A phase detection focusing method, an imaging system, an image sensor and a terminal

Abstract

The application discloses a phase detection focusing method, an imaging system, an image sensor and a terminal, relates to the field of phase detection auto-focusing, and solves the problem that when an image sensor adopting a correlated double sampling technology reads a pixel charge amount, a first part of pixel charge amounts and a second part of pixel charge amounts are deviated, a phase detection auto-focusing purpose cannot be achieved, and thus the focusing precision of an imaging process is affected. Technical scheme points are as follows: according to a feedback coefficient generated in an exposure multiplication area, an analog-digital conversion process of the first part of pixel charge amounts of an exposure processing area is adjusted, so that the first part of pixel charge amounts read from the exposure processing area is equal to the second part of pixel charge amounts, and phase focusing is completed. The application makes the first part of pixel charge amounts and the second part of pixel charge amounts read from the exposure processing area not deviated, achieves the phase detection auto-focusing purpose, and improves the focusing precision of the imaging process.

Description

Technical Field

[0001] This invention relates to the field of phase detection autofocus, and more specifically, to a phase detection autofocus method, an imaging system, an image sensor, and a terminal. Background Technology

[0002] With the widespread application of phase detection autofocus (PDAF) technology, among the three common types of PDAF (shield pixel, 2x1 on-chip lens (2x1OCL), and Dual PD), 2x1OCL and Dual PD, being dual-core systems, both undergo a process of reading pixel charge twice (i.e., during pixel photoelectric conversion, the TG (Transfer Gate) is opened twice to read the pixel charge, distinguishing between the first and second parts of the pixel).

[0003] When an image sensor equipped with CDS (Correlated Double Sampling) technology samples a signal, the relevant components of CDS will remain in an accumulated charge state until the TG (Transfer Gate) is opened. This causes a certain deviation between the actual second part of the pixel charge and the ideal state, making the first part of the pixel charge not equal to the second part of the pixel charge. This fails to achieve the purpose of phase detection autofocus and thus affects the focusing effect. Summary of the Invention

[0004] The purpose of this invention is to provide a phase detection focusing method, imaging system, image sensor, and terminal. This invention solves the problem that when an image sensor using correlation dual sampling technology reads the charge of a pixel, there is a deviation between the first part of the pixel charge and the second part of the pixel charge, which makes it impossible to achieve the purpose of phase detection autofocus and thus affects the focusing accuracy of the imaging process.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides a phase detection focusing method applied to an image sensor employing correlated double sampling technology. The method includes: adjusting the analog-to-digital conversion process of a first portion of pixel charge in an exposure processing region based on a feedback coefficient generated in an exposure multiplication region, so that the first portion of pixel charge read from the exposure processing region is equal to the second portion of pixel charge, thereby completing phase detection focusing.

[0007] In one implementation, the feedback coefficient generated in the exposure multiplication region is specifically:

[0008] Determine the exposure time and interval time required to read the pixel charge of the first part and the pixel charge of the exposure multiplication area;

[0009] The phase-detection autofocus ratio coefficient is calculated based on the exposure time and interval time.

[0010] The proportional coefficient is multiplied by the preset conversion coefficient, analog signal quantity, and digital signal quantity to obtain the feedback coefficient; wherein, the conversion coefficient refers to the bias in the analog-to-digital conversion or digital-to-analog conversion process.

[0011] In one implementation, the interval is the time difference between two openings of the transmission gate of the photodiode connecting the first set of pixels.

[0012] In one implementation, the phase-detection autofocus scaling factor is calculated based on the exposure time and the interval time, specifically as follows:

[0013] The reading time for reading the first part of the pixel charge is obtained based on the difference between the exposure time and the interval time.

[0014] The ratio of exposure time to readout time is used to obtain the phase-detection autofocus scaling factor.

[0015] In one implementation, the conversion coefficient is 1.

[0016] In one implementation, the multiplication expression for the proportional coefficient based on the preset conversion coefficient, analog signal quantity, and digital signal quantity is as follows: ;in, a The input signal represents the feedback coefficient, the output signal represents the analog signal processed by the digital-to-analog converter (DAC), the output signal represents the digital signal processed by the analog-to-digital converter (ADC), and the output signal represents the exposure time. Indicates the interval time.

[0017] In one implementation, the analog-to-digital conversion process for the pixel charge of the first portion of the exposure processing area is adjusted, specifically as follows:

[0018] The feedback coefficients are converted from digital to analog to obtain an analog signal;

[0019] The ramp voltage starting position of the analog converter used to read the first part of the pixel charge is raised according to the value of the analog signal, so as to increase the counting time for reading the first part of the pixel charge and complete the compensation of the first part of the pixel charge.

[0020] A second aspect of the present invention provides a graphic sensor employing correlated double sampling technology for performing a phase detection focusing method as provided in the first aspect of the present invention.

[0021] A third aspect of the present invention provides a phase detection focusing imaging system, the phase detection focusing imaging system comprising:

[0022] As provided in the second aspect of the present invention, a graphics sensor employing correlated double sampling technology; and

[0023] An application processor is used to process the pixel data output by the image sensor employing correlated double sampling technology to generate an image.

[0024] A fourth aspect of the present invention provides a terminal comprising a phase detection focusing imaging system as provided in the third aspect of the present invention.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In the phase detection focusing method, imaging system, image sensor, and terminal provided by this invention, a feedback coefficient is generated in the exposure multiplication region of the imaging area of ​​the image sensor to compensate for the first part of the pixels in the exposure processing area. Based on the feedback coefficient, the read voltage of the analog-to-digital conversion circuit is biased and adjusted, thereby realizing the exposure compensation of the first part of the pixels in the exposure processing area. This ensures that there is no deviation between the charge of the first part of the pixels and the charge of the second part of the pixels read from the exposure processing area, thereby achieving the purpose of phase detection autofocus and improving the focusing accuracy of the imaging process. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 This is a block diagram illustrating the principle of a phase detection focusing imaging system provided in an embodiment of the present invention.

[0029] Figure 2 A schematic diagram of phase focusing principle provided for existing technology;

[0030] Figure 3 Pixel circuit schematics provided for existing technologies;

[0031] Figure 4 Example diagram of charge accumulation in the first and second part of pixels provided for the prior art;

[0032] Figure 5 Example diagrams of pixel charge sampling for existing dual-sampling techniques;

[0033] Figure 6 Example diagram of pixel charge reading for existing dual-sampling techniques;

[0034] Figure 7 An example diagram of the feedback system of the phase detection focusing imaging system provided in the embodiment of the present invention;

[0035] Figure 8 A pixel region map of an image sensor provided for existing technology;

[0036] Figure 9 Example diagram of pixel charge readings with relevant double sampling provided for existing technology;

[0037] Figure 10 This is an example diagram of pixel charge reading with related double sampling provided in an embodiment of the present invention.

[0038] Figure labels and figure descriptions:

[0039] S01, Pixel array; S02, Analog circuit; S03, Digital circuit; S04, Feedback system; S05, Firmware; S06, Application processor; S12, ADC; S13, Digital signal processing unit; S14, Feedback coefficient; S15, DAC; S16, Exposure multiplication area; S17, Exposure processing area. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0041] It should be noted that the terms "comprising" or "may include" used in the various embodiments of this application indicate the presence of the claimed function, operation, or element, and do not limit the addition of one or more functions, operations, or elements. Furthermore, as used in the various embodiments of this application, the terms "comprising," "having," and their cognates are intended only to indicate a specific feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as primarily excluding the presence of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or adding one or more combinations of the foregoing.

[0042] It should be understood that terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] This invention provides a phase detection focusing method, which is applied to an image sensor employing correlated double sampling technology, such as a CCD image sensor or a CMOS image sensor. The phase detection focusing method includes: adjusting the analog-to-digital conversion process of the first part of the pixel charge in the exposure processing area according to the feedback coefficient generated in the exposure multiplication area, so that the first part of the pixel charge read from the exposure processing area is equal to the second part of the pixel charge, thereby completing phase detection focusing.

[0044] Specifically, the focusing principle of phase detection autofocus (PDAF) will be introduced first, such as... Figure 2 As shown in S07-S09, the focus offset and phase difference information are determined based on the distance and changes between pixels, thus identifying the state where the lens is in the clearest focus relative to its current position. Figure 2 The position of the focused state (S08) with zero phase difference is shown, thus obtaining the vector that the lens should move. Secondly, since PDAF is a common technology, the explanation of the underfocus state shown in S07 and the overfocus state shown in S09 is omitted in this embodiment. To achieve the above focusing function, the image sensor must support PDAF (phase detection autofocus), and the camera needs to calibrate phase data at different distances. The data mainly needs to include the correspondence between phase difference and object distance. By adjusting the lens, phase difference information can be obtained. Based on the internal calibration data, the current position of the lens is obtained, and the direction and distance to be moved are calculated, greatly improving the focusing speed.

[0045] Secondly, the optical signal sampling process of the image sensor is introduced, such as... Figure 3 As shown, first, pixel exposure (signal accumulation) is performed, and the TG (Transfer Gate), Reset, and Select are turned off. The PD (photodiode) receives the light source, performs photoelectric conversion, and accumulates photoelectrons. Then, the Select and Reset transistors are turned on to perform a reset. After the reset is completed, the Reset transistor is turned off again. Finally, the TG is turned on to transfer the photoelectrons in the PD to the FD (floating diffusion region). Then, the TG is turned off again to avoid the subsequent photoelectric conversion in the PD affecting the FD. At the same time, the voltage generated by the FD due to the photoelectrons it receives controls the switch to transmit the signal.

[0046] Based on the photoelectric conversion principle of image sensors and the related dual sampling principle of phase focusing drive, this embodiment takes a typical phase focusing mode in which a pixel is divided into two parts for pixel reading as an example (analogous to the dual-core system of 2x1OCL and Dual PD). Other phase focusing modes are also applicable.

[0047] The pixel sampling process of an image sensor is explained as follows: Figure 4 As shown, a phase-focused pixel is divided into two parts, each of which is configured with a PD structure for photoelectric conversion. First, the charge S10 of the first pixel (PD1) is read out. After reading the electrical signal of the first pixel, the second pixel (PD2) of the same pixel is read out. At this time, the charge S10 of the first pixel and the sum of the charges S11 of the first and second pixels can be obtained by reading the signals twice.

[0048] S10: For the same phase-focused pixels, the amount of charge accumulated in the first part of the pixels.

[0049] S11: For the same phase-focused pixels, the total charge accumulated in the first part of the pixels and the second part of the pixels.

[0050] As can be seen from the principle of phase detection autofocus, to achieve... Figure 2 In the focus state where the recorded phase difference is zero (S08), the charge amounts of the two parts of the same pixel corresponding to the phase-focused pixel point must be kept at the same level. However, due to the pixel reading order involved in phase focusing, the total charge accumulated by the first part of the pixel plus the second part of the pixel (S11) - the charge amount of the first part of the pixel (S10) ≠ the charge amount of the second part of the pixel. In other words, the charge amounts accumulated and read by PD1 and PD2 are different.

[0051] The reason for the above problem is that when reading pixels using CDS technology, it is necessary to first read the charge of the first part of the pixels (S10). This involves opening the TG (transmission gate) of the photodiode connected to the first part of the pixels to complete the reading of the charge of the first part of the pixels. Next, to further read the total charge of the first part of the pixels and the second part of the pixels (S11), it is necessary to simultaneously open the TG of the photodiodes connected to the first part of the pixels and the second part of the pixels. For the first part of the pixels, the photodiode, which should have been read in one operation, accumulates additional charge during the interval between the two TG openings, and this additional charge is newly accumulated after the charge of the first part of the pixels has been read. Therefore, after the total charge of the first part of the pixels plus the second part of the pixels (S11) is read, due to this additional accumulated charge, the final result is that the total charge of the first part of the pixels + the second part of the pixels (S11) - the charge of the first part of the pixels (S10) ≠ the charge of the second part of the pixels.

[0052] like Figure 5 As shown, the sampling process of pixel charge quantity using the related double sampling technique is as follows:

[0053] Step 1: The photodiodes connecting the first and second part of the pixels accumulate charge simultaneously, and the amount of charge on both sides is the same;

[0054] Step 2: Turn on the TG of the photodiode connected to the first part of the pixels, and first read the charge of the photodiode PD1 of the first part of the pixels;

[0055] Step 3: Turn on the TG of the photodiode connected to the second part of the pixels and read out the accumulated charge of the photodiode PD2 of the second part of the pixels; since photoelectric accumulation also occurs during the TG period when reading the charge of the first part of the pixels, the photodiode will accumulate a small amount of charge when reading the charge of the second part of the pixels during this period.

[0056] Step 4: Read out the pixel signals of the first and second parts. Ideally, the pixel readings of the first and second parts should be the same. However, due to the small amount of charge accumulated in Step 3, the charge of the second part of the pixels is not equal to the charge of the first part of the pixels, which ultimately leads to a deviation in phase focusing.

[0057] In order to improve the accuracy of phase focusing, this embodiment aims to add the extra charge of the second part of the pixels to the charge of the first part of the pixels in the same proportion by means of digital-to-analog conversion, so that the charge of the two parts of the same pixel remains at the same level.

[0058] In some embodiments, the feedback coefficient generated in the exposure multiplication region specifically involves: determining the exposure time and interval time required to read the first part of the pixel charge and the second part of the pixel charge in the exposure multiplication region; calculating the phase focusing scaling factor based on the exposure time and interval time; multiplying the scaling factor based on a preset conversion factor, analog signal, and digital signal to obtain the feedback coefficient; wherein the conversion factor refers to the bias in the analog-to-digital conversion or digital-to-analog conversion process.

[0059] like Figure 1 As shown, the proportional coefficient for compensating and adjusting the first part of the pixels is calculated by the exposure processing unit installed in firmware S05. Since the process of calculating the signal deviation between the first and second parts of the pixels after the exposure time is detected can be programmed, firmware S05 is introduced to save loop area and simplify the processing. The function of firmware S05 is to control the hardware. The exposure time processing unit is installed in firmware S05 to realize the control interaction with the image sensor.

[0060] The specific operation of the exposure processing unit is as follows: For the CDS readout diagram of the phase-detection autofocus pixel, as shown... Figure 6As shown, Vrst is the reset noise value read for the first time, Vsig1 is the charge of the first part of the pixels, and Vsig2 is the total charge of (the first part of the pixels plus the second part of the pixels). The results obtained by Vsig1-Vrst and Vsig2-Vrst are the CDS results of the first part of the pixels and the CDS results of the first part of the pixels plus the second part of the pixels, respectively.

[0061] As can be seen from the order of exposure time reading, Vsig1 is read first, followed by Vsig2. There is a certain time difference within the TG activation time. It is precisely because of this difference in exposure time that, after CDS processing, the total charge of the first and second pixel groups (S11) - the charge of the first pixel group (S10) ≠ the charge of the second pixel group. Therefore, the interval time △T, or interval time difference △T, can be obtained, usually in line unit time. The exposure time T for reading the charge of the first and second pixel groups can also be obtained; thus, the reading time of the first pixel group can be obtained through (T-△T). Furthermore, based on the cumulative charge deviation during the reading process described above, this embodiment requires compensation adjustment (magnification) of the first pixel group Vsig1. In other words, the magnification ratio required to complete phase focusing is T / (T-△T). This ratio can also be referred to as the exposure time coefficient in the following description, and it is calculated by the exposure time processing unit of the phase detection focusing imaging system.

[0062] After determining the scaling factor for compensating and adjusting the first part of pixels Vsig1, the digital signal processing unit S13 of the phase detection focusing imaging system performs multiplication processing on it, and the output is fed back to the analog signal converter (ADC) as part of the feedback system. The specific implementation process is as follows:

[0063] When the scaling factor is 1, it can be seen that the charge levels of the first and second part of the pixels remain at the same level, such as... Figure 2 The focus state shown in S08, with a phase difference of 0, achieves the purpose of phase focusing.

[0064] Since the target signals in analog signal conversion (ADC) and digital signal conversion (DAC) are the same, but they are different processes, in an ideal state, ADC × DAC = conversion coefficient. It should be understood that this conversion coefficient is 1 in an ideal state, but in reality it will include the bias caused by gain, voltage or device factors in the ADC or DAC process. The influence of this bias is controllable, so the conversion coefficient is used to explain it uniformly.

[0065] Thus, a closed-loop transfer function feedback system is constructed under ideal conditions (conversion coefficient is 1). The feedback channel of this feedback system S04 is 1. The forward path is analog pixel reading. After reading by analog signal converter (ADC), the data is transmitted to digital circuit and the proportional coefficient is obtained through exposure processing unit. Then, the reverse path is constructed by digital circuit, and the data is returned to analog signal converter (ADC) for correlation double sampling through feedback coefficient S14 and digital signal converter (DAC) for processing.

[0066] The feedback coefficient of the first pixel can be obtained. a as follows: ;

[0067] ;in, a The input signal represents the feedback coefficient, the output signal represents the analog signal processed by the digital-to-analog converter (DAC), the output signal represents the digital signal processed by the analog-to-digital converter (ADC), and the output signal represents the exposure time. Indicates the interval time

[0068] It should be noted that the DAC / ADC mentioned in the formula is determined by its own bit width. Here, ADC is the digital signal after processing by the analog-to-digital converter, and DAC is the analog signal after processing by the digital-to-analog converter.

[0069] The feedback coefficient (T / (T-△T)) corrects the problem that the first part of the phase-detection pixels has a small charge due to the exposure time difference, thereby increasing the charge of the first part of the pixels. Ultimately, the desired effect is achieved: the total charge of the first part of the pixels plus the second part of the pixels minus the charge of the first part of the pixels equals the charge of the second part of the pixels.

[0070] Secondly, for the feedback system S04, its specific implementation is as follows: Figure 7 As shown, the first part of the pixels is exposed. After the photoelectric conversion is completed, the proportional coefficient is obtained in the exposure processing unit of ADC (analog signal converter) S12. After analog-to-digital conversion, it is processed by digital signal processing unit S13. A feedback path is constructed by digital circuit. After passing through feedback coefficient S14 and DAC (digital signal converter) S15, it is fed back to ADC (analog signal converter) S12 to make its voltage bias complete the analog-to-digital conversion, so as to achieve the purpose of amplifying the charge of the first part of the pixels.

[0071] In implementing the aforementioned feedback system S04, it's important to note that during the process of converting the analog signal into a digital signal via the ADC (Analog-to-Digital Converter) S12, and then applying the feedback coefficient S14 back to the analog signal for control, there is a certain time and space involved in the response. To achieve this response time, such as... Figure 8As shown, the imaging area of ​​the image sensor (this area is distributed in the pixel array S01, whose basic unit is a photodiode) is shown. Figure 8 Each box in the diagram represents a phase-detection autofocus pixel unit, which is divided into an exposure multiplication area S16 and an exposure processing area S17.

[0072] The exposure multiplication area S16 does not participate in phase focus adjustment or imaging but receives light normally, and usually has 2 or 4 physical rows; the exposure processing area S17 receives light normally and participates in actual phase focus adjustment and imaging.

[0073] Therefore, in this embodiment, the calculation of the proportional coefficient and digital signal processing are completed in the exposure multiplication area S16 to generate a feedback coefficient. Then, the feedback coefficient is converted from digital to analog to obtain an analog signal. Based on the value of the analog signal, the starting position of the ramp voltage of the analog converter used to read the charge of the first part of the pixel is raised to increase the counting time for reading the charge of the first part of the pixel and complete the compensation of the charge of the first part of the pixel. Thus, it can take effect in time before the exposure processing area S17 is reached, thereby achieving compensation and adjustment of the target pixel (the first part of the pixel) in the same imaging area.

[0074] To demonstrate the difference between the phase detection focusing method provided by this invention and the phase detection focusing method provided by the prior art, the following comparative examples are also provided in this embodiment:

[0075] like Figure 9 As shown, this is a schematic diagram of the ADC reading of a phase-focused pixel under normal conditions. The intersection of each ramp voltage and Vin voltage is the quantization value of that stage, i.e., the amount of charge.

[0076] based on Figure 9 We can obtain: Vrst at Figure 9 The quantization value is 1;

[0077] The quantization value of Vsig1 after CDS is 1;

[0078] The quantization value of Vsig2 after CDS is 4;

[0079] Based on the order of exposure time readout, the quantization value of Vsig1 is read out first. During the reading out of Vsig2, an additional interval time ΔT is added based on the exposure time of Vsig1. This interval time ΔT causes the quantization value of the second part of the pixels to be equal to (quantization value of the first part of the pixels + quantization value of the second part of the pixels) – quantization value of the first part of the pixels = 4 - 1 = 3. Therefore, the final quantization values ​​of the first part of the pixels and the second part of the pixels are not equal.

[0080] Through the compensation process described above in this embodiment, the analog signal converted by the feedback coefficient is applied to Vsig1 to act as a bias voltage, such as... Figure 10 As shown, since no compensation was made for the exposure time difference, the quantization value of Vsig2 after CDS is 4.

[0081] Since it is expected that the pixel values ​​of the first and second parts are equal before phase focusing detection, the quantization values ​​of the first and second parts of the pixels in Vsig2 are each 2.

[0082] Furthermore, the quantization value of the second part of the pixels = (quantization value of the first part of the pixels + quantization value of the second part of the pixels) - quantization value of the first part of the pixels = Vsig2 - Vsig1. Without exposure time compensation, Vsig1 is smaller than the expected value, so the feedback analog signal should have the effect of increasing the quantization value of Vsig1.

[0083] according to Figure 10 It can be seen that the quantized value is the intersection of the ramp voltage and Vin when the ramp voltage drops. The longer the time required for the two to intersect, the larger the pixel value of that part. The Vin voltage is determined by the original pixel and cannot be adjusted. Therefore, when Vin is constant, raising the starting position of the ramp voltage of Vsig1 by a part increases the counting time for reading the first part of the pixel charge, which can achieve the purpose of compensating the Vsig1 signal. The compensation ratio is (T / (T-△T)).

[0084] Therefore, we can conclude that Vrst is at Figure 10 The quantization value in is 1;

[0085] Vsig1, after offset voltage and quantization by CDS, has a value of 2;

[0086] The quantization value of Vsig2 after CDS is 4;

[0087] The quantization value of the second part of the pixels = (quantization value of the first part of the pixels + quantization value of the second part of the pixels) - quantization value of the first part of the pixels = Vsig2 - Vsig1 = 2. After adjustment, the quantization values ​​of the first part and the second part of the pixels are equal. Therefore, the focusing method provided in this embodiment can achieve the purpose of phase focusing, and the image sensor uses the pixel unit of this exposure processing area as the pixel output for actual imaging.

[0088] In summary, the exposure compensation provided in this embodiment improves shutter speed and sensitivity by switching from a digital to an analog method. While maintaining the characteristics of phase-detection autofocus, it simultaneously compensates for exposure, reducing noise interference caused by exposure time differences in the focusing circuit and improving focusing accuracy. Furthermore, to ensure that the charge of each pixel is the same before phase-detection autofocus, existing technologies typically add corresponding addition and multiplication digital processing loops in the digital circuit to address signal deviations. This invention, however, uses a feedback mechanism, adding only a proportional coefficient feedback path that directly returns to the analog pixel structure. This ensures that the charge of each pixel is the same after CDS processing by the digital-to-analog converter, saving the digital circuit area and power consumption of existing technologies while ensuring charge compensation.

[0089] This invention also provides an image sensor employing correlated dual sampling technology for use in the phase detection focusing method described in the above embodiments.

[0090] Specifically, such as Figure 1 As shown, the image sensor employing correlated dual sampling technology includes a pixel array S01, an analog circuit S02, a digital circuit S03, a feedback system S04, firmware S05, and an application processor S06. More specifically, the feedback system S05 consists of an analog signal conversion unit, a digital signal processing unit, and a digital signal conversion unit. The analog circuit S02 consists of a photoelectric conversion unit and an analog signal conversion unit. Since each component has been clearly described in the above embodiments, it will not be described in detail here.

[0091] The image sensor using correlated double sampling technology provided in this embodiment generates a feedback coefficient in the exposure multiplication region of the imaging area of ​​the image sensor to compensate for the first part of the pixels in the exposure processing region. Based on this feedback coefficient, the readout voltage of the analog-to-digital conversion circuit is biased and adjusted, thereby realizing the exposure compensation of the first part of the pixels in the exposure processing region. This ensures that there is no deviation between the charge of the first part of the pixels and the charge of the second part of the pixels read out from the exposure processing region, thereby achieving the purpose of phase detection autofocus and improving the focusing accuracy of the imaging process.

[0092] This invention also provides a phase detection focusing imaging system, which includes: a graphic sensor employing correlated double sampling technology as described in the above embodiments; and an application processor for processing pixel data output by the graphic sensor employing correlated double sampling technology to generate an image.

[0093] Specifically, the phase detection autofocus imaging system generates a feedback coefficient in the exposure multiplication region of the imaging area of ​​the image sensor to compensate for the first part of the pixels in the exposure processing area. Based on this feedback coefficient, the readout voltage of the analog-to-digital conversion circuit is biased and adjusted, thereby achieving exposure compensation for the first part of the pixels in the exposure processing area. This ensures that there is no deviation between the charge of the first part of the pixels read out in the exposure processing area and the charge of the second part of the pixels, thus achieving the purpose of phase detection autofocus and improving the focusing accuracy of the imaging process.

[0094] This invention also provides a terminal, including a phase detection focusing imaging system as described in the embodiments above.

[0095] Specifically, the terminal can take photos with high image quality, has autofocus function and high focusing accuracy, and can include, but is not limited to, smartphones, cameras, surveillance cameras, etc.

[0096] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A phase detection focusing method applied to an image sensor using a correlated double sampling technique, characterized by, The methods include: Based on the feedback coefficient generated in the exposure multiplication region, the analog-to-digital conversion process of the first part of the pixel charge in the exposure processing region is adjusted to make the first part of the pixel charge read from the exposure processing region equal to the second part of the pixel charge, thus completing phase focusing. Specifically, the feedback coefficient generated in the exposure multiplication region involves: determining the exposure time and interval time required to read the first and second parts of the pixel charge in the exposure multiplication region; calculating the phase focusing scaling factor based on the exposure time and interval time; and multiplying the scaling factor based on a preset conversion factor, analog signal, and digital signal to obtain the feedback coefficient. The conversion factor refers to the bias in the analog-to-digital conversion or digital-to-analog conversion process. The exposure multiplication area and the exposure processing area are divided by the imaging area. The exposure multiplication area receives light normally but does not participate in phase focus adjustment and imaging, while the exposure processing area receives light normally and participates in actual phase focus adjustment and imaging. The imaging area is distributed in the pixel array of the image sensor.

2. The phase-detection focusing method according to claim 1, wherein The interval time is the time difference between two openings of the transmission gate of the photodiode connecting the first part of the pixels.

3. The phase-detection focusing method according to claim 1, wherein The phase-detection autofocus scaling factor is calculated based on the exposure time and interval time, specifically as follows: The reading time for reading the first part of the pixel charge is obtained based on the difference between the exposure time and the interval time. The ratio of exposure time to readout time is used to obtain the phase-detection autofocus scaling factor.

4. The phase-detection focusing method according to claim 1, wherein The conversion factor is 1.

5. The phase detection focusing method according to claim 1, characterized in that, According to the preset conversion coefficient, the analog signal quantity and the digital signal quantity, the proportional coefficient is multiplied by the expression: ; wherein a represents a feedback coefficient, DAC represents an analog signal quantity processed by a digital-to-analog converter, ADC represents a digital signal quantity processed by an analog-to-digital converter, T represents an exposure time, represents an interval time.

6. The phase detection focusing method according to claim 1, characterized in that, The analog-to-digital conversion process for the first portion of pixel charge in the exposure processing area is adjusted as follows: The feedback coefficients are converted from digital to analog to obtain an analog signal; The ramp voltage starting position of the analog converter used to read the first part of the pixel charge is raised according to the value of the analog signal, so as to increase the counting time for reading the first part of the pixel charge and complete the compensation of the first part of the pixel charge.

7. A pattern sensor employing correlated double sampling technology, characterized in that, Used to perform a phase detection focusing method as described in any one of claims 1 to 6.

8. A phase detection focusing imaging system, characterized in that, The phase detection focusing imaging system includes: A graphics sensor employing correlated double sampling technology as described in claim 7; and An application processor is used to process the pixel data output by the image sensor employing correlated double sampling technology to generate an image.

9. A terminal, characterized in that, Including a phase detection focusing imaging system as described in claim 8.

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