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Researchers Submit Patent Application, "Imaging Device, Imaging Apparatus, Semiconductor Device and Readout Method", for Approval

June 4, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Sonoda, Shuuji (Kumamoto, JP), filed on October 10, 2013, was made available online on May 22, 2014.

The patent's assignee is Sony Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "The present disclosure relates to an imaging device, an imaging apparatus, a semiconductor device and a readout method. In particular, the present disclosure relates to an imaging device, an imaging apparatus, a semiconductor device and a readout method which are capable of suppressing a dark current component of a pixel signal.

"In the related art, in the imaging device, a charge which is accumulated in a photodiode is read out as a signal level of a pixel signal depending on an accumulation time, and the signal level of the pixel signal is subjected to analogue-digital conversion. Various methods have been proposed in the related art for reading out the pixel signal (for example, refer to Japanese Unexamined Patent Application Publication No. 2006-033452).

"For example, in the method taught in Japanese Unexamined Patent Application Publication No. 2006-033452, a pixel signal of the readout period of an n-th row and a reference signal to digitize the pixel signal are compared, a count process is performed in either a down mode or an up mode concurrently with the comparison process, and the count value of the point in time at which the comparison process completes is maintained. Next, using the result of the count process of the n-th row as the initial value, a pixel signal of the readout period of an n+1-th row and a reference signal to digitize the pixel signal are compared, a count process is performed in either a down mode or an up mode concurrently with the comparison process, and the count value of the point in time at which the comparison process completes is maintained. The count value after the count process of the n+1-th row is a subtraction result when the mode of the count process of the n+1-th row is opposite to the count mode of the n-th row, and is an addition result when the count modes are the same.

"By adopting such a method of reading out a pixel signal, it is possible to maintain a compact circuit scale of the analogue-digital converter and a low number of transmission signal lines and also to efficiently perform a product-sum operation."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "However, when adopting the methods of the related art, there are concerns that a dark current will occur due to the gate operation of a Metal Oxide Semiconductor (MOS) transistor, that junction leakage will occur, or the like.

"The charge accumulated in the floating diffusion due to these factors is added to the charge transferred from the photodiode or the like (the signal charge). Accordingly, there is a concern that this additional charge will be manifested in an imaged image as a point defect with a high output level, that is, as a white spot in a closed-shutter state and as a bright spot when light is incident. Furthermore, there is a concern that such point defects will lower the image quality of the imaged image.

"It is desirable to suppress a dark current component of a pixel signal.

"According to an embodiment of the present disclosure, there is provided an imaging device that includes a readout unit which reads out an amount of charge accumulated in a floating diffusion that accumulates a charge transmitted from a light receiving unit that photoelectrically converts incident light as a signal level; a readout control unit which controls the readout unit to perform, a plurality of times, a readout operation to read out the amount of charge of a P-phase and a D-phase accumulated in the floating diffusion; and a calculation unit which is controlled by the readout control unit and obtains differences between the signal levels which are obtained using the readout operation that is performed a plurality of times.

"The readout control unit may cause the plurality of readout operations to be performed within one horizontal synchronization period.

"The readout control unit may cause the readout operation to be performed two times within the one horizontal synchronization period.

"The readout control unit may cause a first readout operation to be performed, and subsequently cause a second readout operation to be performed without initializing the light receiving unit.

"The readout unit may include a reset transistor that controls initialization of the floating diffusion, and a readout transistor that controls movement of a charge from the light receiving unit to the floating diffusion.

"In each of the readout operations, the readout control unit may turn on the reset transistor, initialize the floating diffusion, cause a readout of an amount of charge of a P-phase to be performed, and subsequently turn on the readout transistor, causes a charge of the light receiving unit to be moved to the floating diffusion and cause the readout of an amount of charge of a D-phase to be performed.

"The readout control unit may cause the readout operation to be performed a plurality of times, subsequently turn on the reset transistor and the readout transistor and initialize the light receiving unit and the floating diffusion.

"The readout unit may further include an amplification transistor that amplifies an amount of charge accumulated in the floating diffusion and converts the amplified charge into the signal level, and a select transistor that controls supply of the signal level to the calculation unit, and the readout control unit may turn on the select transistor during the plurality of readout operations.

"The readout control unit may lower a frame rate in comparison to a case in which the readout operation is performed one time, and may cause the readout operation to be performed a plurality of times.

"The calculation unit, in relation to a signal level obtained using a first readout operation, may use 0 as an initial value and count the signal level; in relation to a signal level obtained using a second readout operation, may use a count value of the signal level obtained using the first readout operation as an initial value, and count the signal level in an opposite orientation from the previous readout operation; and in relation to a signal level obtained using a third readout operation onward, may use a difference value of the signal levels obtained until the previous readout operation as an initial value, and count the signal level in an opposite orientation from the previous readout operation.

"The calculation unit, in relation to a signal level obtained using a first readout operation, may use 0 as an initial value and count the signal level; in relation to a signal level obtained using a second readout operation, may invert a sign of a count value of a signal level obtained using the first readout operation, use the inverted count value as an initial value, and count the signal level in a same orientation as the previous readout operation; and in relation to a signal level obtained using a third readout operation onward, may invert a sign of a difference value of the signal levels obtained until the previous readout operation, use the inverted difference value as an initial value, and count the signal level in a same orientation as the previous readout operation.

"The calculation unit may obtain a difference between a signal level obtained by the readout of the P-phase and a signal level obtained by the readout of the D-phase as a signal level obtained using the readout operation.

"According to another embodiment of the present disclosure, there is provided an imaging apparatus which includes: an imaging device which includes a readout unit which reads out an amount of charge accumulated in a floating diffusion that accumulates a charge transmitted from a light receiving unit that photoelectrically converts incident light as a signal level, a readout control unit which controls the readout unit to perform, a plurality of times, a readout operation to read out the amount of charge of a P-phase and a D-phase accumulated in the floating diffusion, and a calculation unit which is controlled by the readout control unit and obtains differences between the signal levels which are obtained using the readout operation that is performed a plurality of times; and an image processing unit which performs image processing on an image of a subject that is photoelectrically converted in the imaging device.

"According to still another embodiment of the present disclosure, there is provided a semiconductor device which includes a readout control unit which controls a readout unit provided on another semiconductor substrate, which reads out an amount of charge accumulated in a floating diffusion that accumulates a charge transmitted from a light receiving unit that photoelectrically converts incident light as a signal level, and causes a readout operation to read out the amount of charge of a P-phase and a D-phase accumulated in the floating diffusion to be performed a plurality of times; and a calculation unit which is controlled by the readout control unit and obtains differences between the signal levels which are obtained using the readout operation that is performed a plurality of times.

"According to still another embodiment of the present disclosure, there is provided a readout method which reads out a signal level corresponding to an amount of charge accumulated in a floating diffusion that accumulates a charge transmitted from a light receiving unit that photoelectrically converts incident light from an imaging device, the method includes performing, a plurality of times, a readout operation to read out the signal level corresponding to the amount of charge of a P-phase and a D-phase accumulated in the floating diffusion that accumulates the charge transmitted from the light receiving unit that photoelectrically converts incident light; and obtaining differences between the signal levels which are obtained using the readout operation that is performed a plurality of times.

"According to an embodiment or still another embodiment of the present disclosure, an amount of charge of a P-phase and a D-phase accumulated in the floating diffusion that accumulates the charge transmitted from the light receiving unit that photoelectrically converts incident light is read out a plurality of times as signal levels, and differences between the signal levels which are obtained using the readout operation that is performed a plurality of times are obtained.

"According to another embodiment of the present disclosure, an amount of charge of a P-phase and a D-phase accumulated in the floating diffusion that accumulates the charge transmitted from the light receiving unit that photoelectrically converts incident light is read out a plurality of times as signal levels, differences between the signal levels which are obtained using the readout operation that is performed a plurality of times are obtained, and an image of a subject obtained as the differences is subjected to image processing.

"According to the present disclosure, it is possible to suppress the dark current component of the pixel signal.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a diagram illustrating a principal configuration example of a CMOS image sensor;

"FIG. 2 is a diagram illustrating a principal configuration example of a unit pixel;

"FIG. 3 is a diagram illustrating a principal configuration example of a column ADC;

"FIG. 4 is a diagram illustrating an example of a state of a signal readout in the related art;

"FIG. 5 is a diagram illustrating an example of a state of a signal readout in the related art;

"FIG. 6 is a flowchart illustrating an example of the flow of a pixel signal readout process;

"FIG. 7 is a flowchart illustrating an example of the flow of a first pixel signal readout process;

"FIG. 8 is a flowchart illustrating an example of the flow of a second pixel signal readout process;

"FIG. 9 is a diagram illustrating an example of a state of a signal readout;

"FIG. 10 is a diagram illustrating an example of a state of a signal readout;

"FIG. 11 is a diagram illustrating another configuration example of a column ADC;

"FIG. 12 is a diagram illustrating another example of a signal readout;

"FIG. 13 is a block diagram illustrating a principal configuration example of an imaging apparatus; and

"FIG. 14 is a block diagram illustrating a principal configuration example of a computer."

For additional information on this patent application, see: Sonoda, Shuuji. Imaging Device, Imaging Apparatus, Semiconductor Device and Readout Method. Filed October 10, 2013 and posted May 22, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4497&p=90&f=G&l=50&d=PG01&S1=20140515.PD.&OS=PD/20140515&RS=PD/20140515

Keywords for this news article include: Electronics, Semiconductor, Sony Corporation.

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Source: Electronics Newsweekly


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