WO2004075541A1

WO2004075541A1 - Imaging device

Info

Publication number: WO2004075541A1
Application number: PCT/JP2004/001925
Authority: WO
Inventors: Fumio Iwase; Taiga Sato
Original assignee: Hamamatsu Photonics K.K.
Priority date: 2003-02-21
Filing date: 2004-02-19
Publication date: 2004-09-02
Also published as: JP2004266372A

Abstract

An imaging device capable of being controlled in shading or the like with a new noise prevented. The imaging device (1a) shown in Fig. 1 comprises an imaging unit (10) provided with an effective pixel unit (101) for photoelectrically converting a light to be measured and an optical black unit (102) shielded against a light to be measured, a clamp circuit (23) for retaining a specified voltage based on an output signal from the optical black unit (102) and regulating the black level of an out put signal from the effective pixel unit (101) by using this retained voltage, and a synchronizing circuit (20) and a control unit (21) for respectively outputting a first instruction signal to instruct the imaging unit(10) to read a charge subjected to photoelectric conversion as an output signal and a second instruction signal to instruct the clamp circuit (23) to retain a specified voltage, wherein the synchronize circuit (20) and the control unit(21) output the second instruction signal before the first instruction signal is output so that time required for retaining a specified voltage is as least exceeded.

Description

Specification

Imaging device

Technical field

[0001] The present invention relates to an imaging device.

Background art

[0002] In an image pickup apparatus using a solid-state image pickup device such as a CCD (Charge Coupled Device), an output signal due to a low current is generated when reading a signal. In order to eliminate the influence of this output signal, an optical black section is provided that blocks some of the CCD pixels from light and does not perform photoelectric conversion. The signal output from this optical black section is The black level is adjusted as an output signal caused by the above.

[0003] A clamp circuit including a capacitor and a switch may be provided for adjusting the black level. If there are multiple periods during which the charge transferred to the CCD horizontal shift register is read (hereinafter referred to as one horizontal period), the capacitor is charged by turning on the clamp circuit switch during each horizontal period, and this charge is performed. The obtained voltage value 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 reading from the CCD effective pixel section is performed continuously, the black level can take a constant value because the clamp operation corresponding to each horizontal period is performed, but reading is not possible. If they are continuous, the black level fluctuates and problems such as shading may occur. As an imaging device for suppressing such shading and the like, there is a technique described in a patent document (Japanese Patent Application Publication, JP-A-2000-125211).

Disclosure of the invention

[0005] In the background art described above, a circuit configuration as shown in FIG. In this circuit configuration, fixed The time constant of the circuit is switched by switching the combination of the resistor and the capacitor, and the clamp operation corresponding to the normal reading and the reading when storing a plurality of fields is performed. By the way, when the circuit elements are added in this way, the generation of noise due to the increase is recognized, and it is necessary to cope with this new noise.

[0106] 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.

[0107] In order to solve the above-described problem, an imaging apparatus according to the present invention includes a solid-state device including: an effective pixel unit that photoelectrically converts light to be measured; An image sensor, an adjustment unit that holds a predetermined voltage based on an output signal from the optical black unit, and adjusts a black level of an output signal from the effective pixel unit using the held voltage; Control means for outputting a first instruction signal for instructing the element to read out a charge to be photoelectrically converted as an output signal, and a second instruction signal for instructing the adjustment means to maintain a predetermined voltage, respectively. The control means outputs the second instruction signal before outputting the first instruction signal so as to exceed at least the time required for maintaining the predetermined voltage.

[0108] According to the imaging apparatus of the present invention, the second instruction signal is output before the first instruction signal is output. Therefore, the black level is output before the output signal from the effective pixel unit is output. The voltage for adjustment can be held. In addition, 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. It is also possible to suppress shading and the like while suppressing the generation of unnecessary noise.

[0109] In the imaging device of the present invention, the solid-state imaging device may be configured to irradiate light among pixels arranged two-dimensionally in a first direction and a second direction that intersect each other. The first pixel group to which the pixel to be measured belongs and the pixels that do not belong to the first pixel group A second pixel group, and a horizontal transfer register that receives and accumulates charges transferred in the first direction from the pixels and transfers the accumulated charges in the second direction. The charges photoelectrically converted by the pixels belonging to the pixels are superimposed in the first direction and accumulated in the horizontal transfer register, and then transferred in the second direction. In the case where the charge is photoelectrically converted by the pixels belonging to the second pixel group and then transferred in the second direction, the control means determines whether the pixels belonging to the first pixel group It is also preferable to output the second instruction signal before the converted charge is transferred. If the pixel belonging to the first pixel group to which the light to be measured is illuminated outputs the second instruction signal before the charge obtained by photoelectric conversion is transferred, the pixel is blacked out before the charge to be measured is transferred. You can set the level.

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. 2A is a diagram for explaining a method of reading out charges in the imaging device of FIG.

FIG. 2B is a diagram for explaining a method of reading out charges in the imaging device of FIG.

FIG. 2C is a diagram for explaining a method of reading out charges in the imaging device of FIG.

FIG. 2D is a diagram for describing a method of reading out charges in the imaging device of FIG.

FIG. 2E is a diagram for describing a method of reading out charges in the imaging device of FIG.

FIG. 3 is a diagram showing a configuration of the clamp circuit of FIG.

FIG. 4 is a diagram showing operation timings of the clamp circuit of FIG. BEST MODE FOR CARRYING OUT THE INVENTION

The findings of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown for illustration 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.

[0108] An imaging device 1a according to an embodiment of the present invention will be described. FIG. 1 is a diagram showing 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 region 10a of the imaging unit (solid-state imaging device) 10 of the camera 1a. In the imaging unit 10, each pixel performs photoelectric conversion and charge transfer in accordance with a pulse signal output from the synchronization circuit (control means) 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 partial synchronization signal. This output timing is appropriately set based on an instruction signal from the control unit (control means) 21.

[0191] The imaging unit 10 is formed of a CCD imaging device. In the case of the present embodiment, a frame transfer method is employed in which each pixel receives and photoelectrically converts electric charges and sequentially transfers data to output data. are doing. A predetermined signal is output from the synchronization circuit 20 to each pixel of the imaging unit 10 via a signal line 20a. Further, 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 metal or the like so that the measured light is not irradiated. In the imaging unit 10, even if the measured light is not output, an output signal due to the 喑 current is generated. Therefore, the output signal from the optical black unit 102 is used as an output signal due to the dark current by the clamp circuit 2. At 3, the black level adjustment is performed.

[0200] Each pixel of the imaging unit 10 is exposed according to an exposure signal from the synchronization circuit 20. Then, the received light is photoelectrically converted. Each pixel of the imaging unit 10 further converts the electric charge that has been photoelectrically converted and stored in response to the transfer signal (first instruction signal) from the synchronization circuit 20 into a direction toward the horizontal transfer register 11 (first direction). Transfer to 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.

[0 0 2 1] The horizontal transfer register 11 transfers the electric charge transferred from the imaging unit 10 in response to the transfer signal from the synchronization circuit 20 in the direction toward the readout circuit 22 (second direction). Forward. Therefore, if the camera 1a is used, the light 5 to be measured irradiating the predetermined area 10a of the imaging unit 10 can be measured, and the measurement result can be output to the outside as output data.

[0223] A more specific method for reading out electric charges is described with reference to FIGS. 2A to 2E. FIG. 2A is a diagram schematically showing a state in which the light to be measured 5 is applied to 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 the first stage 11 1 to the sixth stage 11 16. In each stage, 10 pixels are arranged. Therefore, the pixels of the imaging unit 10 are two-dimensionally arranged in the horizontal and vertical directions. The pixels corresponding to the predetermined area 10a in FIG. 1 are the pixels arranged in the third and fourth rows. In FIG. 2A, the circled area indicates the pixel (first pixel group) irradiated with the measured light 5, and the area with a single diagonal line is substantially This indicates that the target light 5 is not irradiated with the pixel (second pixel group).

[0200] From the state of FIG. 2A, a transfer signal is input from the synchronization circuit 20 to each pixel of the imaging unit 10. The electric charge of each pixel of the imaging unit 10 is transferred one by one in the direction of the horizontal transfer register 11. Therefore, as shown in FIG. 2B, the electric charges accumulated in the pixels of the sixth stage 116 of the imaging unit 10 are transferred to the horizontal transfer register 11. Furthermore, when a transfer signal is input from the synchronization circuit 20 to the imaging unit 10, the electric charges accumulated in the pixels of the fifth stage 115 in FIG. 2A are also transferred to the horizontal transfer register 11. Therefore, in Figure 2C In this case, the charges that have been photoelectrically converted in the pixels at 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.

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. 2). D). Here, from the state of FIG. 2C, the charge that is photoelectrically converted in the pixels of the fourth stage 114 in FIG. 2A is not transferred to the horizontal transfer register 11 because the fourth stage 1 in FIG. This is because the pixel 14 is irradiated with the light 5 to be measured and stores 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 the pixels of the fourth stage 114 in FIG. Then, the photoelectrically converted charge is transferred to the horizontal transfer register 11 (Fig. 2E). Thereafter, a transfer signal is input from the synchronization circuit 20 to the horizontal transfer register 11, and the charge photoelectrically converted in the pixel at the fourth stage 114 in FIG. 2A is swept out to the outside as output data.

Next, 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 2 3 1, a switch 2 3 2, a capacitor 2 3 3, and a differential amplifier 2 3 4. 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 blur 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 to adjust the black level of the output signal from the effective pixel unit 101.

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. At the same time, close the switch to charge. Since the time constant of this clamp circuit is equivalent to several tens of horizontal periods, it is necessary to charge the switch by closing the switch for a sufficiently long time at the time of reading. This charging operation will be described more specifically with reference to FIG. In the signal waveforms shown in FIG. 4, a part is a timing chart showing a signal waveform output from the clamp circuit, and b part is a timing chart showing a waveform of an instruction signal for closing the switch. is there.

According to this example, the section A of the a portion and the b portion was photoelectrically converted in the pixels of the fifth stage 1 15 and the sixth stage 1 16 in FIGS. 2A to 2E. This is the period during which charge is being output, and unnecessary signals are being output. The interval C between the portions a and b is the period during which the photoelectrically converted charge is output in the pixels at the fourth stage 114 in FIGS. 2A to 2E, and is a data as an effective horizontal period. Is read. The section D of the part a and the part b is a period during which the photoelectrically converted charges are output in the pixels of the third stage 113 in FIGS. 2A to 2E, and is also a valid horizontal period. The data is read as Therefore, when reading the data in section C and section D, the black level must be set appropriately, and dummy reading is performed in section B between section A and section C. It is necessary to set the black level of the capacitor 2 3 3 of the clamp circuit 2 3 by closing the switch 2 3 2 of the clamp circuit 2 3 at the time of this dummy reading sufficiently longer than the time in the normal one horizontal period. Voltage is charged and held.

In this embodiment, although the capacitor 23 of the clamp circuit 23 is charged when performing the dummy readout as described above, the portion a in FIG. And b in section A of the section.

In the present embodiment, the switch 23 of the clamp circuit 23 is output before the transfer signal instructing to transfer the electric charge of the pixel irradiated with the light to be measured is output. Since the signal for instructing to close 2 is output, the voltage for adjusting the black level can be held before the output signal from the effective pixel unit 101 is output. In addition, a signal instructing to close the switch 23 of the clamp circuit 23 is output so as to exceed the time required to maintain the predetermined voltage, so that the clamp circuit 23 is necessary for adjusting the black level. Voltage can be maintained. Therefore, by adjusting the output timing and the output time of the above-mentioned instruction signal without adding a new circuit element, a voltage necessary for adjusting the black level can be held at a necessary time, thereby generating new noise. It is also possible to suppress seeding etc.

Further, in the present embodiment, the control means performs photoelectric conversion on the pixels (second pixel group) of the fifth stage 115 and the sixth stage 116 of FIGS. 2A to 2E. After the transferred charges are transferred, the switches of the clamp circuit 23 are switched before the charges obtained by the photoelectric conversion in the pixels (first pixel group) of the fourth stage 114 in FIGS. 2A to 2E are transferred. Since a signal is output to instruct to close 232, the black level can be set before the charge to be measured is transferred.

In the present embodiment, the slit 4 is used to irradiate the predetermined area 10a of the imaging unit 10 of the camera 1a with the measured light 5, but the slit 4 is not necessarily provided. It is not necessary to provide.

Industrial applicability

As described above, according to the present invention, since the second instruction signal is output before the first instruction signal is output, the black level of the black level is output before the output signal from the effective pixel unit is output. The voltage for adjustment can be held. In addition, 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 required time. It also makes it possible to suppress the occurrence of noise and reduce shading.

Claims

Area of claim

1. 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 section and adjusting the black level of the output signal from the effective pixel section using the held voltage;

A first instruction signal that instructs the solid-state imaging device to read out the charge that is photoelectrically converted as an output signal, and a second instruction signal that instructs the adjustment unit to maintain the predetermined voltage are output. Control means; and

The imaging device, wherein the control unit outputs the second instruction signal before outputting the first instruction signal so as to at least exceed a time required for maintaining the predetermined voltage.

2. The solid-state imaging device includes:

A first pixel group to which a pixel to be irradiated with light to be measured among pixels arranged two-dimensionally in a first direction and a second direction crossing each other;

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.

Charges obtained by photoelectric conversion of the pixels belonging to the second pixel group are superimposed in the first direction and accumulated in the horizontal transfer register, and then transferred in the second direction. When the photoelectrically converted charges are accumulated in the first direction one by one and transferred in the second direction,

The control unit may control the second instruction after the transfer of the charges photoelectrically converted by the pixels belonging to the second pixel group and before the transfer of the charges photoelectrically converted by the pixels belonging to the first pixel group. The imaging device according to claim 1, wherein the imaging device outputs a signal.