JP2004266372A - Image pickup unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image pickup unit for suppressing shading, etc., while suppressing the occurrence of new noise. <P>SOLUTION: This image pickup unit 1a is provided with a solid-state image pickup element provided with an effective pixel part for photoelectrically converting light to be measured and an optical black part masked so as not to be irradiated with the light to be measured, an adjusting means for holding prescribed voltage on the basis of an output signal from the optical black part and using the held voltage to adjust the black level of an output signal from the effective pixel part, and a control means for outputting a first instruction signal for instructing the solid-state image pickup device to read an electric charge to be photoelectrically converted as an output signal and a second instruction signal for instructing the adjusting means to hold prescribed voltage, respectively. The control means outputs the second instruction signal so as to exceed a time required to hold at least the prescribed voltage before outputting the first instruction signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an imaging device.
[0002]
[Prior art]
In an imaging device using a solid-state imaging device such as a CCD (Charge Coupled Device), an output signal due to a dark current is generated when reading a signal. In order to eliminate the influence of this output signal, an optical black section is provided in which some of the pixels of the CCD are shielded from light and photoelectric conversion is not performed, and the signal output from the optical black section is caused by dark current. The black level is adjusted as an output signal to be output.
[0003]
In order to adjust the black level, a clamp circuit including a capacitor and a switch may be provided. When there are a plurality of periods (hereinafter, referred to as one horizontal period) for reading out the electric charges transferred to the horizontal shift register of the CCD, the switch of the clamp circuit is turned on in each one horizontal period to charge the capacitor, and the charge is performed. Is used as the black level. The time constant of such a clamp circuit is often set to several tens of horizontal periods in consideration of the balance with noise.
[0004]
Therefore, when the reading from the effective pixel portion of the CCD is performed continuously, the clamp operation corresponding to each horizontal period is performed, so that the black level can take a constant value. In some cases, the black level fluctuates and problems such as shading may occur. There is a technique described in Patent Document 1 below as an imaging device that suppresses such shading and the like.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-125211
[Problems to be solved by the invention]
This conventional technique employs a circuit configuration as shown in FIG. In this circuit configuration, the time constant of the circuit is switched by switching the combination of the fixed resistor and the capacitor, and the clamp operation corresponding to the normal reading and the reading at the time of storing a plurality of fields is performed. By the way, when circuit elements are added in this way, generation of noise due to the increase is recognized, and it is necessary to cope with this new noise.
[0007]
Therefore, an object of the present invention is to provide an imaging apparatus capable of suppressing shading and the like while suppressing generation of new noise.
[0008]
[Means for Solving the Problems]
The imaging device of the present invention is a solid-state imaging device including an effective pixel unit that photoelectrically converts the measured light and an optical black unit that is shielded so that the measured light is not irradiated, and an output signal from the optical black unit. Adjusting means for holding a predetermined voltage based on the voltage, adjusting the black level of an output signal from the effective pixel unit using the held voltage, and instructing the solid-state imaging device to read out a charge that is photoelectrically converted as an output signal. A first instruction signal to perform, and control means for respectively outputting a second instruction signal that instructs the adjustment means to hold a predetermined voltage, before the control means outputs the first instruction signal, The second instruction signal is output so as to exceed at least the time required for maintaining the predetermined voltage.
[0009]
According to the imaging device of the present invention, the second instruction signal is output before the first instruction signal is output, so that the voltage for adjusting the black level is held before the output signal from the effective pixel unit is output. it can. Further, since the second instruction signal is output so as to exceed the time required for maintaining the predetermined voltage, the adjusting means can maintain the voltage required for adjusting the black level. Therefore, by adjusting the output timing and the output time of the first instruction signal and the second instruction signal without adding a new circuit element, the voltage required for adjusting the black level can be held at the necessary time, so that a new It is also possible to suppress shading while suppressing the generation of noise.
[0010]
In the imaging device according to the aspect of the invention, the solid-state imaging device may include, among the two-dimensionally arrayed pixels in the first direction and the second direction that cross each other, a pixel to which irradiated light is to be measured. One pixel group, a second pixel group to which a pixel that does not belong to the first pixel group belongs, and a charge transferred in the first direction received from the pixel and accumulated, and the accumulated charge is transferred in the second direction. A horizontal transfer register, and the pixels belonging to the second pixel group are transferred in the second direction after the photoelectrically converted charges are superimposed in the first direction and accumulated in the horizontal transfer register, and then transferred to the first pixel group. When the charges photoelectrically converted by the pixels belonging to the pixel group are accumulated in the first direction and transferred in the second direction, the control unit transfers the charges photoelectrically converted by the pixels belonging to the second pixel group. After that, the pixels belonging to the first pixel group Before the charges were are transferred, it is also preferable for outputting a second instruction signal. If the pixel belonging to the first pixel group to which the light to be measured is irradiated emits the second instruction signal before the electric charge obtained by photoelectric conversion is transferred, the black level becomes high before the electric charge to be measured is transferred. Can be set.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The findings of the present invention can be readily understood by considering the following detailed description with reference to the accompanying drawings shown by way of example only. Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings. When possible, the same parts are denoted by the same reference numerals, and redundant description will be omitted.
[0012]
An imaging device 1a according to an embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a configuration of the imaging device 1a. The light 5 to be measured passes through the lens 3 and the slit 4 and irradiates a predetermined area 10a of an imaging unit (solid-state imaging device) 10 of the camera 1a. In the imaging unit 10, each pixel performs photoelectric conversion and charge transfer according to a pulse signal output from the synchronization circuit (control unit) 20. The read charge is converted into a voltage by the read circuit 22 and output to the clamp circuit (adjustment means) 23. In the clamp circuit 23, the black level is adjusted and output to the outside (details will be described later). The synchronization circuit 20 outputs a pulse signal to the imaging unit 10 based on the external synchronization signal and the internal synchronization signal. This output timing is appropriately set based on an instruction signal from the control unit (control means) 21.
[0013]
The imaging unit 10 is configured by a CCD imaging device. In the case of the present embodiment, a frame transfer method is adopted in which each pixel receives and photoelectrically converts electric charges and sequentially transfers data to output data. A predetermined signal is output from the synchronization circuit 20 to each pixel of the imaging unit 10 via the signal line 20a. Also, a predetermined signal is output from the synchronization circuit 20 to each charge storage element of the horizontal transfer register 11 via the signal line 20b. The imaging unit 10 includes an effective pixel unit 101 that photoelectrically converts the measured light, and an optical black unit 102 that is shielded by a metal or the like so that the measured light is not irradiated. The output signal from the optical black section 102 is output as a dark current output signal from the optical black section 102 even when the measured light is not output in the image pickup section 10, so that the clamp circuit 23 adjusts the black level. Is performed.
[0014]
Each pixel of the imaging unit 10 is exposed according to an exposure signal from the synchronization circuit 20, and photoelectrically converts the received light. Each pixel of the imaging unit 10 further transfers the electric charge that has been photoelectrically converted and stored in response to the transfer signal (first instruction signal) from the synchronization circuit 20 in the direction toward the horizontal transfer register 11 (first direction). . When the electric charge is transferred to a pixel adjacent to the horizontal transfer register 11 of the imaging unit 10, the electric charge is transferred to the horizontal transfer register 11.
[0015]
The horizontal transfer register 11 transfers the charge transferred from the imaging unit 10 in a direction toward the readout circuit 22 (second direction) in response to a transfer signal from the synchronization circuit 20. Therefore, if the camera 1a is used, it is possible to measure the light 5 to be measured irradiated on the predetermined area 10a of the imaging unit 10, and output the measurement result as output data to the outside.
[0016]
A more specific charge reading method will be described with reference to FIGS. FIG. 2A is a diagram schematically illustrating a state where the light to be measured 5 is irradiated on the imaging unit 10 and each pixel of the imaging unit 10 receives light. The pixels of the imaging unit 10 are arranged separately in a first stage 111 to a sixth stage 116. Ten pixels are arranged in each stage. Therefore, the pixels of the imaging unit 10 are two-dimensionally arranged in the horizontal direction and the vertical direction. The pixels corresponding to the predetermined area 10a in FIG. 1 are the pixels arranged in the third and fourth rows. In FIG. 2A, a region with a circle indicates a pixel (first pixel group) irradiated with the light 5 to be measured, and a region with a single diagonal line indicates a substantial region. Indicates a pixel (second pixel group) not irradiated with the light 5 to be measured.
[0017]
From the state of FIG. 2A, a transfer signal is input to each pixel of the imaging unit 10 from the synchronization circuit 20. The charge of each pixel of the imaging unit 10 is transferred one by one toward the horizontal transfer register 11. Therefore, as shown in FIG. 2B, the electric charges accumulated in the pixels at the sixth stage 116 of the imaging unit 10 are transferred to the horizontal transfer register 11. Further, when a transfer signal is input from the synchronization circuit 20 to the imaging unit 10, the electric charge accumulated in the pixel at the fifth stage 115 in FIG. 2A is also transferred to the horizontal transfer register 11. Therefore, in FIG. 2C, the charges photoelectrically converted in the pixels of the fifth stage 115 and the sixth stage 116 in FIG. 2A are superimposed in the horizontal transfer register 11. In FIG. 2C, the double diagonal lines in each area of the horizontal transfer register 11 indicate that electric charges over two stages are overlapped.
[0018]
From the state of FIG. 2C, a transfer signal is input from the synchronization circuit 20 to the horizontal transfer register 11, and the charges accumulated in the horizontal transfer register 11 are sequentially swept out (FIG. 2D). Here, the reason why the charge that has been photoelectrically converted in the pixel of the fourth stage 104 in FIG. 2A is not transferred to the horizontal transfer register 11 from the state in FIG. This is because the pixels in the stage 114 are irradiated with the measured light 5 and accumulate valid data. Therefore, after all the charges accumulated in the horizontal transfer register 11 have been swept out, a transfer signal is input from the synchronization circuit 20 to the imaging unit 10 and photoelectrically converted in the pixels of the fourth stage 114 in FIG. The transferred charge is transferred to the horizontal transfer register 11 (FIG. 2E). After that, a transfer signal is input from the synchronization circuit 20 to the horizontal transfer register 11, and the charges photoelectrically converted in the pixels of the fourth stage 114 in FIG.
[0019]
Subsequently, the clamp circuit 23 will be described with reference to FIG. FIG. 3 is a diagram showing a configuration of the clamp circuit 23. The clamp circuit 23 includes a fixed resistor 231, a switch 232, a capacitor 233, and a differential amplifier 234. An instruction signal (second instruction signal) is output from the control unit 21 to the clamp circuit 23 at the timing when the output signal from the optical black unit 102 is output. When this instruction signal is input, the switch 232 is closed, and the capacitor 233 is charged and held at a voltage corresponding to the output signal. This voltage is fed back to the output signal via the differential amplifier 234, and the black level of the output signal from the effective pixel unit 101 is adjusted.
[0020]
In the read method described with reference to FIGS. 2A to 2E, the control unit 21 outputs a dummy read signal at a timing between FIGS. 2D to 2E, and Close the switch to charge. Since the time constant of this clamp circuit is equivalent to several tens of horizontal periods, charging is performed by closing the switch for a sufficiently long time at the time of reading. The charging operation will be described more specifically with reference to FIGS. 4A and 4B. FIG. 4A is a timing chart showing a signal waveform output from the clamp circuit, and FIG. 4B is a timing chart showing a waveform of an instruction signal for closing the switch.
[0021]
According to this example, the section A in FIGS. 4A and 4B is photoelectrically converted in the pixels of the fifth stage 115 and the sixth stage 116 in FIGS. 2A to 2E. This is a period during which charge is being output, and unnecessary signals are being output. 4A and FIG. 4B is a period during which the photoelectrically converted charge is output in the pixel of the fourth stage 114 in FIGS. 2A to 2E, and is effective. Data is read as one horizontal period. 4 (a) and 4 (b) is a period during which the photoelectrically converted charge is output from the pixels of the third stage 113 in FIGS. 2 (a) to 2 (e). , Data is read as one effective horizontal period. Therefore, when reading the data in the sections C and D, the black level needs to be set appropriately, so that dummy reading is performed in the section B between the sections A and C. At the time of this dummy reading, the switch 232 of the clamp circuit 23 is closed sufficiently longer than the time in one normal horizontal period, so that the capacitor 233 of the clamp circuit 23 is charged with the voltage required for setting the black level and held. You.
[0022]
In this embodiment, although the capacitor 233 of the clamp circuit 23 is charged when performing the dummy reading as described above, in the unnecessary period, the section A in FIGS. 4A and 4B. You may go.
[0023]
In the present embodiment, a signal for instructing to close the switch 232 of the clamp circuit 23 is output before a transfer signal for instructing to transfer the charge of the pixel irradiated with the light to be measured is output. Since the output is performed, the voltage for adjusting the black level can be held before the output signal from the effective pixel unit 101 is output. In addition, since the signal instructing to close the switch 232 of the clamp circuit 23 is output so as to exceed the time required for maintaining the predetermined voltage, the clamp circuit 23 holds the voltage required for adjusting the black level. it can. Therefore, by adjusting the output timing and output time of the above-mentioned instruction signal without adding a new circuit element, the voltage required for adjusting the black level can be held at the required time, thereby suppressing the occurrence of new noise. In addition, shading and the like can be suppressed.
[0024]
Further, in the present embodiment, the control unit transfers the charges photoelectrically converted in the pixels (second pixel group) at the fifth stage 115 and the sixth stage 116 in FIGS. 2A to 2E. Later, the switch 232 of the clamp circuit 23 is closed before the charges that have been photoelectrically converted in the pixels (first pixel group) of the fourth stage 114 in FIGS. 2A to 2E are transferred. Since the command signal is output, the black level can be set before the charge to be measured is transferred.
[0025]
【The invention's effect】
According to the present invention, since the second instruction signal is output before the first instruction signal is output, the voltage for adjusting the black level can be held before the output signal from the effective pixel unit is output. Further, since the second instruction signal is output so as to exceed the time required for maintaining the predetermined voltage, the adjusting means can maintain the voltage required for adjusting the black level. Therefore, by adjusting the output timing and the output time of the first instruction signal and the second instruction signal without adding a new circuit element, a voltage necessary for adjusting the black level can be held at a necessary time, so that a new It is also possible to suppress shading while suppressing the generation of noise. Therefore, an object of the present invention is to provide an imaging apparatus capable of suppressing shading and the like while suppressing generation of new noise.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an imaging device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a method of reading charges in the imaging device of FIG. 1;
FIG. 3 is a diagram illustrating a configuration of a clamp circuit of FIG. 1;
FIG. 4 is a diagram showing operation timings of the clamp circuit of FIG. 1;
[Explanation of symbols]
1a: camera, 10: imaging unit, 10a: predetermined area, 11: horizontal transfer register, 20: synchronization circuit, 20a, 20b: signal line, 21: control unit, 22: readout circuit, 23: clamp circuit, 3: lens Reference numeral 4 denotes a slit, 5 denotes a light to be measured, 101 denotes an effective pixel portion, and 102 denotes an optical black portion.

Claims (2)

A solid-state imaging device including an effective pixel unit that photoelectrically converts the measured light and an optical black unit that is shielded so that the measured light is not irradiated,
Adjusting means for holding a predetermined voltage based on the output signal from the optical black unit and adjusting the black level of the output signal from the effective pixel unit using the held voltage;
Control for outputting a first instruction signal for instructing the solid-state imaging device to read out the charge to be photoelectrically converted as an output signal and a second instruction signal for instructing the adjustment unit to maintain the predetermined voltage, respectively. Means,
The imaging apparatus, wherein the control unit outputs the second instruction signal so as to exceed at least a time required for maintaining the predetermined voltage before outputting the first instruction signal. The solid-state imaging device,
Among the pixels two-dimensionally arranged in a first direction and a second direction that intersect with each other, a first pixel group to which a pixel to be irradiated is to be measured,
A second pixel group to which a pixel that does not belong to the first pixel group belongs;
A horizontal transfer register that receives and accumulates the charge transferred in the first direction from the pixel, and transfers the accumulated charge in the second direction.
After the electric charges obtained by the photoelectric conversion of the pixels belonging to the second pixel group are superimposed in the first direction and accumulated in the horizontal transfer register, the electric charges are transferred in the second direction, and the pixels belonging to the first pixel group are When the photoelectrically converted charges are accumulated in the first direction and transferred in the second direction,
The control unit may control the second instruction signal after transferring the photoelectrically converted charges of the pixels belonging to the second pixel group and before transferring the photoelectrically converted charges of the pixels belonging to the first pixel group. The imaging device according to claim 1, wherein the imaging device outputs the image data.

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