CN108777771B - Image sensor and operation method of imaging system - Google Patents
Image sensor and operation method of imaging system Download PDFInfo
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Abstract
The invention provides an operation method of an image sensor, which comprises the following steps: generating a high level signal and a low level signal with the driving circuit; exposing all of the sensing pixels to store a plurality of first charge amounts simultaneously with respect to the high-level signal period; transferring the first charge amount of the sensing pixels of the first column to the first storage circuit with respect to the low-level signal period; exposing the sensing pixels of the first column to store a plurality of second charge amounts relative to the low-level signal period; transferring the second charge amount of the sensing pixels of the first column to the second storage circuit with respect to the low-level signal period; and performing analog difference on the first charge amount in the first storage circuit and the second charge amount in the second storage circuit by the difference unit to output an analog image signal corresponding to a first column.
Description
The present application is a divisional application of the chinese patent application entitled "image sensor and operating method thereof", having an application date of 09/10/2014 and an application number of 201410457506.5.
Technical Field
The present invention relates to an image sensor, and more particularly, to an image sensor using analog difference to eliminate ambient light interference and a method for operating the same.
Background
Known image sensors typically have a plurality of sensing pixels arranged in an array, wherein one method of operation of the image sensor may use a Rolling Shutter (Rolling Shutter), for example, to sequentially activate the sensing pixels of each column in the image sensor with a control signal to acquire an image. Since the sensing pixels of each row are activated sequentially rather than simultaneously (i.e., the sensing pixels of each row start to be exposed at different times), when acquiring an image of a fast moving object, the image acquired by using a rolling shutter may have a distortion (distortion) problem.
Another method for operating an image sensor may use a Global Shutter (Global Shutter), for example, to control all the sensing pixels in the image sensor to be activated simultaneously so that the sensing pixels in each row can start exposure at the same time to acquire an image, and thus, the image sensor using the Global Shutter can avoid the image distortion problem.
However, in order to eliminate the interference of ambient light or reduce image noise when an image is acquired by an image sensor using a global shutter, a solution is known in which two digital image frames are directly subtracted by means of image post-processing to obtain a differential image frame. For example, referring to fig. 1A and 1B, fig. 1A is a timing diagram illustrating image acquisition of an image sensor 91 using a known global shutter. Assuming that the image sensor 91 has 4 sensing pixel columns R1-R4, in a first period P1, a light source is turned on for a preset time and the sensing pixel columns R1-R4 are exposed simultaneously, then the light source is turned off and the sensing pixel columns R1-R4 are read in sequence to output a first image signal; in a second period P2, the light source is turned off and simultaneously exposes the sensing pixel columns R1-R4 for the preset time and sequentially reads the sensing pixel columns R1-R4 to output a second image signal.
Next, referring to fig. 1B, the first image signal output by the image sensor 91 is first converted into a first digital signal 9a by an analog-to-digital converter 93 and stored in a digital buffer 95. Then, the second image signal is converted into a second digital signal 9b by the analog-to-digital converter 93. Finally, the second digital signal 9b is subtracted from the first digital signal 9a to obtain a third digital signal 9c with ambient light removed. However, in this method, the system including the image sensor 91 needs to set the digital buffer 95 and the image sensor 91 must output two image frames (for example, the image frame formed according to the first digital signal 9a and the second digital signal 9 b) continuously to obtain a processed image frame (for example, the image frame formed according to the third digital signal 9 c).
Disclosure of Invention
The present invention provides a method for eliminating ambient light interference by using analog difference and an image sensor using the same.
The present invention provides an image sensor, which outputs each analog image to eliminate the interference of the ambient light.
It is another object of the present invention to provide an image sensor that can reduce power consumption by approximately one time without using a digital buffer for storing image frames for performing a difference operation between two digital image frames.
To achieve the above objective, the present invention provides an operating method of an image sensor. The image sensor comprises a driving circuit, a plurality of sensing pixels arranged in an array and an output circuit. The output circuit comprises a first storage circuit, a second storage circuit and a differential unit. The operation method comprises the following steps: generating a high level signal and a low level signal with the driving circuit; exposing all of the sensing pixels to store a plurality of first charge amounts simultaneously with respect to the high-level signal period; transferring the first charge amount of the sensing pixels of the first column to the first storage circuit with respect to the low-level signal period; exposing the sensing pixels of the first column to store a plurality of second charge amounts relative to the low-level signal period; transferring the second charge amount of the sensing pixels of the first column to the second storage circuit with respect to the low-level signal period; and performing analog difference on the first charge amount in the first storage circuit and the second charge amount in the second storage circuit by the difference unit to output an analog image signal corresponding to a first column.
The invention also provides an operation method of the imaging system. The imaging system comprises a light source, a plurality of sensing pixels arranged in an array and an output circuit. The output circuit comprises a first storage circuit, a second storage circuit and a differential unit. The operation method comprises the following steps: turning on the light source and simultaneously exposing all of the plurality of sensing pixels to store a plurality of first charge amounts; turning off the light source and transferring the first charge amount of the sensing pixels of a first column to the first storage circuit; exposing the sensing pixels of the first column to store a plurality of second charge amounts; transferring the second amount of charge of the sense pixels of the first column to the second storage circuit; and performing analog difference on the first charge amount in the first storage circuit and the second charge amount in the second storage circuit by the difference unit to output an analog image signal corresponding to a first column.
In order that the manner in which the above recited and other objects, features and advantages of the present invention are obtained will become more apparent, a more particular description of the invention briefly described below will be rendered by reference to the appended drawings. In the description of the present invention, the same components are denoted by the same reference numerals and will be described later.
Drawings
FIG. 1A is a timing diagram of image acquisition of a known image sensor using a global shutter;
FIG. 1B is a block diagram of two known image frames being subjected to a difference operation at the digital end;
FIG. 2 is a circuit diagram of an image sensor according to some embodiments of the invention;
FIG. 3 is a flow chart of a method of operating an image sensor according to some embodiments of the present invention;
FIG. 4 is a timing diagram of a plurality of switching elements corresponding to FIGS. 2 and 3;
FIG. 5 is a block diagram of an image sensor in accordance with certain embodiments of the present invention;
FIG. 6 is a schematic view of an imaging system including a plurality of sensing pixels according to some embodiments of the invention;
fig. 7 is a timing diagram corresponding to fig. 6.
Description of the reference numerals
S1-S5 steps
Detailed Description
Fig. 2 is a circuit diagram of the image sensor 1 according to some embodiments of the invention. The image sensor 1 is used for sensing light energy and converting the light energy into an electrical signal. The image sensor 1 comprises at least a photoelectric conversion circuit 10 and an output circuit 20, wherein the output terminal of the photoelectric conversion circuit 10 is connected to the input terminal of the output circuit 20 via a bit line 70. The image sensor may have a plurality of photoelectric conversion circuits arranged in an array as sensing pixels, and an output terminal of the photoelectric conversion circuit of each column may be electrically connected to an input terminal of the output circuit through a bit line. For example, an image sensor including M × N pixels generally has M × N photoelectric conversion circuits and M or N output circuits and bit lines. To simplify the drawing, fig. 2 shows only two photoelectric conversion circuits 10, 10', one output circuit 20, and one bit line 70 in the image sensor 1 by way of example. It can be understood that the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10' have the same structure although they have different numbers, so as to represent two sensing pixels (e.g. a sensing pixel in a first row and a first column and a sensing pixel in a first row and a second column) in one row of the image sensor 1.
It should be noted that, when acquiring an image frame, the image sensor 10 may be configured with at least one light source (not shown) for providing light required for image acquisition, so the light source may be referred to as a fill-in lamp (e.g., a light emitting diode). The image sensor 10 includes a signal generator or a timing controller (not shown) for sequentially sending a high level signal and a low level signal to drive the light source to turn on or off, but is not limited thereto. In other embodiments, the high level signal and the low level signal may be provided by an imaging system including the image sensor 10, for example, by a control circuit of the imaging system, and provided to the image sensor 10. In some embodiments, the light source and the image sensor may be included in the same image sensor package, and the operation of the light source and the operation of the image sensor may be simultaneously controlled by the timing controller. In some embodiments, the light source is external to the image sensor, and the image sensor may generate the high level signal and the low level signal to control the light source. It should be noted that although the high level signal and the low level signal are described separately, the signal generator, the timing controller or the control circuit may only generate the high level signal, and the low level signal indicates that no signal is generated, for example, the signal value is zero.
The photoelectric conversion circuit 10 is used for storing a first charge amount Q during a relatively high level signal period1And a second amount of charge Q stored during a relatively low level signal2Wherein the high level signal drives the light source to turn on and the low level signal controls the light source to turn off. That is, the photoelectric conversion circuit 10 stores the first charge amount Q1While the light source is on and the photoelectric converter is onThe conversion circuit 10 stores the second charge amount Q2While the light source is off.
The photoelectric conversion circuit 10 includes a photoelectric element 101, a pixel capacitance 102, and a transfer circuit 103. The optoelectronic device 101 can be, for example, a photodiode (photodiode) for converting incident light Li into photocurrent IL(ii) a Wherein the photocurrent ILIs related to the intensity of the incident light Li. The pixel capacitor 102 is used for storing the photocurrent ILIs the first charge amount Q1Or the second charge amount Q2. It can be understood that, when the light source is turned on, the incident light Li includes light emitted by the light source and ambient light, and the photoelectric element 101 converts the light emitted by the light source and the ambient light into the photocurrent ILAnd stores the charge amount (i.e., the first charge amount Q) in the pixel capacitor 1021). When the light source is turned off, the incident light Li only includes the ambient light, and the photoelectric element 101 converts the ambient light into a photocurrent ILAnd stores another charge amount (i.e., the second charge amount Q) in the pixel capacitor 1022). It should be noted that the transfer circuit 103 is coupled between the pixel capacitor 102 and the output circuit 20, and the second charge amount Q is stored in the pixel capacitor 1022Before, the transfer circuit 103 transfers the first charge amount Q from the pixel capacitor 1021To the output circuit 20, then the second charge amount Q2Is stored to the pixel capacitor 102.
In some embodiments, the transfer circuit 103 includes a switch element for controlling the charge transfer according to the on/off of the switch element, for example, fig. 2 shows a first gate 103a and a second gate 103 b. When the first charge amount Q1Or the second charge amount Q2When stored in the pixel capacitor 102, the node N of FIG. 2 has a corresponding first charge Q1Or the second charge amount Q2Potential (V ═ Q/C). To transfer charge to the output circuit 20, the first gate 103a of the transfer circuit 103 can be, for example, a source follower transistor (source follower transistor) and coupledThe node N outputs a charge to the output circuit 20. On the other hand, since the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10' are coupled to the same output circuit (i.e., the output circuit 20) at the same time, the second gate 103b of the photoelectric conversion circuit 10 and the second gate 103b of the photoelectric conversion circuit 10' may not be turned on at the same time, so that the output circuit 20 may sequentially receive the charges of the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10 '.
In addition, in some embodiments, the photoelectric conversion circuit 10 further includes a third gate 106, a fourth gate 107 and a fifth gate 108. The third gate 106 is coupled to the node N and is used to charge or discharge the pixel capacitor 102 to a predetermined charge, so the third gate 106 can be referred to as a reset transistor (reset). The fourth gate 107 is coupled between the photo element 101 and the pixel capacitor 102 and is used for controlling the photocurrent converted by the photo element 101 to be output to the pixel capacitor 102 so as to temporarily store the first charge amount Q in the pixel capacitor 1021Or the second charge amount Q2. The fifth gate 108 is coupled to the output terminal of the photo cell 101 and is used for releasing the charges accumulated in the photo cell 101 during a non-exposure period (i.e., a shutter-off period).
Referring to fig. 2, the output circuit 20 includes a first storage circuit 201 and a second storage circuit 202 for storing the first charge amount Q transferred from the photoelectric conversion circuit 10 (or the photoelectric conversion circuit 10'), respectively1And the second charge amount Q2. In some embodiments, the first storage circuit 201 and the second storage circuit 202 respectively include a switching element and a storage capacitor, as shown in fig. 2, the first storage circuit 201 includes a switching element 201s and a storage capacitor 201c, and the second storage circuit 202 includes a switching element 202s and a storage capacitor 202 c. When the second gate 103b of the transfer circuit 103 is turned on, the switching element 201s or the switching element 202s is also turned on to transfer the first charge amount Q from the pixel capacitance 1021To the storage capacitor 201c of the first storage circuit 201 or to transfer the second charge amount Q2To the storage capacitor 202c of the second storage circuit 202. That is, the switching elements 201s, 202s may be used to control the first charge amount Q of the photoelectric conversion circuit 101And the second charge amount Q2And transferred to the storage capacitors 201c, 202c for storage.
Accordingly, the first charge amount Q is converted from the pixel capacitance 102 during the period of the transfer circuit 103 of the photoelectric conversion circuit 10 with respect to the low-level signal1After the first storage circuit 201, the photoelectric conversion circuit 10 stores the second charge amount Q2To the pixel capacitance 102. Then, the transfer circuit 103 transfers the second charge amount Q again2To the second storage circuit 202, as shown in fig. 2.
The output circuit 20 further comprises a difference unit 205 for comparing the first charge amount Q in the first storage circuit 2011And the second charge amount Q in the second storage circuit 2022To output the analog image signal, wherein the first storage circuit 201 and the second storage circuit 202 are respectively coupled to two input terminals of the difference unit 205. The difference unit 205 may be, for example, a differential amplifier (differential amplifier). Thereby, the output circuit 20 can utilize the difference unit 205 to couple the first charge amount Q in the first storage circuit 2011And the second charge amount Q in the second storage circuit 2022Performing analog difference to output the analog image signal. In more detail, the first charge amount Q stored in the storage capacitor 201c1And the second charge amount Q stored in the storage capacitor 202c2Two input voltages are respectively formed at the two input ends of the differential unit 205, for example, corresponding to the first charge amount Q1First voltage V of1And corresponding to the second charge amount Q2Second voltage V2. Then, the output voltage Vout of the differential unit 205 can be obtained by the formula of a known differential amplifier, for example, Vout ═ Ad × (V)1-V2)+Ac×(V1+V2) 2, where Ad is expressed as differential-mode gain, AcDenoted common-mode gain.
It is understood that the output terminal of the output circuit 20 may be coupled to an analog-to-digital converter (not shown) for converting the analog image signal into a digital image signal for digital image processing by a digital signal processor (digital signal processor), but the invention is not limited thereto. In other embodiments, the output terminal of the output circuit 20 may be coupled to a logic circuit (e.g., for adjusting image brightness, rotating image, cropping image, removing red eye …, etc.) or a memory unit (e.g., for storing as image data), depending on the application.
Due to the first charge quantity Q1With respect to the high level signal period (the light source is turned on so that the incident light Li includes the light emitted by the light source and the ambient light) is stored and the second charge amount Q2With respect to the period of the low level signal (the light source is turned off so that the incident light Li only includes the ambient light) being stored, the first charge amount Q is compared in the differentiating unit 205 of the output circuit 201And the second charge amount Q2Then, the analog image signal output by the image sensor 1 is free from the interference of the ambient light (the same applies to the digital image signal). Therefore, after the analog image signal is converted into the digital image signal, the digital image signal can be directly processed at a digital end (for example, including the digital signal processor) to generate one digital image frame, and the difference processing of the two digital image frames is not required.
Furthermore, an auto exposure (auto exposure) mechanism considers the intensity of the incident light to adjust the exposure time accordingly, for example, when the incident light Li is strong, the image sensor 1 can reduce the exposure time (or adjust the aperture size, white balance …, etc.) to avoid overexposure of the output image. In some embodiments, to implement the automatic exposure mechanism, the first storage circuit 201 of the image sensor 1 further comprises a comparator 201a for comparing the voltage of the storage capacitor 201c (i.e. the first voltage V)1) And a reference voltage Vref to determine whether to perform the auto-exposure mechanism, as shown in FIG. 2Shown in the figure. For example, when the reference voltage Vref is greater than the first voltage V1When the value of the output of the comparator 201a is 0, the imaging system including the image sensor 1 does not adjust the exposure time of the image sensor 1; when the reference voltage Vref is equal to or less than the first voltage V1At this time, the comparator 201a outputs a value of 1 so that the imaging system can reduce the exposure time of the image sensor 1.
FIG. 3 is a flowchart of a method for operating an image sensor including a photo device, a pixel buffer circuit, a first storage circuit, a second storage circuit, and a difference unit according to some embodiments of the present invention. The first storage circuit and the second storage circuit are respectively coupled to two input ends of the differential unit. The photoelectric element is used for generating photocurrent relative to a high level signal and a low level signal and storing the photocurrent in the pixel buffer circuit, wherein the high level signal and the low level signal are used for driving the on and off of a light source. The operation method comprises the following steps: storing a first amount of charge from the photoelectric element to the pixel buffer circuit during the high-level signal (step S1); transferring the first amount of charge of the pixel buffer circuit to the first storage circuit during the low-level signal (step S2); storing a second amount of charge from the photoelectric element to the pixel buffer circuit during the low-level signal after the first amount of charge is transferred (step S3); transferring the second charge amount of the pixel buffer circuit to the second storage circuit (step S4); and comparing the amounts of charges stored in the first and second storage circuits with the difference unit to output an analog image signal (step S5).
In one embodiment, the method of operating the image sensor of fig. 3 may correspond to the image sensor 1 of fig. 2, wherein the optoelectronic device may be the optoelectronic device 101 of the photoelectric conversion circuit 10 (or the photoelectric conversion circuit 10'), and the pixel buffer circuit may include the pixel capacitor 102 and the transfer circuit 103. Referring to fig. 2-4, wherein fig. 4 is a timing diagram of a plurality of switching elements corresponding to fig. 2 and 3, the operation of the image sensor will be described.
Step S1: first, during the high level signal period (for example, a driving circuit drives a light source to turn on), the fifth gate 108 is turned off for a predetermined time so that the photocurrent generated by the optoelectronic device 101 is not discharged through the fifth gate 108, and therefore, the period during which the fifth gate 108 is turned off (i.e., the predetermined time) can be defined as an effective exposure period of the optoelectronic device 101. Then, the third gate 106 is turned on to charge or discharge the pixel capacitor 102 to a predetermined amount of charge. When the pixel capacitor 102 has the predetermined amount of charge, the third gate 106 is turned off and the fourth gate 107 is turned on, and the photoelectric element 101 can store the first charge amount Q during the high-level signal1To the pixel buffer circuit (e.g., the pixel capacitor 102).
Similarly, the photoelectric element 101 of the photoelectric conversion circuit 10' also stores the first charge amount Q during the high-level signal1To the pixel capacitance 102 of the photoelectric conversion circuit 10'. It should be noted that the first charge amount Q stored in the photoelectric conversion circuit 101And the first charge amount Q stored in the photoelectric conversion circuit 101Only to represent the charge stored during the period of time relative to the high signal. Since the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10 'are provided at different positions of the image sensor 1, the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10' do not necessarily receive the same amount of light energy, and thus the first charge amount Q of the photoelectric conversion circuit 10 is not always the same1The first charge amount Q of the photoelectric conversion circuit 101Not necessarily of the same charge amount.
It should be noted that the photoelectric element 101 converts incident light into photocurrent at all times, so the off time (i.e. the predetermined time) of the fifth gate 108 can be regarded as the exposure time of the image sensor 1, but the invention is not limited thereto. In other embodiments, the imaging system including the image sensor 1 can issue a shutter signal to control the photo element 101 to start or stop generating a photo current, and the image sensor 1 may not be provided with the fifth gate 108.
Step S2: then, during the low level signal (for example, the control circuit drives the light source to turn off or does not drive the light source to turn on), the fifth gate 108 of the photoelectric conversion circuit 10 is turned off so that the photocurrent generated by the photoelectric element 101 is not discharged through the fifth gate 108. The low-level signal period is different from the high-level signal period in that the second gate 103b and the first switch 201s of the first storage circuit 201 are simultaneously turned on to transfer the first charge amount Q of the pixel capacitor 102 before the third gate 106 is turned on to reset the pixel capacitor 102 during the low-level signal period1To the storage capacitor 201c of the first storage circuit 201.
As previously mentioned, in some embodiments, the first amount of charge Q1After the transfer (i.e., after step S2), the comparator 201a included in the first storage circuit 201 compares the voltage of the storage capacitor with the reference voltage Vref to determine whether to perform an auto-exposure mechanism.
Step S3: in the first charge amount Q1After the pixel capacitor 102 is transferred to the first storage circuit 201, the second gate 103b and the first switch 201s are turned off and the third gate 106 is turned on to charge or discharge the pixel capacitor 102 to the predetermined amount of charge. When the pixel capacitor 102 has the predetermined amount of charge, the third gate 106 is turned off and the fourth gate 107 is turned on, so that the photoelectric element 101 can store the second charge amount Q2To the pixel buffer circuit (e.g., the pixel capacitor 102).
Step S4: in the second charge amount Q2After storing the charge in the pixel capacitor 102, the second gate 103b and the second switch 202s are simultaneously turned on to control the second charge amount Q of the pixel capacitor 102 in the photoelectric conversion circuit 102To the second storage circuit 202. It can be understood that the image sensor 1 transfers the first charge from the pixel buffer circuit through the transfer circuit 103Quantity Q1To the first storage circuit 201 and transfers the second charge amount Q2To the second storage circuit 202. At this time, the storage capacitor 201c of the first storage circuit 201 and the storage capacitor 202c of the second storage circuit 202 store the first charge amount Q, respectively1And the second charge amount Q2And forms the first voltage V at the two input terminals of the differential unit 2051And said second voltage V2。
Step S5: finally, the difference unit 205 compares the first voltage V of the first storage circuit 2011And said second voltage V of said second storage circuit 2022To output an analog image signal. Thereby, the interference of the ambient light can be eliminated before the analog image signal is converted into the digital image signal by the analog-to-digital converter.
In some embodiments, the first storage unit 201 stores the first charge amount Q1And the second storage unit 202 stores the second charge amount Q2The shorter the interval time is, the better the first charge amount Q stored in the storage capacitor 201c is prevented1Storing the second charge amount Q in the storage capacitor 202c2So that the differential cell 205 can accurately follow the first voltage V1And said second voltage V2The analog image signal is output, for example, the interval time may be less than or equal to the turn-off time of the fifth gate 108 (i.e., the preset time or the high level signal period).
It should be noted that, when the photoelectric conversion circuit 10 is coupled to the same output circuit (i.e., the output circuit 20) as the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10', the first charge amount Q is transferred by the photoelectric conversion circuit 101Or the second charge amount Q2The photoelectric conversion circuit 10' cannot transfer the first charge amount Q to the output circuit 20 at the same time1Or the second charge amount Q2To the output circuit 20. Accordingly, the image sensor 1 sequentially turns on the second gate electrode 103b and the first gate electrode 103b of the photoelectric conversion circuit 10A switch 201s, the second gate 103b and the second switch 201s of the photoelectric conversion circuit 10, the second gate 103b and the first switch 201s of the photoelectric conversion circuit 10', and the second gate 103b and the second switch 201s of the photoelectric conversion circuit 10', such that the first charge amount Q of the photoelectric conversion circuit 101And the second charge amount Q2The first charge amount Q of the photoelectric conversion circuit 101And the second charge amount Q2May be transferred in sequence as shown in fig. 4.
It can be understood that the first charge amount Q stored by the photoelectric conversion circuit 10' is relative to the high-level signal period (i.e. the period when the fifth gate 108 is turned off for the first time)1The second gate 108 is turned off for the second time, and the second charge amount Q is transferred to the output circuit 20, so that the photoelectric conversion circuit 102Before the output circuit 20, the second gates 103b of the photoelectric conversion circuits 10' are all kept in a closed state. In some embodiments, a control signal (e.g., issued by the image sensor 1 or the imaging system) controls the fifth gates 108 of the photoelectric conversion circuits 10 and 10 'to be turned off simultaneously during the high-level signal, and then sequentially turns off the fifth gates 108 of the photoelectric conversion circuits 10 and 10' during the low-level signal. As described above, the period during which the fifth gate 108 is turned off can be defined as the effective exposure period of the photoelectric element 101; in other words, the image sensor 1 simultaneously exposes the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10 'during the high-level signal, and then sequentially exposes the photoelectric conversion circuit 10 and the photoelectric conversion circuit 10' during the low-level signal.
FIG. 5 is a block diagram of an image sensor 3 according to some embodiments of the invention. The image sensor 3 includes a driving circuit 30, a photoelectric conversion circuit 31, a first storage circuit 321, a second storage circuit 322, and a difference unit 325, wherein the driving circuit 30 is electrically connected to the photoelectric conversion circuit 31, the input terminals of the first driving circuit 321 and the second driving circuit 322 are coupled to the output terminal of the photoelectric conversion circuit 31, and the difference unit 325 includes two input terminals coupled to the first storage circuit 321 and the second storage circuit 322, respectively.
The driving circuit 30 may be, for example, a signal generator or a timing controller for sequentially generating high level signals SHAnd a low level signal SLWherein the high level signal SHAnd said low level signal SLRespectively, for controlling the light source 5 to be turned on during the first period and to be turned off during the second period. In addition, the driving circuit 30 simultaneously generates at least one control signal Sc to control on/off of a plurality of switch elements in the photoelectric conversion circuit 31, the first storage circuit 321, and the second storage circuit 322, for example, on/off of the second gate 103b, the third gate 106, the fourth gate 107, the fifth gate 108, the first switch 201s, and the second switch 202s in fig. 2 and 4 can be controlled. In other embodiments, the imaging system including the image sensor 3 further provides a control circuit to control the on/off of the light source 5, and a control signal of the light source 5 is transmitted to the driving circuit 30 of the image sensor 3, so that the driving circuit 30 controls the switch element accordingly.
When the light source 5 is turned on during the first period, the photoelectric conversion circuit 31 simultaneously receives the light source intensity I of the light source 55And ambient light intensity IAB(ii) a When the light source 5 is turned off during the second period, the photoelectric conversion circuit 31 only receives the ambient light intensity IAB. Accordingly, the photoelectric conversion circuit 31 may generate a photocurrent corresponding to the light source 5 and the ambient light during the first period and generate a photocurrent corresponding to the ambient light during the second period. It must be noted that the light source intensity I5The light source 5 is the reflected light from the object to be detected, i.e. the light source is used to illuminate the object to be detected in this embodiment.
Then, the first storage circuit 321 stores a first charge amount corresponding to the photocurrent during the first period during the second period; in the above-mentionedAfter the first charge amount is stored, the second storage circuit 322 stores a second charge amount corresponding to the photocurrent during the second period. It can be appreciated that the first amount of charge is related to the light source intensity I5And the intensity of said ambient light IABThe second amount of charge being related only to the ambient light intensity IAB。
Finally, the difference unit 325 compares the amount of charge stored in the first storage circuit 321 and the second storage circuit 322 (e.g., the first charge amount Q of fig. 2)1And the second charge amount Q2) To eliminate the interference of the ambient light and output an analog image signal Sa. In some embodiments, the difference unit 325 directly performs analog difference on the amount of charges stored in the first storage circuit 321 and the second storage circuit 322 and outputs the analog image signal Sa.
Similarly, in some embodiments, to implement the auto-exposure mechanism, the first storage circuit 321 may further include a comparator 321a for comparing the voltage of the storage capacitor in the first storage circuit 321 with a reference voltage to determine whether to implement the auto-exposure mechanism. It should be noted that, although fig. 5 shows that the comparator 321a is coupled between the first storage circuit 321 and the differential unit 325, the connection position is not limited as long as the comparator can be coupled to the voltage of the storage capacitor in the first storage circuit 321.
As described above, the image sensor according to some embodiments of the present invention has a plurality of photoelectric conversion circuits arranged in an array as sensing pixels. Referring to fig. 6 and 7, fig. 6 is a schematic diagram of an imaging system 4 including a plurality of photoelectric conversion circuits according to some embodiments of the present invention, and fig. 7 is a timing diagram corresponding to fig. 6. The imaging system 4 includes a light source 5, a driving circuit 30 (or control circuit), a plurality of photo-conversion circuits 31 arranged in a 6 x 8 array, an output circuit 32, an analog-to-digital converter 35, a processor 37, wherein the photo-conversion circuits 31 of a first column may be defined as a sensing pixel column R1, the photo-conversion circuits 31 of a second column may be defined as a sensing pixel column R2 …, and so on.
When the driving circuit 30 controls the light source 5 to be turned on in the first period P1, the driving circuit 30 simultaneously controls all the photoelectric conversion circuits 31 to be simultaneously exposed to store a plurality of first charge amounts.
When the driving circuit 30 controls the light source 5 to turn off during the second period P2, the driving circuit 30 first controls the photoelectric conversion circuits 31 (i.e., the sensing pixel row R1) of the first column to transfer the first charge amount to the output circuit 32, to expose again to store a plurality of second charge amounts, and to transfer the second charge amounts to the output circuit 32, so that the output circuit 32 can compare each of the first charge amounts and each of the second charge amounts to output the analog image signal Sa corresponding to the first column. Next, the driving circuit 30 sequentially controls the photoelectric transfer circuits 31 of the second to sixth columns to output the analog image signals Sa corresponding to the second to sixth columns, as shown in fig. 7.
In some embodiments, the imaging system 4 may provide an amplifier at the input of the analog-to-digital converter for amplifying the analog image signal Sa. Finally, the processor 37 may output an image according to the digital image signal Sd corresponding to the sensing pixel (i.e., the photoelectric conversion circuit 31) through the analog-to-digital converter 35. It can be understood that the image outputted by the imaging system 4 has been removed from the interference of the ambient light, and can be directly processed.
In some embodiments, the first storage circuit and the second storage circuit respectively include a switching element and a storage capacitor, and the switching element is configured to control the first charge amount and the second charge amount of the photoelectric conversion circuit to be transferred to the storage capacitor.
In some embodiments, the first storage circuit further comprises a comparator for comparing the voltage of the storage capacitor with a reference voltage to determine whether to implement an auto-exposure mechanism.
In some embodiments, the image sensor further comprises a driving circuit for sequentially generating the high level signal and the low level signal.
The image sensor of the embodiment of the invention can directly compare the first charge quantity related to the light source and the ambient light and the second charge quantity related to the ambient light only by means of time sequence control, and does not perform differential operation on digital image frames formed by the first charge quantity and the second charge quantity respectively, thereby eliminating the interference of the ambient light while not reducing power consumption.
As described above, the known image sensor uses two digital image frames (one corresponding to the light source and the ambient light, and the other corresponding to only the ambient light) to perform a differential operation to eliminate the interference of the ambient light, thereby having higher power consumption. Therefore, the present invention provides an image sensor (fig. 2 and 3) and an operating method thereof (fig. 3 and 7), which can directly compare a first charge amount associated with the light source and the ambient light with a second charge amount associated with only the ambient light by timing control to eliminate the interference of the ambient light without reducing power consumption.
Although the present invention has been disclosed in the context of the foregoing embodiments, it is not intended to be limited thereto, and various changes and modifications can be made by one skilled in the art without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the scope of the appended claims.
Claims (10)
1. An operation method of an image sensor, the image sensor comprising a driving circuit, a plurality of sensing pixels arranged in an array, and an output circuit, the output circuit comprising a first storage circuit, a second storage circuit, and a differential unit, the operation method comprising:
sequentially generating a high level signal and a low level signal by the driving circuit;
exposing all of the sensing pixels to store a plurality of first charge amounts simultaneously with respect to the high-level signal period;
transferring the first charge amount of the sensing pixels of the first column to the first storage circuit with respect to the low-level signal period;
exposing the sensing pixels of the first column to store a plurality of second charge amounts during the same low-level signal period;
transferring the second charge amount of the sensing pixels of the first column to the second storage circuit during the same low-level signal period; and
and performing analog difference on the first charge amount in the first storage circuit and the second charge amount in the second storage circuit by using the difference unit to output an analog image signal corresponding to a first column.
2. The method of claim 1, wherein the first storage circuit and the second storage circuit respectively comprise a switching element and a storage capacitor, the method further comprising:
controlling the first and second charge amounts of the sensing pixel to be transferred to the storage capacitor with the switching element.
3. The method of claim 2, wherein the first storage circuit further comprises a comparator, the method further comprising:
the comparator compares the voltage of the storage capacitor with a reference voltage to determine whether to perform auto exposure.
4. The method of claim 1, further comprising:
and sequentially outputting analog image signals of the sensing pixels corresponding to each column after the second column.
5. The method of claim 1, wherein each of the plurality of sensing pixels comprises a transfer circuit, the method further comprising:
transferring the first charge amount from the sensing pixel to the first storage circuit or transferring the second charge amount to the second storage circuit with the transfer circuit.
6. An operating method of an imaging system, the imaging system including a light source, a plurality of sensing pixels arranged in an array, and an output circuit, the output circuit including a first storage circuit, a second storage circuit, and a differential unit, the operating method comprising:
turning on the light source and simultaneously exposing all of the plurality of sensing pixels to store a plurality of first charge amounts;
turning off the light source and transferring the first charge amount of the sensing pixels of a first column to the first storage circuit;
exposing the sensing pixels of the first column to store a plurality of second charge amounts;
transferring the second amount of charge of the sense pixels of the first column to the second storage circuit; and
and performing analog difference on the first charge amount in the first storage circuit and the second charge amount in the second storage circuit by using the difference unit to output an analog image signal corresponding to a first column.
7. The method of claim 6, wherein the first storage circuit and the second storage circuit respectively comprise a switching element and a storage capacitor, the method further comprising:
controlling the first and second charge amounts of the sensing pixel to be transferred to the storage capacitor with the switching element.
8. The method of claim 7, wherein the first storage circuit further comprises a comparator, the method further comprising:
the comparator compares the voltage of the storage capacitor with a reference voltage to determine whether to perform auto exposure.
9. The method of claim 6, further comprising:
and sequentially outputting analog image signals of the sensing pixels corresponding to each column after the second column.
10. The method of claim 6, wherein the plurality of sensing pixels each comprise a transfer circuit, the method further comprising:
transferring the first charge amount from the sensing pixel to the first storage circuit or transferring the second charge amount to the second storage circuit with the transfer circuit.
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| CN108445499A (en) * | 2018-02-07 | 2018-08-24 | 余晓智 | A kind of the ambient light suppression system and method for TOF sensor |
| CN112218011B (en) * | 2019-06-25 | 2023-10-31 | 上海耕岩智能科技有限公司 | Image sensor |
| CN112560835A (en) * | 2019-09-26 | 2021-03-26 | 苏州立创致恒电子科技有限公司 | Imaging assembly for shielding ambient light interference and image imaging method |
| US11317042B2 (en) * | 2020-08-25 | 2022-04-26 | Pixart Imaging Inc. | Image sensor apparatus and processing circuit capable of preventing sampled reset/exposure charges from light illumination as well as achieving lower circuit costs |
| CN112422853A (en) * | 2020-11-19 | 2021-02-26 | 苏州新晶腾光电科技有限公司 | Stray light resisting method of image sensing chip |
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| JP2001008108A (en) * | 1999-06-23 | 2001-01-12 | Nec Corp | Image pickup method and device, and information storage medium |
| JP5142749B2 (en) * | 2008-02-14 | 2013-02-13 | キヤノン株式会社 | IMAGING DEVICE, IMAGING DEVICE CONTROL METHOD, AND IMAGING SYSTEM |
| FR2939999B1 (en) * | 2008-12-12 | 2011-02-25 | E2V Semiconductors | DUAL LOAD TRANSFER IMAGE SENSOR FOR HIGH DYNAMIC AND READING METHOD |
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| US20130113967A1 (en) * | 2011-11-04 | 2013-05-09 | Honeywell International Inc. Doing Business As (D.B.A.) Honeywell Scanning & Mobility | Apparatus comprising image sensor array having global shutter shared by a plurality of pixels |
| CN102833495B (en) * | 2012-08-16 | 2015-06-10 | 格科微电子（上海）有限公司 | Highly-dynamic image sensor driving method |
| KR102009165B1 (en) * | 2013-01-24 | 2019-10-21 | 삼성전자 주식회사 | Image sensor, multi chip package, and electronic device |
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