KR101326989B1 - Image sensor and method for driving thereof - Google Patents

Abstract

The present invention relates to an image sensor for processing a signal output from a plurality of pixels and a method of driving the same, wherein the image sensor comprises an array of columns and rows including the plurality of pixels. A counter circuit receiving an image signal output from the pixel array to be converted into digital data, the counter circuit including a comparator corresponding to a column of the pixel array; And an adjusting circuit including a plurality of switches and a line in which the plurality of switches are arranged, so that noise generated in the comparator and the analog circuit stage of the counter circuit can be detected.

Description

Image sensor and its driving method {IMAGE SENSOR AND METHOD FOR DRIVING THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor and a driving method thereof. In particular, the present invention relates to an image sensor and a driving method thereof. The present invention relates to an image sensor and a driving method thereof. The present invention relates to an image sensor capable of compensating for noise and a driving method thereof.

Analog Correlated Double Sampling (CDS) circuits were proposed in 1974 to reduce noise in CCD image sensors, and later in CMOS image sensors.

Fig. 1A shows an example of the analog CDS circuit and Fig. 1B shows the operation timing. An operation of the CDS circuit according to the operation of the pixel will be described with reference to FIGS. 1A and 1B. First, in step 1, when the reset transistor RST is turned on in the unit pixel cell 10, the voltage of the floating diffusion region FD reaches the power supply voltage Vaapix. When the switch PCLP and the switch SH are closed in the column cell 20 of the column line in which a plurality of pixels are arranged along the column, a voltage of Vclp is applied to the node b so that the voltage of the capacitor Csh is 0V. Is initialized. Next, in step 2, the voltage level Vaapix of the floating diffusion region FD is output through the transistor M1, and the output node a is subjected to the Va_rst voltage. Next, in step 3, the switch PCLP is turned off so that a sampling operation can be performed. In step 4, when the transfer transistor TX is turned on, the voltage of the floating region FD_ is integrated in the photodiode PD and is transferred to the photoelectric charge transferred to the floating region FD via the transfer transistor TX. The image voltage Vimg is applied to the output node a through the transistor M1, so that the output node a voltage becomes Va_rst to Va_img, and thus at node b. The applied voltage also changes from Vclp to Vclp-(Va_rst-Va_img) = Vclp-ΔV.

At this time, since the voltage difference is detected by the capacitor Csh, the influence of the noise of the transistor M1 can be eliminated. However, it is vulnerable to noise generated at the stage after the capacitor Csh, for example, fixed pattern noise of the comparator itself. In particular, in the case of a plurality of comparators arranged for each column, the offset voltages of several comparators vary from device to device, so column-specific noise processing is required, and even one comparator depends on the distance from the comparator. Since noise varies from row to row, noise processing considering them is also necessary. The fixed pattern noise generated by the comparator may be generated due to fluctuation of the reference signal generator input to the comparator.

In order to solve the above-described problem, the comparator is configured to detect the noise of the reference signal on a column-by-column basis in the pixel array circuit of the image sensor, so that the comparator is used to shake the reference signal. Therefore, the occurrence of the fixed pattern noise is attenuated so that accurate image processing can be performed.

An image sensor for processing a signal output from a plurality of pixels according to an embodiment of the present invention, the image sensor including the plurality of pixels, and outputs an image signal output from a pixel array consisting of a column (column) and a row (row) A counter circuit that is applied to convert digital data and includes a comparator corresponding to a column of the pixel array; A plurality of switches and one column line and one row line on which the plurality of switches are disposed, one end of the plurality of switches being applied with a reference signal used for a comparison operation of the counter circuit, and the other end of the plurality of switches; A regulating circuit connected to the comparator; And a controller for generating a control signal for driving a plurality of switches arranged in one line of the adjustment circuit and detecting noise of a plurality of comparators corresponding to each column of the pixel array.

An image sensor for processing a signal output from a plurality of pixels according to an embodiment of the present invention, the image sensor including the plurality of pixels, and outputs an image signal output from a pixel array consisting of a column (column) and a row (row) A counter circuit that is applied to convert digital data and includes a comparator corresponding to a column of the pixel array; A plurality of switches and a working line in which the plurality of switches are disposed, one end of the plurality of switches is applied with a reference signal used for a comparison operation of the counter circuit, and the other end is connected to the plurality of comparators Adjusting circuit; Each control of the row line of the pixel array generates a control signal for driving a plurality of switches arranged in one row line of the adjustment circuit, and controls to detect noise of a plurality of comparators corresponding to each column of the pixel array. It includes a controller.

In a driving method of an image sensor for processing a signal output from a plurality of pixels according to an embodiment of the present invention, the image sensor includes the plurality of pixels and is composed of a column and a row. A counter circuit receiving an image signal output from the pixel array and converting the image signal into digital data, the counter circuit including a comparator corresponding to a column of the pixel array; And a regulating circuit comprising a plurality of switches and a work line in which the plurality of switches are arranged, the driving of the plurality of switches arranged in the work line of the adjustment circuit; Generating a reference signal according to an operation timing of the plurality of comparators; Detecting noise of a plurality of comparators corresponding to each column of the pixel array; Controlling a plurality of pixels for each row of the pixel array for a predetermined period; And removing noise from image signals corresponding to the plurality of pixels based on the noise detected from the plurality of comparators.

According to the present invention, the fixed pattern noise generated at the analog circuit stages constituting the image sensor can be easily removed by an additional circuit configuration.

FIG. 1A shows a correlated double sampling (CDS) circuit and FIG. 1B shows an example of a timing diagram of a CDS circuit.
2 illustrates a configuration of an image sensor according to an embodiment of the present invention.
3 shows a configuration of an image sensor according to another embodiment of the present invention.
4 is a flowchart illustrating a method of driving an image sensor according to an exemplary embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the drawings. The "pixel control per row of a pixel array" described in the present invention may output a pixel control signal for controlling the pixels of each row for each row. The pixel control signal performs a series of operations performed on the pixels by a signal applied from a raw decoder, for example, by outputting a reset signal and an image signal from each pixel by controlling on-off of transistors constituting the pixel. It can be explained.

2 illustrates a configuration of an image sensor according to an embodiment of the present invention. Referring to FIG. 2, an image sensor according to an embodiment of the present invention may include a pixel array 100, an adjustment circuit 200, a row decoder 300, a counter circuit 400, and a controller 500. have.

The pixel array 100 may include a plurality of pixels and may be configured of a column and a row.

The counter circuit 400 may receive image signals output from the pixel array 100, convert the image signals into digital data, and include comparators 401 and 402 corresponding to columns of the pixel array 100.

The adjustment circuit 200 includes one column line 210 and one furnace line (a plurality of switches SW1, SW2, SW3, SW4, SW5) and a plurality of switches SW1, SW2, SW3, SW4, and SW5. 220). The plurality of switches SW1, SW4, and SW5 may be disposed in one column line 210 so that one end of the plurality of switches SW1, SW4, and SW5 may be connected to the comparator. The plurality of switches SW1, SW2, and SW3 may be disposed in one line 22 so that a reference signal Vref is applied at one end thereof and the other end thereof is connected to the column lines 101 and 103 of the pixel array 100. .

One end of the plurality of switches SW1, SW2, SW3, SW4, and SW5 may receive a reference signal used for a comparison operation of the counter circuit 400, and the other end may be connected to the plurality of comparators 401 and 402.

The controller 500 generates a control signal for driving the plurality of switches SW1, SW2, and SW3 disposed on the line 220 of the adjusting circuit 200 and the adjusting circuit 200, and generates the pixel array 100. The noise of the plurality of comparators 401 and 402 corresponding to each column may be controlled to be detected. In addition, the image sensor may further include one additional comparator 410 for detecting a noise signal output from one column line 210 of the adjustment circuit 200. In addition, the image sensor may further include a row decoder 300 that outputs a pixel control signal for controlling the pixels of each row according to the control of the controller 50 for each row.

The controller 300 may control to output the image signal from the pixel array 100 while controlling the pixel array 100 for each row. The controller 500 may adjust the circuit before sequentially applying the control signal of the pixel to each of the rows 104 and 102 during a frame for outputting and converting an image signal from all pixels of the pixel array 100, for example. Signals for driving the plurality of switches arranged in the line 220 of the line 200 may be applied. Accordingly, the additional comparator 410 and the plurality of comparators 401 and 402 are driven in synchronization with the controller 500 outputting a signal from the line 220, thereby causing noise of the comparators 401 and 402. Can be detected.

For example, even if there is noise from the additional comparator 410, as long as the power / ground noise measured in the furnaces 102 and 104 is the same as the noise and power ground noise measured in the furnace 220, The difference between the signals from the additional comparator 410 per (102, 104, 220) will be zero.

In addition, since the electrical characteristics of the comparators 401 and 402 are different, small level differences appear between the output signals of the comparators 401 and 402 even if the same input is applied to the comparator. Due to the above-described electrical characteristic difference, the small level difference generated at the output of the comparator becomes fixed pattern noise. That is, if the fixed pattern noise generated in the column (101, 103) line of the pixel array 100 is Na, Nb, respectively, the noise from the difference between the signals per furnace (102, 104) output from the pixel array 100 accordingly, By subtracting Na and Nb, respectively, the fixed pattern noise may be removed from the image signal output from the pixel array and output. That is, before outputting and converting the signal from the pixel array 100 for one frame, the additional comparator 410 is driven by driving the switches SW1, SW2, and SW3 of the line 220 of the adjusting circuit 200. And detecting a noise signal detected from the plurality of comparators 401 and 402, and removing the detected noise from the image signal from the pixel array 100 using the detected noise signal to obtain a fixed pattern noise. You can read it out.

In addition, an image sensor according to an exemplary embodiment may include one end of a plurality of switches SW1, SW2, SW3, SW4, and SW5 disposed in one column line 210 and one furnace line 220 of the adjustment circuit 200. The apparatus may further include a reference signal generator 450 for applying a reference signal Vref. The reference signal Vref may be, for example, a ramp signal. The reference signal Vref may be applied to one end of the plurality of switches SW1, SW2, SW3, SW4, and SW5 to be used for the comparison operation of the comparators 410, 401, and 402.

In the previous paragraph, the fixed pattern noise generated under the assumption that the power / ground noise measured for each of the furnaces 102, 104, and 220 is the same. In practice, however, noises may vary from row to row of the pixel array 100. Row-specific noise differences of the pixel array 100 may be due to power / ground noise generated by different driving environments and different driving timings of the circuit. For example, the reference signal Vref fluctuates for each row driving timing whenever the row signal is applied by the row decoder 300. That is, since the per-row power / ground noise generated by the driving timing is different at that time, it is not guaranteed that a noise-free signal is detected even if the fixed pattern noise between the comparators is removed.

Thus, the per-pixel power / ground noise of the pixel array may be extracted based on the noise detected from one column line 210 of the adjustment circuit 200. For example, as illustrated above, even if the noise signal of the additional comparator 410 detected during the operation of the furnace line 220 of the adjustment circuit 200 is zero, the respective paths 102 and 104 of the pixel array 100 are zero. Each time a separate signal is applied, a signal is also applied to one column line 210 of the adjustment circuit 200 to drive the switches SW4 and SW5, and at this time, a value other than 0 from the additional comparator 410 is applied. For example, noise with Nc and Nd values can be detected. Accordingly, when correcting the image signal for each pixel array 100, (Na + Nc, Nb + Nc, Na + Nd, Nb + Nd) as the noise from the image signal of the pixels 10, 20, 30, 40 Handling can eliminate noise by mathematical operations, i.e. subtraction.

Thus, according to the present invention, the adjustment circuit 200 is additionally configured in the existing pixel array 100, and the switches SW1, SW2, SW3, and SW4 disposed in the adjustment circuit 200 when the pixel array 100 is driven. , Only SW5) can detect the fixed pattern noise and the power / ground noise of each row of the comparators 401 and 402 of each pixel array of the pixel array every frame, and based on this, the pixel array 100 can be detected. The noise of each image signal output from the camera can be completely removed.

3 shows a configuration of an image sensor according to another embodiment of the present invention. Referring to FIG. 3, an image sensor according to another embodiment of the present invention receives an image signal output from a pixel array including a plurality of pixels and is composed of columns and rows, and converts the image signals into digital data. The counter circuit 400 including the comparators 401 and 402 corresponding to the columns 101 and 103 of the array, in which a plurality of switches SW1, SW2 and SW3 and a plurality of switches SW1, SW2 and SW3 are disposed. A row line 220, one end of the plurality of switches SW1, SW2, and SW3 is applied with a reference signal Vref used for the comparison operation of the counter circuit 400, and the other end of the plurality of switches SW1, SW2, SW3. The plurality of switches SW1, SW2, and SW3 disposed in the row line 220 of the adjustment circuit every time the control circuit 250 and the row lines 102 and 104 of the pixel array 100 are connected to the 402. Generating a control signal for driving the plurality of pixels and corresponding to the respective columns 101 and 103 of the pixel array 100 The comparator may include a controller 500 for controlling to detect the noise of the (SW1, SW2, SW3). In FIG. 3, in contrast to FIG. 2, the adjusting circuit 250 is composed of an ellipse line 220 and does not have one column line. Instead, the output signal of the calculator 230 may be applied to the additional comparator 410 to drive the additional comparator 410. The operator 230 may be, for example, an OR operator, and a row driving signal row_sel of the pixel array 100 may be applied as an input signal. That is, each time a row-by-row signal is applied to the pixel array 100, row_sel is turned on so that the output of the calculator 230 is turned on. Accordingly, a signal may be output from the additional comparator 410. The additional comparator 410 may detect noise by detecting the reference signal Vref each time. In the driving of the image sensor illustrated in FIG. 3, one column line is not disposed in the adjustment circuit 250, and instead, an operator 230 is disposed so that an additional comparator 410 is provided for each row control of the pixel array 100. Except for the driven configuration, the description thereof is omitted since it is the same as that of FIG. 2.

4 is a flowchart illustrating a method of driving an image sensor according to an exemplary embodiment of the present invention.

In step S11, the switch is driven to one line of the adjustment circuit disposed in the image sensor.

In step S12, a reference signal is generated in accordance with the operation timing of the plurality of comparators. The generation of the reference signal may be continuous according to the timing of generation of the reference signal before the operation of step S11.

In step S13, noise of a plurality of comparators corresponding to each column of the pixel array is detected. That is, by driving the switch to one line of the adjustment circuit disposed in the image sensor, noise of a plurality of comparators connected to the switch and additional comparators of the adjustment circuit can be detected. The detected noise is then used in the noise removal of the image signal so that the detected noise can be temporarily stored, for example during the drive frame of the pixel array.

In step S14, a plurality of pixels are controlled for each row of the pixel array for a predetermined period. For example, signals are sequentially applied from the raw decoder during the driving frame of the pixel array to output an image signal from all the pixels of the pixel array.

In operation S15, noise is removed from an image signal corresponding to the plurality of pixels based on the noise detected from the plurality of comparators.

Meanwhile, the driving method of the image sensor illustrated in FIG. 4 may be applied to all of the driving methods of the image sensor illustrated in FIGS. 2 and 3. That is, a series of operations in which a switch of a line is driven before the operation of one frame of the pixel array, the noise of the plurality of comparators is first detected, and then an image signal is output and corrected from the pixel arrays is performed. Both Figures 2 and 3 may be common. This is because the driving timings of the switches SW4 and SW5 arranged in one column line of the adjusting circuit are not separately performed in FIG. 3 but are synchronized with the driving of the pixels of the pixel of the pixel array.

The driving method of the image sensor according to the exemplary embodiment of the present invention has been described above. The driving method of the image sensor of the present invention can be applied to a method for a user interface that follows a movement of a stored detection target region and inputs corresponding movement information, and stores it as an electronic recording code in a computer-readable recording medium. Can be provided.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (17)

An image sensor for processing a signal output from a plurality of pixels,
A counter circuit which receives an image signal output from a pixel array in which the plurality of pixels are arranged in columns and rows, converts the image signal into digital data, and includes a plurality of comparators corresponding to the columns of the pixel array;
A plurality of switches and one column line and one furnace line on which the plurality of switches are disposed, wherein the plurality of switches are provided with a reference signal used for a comparison operation of the counter circuit at one end thereof, and the other end of the plurality of switches. An adjusting circuit disposed in a row and a column adjacent to the pixel array to be connected to a line or one column line; And
Generating a control signal for driving a plurality of switches connected to one line of the adjustment circuit, detecting noise of a plurality of comparators corresponding to each column of the pixel array, and driving the switches connected to the one column line A controller for controlling to detect noise per furnace of the pixel array,
The plurality of switches connected to the one column line of the adjustment circuit are driven together with the pixels of the pixel array arranged in each furnace, and the plurality of switches connected to the one line are the pixels of the pixel array arranged in each column. And an image sensor coupled with said comparator of said counter circuit. The method of claim 1,
An additional comparator coupled to one column line of said adjustment circuit, said additional comparator detecting a noise signal of said pixel array. 3. The method of claim 2,
And the controller controls to detect row noise in the pixel array based on the noise signal of the additional comparator. The method of claim 1,
And a reference signal generator configured to apply a reference signal to one column line of the adjustment circuit and one end of a plurality of switches arranged in the furnace line. The method of claim 1,
The controller sequentially controls a plurality of pixels arranged in a plurality of row lines constituting the pixel array at predetermined periods, and drives signals for driving a plurality of switches arranged in one row of the adjustment circuit at each period. Image sensor. 3. The method of claim 2,
And the controller sequentially drives a plurality of comparators of the counter circuit every predetermined period, and generates a signal for driving the additional comparator at each period. The method according to claim 5 or 6,
And the controller removes noise from an image signal output from a pixel array based on noise detected from the additional comparator and the plurality of comparators. An image sensor for processing a signal output from a plurality of pixels,
A counter circuit including the plurality of pixels and receiving an image signal output from a pixel array including columns and rows, converting the image signal into digital data, and including a comparator corresponding to the columns of the pixel array;
A plurality of switches and a working line in which the plurality of switches are disposed,
One end of the plurality of switches is provided with a reference signal used for the comparison operation of the counter circuit, and the other end thereof is connected to a comparator of the counter circuit which is identical to the pixels of the pixel array arranged in each column;
Each control of the row line of the pixel array generates a control signal for driving a plurality of switches arranged in one row line of the adjustment circuit, and controls to detect noise of a plurality of comparators corresponding to each column of the pixel array. Image sensor containing a controller. 9. The method of claim 8,
The working line of the adjustment circuit further includes an additional switch not connected with the pixel array,
The image sensor
And an additional comparator coupled to said working line via said additional switch and for detecting noise in said reference signal or noise in said comparator. 9. The method of claim 8,
And a reference signal generator configured to apply a reference signal to one end of a plurality of switches arranged in a line of the adjustment circuit. 10. The method of claim 9,
And the controller sequentially controls a plurality of comparators of the counter circuit at predetermined cycles, and generates a signal for driving the additional comparator at each cycle. 12. The method of claim 11,
And the controller removes noise from an image signal output from the pixel array based on noise signals detected from the additional comparator and the plurality of comparators. A counter circuit including a plurality of pixels and receiving an image signal output from a pixel array consisting of columns and rows, converting the image signal into digital data, and including a comparator corresponding to the columns of the pixel array; And a regulating circuit including a plurality of switches and a working line in which the plurality of switches are arranged.
Driving a plurality of switches arranged in one line of the adjustment circuit;
Generating a reference signal according to an operation timing of the plurality of comparators;
Detecting noise of a plurality of comparators corresponding to each column of the pixel array;
Outputting an image signal by controlling a plurality of pixels for each row of the pixel array for a predetermined period; And
And removing noise from image signals corresponding to the plurality of pixels based on the noise detected by the plurality of comparators. The method of claim 13,
The regulation circuit further includes one column line in which a plurality of switches are arranged,
Driving a plurality of switches arranged in the one column line whenever the plurality of pixels of each row of the pixel array are controlled; And
And detecting a noise signal for each row of the pixel array. The method of claim 13,
And applying a reference signal to one end of a plurality of switches arranged in a line of the adjustment circuit. The method of claim 13,
Detecting noise of a plurality of comparators corresponding to each column of the pixel array may further include generating a signal for driving a plurality of switches arranged in one line of the adjustment circuit at each predetermined period. Method of driving. The method of claim 13,
The adjustment circuit further comprises an additional comparator for detecting a noise signal of a reference signal generator for generating the reference signal,
And a noise of the plurality of comparators is detected using the signal from the additional comparator.

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