DEVICE AND METHOD OF PHOTO-ELECTRICALLY CONVERTING LIGHT INTO ELECTRICAL SIGNAL

Abstract: A photoelectric transducer device controls a potential of a control electrode region (4) of a semiconductor transistor through a capacitor to perform a storage operation for stor­ ing carriers generated upon light excitation of the control el­ ectrode region (4), a read operation for reading a signal from a main electrode region of the semiconductor transistor. A semiconductor region (6) having the same conductivity type as that of the main electrode region and having an impurity concentration lower than that of the main electrode region (5) is formed in the control electrode region. Control means is provided for controlling the potential of the control electrode through the capacitor to electrically neutralize the carriers and means for injecting carriers into the control electrode immediately prior to electrical neutralization of the carriers by the control means is provided.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a device and method of photoelectrically converting light into an electrical signal wherein a potential at a base region of a semiconductor transistor is controlled through a capacitor to store carriers excited with light in the base region, thereby controlling an output from the semiconductor transistor. Related Background Art Fig. 1A is a plan view of a photoelectric transducer device described in EP-A-0132076, Fig. 1B is a sectional view of the device taken along the line I - I thereof, and Fig. 1C is a diagram of an equivalent circuit thereof. Referring to Figs. 1A to 1C, photoelectric transducer cells are arranged on an n-type silicon substrate 101. The photoelectric transducer cells are electrically insulated by an element isolation region 102 made of SiO₂, Si₃N₄ or polysilicon. Each photoelectric transducer cell has the following construction. A p-type impurity is doped to form a p-type region 104 on an n⁻-type region 103 having a low impurity concentration formed by an epitaxial technique or the like. An n⁺-type region 105 is formed in the p-type region 104 by impurity diffusion or ion implantation. The p- and n⁺-type regions 104 and 105 serve as the base and emitter of each bipolar transistor. An oxide film 106 is formed on the n⁻-type region 103. A capacitor electrode 107 having a predetermined area is formed on the oxide film 106. The capacitor electrode 107 opposes the p-type region 104, interposing the oxide film 106 therebetween, thereby constituting a capacitor C ox . Upon application of a pulse voltage to the capacitor electrode 107, the potential of the p-type region 104 in the floating state is controlled. An emitter electrode 108 connected to the n⁺-type region 105, a wiring 109 for extracting the signal from the emitter electrode 108, and a wiring 110 connected to the capacitor electrode 107 are formed at the upper surface side of the substrate 101. An n⁺-type region 111 having a high impurity concentration and an electrode 112 for applying a voltage to the collector of a bipolar transistor are sequentially formed on the lower surface of the substrate 101. The basic operation of the photoelectric transducer device will be described below. Assume that the p-type region 104 as the base region of the bipolar transistor is set in the initial state of a negative potential. Light 113 is incident on the p-type region 104 and carriers corresponding to the amount of light are stored in the p-type region 104 (storage operation). The base potential is changed by the charged carriers. The change in base potential controls a current supplied to an emitter-collector path, and an electrical signal having a level corresponding to the amount of incident light is extracted from the floating emitter electrode 108 (read operation). In order to remove the carriers stored in the p-type region 104, the emitter electrode 108 is grounded and a refresh positive voltage pulse is supplied to the capacitor electrode 107. Upon application of this positive voltage, the p-type region 104 is forward-biased with respect to the n⁺-type region 105, thereby removing the charged carriers. When the refresh pulse falls, the p-type region 104 returns to the initial state of the negative potential (refresh operation). The cycle of storage, read, and refresh operations is repeated. According to the method proposed here, the carriers generated upon reception of light are stored in the p-type region 104 as the base region, and the current supplied between the emitter and collector electrodes 108 and 112 is controlled by the stored carriers. Therefore, the stored carriers are amplified by the amplification function of each cell, and the amplified carriers are read out. Therefore, a high output with high sensitivity and low noise can be obtained. The potential Vp generated by the base by the carriers stored in the base upon light excitation is given by Q/C where Q is the charge of the carriers stored in the base, and C is the capacitance connected to the base. As is apparent from the above mathematical expression, both Q and C are reduced according to the reduction of the cell size when the transducer device is highly integrated. It is thus found that the potential Vp generated by light excitation is kept substantially constant. Therefore, the method proposed by the above prior art is advantageous in a future high-resolution implementation. The change in base potential Vb during the application of the positive refresh voltage to the capacitor electrode 107 is given as follows: (Cox + Cbe + Cbc)dVb/dt = -Ib where Cbe is the capacitance between the base and emitter of the bipolar transistor, Cbc is the capacitance between the base and collector thereof, and Ib is the base current. Fig. 2 is a graph showing changes in base potential Vb during the application of the positive refresh voltage as a function of time. Referring to Fig. 2, the initial base potential at the time of the application of the refresh pulse varies according to the magnitude of the storage voltage Vp. The negative potential in the initial state is changed in the positive direction by the storage voltage Vp upon the storage operation. In this state, when the positive refresh pulse is applied to the capacitor electrode 107, the initial base potential is increased by the storage voltage Vp. As is also apparent from the graph in Fig. 2, the time for maintaining the initial base potential varies according to the magnitude of the initial base potential. However, after the lapse of this period, the base potential Vb is decreased at a constant rate regardless of the initial base potential. If the refresh time t is sufficiently long, the base potential Vb can be controlled to be substantially 0 V regardless of the magnitude of the storage voltage Vp. Therefore, the base potential Vb returns to the predetermined negative potential of the initial state when the refresh pulse falls. However, in order to achieve high-speed operation, the refresh operation is terminated at the refresh time t = t0 and the base potential Vb - Vk in practice. Even if a residual potential of the base potential Vb is present, the base potential Vb can return to the predetermined negative potential when the refresh pulse falls under the conditions wherein the refresh time t = t0 is established and the base potential Vb is constantly the predetermined potential Vk. Therefore, the negative potential can be set to be the initial state. However, in the conventional photoelectric transducer device described above, when the refresh operation is repeated, the residual potential Vk is gradually decreased to undersirably cause an after image phenomenon. Referring to Fig. 2, assume that the initial base potential of a cell receiving a large amount of light is 0.8 V and that the initial base potential of a cell receiving a small amount of light is 0.4 V. When the refresh time the has elapsed, the base potential Vb of the cell receiving a large amount of light becomes the predetermined residual potential Vk. However, the base potential Vb of the cell receiving a small amount of light becomes a residual potential Vl lower than the predetermined residual potential Vk. In this state, if the refresh pulse rises, the base potential Vb of the cell receiving a small amount of light becomes lower than the negative potential of the initial state. From a potential lower than the initial negative potential, storage and read operations are started. Therefore, if the refresh operation is repeated in a low illuminance state, the residual potential of the base is gradually decreased. Even if a high illuminance state is obtained, the resultant output has a level lower than that corresponding to the amount of incident light. In other words, the after image phenomenon occurs due to the following reason. When the refresh operation is repeated, the holes in the base region are recombined to result in their shortage. If the shortage of holes cannot be compensated for a long period of time, i.e., if the low illuminance state continues for a long period of time, the after image phenomenon typically occurs. In a conventional photoelectric transducer device, if its cells are arranged in a matrix form, the following blooming phenomenon also occurs undesirably. Fig. 3 is a schematic circuit diagram of an area sensor using a conventional photoelectric transducer device. Referring to Fig. 3, conventional photoelectric transducer cells 120 of a 3 x 3 matrix are arranged in the area sensor. Emitter electrodes 108 of the cells 120 are connected to corresponding vertical lines in units of columns. Capacitor electrodes 107 are connected to horizontal lines in units of rows. A positive voltage from a vertical scanning unit 121 is applied to the photoelectric transducer cells 120 to perform read access or refresh operation in units of rows. If a given photoelectric transducer cell receives a large amount of light and the potential of the base region 104 is higher than that of the corresponding emitter region 105, the potential of the vertical line connected to this emitter electrode 108 is increased although read access is not performed. If other photoelectric transducer cells, the emitter electrodes 105 of which are connected to the same vertical line, are subjected to read access, a readout signal is output to the corresponding vertical line although the given cell does not receive light. In other words, the blooming phenomenon occurs along the vertical direction. EP-A-0132076 also discloses, in Figures 18 and 19 thereof, an arrangement in which a further p type region is formed in contact with the n- region 103 and spaced from the p type region 104, to provide a further bipolar transistor. In the arrangement of Figure 18 of EP-A-0132076, this p type region is formed beneath the n- region 103, and in use the further p type region is biased sufficiently that the n- region is punched through so that holes are injected into the p type base region 104. This brings the base to zero or a slightly positive potential before the refresh operation is carried out. Figure 20 of EP-A-0132076 shows an arrangement in which a pn junction diode is formed separated from the base and emitter regions of the transistor by an insulating region, and a metal insert makes ohmic contact with the n region of the diode and the p type base of the transistor. A negative clamping potential is supplied from a conductor through the diode to the base of the transistor, so that the base of the transistor cannot go below this clamping potential. SUMMARY OF THE INVENTION According to the present invention there is provided a photoelectric transducer device as set out in claim 1. The remaining claims set out methods of operating such a device. Embodiments of the present invention, given by way of non-limiting example, will be described with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1A is a schematic plan view of a photoelectric transducer device described in EP-A-0132076, Fig. 1B is a sectional view of the device in Fig. 1A taken along the line I - I thereof, and Fig. 1C is an equivalent circuit diagram of the device in Fig. 1A; Fig. 2 is a graph showing changes in base potential during refresh operation as a function of time; Fig. 3 is a circuit diagram of an image pickup device using the photoelectric transucer device described in EP-A-0132076; Fig. 4A is a schematic plan view showing a photoelectric transducer device according to an embodiment of the present invention, Fig. 4B is a sectional view of the device in Fig. 4A taken along the line A - A thereof, Fig. 4C is a sectional view of the device in Fig. 4A taken along the line B - B thereof, and Fig. 4D is an equivalent circuit diagram of the device in Fig. 4A; Fig. 5A is a circuit diagram of an image pickup device using the embodiment of the present invention, and Fig. 5B is a timing chart for explaining the operation of the image pickup device in Fig. 5A; Fig. 6A is a circuit diagram of another image pickup device using the embodiment of the present invention, and Fig. 6B is a timing chart for explaining the operation of the image pickup device in Fig. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS : Preferred embodiments of the present invention will be described with reference to the accompanying drawings below. Fig. 4A is a plan view of a photoelectric transducer device according to an embodiment of the present invention, Fig. 4B is a sectional view of the device taken along the line A - A thereof, Fig. 4C is a sectional view of the device taken along the line B - B thereof, and Fig. 4D is an equivalent circuit diagram of the device. Referring to Figs. 4A to 4C, an n⁻-type epitaxial layer 2 is formed on an n-type silicon substrate 1. Photoelectric transducer elements electrically isolated from each other by an element isolation region 3 are arranged. Note that the element isolation region 3 comprises an SiO₂, Si₃N₄, polysilicon or n⁺-type diffusion region. A p-type base region 4 of a bipolar transistor is formed on the n⁻-type epitaxial layer 2 by impurity diffusion or ion implantation. An n⁺-type emitter region 5 and an n-type region 6 having the same impurity concentration as that of the p-type base region 4 are formed in the p-type base region 4 by impurity diffusion or ion implantation. The n-type region 6 and the p-type base region 4 constitute a diode structure. An oxide film 7 is formed on the n⁻-type epitaxal layer 2, and a capacitor electrode 8 made of polysilicon or the like is formed on the oxide film 7 to supply a pulse to the p-type base region 4. An emitter electrode 9 connected to the n⁺-type emitter region 5, and an electrode 10 connected to the n-type region 6 are formed on the oxide film 7 formed on the substrate 1. An n⁺-type region 11 and a collector electrode 12 are sequentially formed on the lower surface of the substrate 1. A protective film 13 is formed to cover each photoelectric transducer cell. In order to form the diode structure constituted by the control electrode region and the semiconductor region, a proper voltage is applied to the semiconductor region, and thus carriers are injected in the control electrode. For this reason, the potential of the control electrode region at the beginning of refresh operation can be kept sufficiently high. As a result, the potential of the control electrode region at the end of refresh operation can be kept at a desired value, and thus the after image phenomenon can be prevented, unlike in the conventional structure. Even if strong radiation is applied to the photoelectric transducer cell, the excessive carriers can be eliminated through the diode structure. Therefore, the blooming phenomenon can be prevented. The operation of the photoelectric transducer device having the structure described above will be described below. In the strage operation, the p-type base region 4 is kept at a negative potential of the initial state, the emitter region 5 is set at zero potential in the floating state, the capacitor electrode 8 is set at zero potential, and the n-type region 6 is set at zero or a negative potential with a very small magnitude. Thereafter, the collector electrode 12 is kept at the positive potential. In this state, light is incident on each photoelectric transducer element, carriers (holes in this case) corresponding to the amount of incident light are stored in the p-type base region 4. When the potential of the p-type base region 4 is increased upon reception of strong light, the diode formed by the p-type base region 4 and the n-type region 6 is forward--biased. The holes excessively stored in the p-type base region are eliminated outside through the electrode 10. Therefore, the potential of the n⁺-type emitter region 5 is not changed, and no blooming phenomenon occurs. In the read operation, the n⁺-type emitter region 5 and the n-type region 6 are maintained in the floating state. A positive read voltage pulse is applied to the capacitor electrode 8. As described above, an electrical signal corresponding to the amount of light incident on the emitter electrode 9 is read out. In the hole injection operation, the capacitor electrode 8 is set at zero potential, and the n⁺-type emitter region 5 is kept in the floating state. A proper positive potential is applied to the n-type region 6 constituting the diode to reverse-bias the diode so that a depletion layer extends up to the electrode 10. The extended depletion layer causes punch-through, and thus the holes are injected into the p-type base region through the n-type region 6. The potential of the p-type base region 4 is increased. In the refresh operation, the n⁺-type emitter region 5 and the n-type region 6 are grounded. In this state, when a positive refresh voltage pulse is applied to the capacitor electrode 8, the holes stored in the p-type base region 4 are eliminated through the n⁺-type emitter region 5 and the n-type region 6. It should be noted since the potential of the p-type base region 4 is sufficiently high by the hole injection operation, the initial base potential upon application of the refresh pulse is sufficiently higher than the residual potential Vk although this cell is whole in the dark state (Fig. 2). After the lapse of the refresh time t0, the potential at the p-type base region 4 can be kept at the predetermined potential Vk regardless of the amount of the light. In this state, if the positive refresh voltage pulse falls, the p-type base region 4 is kept at the predetermined initial negative potential. By performing the hole injection operation, repetition of the refresh operation does not cause shortage of holes in the p-type base region 4. Therefore, the after image phenomenon occurring in the low illuminance state can be completely prevented. An image pickup device having a two-dimensional configuration of photoelectric transducer cells having the above structure and operated as described above will be described with reference to the accompanying drawings. Fig. 5 is a circuit diagram of an image pickup device having the two-dimensional configuration of photoelectric transducer devices, and Fig. 5B is a timing chart for explaining the operation thereof. Referring to Fig. 5A, photoelectric transducer cells 20 are arranged in a 3 x 3 matrix. Capacitor electrodes 8 of the cells 20 are respectively connected to horizontal lines 21, 21' and 21'' in units of rows. Each horizontal line is connected to a terminal 24 through transistors 23, 23' and 23''. A positive read voltage pulse r is applied to the terminal 24. Each horizontal line is also connected to a terminal 26 through transistors 25, 25' and 25''. A positive refresh voltage pulse f is applied to the terminal 26. Pulse signals r1 to r3 from a vertical shift register 22 are respectively supplied to the gate electrodes of the transistors 23, 23' and 23''. Pulse signals f1 to f3 from the vertical shift register 22 are respectively supplied to the gate electrodes of the transistors 25, 25' and 25''. Electrodes 10 of the photoelectric transducer cells 20 are commonly connected to horizontal lines 27, 27' and 27'' in units of rows. Pulse signals 1 to 3 from the vertical shift register 28 are respectively supplied to the horizontal lines. The emitter electrodes 9 of the photoelectric transducer cells 20 are commonly connected to vertical lines 29, 29' and 29'' in units of columns. The vertical lines are respectively connected to an output line 34 through transistors 33, 33' and 33'' for outputting serial readout signals from the photoelectric transducer cells. The gate electrodes of the transistors 30, 30' and 30'' are commonly connected to a terminal 31, and a pulse signal rs is applied to the terminal 31. Pulse signals h1 to h3 from a horizontal shift register 32 are respectively applied to the gate electrodes of the transistors 33, 33' and 33''. The output line 34 is grounded through a refresh transistor 36 and connected to the gate electrode of a signal amplification transistor 35. An amplified signal from the transistor 35 appears at a terminal 38. The operation of the image pickup device having the arrangement described above will be described with reference to Fig. 5B. The storage operation is performed until time t1. Holes corresponding to the amount of incident light are stored in the p-type base regions 4 of the photoelectric transducer cells 20. It should be noted that even if strong light is incident on some of the photoelectric transducer cells 20, the excessive holes are removed to the horizontal lines 27, 27' and 27'' through the corresponding electrodes 10, thereby maintaining the vertical lines 29, 29' and 29'' at zero potential in the floating state. At time t1, the pulse signal r1 rises, and the transistor 23 is turned on. Subsequently, the pulse r rises to supply the positive read voltage to the horizontal line 21. The photoelectric transducer cells 20 of the first row start reading. In this read operation, the read signals from the cells of the first row appear on the vertical lines 29, 29' and 29''. When the read operation is completed, the transistor 36 is turned on in response to the pulse signal 1rs, so that the residual charge in the output line 34 is refreshed. At time t2, the pulse signal h1 rises to turn on the transistor 33. The signal generated by the photoelectric transducer cell of the first row and the first column and appearing on the vertical line 29 is input to the transistor 35 through the transistor 33 and the output line 34. The amplified signal appears at the terminal 38. Upon completion of this output operation, the pulse signal 1rs rises to refresh the output line 34. Subsequently, the pulse signals h2 and h3 sequentially rise to output signals from the photoelectric transducer cell of the first row and the second column and the cell of the first row and third column to the output terminal 38. Every time an output appears on the output line 34, it is refreshed. When the output operation is completed, the pulse signal 1 from the vertical shift register 28 rises at time t3. The positive voltage is applied to the electrodes 10 of the photoelectric transducer cells 20 of the first row. Hole injection is then performed as described above. Subsequently, at time t4, the pulse signals f1 and rs rise to turn on the transistors 25, 30, 30' and 30'', and the respective vertical lines are grounded. The pulse signal f then rises to apply the positive refresh voltage pulse to the horizontal line 21. As described above, the refresh operation is performed. When the read, hole injection, and refresh operations of the photoelectric transducer cells 20 of the first row are completed, the storage operation is started at time t5. The same operation as in the cells of the first row is started for the cells of the second row at time t5 and the cells of the third row at time t6. More specifically, by sequentially allowing the pulse signals r2, 2 and f2 to rise, the photoelectrical transducer cells 20 of the second row are selected and subjected to the read, hole injection, and refresh operations. At time t6, upon storage operation of the cells of the second row at time t6, the pulse signals r3, 3 and f3 sequentially rise, and the photoelectric transducer cells 20 of the third row are selected. Upon starting of the storage operation of the cells of the third row, the cells of the first row are selected, and the subsequent operations are performed in the same manner as described. All read signals corresponding to the amounts of light incident on the photoelectric transducer cells 20 serially appear at the terminal 38. Since the storage time of the cells 20 of each row is predetermined, the image pickup device is applicable to a television video camera or the like. Fig. 6A is a circuit diagram of an image pickup device using the embodiment described above, and Fig. 6B is a timing chart for explaining the operation thereof. Referring to Fig. 6A, three photoelectric transducer cells 20 are arranged one-dimensionally, and collector electrodes 12 thereof are commonly connected. A positive voltage is applied to the collector electrodes 12. Capacitor electrodes 8 are commonly connected to a terminal 41 through a line 40. A pulse signal r is applied to the terminal 41 so as to perform read and refresh operations. Emitter electrodes 9 are connected to vertical lines 44, 44' and 44''. Electrodes 10 of diodes are commonly connected to a horizontal line 42. The horizontal line 42 is connected to a control circuit 43, and is applied with a pulse signal i or grounded. The vertical lines 44, 44' and 44'' are grounded through transistors 45, 45' and 45'', respectively. The gate electrodes of the transistors 45, 45' and 45'' are commonly connected to a terminal 47 through a line 46. A signal rs is applied to the terminal 47. Each of the vertical lines 44, 44' and 44'' is connected to a corresponding one of the main electrodes of the transistors 48, 48' and 48''. The gate electrodes of the transistors 48, 48' and 48'' are commonly connected to a terminal 50 through a line 49. A signal t is applied to the terminal 50. The other main electrode of each of the transistors 48, 48' and 48'' is grounded through a corresponding one of charge storage capacitors 51, 51' and 51'', and is connected to an output line 54 through a corresponding one of transistors 53, 53' and 53''. The gate electrodes of the transistors 53, 53' and 53'' are connected to parallel output terminals of a shift register 52, respectively. Signals h1 to h3 appear at the parallel output terminals, respectively. The output line 54 is grounded through a refresh transistor 55 and connected to the gate electrode of a transistor 57 serving as an output amplifier. The gate electrode of the transistor 55 is connected to the terminal 56. A signal 1rs is applied to the terminal 56. An output terminal 58 of the transistor 57 is connected to an output terminal 60 through a capacitor and an amplifier 59. The output terminal of the control circuit 43 is connected to a gain control terminal of the amplifier 59 so as to control a gain of the amplifier 59 in response to a signal from the horizontal line 42. The operation of the image pickup device having the arrangement described above will be described with reference to Fig. 6B. The pulse signals rs and 1rs are set at high level to turn on the transistors 45, 45', 45'' and 55. The emitter electrodes 8 of the photoelectric transducer cells 20 and the output line 54 are grounded, and thus the residual charge of the output line 54 is removed. At time t1, the pulse signal t rises to turn on the transistors 48, 48' and 48''. The charge storage capacitors 51, 51' and 51'' are grounded to remove the residual charge. At time t2, the signal t and then the pulse signal i from the control circuit 43 rise. A positive voltage is applied to the horizontal line 42 until time t3. Holes are injected in the p-type base regions 4 of the photoelectric transducer cells 20 (hole injection operation). At time t3, the pulse signal 1 falls to set the horizontal line 42 at the ground potential. The pulse signal r rises to apply a positive refresh voltage to the capacitor electrode 8 of each photoelectric transducer cell 20. Since each electrode 8 is maintained at the ground potential, a refresh operation is performed, as described above. When the signal r rises at time t4, the p-type base region 4 of each photoelectric transducer cell 20 is set at the initial negative potential. Upon completion of the refresh operation, the signals rs and 1rs rise to turn off the transistors 45, 45', 45'' and 55. In this state, the holes of the electron-hole pairs excited by incident light are stored as optical information in the p-type base regions of the photoelectric transducer cells 20. The base potential of each photoelectric transducer cell is increased by the storage voltage component corresponding to the amount of light from the initial negative potential (storage operation). When the storage operation is performed for a desired period of time, the horizontal line 42 is set in the floating state by the control circuit 43. The signal t is set at high level to turn on the transistors 48, 48' and 48'', thereby respectively connecting the vertical lines 44, 44' and 44'' and the charge storage capacitors 51, 51' and 51''. At time t5, the signal r rises to supply the positive read voltage to the capacitor electrodes 8 of the photoelectric transducer cells 20. The read operation as previously mentioned is performed, and thus the read signals corresponding to the optical information of the photoelectric transducer cells 20 are respectively stored in the charge storage capacitors 51, 51' and 51''. At the same time, the read signals corresponding to the optical information of the photoelectric transducer cells 20 are output to the electrodes 10 through the corresponding diodes. However, since the electrodes 10 are commonly connected to the horizontal line 42 in the floating state, the read signal of the photoelectric transducer cell which has a largest amount of incident light appears as a peak voltage on the horizontal line 42. The control circuit 43 adjusts the gain of the amplifier 59 on the base of this peak voltage, thereby controlling the range of the read signals. The amplifier 59 serves as an automatic limiter. Since the gain of the amplifier 59 is controlled, the signals r and t fall, and the pulse of the signal 1rs is applied to the terminal 56. The transistors 48, 48' and 48'' are turned off, and the output line 54 is refreshed. Subsequently, the shift register 52 is started from time t6. The read signals stored in the charge storage capacitors 51, 51' and 51'' are sequentially output. The pulse signal hi output from the first output terminal of the shift register 52 rises to turn on the transistor 53. The read signal stored in the charge storage capacitor 51 is read out onto the output line 54. The readout signal is input to the gain-controlled amplifier 59 through the transistor 57 and is output from the terminal 60. Subsequently, when the signal h1 falls, the signal 1rs rises to ground the output line 54 through the transistor 55, thereby removing the residual charge. In the same manner as described above, the signals h2 and h3 output from the shift register 52 sequentially rise to read out the read signals from the charge storage capacitors 51, 51' and 51'' onto the output line 54. Every time a signal is read out, the pulse signal 1rs rises to refresh the output line 54. In this manner, the read signals from the photoelectric transducer cells 20 are serially output from the gain-controlled amplifier 59. In the same manner as described above, the refresh, storage, and read operations are repeated. Every time a read operation is performed, the peak value is detected to adjust the gain of the amplifier 59. In the photoelectric transducer device of the embodiment as described above in detail, the base region has a semiconductor region having the same conductivity type as that of the emitter region of the semiconductor transistor and having a lower impurity concentration than that to constitute a diode structure. Therefore, a proper voltage is applied to the semiconductor region, and the carriers can be properly injected into the base region. For this reason, the potential of the base region can be sufficiently high at the beginning of refreshing. The potential of the base region at the end of refreshing can be maintained at a desired predetermined value. That is, unlike in the conventional device, the after image phenomenon can be prevented. In addition, even if strong light is incident on the photoelectric transducer device, the excessive carriers can be eliminated through the diode structure. Therefore, the blooming phenomenon can also be prevented. Since the peak value can be easily detected by the semiconductor region, there is easily provided an image pickup device having a light metering function.

Claims: A photoelectric transducer device comprising a bipolar transistor having a base region (4), an emitter region (5) formed in the base region and a collector region (1, 2, 11), the base region (4) being capacitively coupled to a control electrode (8) and the device being operable to store charge carriers in the base region in response to incident light, read a signal from the emitter region in accordance with a storage voltage generated by the said stored charge carriers, and refresh the base region by neutralising the charge carriers stored in it, characterised in that the bipolar transistor has a further region (6) formed in the base region (4) spaced from the emitter region (5), the further region (6) having the same conductivity type as the emitter region (5) but a lower impurity concentration, so as to form a diode with the base region. A method of operating a photoelectric transducer device according to claim 1, in which immediately prior to refreshing the base, charge carriers are injected into the base via the further region (6). A method according to claim 2, in which said charge carrier injection is carried out by applying a reverse-biassing voltage to the said further region (6) by an electrode (10) in contact with it, sufficient to deplete the further region (6) from its junction with the base region to the electrode, whereby charge carriers pass from the electrode to the base region by punching through the further region.

Inventors: HARADA, TADANORI, OHMI, TADAHIRO, SUGAWA, SHIGETOSHI, SUZUKI, TOSHIJI, TANAKA, NOBUYOSHI
Applicants: CANON KABUSHIKI KAISHA
Application year: 1986
Main classification: H01L27
IPC codes: H01L27, H04N3