 3A is a graph showing read out voltage and read out time as a function of storage voltage;
Fig. 3B is a graph showing the read out time as a function of the bias voltage;
Fig. 4A is an equivalent circuit diagram during a refresh operation;
Fig. 4B is a graph showing base voltage as a function of refresh time;
Fig. 5 is a circuit diagram showing an image sensing photoelectric conversion device;
Fig. 6 is a diagram for explaining the drive method of the device shown in Fig. 5;
Fig. 7 is a block diagram showing an example of an image sensing apparatus;
Fig. 8A is a block diagram showing the configuration of a second embodiment of the present invention;
Fig. 8B shows waveforms of signals at respective points in the circuit shown in Fig. 8A;
Fig. 9 is a diagram for explaining the drive method of the second embodiment;
Fig. 10 is a block diagram showing the configuration of a switch circuit 101;
Fig. 11 is a table for explaining the operation of the switcn circuit 101;
Fig. 12 is a block diagram showing a third embodiment of the present invention;
Fig. 13 is a table showing the drive method of a switch circuit 80;
Fig. 14 is a block diagram showing a fourth embodiment of the present invention;

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~ ig. 15A is a block diagram of a conventional edge compensation circuit; and Fig. 15B shows waveforms of signals at respective parts of the circuit shown in F:ig. 15A.

DETAII.ED DESCRIPTION OF THE PREFERRED EMBODIMEN~S
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
Figs. lA and lB are diagrams explaining the basic structure of a photosensor cell and its operation in a photoelectric conversion device utilized in embodiments of the present invention.
Fig. lA shows a plan view of a photosensor cell 100 used as a photoelectric conversion element. Fig. lB shows a sectional view of the structure of Fig. lA along the line A-A', and Fig. 2 shows an e~uivalent circuit for the structure. The same reference numerals throughout Figs. lA, lB, and 2 denote the same parts.
In Fig. 1, a plan view of an aligned array system is illustrated. In order to improve horizontal resolution, a pixel shifting (staggered) arrangement can be adopted.
The photosensor cell as shown in Figs. lA and lB
comprises~
A passivation film 2 which is formed of a PSG film or the like on a silicon substrate 1 and in which an impurity such as phosphorus (P), antimony (Sb) or arsenic (As) is doped to obtain a conductivity type of n or n~;
an insulating oxided film 3 consisting of a silicon oxide film (Sio2);
an element isolation region 4 comprising insulating films or polysilicon films consisting of SiO2 or Si3N4 for electrically isolating adjacent photosensor cells;
an n -type region 5 having a low impurity concentration and formed by epitaxy;

~8Ç,~l a p-type region 6, which serves as the base of a bi~olar transistor obtained by the doping of an impurity with an impurity diffusion technique or an ion-implantation technique;
an n~-type region 7, which serves as the emitter of a bipolar transistor formed by an impurity dif~usion technique or an ion-implantation technique;
a lead 8 consisting of a conductive material such as Al, Al-Si, Al-Cu-Si or the like for the external readout of signals;
an electrode 9 for applying a pulse to the floating p-type region 6;
a lead 10 for the electrode 9;
an n~-type region 11 having a high impurity concentration and formed by an impurity diffusion technique or the like on the rear side of the substrate l to obtain an ohmic contact; and an electrode 12 for providing a substrate potential and consisting of a conductive material such as aluminum to provide a collector potential for the bipolar transistor.
A contact 19 shown in Fig. lA connects the n+-type region 7 and the lead 8. The intersection of the leads 8 and is a double layer structure, in which the leads are insulated from one another by an insulating region composed of an insulating material such as SiO2, to provide a bilayered metal wiring structure.
A capacitor Cox 13 in the equivalent circuit shown in Fig. 2 has a MOS structure consisting of the electrode 9, the insulating film 3, and the p-type region 6. A bipolar transistor 14 consists of the n~-type region 7 as an emitter, the p-type region 6 as a base, the n~-type region 5 having a low impurity concentration, and the n~ or n~-type region 1 as a collector. As can be seen from the accompanying drawings, the p-type region 6 is a floating region.
The second equivalent circuit shown in Fig. 2 is expressed by a base-emitter junction capacitance Cbe 15, a 1'~786~

hase-emitter p-n junction diode ~be 16, a ~ase-collector junction capacitance Cbc 17, a base-collector p-n junction diode Dbc 18, and ~urrent sources 19 and 20.
ThP base operation of the photosensor cell will be described below with reference to Figs. lA, lB and 2, and involves a charge storage operation upon light reception, a read out operation, and a refresh operation. In the charge storage operation, the emitter is grounded through the lead 8, and the collector is biased to a positive po~ential lo through the electrode 12. The base is set to a negative potential, i.e., reverse biased with respect to the emitter region 7 by applying a positive pulse voltage through the lead lo to the capacitor cox 13. siasing to the negative potential of the base 6 by application of a pulse to thP
capacitor Cox 13 will be described in detail with reference to the refresh operation below.
When light 20 becomes incident on the photosensor cell shown in Fig. lB, electron-hole pairs are generated in the semiconductor. Since the n-type region 1 is biased to a positive potential, electrons flow to the side of the n-type region 1. However, holes are stored in the p-type region 6.
When holes are stored in the p-type region 6 in this manner, the potential of the p-type region 6 gradually changes toward a positive potential.
Referring to Figs. lA and lB, the lower light-receiving surface of each cell is mostly occupied by a p-type region and is partially occupied by the n+-type region 7.
Naturally, the concentration of electron-hole pairs which are photo-excited increases toward the surface. Therefore, many electron-hole pairs are excited by light in the p-type region 6. If electrons photo excited in the p-type region flow without recombination and are absorbed by the n-type region, holes excited by the p-type region 6 are stored and move the region 6 to a positive potential. If the impurity concentration in the p-type region 6 is uniform, photo-excited electrons flow to the p-n junction between the p-l~q86~

type region 6 and the n~-type region 5. Thereafter, the electrons are absorbed in the n-type collector region 1 by drift due to a strong electric field applied to the n -type regior,. Note that electrons in the p-type reyion 6 can be 5 transferred by diffusion alone. However, if the impurity concentration of the p-type base is controlled to increase from the surface to the inside, an electric field given by:
Ed = (l/WB) (kT/q) ln (NAs/2~Ai) (where WB is the depth of the p-type region 6 from the light-incident surface, k is the Bolzmann's constant, T is theabsolute temperature q is the unit charge, NAs is the surface impurity concentration of the p-type base region, and NAi is the impurity concentration at the interface between the p-type region 6 and the n~-type high-resistance region 5) directed toward the surface from the inside of the base is formed in the base due to the impurity concentration difference.
If we assume that NAs/NAi > 3, transfer of electrons in the p-type region 6 is performed by drift in place of diffusion. In order to effectively obtain carriers photo excited in the p-type region 6 as a signal, the impurity concentration of the p-type region 6 preferably reduces from the light-incident surface to the inside. When the p-type region 6 is formed by diffusion, the impurity concentration reduces from the surface to the inside.
A portion of the sensor cell below the light-receiving surface is partially occupied by the n+-type region 7. Since the depth of the n+-type region 7 is normally about 0.2 to 0.3 ~m or less, the amount of light absorbed by the n+-type region 7 is not large and does not present a problem.
However, for light having short wavelengths, in particular, for blue light, the presence of the n+-type region 7 may lower sensitivity. The impurity concentration of the n+-type region 7 is normally designed to be about 1 x 102 cm~3 or more. The diffusion distance of holes in the n+-type region 7 in which an impurity is doped to a high concentration is 1~7~6~

0.15 to 0.2 ~m. Therefore, in order that holes photo-excited in the n+-type region 7 may effectively flow into the p-type region 6, the n'-type region 7 also preferably has a structure wherein the impurity concentration decreases from the light-incident surface to the inside. When the impurity concentration of the n'-typ region 7 is as described above, a strong drif~ electric field directed from the light-incident surface to the inside is generatea~ and holes photo-excited in the n'-type region 7 immediately flow into the p-type re~ion 6. When the impurity concentrations of the n'-type region 7 and the p-type region 6 decreases from the light-incident surface to the inside, carriers photo-excited in the n~-type region 7 and the p-type region 6 at the light-incident surface side of the sensor cell all serve to generate a photo signal. When the n+-type region 7 is formed by impurity diffusion from a silicon oxide film or a polysilicon film in which As or P is doped in a high concentration, an n~-type region having a preferable impurity concentration profile as described above can be obtained.
Upon storage of holes, the base potential changes to the emitter potential and then to ground level where it is clipped. More specifically, the base-emitter path is forward-biased, and clipped at a voltage at which the holes stored in the base begin to flow to the emitter. The saturation potential of the sensor cell is approximately given by the potential difference between the ground potential and the bias potential, which is used to bias the p-type region 6 first to a negative potential. If the n'-type region 7 is not grounded and a charge is stored by a photo input in the floating state, the p-type region 6 can store the charge to a potential which is substantially the same as that at the n-type region l. In the MOS sensor, fixed pattern noise due to variations in the parasitic capacitance of a switching MOS transistor for external read out, and random noise due to a high wiring capacitance or an output capacitance are high, and a satisfactory S/N ratio 12786;2 1 cannot be obtained. In the photosensor cell of the structure shown in Figs. lA, lB and 2, the voltage stored in the p-type region 6 is externally read out. Since the voltage is relatively high, fixed pattern noise and random noise due to output capacitance is reduced relative to the high voltage, and signals with an excellent S/N ratio can be produced.
Another advantage of the photosensor cell of the above configuration is a provision of non-destructive read out of holes stored in the p-type region 6 due to a low recombination rate between electrons and holes in this region 6. When a voltage VR applied to the electrode 9 during read out is returned to zero volts, the potential of the p-type region 6 is reverse-biased as before application of the voltage VR. Thus, the stored voltage VR generated before light irradiation is maintained unless another light irradiation is performed. When the photosensor cell of the above configuration is used to constitute a photoelectric conversion device, this capability of non-destructive read outs provides the potential for new systems having new modes of operation.
A time for which the stored voltage Vp can be stored in the p type region 6 is very long, and the maximum storage time is limited by a dark current which is thermally generated in a depletion layer at the junction. This is because the photosensor cell is saturated by a thermally generated dark current. However, in the photosensor cell of the configuration described above, the region of the depletion layer is the n~-type region 5, having a low 30 impurity concentration such as about 1012 cm~3 to 1014 cm~3; it has a very good crystallinity and only a small number of electron hole pairs are thermally generated as compared to a MOS or CCD sensor. The dark current is therefore lower than other conventional devices, and the photosensor cell of above-described configuration has low noise.

lX78~1 Refresh operation of the charge stored in the p-type region 6 will now be described. In a photosensor cell of the configuration described above, the charge stored in the p-type region 6 is held unless it is removed. Therefore, in order to input new optical information, a refresh operation for erasing the previous charge is required. At the same time, the potential of the floating p-type region 6 must be charged to a predetermined negative potential.
As in the case of a read out operation, a refresh operation is performed by applying a positive voltage to the electrode 9 through the lead 10. The emitter is grounded through the lead 8. The collector is set at the ground potential or at a positive potential through the electrode 12.
Fig. 3A is a graph showing read out voltage and read out time as a function of storage voltage. Fig. 3B is a graph showing read out time as a function of bias voltage.
Fig. 4A is an equivalent circuit diagram of the refresh operation, and Fig. 4B is a graph showing base voltage as a function of refresh time.
As described above, the basic structure of the photosensor cell of the above configuration is simpler than those disclosed in Japanese Laid-Open Patent Gazettes Nos.
150878/1981, 157073/1981 and 165473/1981. The structure allows high-resolution applications which are feasible in the near future while it also maintains advantages of conventional structures such as low noise, high output, wide dynamic range, and non-destructive read out.
An embodiment of a photoelectric conversion device having two arrays of photosensor cells will be described below. Fig. 5 shows the configuration of a circuit of a photoelectric conversion device having a two-dimensional array (matrix) of basic photosensor cells.
The device has basic photosensor cells 30 (the collector of the bipolar transistor is connected to the substrate and the substrate electrode) an example of which is 1 ~78~

surrounded by a dotted line; horizontal lines 31, 31', 31",..., for applying read out pulses and refresh pulses; a vertical shift register 32 for generating read out pulses;
buffer MOS transistors 33, 33', 33", ..., bstween the 5 vertical shift register 32 and the horizontal lines 31, 31', 31" ...,; a terminal 34 for applying pulses to the gates of the transistors 33, 33', 33" ...,; buffer MOS transistors 35, 35', 35", ..., for applying refresh pulse~;; a terminal 36 for applying pulses to the gates of the transistors 35, 35', 35", 10 ...,; a vertical shift register 52 for applying refresh pulses; vertical lines 38, 38', 38", ..., and 51, 51', 51"
..., for reading out stored voltages from the basic photosensor cells 30; a horizontal shift register 39 for generating pulses so as to select the respective vertical 15 lines; gate MOS transistors 40, 40', 40", .. , and 49, 49', 49" ..., for enabling or disabling the respective vertical lines; output lines 41 and 59 for reading out the stored voltages to an amplifier section; MOS transistors 42 and 53 for refreshing the charge stored on an output line; terminals 20 43 and 54 for applying refresh pulses to the MOS transistors 42 and 53, transistors 44 and 55 (e.g., bipolar, MOS, FET, J-FET transistors) for amplifying output signals; tsrminals 46 and 57 for connecting load resistors 45 and 56 and the transistors 44 and 55 to a power source; signal output 25 terminals 47 and 58; MOS transistors 48, 48', 48", .. , and 50, 50', 50", ..., for refreshing the charges stored on the vertical lines 38, 38', 38", ..., and 51, 51', 51", ...,; and a terminal 60 for applying pulses to the gates of the MOS
transistors 48, 48', 48", ..., and 50, 50', 50", ...
The image sensing apparatus comprises a clock driver CKD for supplying drive pulses to the respective portions 32, 34, 36, 39, 43, 54 and 60 of the photoelectric conversion device, and a clock generator CKG for supplying timing pulses to the clock driver CKD. The clock driver CKD and the clock 35 generator CKG constitute the control means.

lX786~1 Fig. 6 is a diagram showirlg the me~hod of driving the apparatus by the control means. In odd fields, line data 11 and 12 forms horizontal scanning line nl, line data 13 and 14 forms horizolltal scanning line n2, and line data 15 and 16 form horizontal scanning line n3. In even fields, line data 12 and 13 form horizontal scanning line ml, line data 14 and 15 form horizontal scanning line m2, and line data 16 and 17 form horizontal scanning line m3.
Line data of two horizontal lines is simultaneously read out, and the read out data appears at the output terminals 47 and 58.
Fig. 7 shows a first configuration of image sensing apparatus utilizing a photoelectric conversion device 100 as shown in Fig. 5 and providing edge correction. It comprises a switch circuit 68 for inputting the two line signals from the device 100 to different terminals 72 and 73 for each field, a subtractor 69, a level adjustment resistor 70, and an adder 71. Such an arrangement is also applicable to a conventional X-Y address type MOS image sensor.
In an odd field, an edge signal is obtained in block APC by subtracting an output at the terminal 47 from an output from the terminal 58. After the level of the edge signal is adjusted by the resistor 70, it is added to the original signal from terminal 47 by the adder 71 so as to obtain an edge-corrected video signal. In an even field, the output from the terminal 58 is subtracted from that from the terminal 47 to obtain an edge signal. After the level of the edge signal is adjusted by the resistor 70, it is added to the original signal from terminal 58 by the adder 71.
The clock driver CKD switches the switch 68 for each field. Edge correction can be performed without using a delay circuit, using the very simple circuit shown in block APC in Fig. 7, which provides an edge signal generation block acting as a processing means or an edge signal generating means which provides a differentiated correction signal.

.

Fig. 8A is a block diagram showing a further embodiment of processing means. The embodiment uses a photoelectric conversion device which is generally similar to that of Figure 5 except that it simultaneously reads the line 5 information of three horizontal lines.
Certain of the same reference numerals as are used in Fig. 5 are used to denote similar parts in Fig. 8A. In Fig.
8A, the clock driver circuit CKD also controls a switch circuit lOl.
Fig. 8B shows waveforms of the signals f(a), f(b), f(c) and f(d) at the correspondingly identified points a, b, c and d of the circuit shown in Fig. 8A. Plots a to d show the waveforms in odd fields; d', the output waveform from an adder 65 in an even field; and d", a double differentiated edge signal in a frame image, equal to d + d'.
The signal f(d) (plot d in Figure 8b) at point d in Figure 8A is the second differential of the signal f(c) (plot c in Figure 8b). By mathematical definition, the first differential df(c)/dt of signal f(c) at the terminal c is provided by the following expression:
df(c)/dt = lim f(c)-f(c+~t) /~t............ (l) ~ t~0 and its second differential is as follows:
dZf(c)/dt2 = lim ~f(c)-ftc+~t)~ - ~f~c+~t)-f!c+2 ~t~0 (~t) ............ (2) in which f(c+~t) and f(c+2~t) are signals at time lags4t and 2~t respectively from the signal f(c). If 4t = lH, f(c+4t) and f(c+2~t) can be replaced with f(b) and f(a) respectively, that is, f(c+~t) = f(b) and f(c+2~t) = f(a), and expression (2) becomes:
d2f(c)/dt2 = lim i(f(c)-f(b))-(f(b)-f(a)~ /(4t)2 ~t~0 = lim ~ 2 f(b)-(f(a~+f(c))/2~ --(3) ~t~0 2 (~t~ _ 7862~

Because ~t = lH~0, d2f(c)/dt2 approximates to a slope of the first differential for a section ~t, that is, d f(c)/dt ~ ~ --{f(b)-(f(a)+f(c))/2~ .. (4) which in turn ~valuates to:
2 _ f(d) (4t) since f(b)-(f(a)+f(c))/2 is the function performed by the 10circuit formed by the parts 64, 65, 66 and 67 in Figure 15a.
Moreover 2 2 iS a constant, so that the signal f(d) at (4t) terminal d is proportional to the second differential of the signal f(c).
15Signals, successively delayed by lH intervals, for producing an edge emphasized signal as discussed above and as graphically illustrated in Figure 15B, could be obtained using lH delay lines 60 and 61 as shown in Figure 15A. The function f(b)-(f(a)+f(c))/2 is performed by adders 63, 65 and 66, a coefficient circuit 64, and a level adjustment resistor 67.
In Fig. 15B, plots a to d show waveforms of signals in odd fields; plot d', an output from the adder 65 in even fields; plot d", an edge signal of a frame image; and plot e", an edge emphasized signal of a frame image.
The arrangement of Figure 15A has the disadvantage that two expensive delay lines must be used, and the circuit configuration becomes complex. Since signals delayed by successive lH intervals are available simultaneously in the arrangement of Figure 8A, these disadvantages can be avoided.
Fig. 9 is a diagram showing the wiring of output lines of the photoelectric conversion device 100 and the method of read out of these lines by the clock driver.
In this embodiment, in an odd field, the clock driver simultaneously reads out lines ll to 13 as the horizontal scanning line nl, then lines 13 to 15 as the horizontal 1;~7~36~1 scanning line n2, lines 15 to 17 as the horizontal scanning line n3, and lines 17 to 19 as the horizontal scanning line n4.
In an even field, the clock driver simultaneously reads out line 12 to 14 as the horizontal scanning line ml, lines 14 to 16 as the horizontal scanning line m2, and lines 16 to 18 as the horizontal scanning line m3.
~ ig. lo shows the inter~al functions of the switch circuit 101 for establishing correspondence between output terminals 01, 02 and 03 of the device 100 and outputs a, _ and c of switch 101 as in Fig. 8A. The clock driver CKD
switches the outputs in combinations which are different for each field and each line, as shown in Fig. 11. Since the switch circuit 101 is disposed between the device loO and the circuit APC as shown in Fig. 8A, an edge compensation circuit need only be incorporated for one combination of the outputs a, b and _ as shown in Fig. 8A, so that the overall construction is simplified.
Fig. 12 is a block diagram showing a further embodiment. The apparatus has adders 74, 76, 78 and 83, weighting circuits 75 and 79, a level adjustment resistor 77, a switch circuit 80, an intensity signal processing circuit 81, and a color signal processing circuit 82.
In this embodiment, as in the previous embodiment, edge correction can be performed without using delay lines or the like, but the configuration of the switch circuit 80 can be simplified. In addition, only one series of parts 75 and 79 is required, and the wiring in the device 100 can be simplified. In this case the various switching combinations as shown in Figure 11 can be achieved by the action of switching circuit 80, which selects one of the signals 01, 02 and 03, the amplitude of the selected signal being increased by 50% so as to cancel the component of that signal in the output of the divider 75. The end result is the same as that produced by the circuit of Figure 8A, but the switching is much simpler.

~ 786~1 Fiy. 13 shows how the switching operation of the switch circuit 80 can be controlled. of three horizontal lines simultaneously read, the central horizontal line is handled as an original signal, and the upper and lower line signals correspond to signals relatively delayed and advanced by lH, respectively.
Thus by simultaneously reading a plurality of lines of a photoelectric Con~ersion device, ~he signals from a plurality of lines are immediately available to generate an edge-corrected signal, greatly simplifying the signal processing system. A switch circuit is provided for changing the combination in which the p]urality of line signals are supplied to a processing circuit so that only a single processing circuit is required, and the overall configuration is simplified. Connections within the photoelectric conversion device are also simplified.
When a photoelectric conversion device capable of non-destructive read out is used, three or more horizontal lines can be simultaneously read out, whilst the signals can be read out in part-ally overlapped groups upon each horizontal scan, thereby improving vertical correlation. An edge signal of the second order or greater can be obtained.
The switching circuit can be incorporated in the photoelectric conversion device.
Since the vertical correlation distance is small, inclusion of a false signal is rare. By providing a switching circuit for switching the output lines of the photoelectric conversion device, the construction of the edge signal generating means and the photoelectric conversion device can be simplified.
Fig. 14 shows an arrangement such that a defective pixel in a photoelectric conversion device can be corrected.
The same reference numerals used in Fig. 13 denote the same parts in Fig. 14.
The apparatus shown in Fig. 14 has an adder 84, a weighting circuit 85, a switch 86 as a switching means, a 127~36~1 subtracter 87, and a ROM storing the position of a defective pixel. The parts 84 to 87, 66, 67, and the like constitute an edge correction processing means.
A switch circuit lol converts the three horizontal line signals read out from output terminals ol, 02 and 03 of the device 100 to obtain signals a, b and c as in Fig. 11.
The signal b is the middle of the three horizontal lines read out simultaneously from the photoelectric conversion device.
It is assumed for purposes of illustration that the signal b contains a dropout at a predetermined pixel position.
The position of the defective pixel is prestored in the ROM 88. The ROM 88 is driven by a sync signal from a clock generator CKG. The switch 86 is switched from a position x to a position y at the position of the defective pixel. With the switch in the y position, the signal b is replaced by a signal which is an average of the signals a and c. The adder 84 and the weighting circuit 85 form the average signal. The average signal is also subjected to subtraction at the subtracter 87 to form an edge signal d.
Operation is otherwise the same as that previously described.
Correction of a defective pixel can thus be performed without using a delay line, whilst the circuit configuration can be simplified, and the image quality improved. The manufacturing yield of the photoelectric conversion device can also be improved. Dropouts of the signal b could be directly detected, and the switch 86 driven directly.
A defective pixel can thus be corrected by a simple circuit, and is replaced by a signal derived from adjacent pixels having high correlation.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS :

1. An image input arrangement comprising:
a photoelectric conversion device comprising a plurality of photoelectric conversion elements which are arranged in row and column directions, said elements being capable of non-destructive read out; and signal processing means, for operating upon signals of three adjacent rows which are read out simultaneously to generate a double differentiation correction signal.

2. An arrangement according to claim l, further comprising control means for simultaneously reading out signals of said three rows in each horizontal scanning, said each set of three rows being selected to partially overlap with another said set.

3. An arrangement according to claim l, wherein the signal processing means generates the correction signal by subtracting the average of two of the signals from the third.

4. An arrangement according to claim 3, wherein switching means is provided to determine which of the signals forms which function in the signal processing means.

5. An arrangement according to claim 4, wherein the switching means selects each of the signals utilized in the processing means.

6. An arrangement according to claim 4, wherein the switching means selects only the third signal, and the signal processing adds all three signals, divides the sum by two and subtracts it from the third signal augmented by half.