Slope generation module, quantization control circuit and image sensor

Abstract

The utility model provides a slope generation module, a quantization control circuit and an image sensor, and the slope generation module comprises a slope unit and a compensation unit. The slope unit is used for generating a slope voltage, and the compensation unit is connected with the slope unit and is used for generating a compensation amount according to a current change of a pixel power supply in the first pixel and compensating the compensation amount to the slope voltage so as to obtain a quantization result of the second pixel based on the compensated slope voltage, the first pixels and the second pixels are provided with a pixel power supply through the same power line. According to the slope generation module, the quantization control circuit and the image sensor provided by the utility model, the problem that no effective compensation scheme exists to solve the dispersion phenomenon of the image sensor so as to improve the image quality in the prior art is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of image sensors, in particular to a slope generating module, a quantization control circuit and an image sensor. Background Art

[0002] In CMOS image sensors, smear has always been a concern. When strong light shines on a certain area of ​​the CMOS image sensor, the adjacent areas with weaker light may also be affected, and the brightness of the affected areas changes, causing image quality to deteriorate. Currently, there is no good compensation solution for this phenomenon. Utility Model Content

[0003] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a ramp generation module, a quantization control circuit and an image sensor, which are used to solve the problem that there is no effective compensation solution in the prior art to solve the dispersion phenomenon of the image sensor to improve the image quality.

[0004] In order to achieve the above-mentioned purpose and other related purposes, the utility model provides a slope generating module, including a slope unit and a compensation unit;

[0005] The ramp unit is used to generate a ramp voltage;

[0006] The compensation unit is connected to the ramp unit, and is used to generate a compensation amount according to the current change of the pixel power supply in the first pixel and compensate it to the ramp voltage, so as to obtain the quantization result of the second pixel based on the compensated ramp voltage; wherein, the first pixel and the second pixel are provided with pixel power through the same power line.

[0007] Optionally, the light intensity of the area where the first pixel is located is greater than the light intensity of the area where the second pixel is located.

[0008] Optionally, the first pixel further corresponds to a clamp power supply, and a current change of the pixel power supply in the first pixel causes a current change of the clamp power supply.

[0009] Optionally, the ramp unit includes a ramp current part and a load output part, and the compensation unit includes a current detection part and a current compensation part;

[0010] The ramp current part is used to generate a ramp current, and the load output part is connected to the ramp current part and is used to convert the ramp current into the ramp voltage;

[0011] The current detection part is used to detect whether the current of the corresponding power supply changes, and the current compensation part is connected to the current detection part, and is used to generate a compensation current when the current of the corresponding power supply changes, so as to convert the compensation current into the compensation amount through the load output part and compensate it to the ramp voltage;

[0012] When the first pixel does not correspond to a clamped power supply, the corresponding power supply refers to a pixel power supply; when the first pixel corresponds to a clamped power supply, the corresponding power supply refers to a pixel power supply or a clamped power supply.

[0013] Optionally, the ramp current part includes M first current branches, the first current branch includes a current source and a first switch, and the load output part includes a load resistor; the M first current branches are connected in parallel to a first reference potential via the load resistor, and in any first current branch, the current source and the first switch are connected in series between a working power supply and a parallel node, wherein M is an integer greater than 1.

[0014] Optionally, the load output part further includes a filter capacitor connected in parallel to both ends of the load resistor.

[0015] Optionally, the current detection part includes a first transistor, the current compensation part includes N second current branches, the second current branches include a second transistor and a second switch; the control end of the first transistor is connected to the control end of each of the second transistors, the first end is connected to its control end and realizes current change detection, and the second end is connected to a working power supply, wherein, when the corresponding power supply refers to a clamping power supply, the first end of the first transistor is connected to its control end and generates a clamping power supply; the first end of each of the second transistors is connected to the load output part via each of the second switches, and the second end is connected to the working power supply; wherein N is an integer greater than or equal to 1.

[0016] The utility model also provides a quantization control circuit, comprising the ramp generation module and the comparator module as described above;

[0017] The ramp generating module is used to provide the ramp voltage;

[0018] The first input terminal of the comparator module is connected to the pixel voltage, and the second input terminal is connected to the ramp voltage. The quantization result is generated by comparing the pixel voltage with the ramp voltage.

[0019] The utility model also provides an image sensor, comprising a pixel array and a plurality of quantization control circuits as described above;

[0020] The pixel array includes a plurality of pixels arranged in an array in rows and columns, and the pixels are used to generate pixel voltages;

[0021] Each of the quantization control circuits corresponds to each pixel in the pixel array, and is used for quantizing the pixel voltage of each of the pixels according to the ramp voltage.

[0022] Optionally, the comparator module corresponds one-to-one to the pixel columns in the pixel array, the slope unit of the slope generating module corresponds to the pixel array, and when the compensation unit of the slope generating module includes a current detection part and a current compensation part, the current detection part corresponds to the pixel array or corresponds one-to-one to the pixel columns in the pixel array, and the current compensation part corresponds to the slope unit.

[0023] Optionally, the pixel includes a photosensitive element, a transfer transistor, a reset transistor and a source follower transistor; the control end of the transfer transistor is connected to a transmission control signal, the first end is connected to a floating diffusion node, and the second end is connected to a second reference potential via the photosensitive element; the control end of the reset transistor is connected to a reset control signal, the first end is connected to a pixel power supply, and the second end is connected to a floating diffusion node; the control end of the source follower transistor is connected to a floating diffusion node, the first end is connected to a pixel power supply, and the second end is connected to a corresponding column line; wherein the corresponding column line is connected to a third reference potential via a corresponding tail current source.

[0024] Optionally, the pixel further includes a row selection transistor connected between the second end of the source follower transistor and the corresponding column line, and a control end thereof is connected to a row selection signal.

[0025] Optionally, the image sensor further comprises a plurality of clamping circuits, each of the clamping circuits corresponding to each pixel column in the pixel array, and configured to start voltage clamping when a corresponding column line voltage drops to a set value.

[0026] Optionally, the clamping circuit includes a clamping transistor and a switching transistor; the control end of the clamping transistor is connected to a reference voltage, the first end is connected to a clamping power supply, and the second end is connected to the first end of the switching transistor; the control end of the switching transistor is connected to a clamping enable signal, and the second end is connected to a corresponding column line.

[0027] As described above, the slope generating module, quantization control circuit and image sensor of the utility model introduce the current change of the pixel power supply in the pixels in the strong light area into the slope voltage. In this way, when the pixel voltage of the pixels in the weak light area is quantized based on the slope voltage, the differential amplification of the comparator module can weaken or even offset the influence of the diffusion phenomenon on the pixels in the weak light area, thereby improving the image quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Shown is a circuit diagram of an image sensor.

[0029] Figure 2 Display as Figure 1 The waveform diagram shown is when the comparator module quantizes the pixel voltage based on the ramp voltage.

[0030] Figure 3 A schematic diagram showing the mechanism of image sensor blooming.

[0031] Figure 4 A waveform diagram showing the quantization of pixels affected by blooming in an image sensor.

[0032] Figure 5 Shown is a schematic structural diagram of the image sensor of the utility model.

[0033] Figure 6 Shown is a circuit diagram of the image sensor of the present utility model.

[0034] Figure 7 Shown is a structural schematic diagram of the slope generating module of the utility model.

[0035] Figure 8 Shown is a circuit diagram of the ramp generating module of the utility model.

[0036] Fig. 9 Shown is a circuit diagram of the compensation unit of the present invention.

[0037] Fig.10 Shown is a waveform diagram of the second pixel quantization in the image sensor of the present invention.

[0038] Fig.11 Shown is a waveform diagram of the first pixel quantization in the image sensor of the present invention.

[0039] Component number description

[0040] 10 Image Sensor

[0041] 100 pixel array

[0042] 110 pixels

[0043] 200 Clamping Circuit

[0044] 300 Quantization Control Circuit

[0045] 310 Ramp generation module

[0046] 311 Slope Unit

[0047] 311a Ramp Current Section

[0048] 311b Load output section

[0049] 312 Compensation unit

[0050] 312a Current detection section

[0051] 312b Current compensation section

[0052] 320 Comparator Module DETAILED DESCRIPTION

[0053] The following is an explanation of the implementation of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0054] See also Figures 1 to 11 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the utility model in a schematic manner, and the illustrations only show the components related to the utility model rather than the number, shape and size of the components in actual implementation. The form, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the component layout may also be more complicated.

[0055] Figure 1 A circuit implementation of an image sensor is shown, wherein PIXVDD is a pixel power supply, PD is a photosensitive element, M1 is a transfer transistor, FD is a floating diffusion node, M2 is a reset transistor, M3 is a source follower transistor, M4 is a row selection transistor, bitline is a column line, vln is a tail current source, CMP is a comparator, Vpix is ​​a pixel voltage, including a reset voltage Vrst and a signal voltage Vsig, and Vramp is a ramp voltage.

[0056] When working: first reset, reset transistor M2 is turned on, transfer transistor M1 is turned off, row selection transistor M4 is turned on, floating diffusion node FD is pulled up to PIXVDD, column line bitline is also pulled to high level, at this time, the voltage of column line bitline is reset voltage, called Vrst in quantization process. When light shines on photosensitive element PD, photosensitive element PD generates electrons and injects them into floating diffusion node FD through turned-on transfer transistor M1, so that the voltage of floating diffusion node FD drops from PIXVDD after reset to a certain voltage, and the voltage of column line bitline also drops to a certain voltage, at this time, the voltage of column line bitline is signal voltage, called Vsig in quantization process. The difference between reset voltage Vrst and signal voltage Vsig represents the size of illumination signal (i.e., input signal), the larger the difference between the two, the larger the input signal and the stronger the illumination.

[0057] Figure 2 The quantization process of the comparator CMP is shown: when the ramp voltage Vramp starts to decrease, the output of the comparator CMP is pulled from a low level to a high level, until the ramp voltage Vramp decreases to be equal to the voltage of the column line bitline, the output of the comparator CMP flips from a high level to a low level, wherein the time that the output of the comparator CMP maintains a high level is the quantization time.

[0058] For the reset voltage Vrst and the signal voltage Vsig, each has a quantization time Trst and Tsig. Corresponding to the quantization time, the quantization result of the input signal can be obtained by subtracting the quantization result of the reset voltage Vrst from the quantization result of the signal voltage Vsig; therefore, the stronger the light, the larger the input signal, the lower the level of the signal voltage Vsig, and the longer the time for quantizing the signal voltage Vsig, so the larger the result of Tsig-Trst, the larger the quantization result; when the level of the signal voltage Vsig is too low to intersect with the ramp voltage Vramp, the comparator CMP will flip at the end of the ramp voltage Vramp, and the output end will be pulled from a high level to a low level, and the quantization will end. It is considered that the signal voltage Vsig at this time exceeds the quantization range, and the output result is reflected as a full-scale output.

[0059] Figure 3 The diagram shows the mechanism of smear phenomenon in CMOS image sensors, where the illumination in area A is strong and that in area B is weak. In addition, the rectangular box on PIXVDD in the diagram is a wiring resistor. When the current on PIXVDD increases, the voltage value of PIXVDD of pixels in area B decreases due to the voltage drop caused by the current passing through the resistor. In one implementation, power can be supplied simultaneously from the left and right sides of the power line corresponding to PIXVDD.

[0060] The stronger the light, the more electrons the photosensitive element PD injects into the floating diffusion node FD, the greater the voltage drop of the floating diffusion node FD, and the lower the level; when the level of the floating diffusion node FD in the pixel of area A is low to a certain extent, the source follower transistor can no longer be turned on or even turned off. At this time, the current on PIXVDD in the pixel of area A decreases, the corresponding voltage drop IR decreases, the PIXVDD voltage value of the pixel in area B increases, and the voltage of the column line bitline in the pixel of area B also increases. The increased voltage amplitude is Vrise. It can be seen that the signal voltage Vsig of the pixel in area B is higher than that in area A when there is no strong light irradiation, resulting in a smaller quantization result, such as Figure 4As shown in the figure, vinn0 is the vinn input when the pixels in area B are not affected by diffusion, and vinn1 is the vinn input when the pixels in area B are affected by diffusion. It can be seen that the voltage input to vinn is raised, which reduces Tsig and Tsig-Trst, which is reflected in the image that the pixels in area B become darker.

[0061] In order to improve the image quality of the pixels in the B area, this embodiment proposes a dispersion compensation scheme, that is, a compensation amount is generated according to the current change on PIXVDD in the pixels in the A area and compensated to the ramp voltage Vramp, so that the ramp voltage Vramp is raised accordingly, thereby weakening or even offsetting the influence of the dispersion phenomenon on the pixels in the B area, thereby improving the image quality of the pixels in the B area.

[0062] like Figure 5 As shown, this embodiment provides an image sensor 10, including a pixel array 100 and a plurality of quantization control circuits 300, and further including a plurality of clamping circuits 200; wherein the pixel array 100 includes a plurality of pixels 110 arranged in an array in rows and columns.

[0063] In the application, each clamping circuit 200 corresponds to each pixel column in the pixel array 100, such as a one-to-one correspondence, and each quantization control circuit 300 corresponds to each pixel column in the pixel array 100, such as a one-to-one correspondence, wherein the one-to-one correspondence between each quantization control circuit 300 and each pixel column mainly means that each comparator module 320 in the quantization control circuit 300 corresponds to each pixel column one-to-one.

[0064] The pixel 110 is used to generate a pixel voltage Vpix, wherein the pixel voltage Vpix includes a reset voltage Vrst and a signal voltage Vsig.

[0065] As an example, Figure 6 As shown, the pixel 110 includes a photosensitive element PD, a transfer transistor M1, a reset transistor M2 and a source follower transistor M3, and further includes a row selection transistor M4.

[0066] The control end of the transfer transistor M1 is connected to the transmission control signal TX, the first end is connected to the floating diffusion node FD, and the second end is connected to the second reference potential (e.g., the reference ground potential) via the photosensitive element PD; the control end of the reset transistor M2 is connected to the reset control signal RST, the first end is connected to the pixel power supply PIXVDD, and the second end is connected to the floating diffusion node FD; the control end of the source follower transistor M3 is connected to the floating diffusion node FD, the first end is connected to the pixel power supply PIXVDD, and the second end is connected to the corresponding column line.

[0067] When the pixel 110 also includes a row selection transistor M4, the row selection transistor M4 is connected between the second end of the source follower transistor M3 and the corresponding column line, and the control end is connected to the row selection signal RS; for example, the control end of the row selection transistor M4 is connected to the row selection signal RS, the first end is connected to the second end of the source follower transistor M3, and the second end is connected to the corresponding column line.

[0068] In one implementation, the pixel 110 includes a photosensitive element PD, a transfer transistor M1, a reset transistor M2, a source follower transistor M3 and a row selection transistor M4; wherein the photosensitive element PD is a photodiode, and all transistors are NMOS tubes. At this time, the control end in the above text refers to the gate, the first end refers to the drain, and the second end refers to the source; of course, in other implementations, the photosensitive element PD includes a grating or a photoconductor, and it is also feasible that all transistors are PMOS tubes.

[0069] In the above-mentioned pixel 110, the corresponding column line is connected to the third reference potential (e.g., reference ground potential) via the corresponding tail current source; in fact, the pixel array 100 also includes a plurality of tail current sources vln, each tail current source vln corresponds one-to-one to each pixel column in the pixel array and is connected to a plurality of pixels 110 in each pixel column through each column line, so as to provide output drive for the corresponding column line, so that the pixel voltage Vpix generated by the corresponding pixel 110 can be output through the corresponding column line.

[0070] The clamp circuit 200 is used to start voltage clamping when the corresponding column line voltage drops to a set value to prevent the corresponding column line voltage from continuing to drop. It should be noted that the so-called set value should be determined by actual needs, and this embodiment does not limit its size.

[0071] As an example, Figure 6 As shown, the clamp circuit 200 includes a clamp transistor M5 and a switch transistor M6; the control end of the clamp transistor M5 is connected to the reference voltage VREF, the first end is connected to the clamp power supply CLAMPVDD, and the second end is connected to the first end of the switch transistor M6; the control end of the switch transistor M6 is connected to the clamp enable signal CLAMP_EN, and the second end is connected to the corresponding column line.

[0072] In one implementation, the clamping transistor M5 and the switching transistor M6 are NMOS transistors. In this case, the control end in the above text refers to the gate, the first end refers to the drain, and the second end refers to the source. Of course, in other implementations, it is also feasible that the clamping transistor M5 and the switching transistor M6 are PMOS transistors.

[0073] In the clamp circuit 200, when the clamp function is turned on, the clamp enable signal CLAMP_EN is valid, for example, becomes high level, and the switch transistor M6 is turned on. When the voltage of the corresponding column line drops to the set value, the clamp transistor M5 clamps the voltage of the corresponding column line (for example, the voltage of the corresponding column line is clamped based on the reference voltage VREF of the control terminal of the clamp transistor M5), so as to prevent the voltage of the corresponding column line from continuing to drop.

[0074] The quantization control circuit 300 is used to quantize the pixel voltage Vpix of each pixel 110 according to the ramp voltage Vramp; wherein the quantization control circuit 300 includes a ramp generation module 310 and a comparator module 320, such as Figure 7 shown.

[0075] In applications, the quantization control circuit 300 usually quantizes and outputs the pixel voltage Vpix of each pixel 110 in the same pixel row in sequence according to the ramp voltage Vramp. It should be noted that the layout of each module of the quantization control circuit 300 can be designed according to actual needs.

[0076] The ramp generation module 310 is used to provide a ramp voltage Vramp; wherein the ramp generation module 310 includes a ramp unit 311 and a compensation unit 312, such as Figure 8 shown.

[0077] The ramp unit 311 is used to generate a ramp voltage Vramp.

[0078] As an example, the ramp unit 311 includes a ramp current part 311a and a load output part 311b. The ramp current part 311a is used to generate a ramp current Iramp; the load output part 311b is connected to the ramp current part 311a and is used to convert the ramp current Iramp into a ramp voltage Vramp for output.

[0079] In one implementation, the ramp current portion 311a includes M first current branches, the first current branch includes a current source (e.g., I11-I1m) and a first switch (e.g., S11-S1m), and the load output portion 311b includes a load resistor R1; wherein the M first current branches are connected in parallel to a first reference potential (e.g., a reference ground potential) via the load resistor R1, and in any first current branch, the current source and the first switch are connected in series between the working power supply AVDD and the parallel node, and M is an integer greater than 1. Further, the load output portion 311b also includes a filter capacitor C1, which is connected in parallel to both ends of the load resistor R1.

[0080] In the above implementation, the current values ​​of the current sources can be the same or different. In applications, the current values ​​of the current sources are usually designed to be the same. In other implementations, the current values ​​of the current sources can also be designed to be different. For example, the ratio of the current values ​​of the current sources is 2. 0 :2 1 :……:2 M-1 Optionally, the ramp voltage Vramp is a decreasing voltage signal, and the ramp current Iramp is controlled to change in a decreasing manner by controlling the opening and closing of each first switch, so that the value of the ramp voltage Vramp changes in a decreasing manner. In applications, in order to reduce the circuit area, each first switch is usually implemented by a MOS tube; in addition, the opening and closing control of each first switch is usually completed by a master controller used in conjunction with the image sensor 10.

[0081] The compensation unit 312 is connected to the ramp unit 311, and is used to generate a compensation amount according to the current change of the pixel power supply PIXVDD in the first pixel and compensate it to the ramp voltage Vramp, so as to obtain the quantization result of the second pixel based on the compensated ramp voltage, thereby correcting the quantization result of the second pixel; wherein the first pixel and the second pixel are provided with the pixel power supply PIXVDD through the same power line.

[0082] The first pixel and the second pixel are usually located in the same pixel row in the pixel array 100; in fact, in the pixel array 100, the pixels 110 in the same pixel row are usually provided with pixel power PIXVDD through the same power line. In addition, the light intensity of the area where the first pixel is located is greater than the light intensity of the area where the second pixel is located; as mentioned above, the pixels in the strong light area will have a diffusion effect on the pixels in the weak light area, and the pixels in the weak light area will cause the signal voltage Vsig to rise due to the diffusion effect.

[0083] In one embodiment, the compensation unit 312 generates the compensation amount directly according to the current change of the pixel power supply PIXVDD in the first pixel, that is, detects whether the current of the pixel power supply PIXVDD in the first pixel changes, and generates the compensation amount when the current change of the pixel power supply PIXVDD is detected.

[0084] Of course, in other embodiments, the compensation unit 312 indirectly generates the compensation amount according to the current change of the pixel power supply PIXVDD in the first pixel. In the case where the image sensor 10 includes the clamping circuit 200, the first pixel also corresponds to the clamping power supply CLAMPVDD. The current change of the pixel power supply PIXVDD in the first pixel will cause the current change of the clamping power supply CLAMPVDD in the corresponding clamping circuit 200. For example, when the level of the floating diffusion node FD in the first pixel is low to a certain extent, the source follower transistor can no longer be turned on or even turned off, which will cause the current change of the pixel power supply PIXVDD in the first pixel, and then cause the current change of the clamping power supply CLAMPVDD in the corresponding clamping circuit 200; at this time, the compensation unit 312 directly generates the compensation amount according to the current change of the clamping power supply CLAMPVDD, that is, detects whether the current of the clamping power supply CLAMPVDD in the clamping circuit 200 corresponding to the pixel column where the first pixel is located changes, and generates the compensation amount when the current change of the clamping power supply CLAMPVDD is detected.

[0085] by Figure 6 For example, pixel 110 is regarded as the first pixel, and the pixel column where the first pixel is located corresponds to the clamp circuit 200. As the light becomes stronger, the level of the floating diffusion node FD becomes lower. When the level of the floating diffusion node FD is low to a certain extent, the source follower transistor M3 can no longer be turned on well or even turned off. At this time, the current originally flowing through the source follower transistor M3 will be transferred to the branch where the clamp transistor M5 is located (satisfying the formula Im3+Im5=Ivln, Im3 is the current flowing through the source follower transistor M3, Im5 is the current flowing through the clamp transistor M5, and Ivln is the current of the tail current source). Therefore, the change of the current flowing through the source follower transistor M3 can be obtained by detecting the change of the current flowing through the clamp transistor M5, that is, the change of the current of the pixel power supply PIXVDD can be obtained by detecting the change of the current of the clamp power supply CLAMPVDD; in fact, the change of the current represents the degree of influence of the dispersion phenomenon.

[0086] As an example, Fig. 9As shown, the compensation unit 312 includes a current detection part 312a and a current compensation part 312b. The current detection part 312a is used to detect whether the current of the corresponding power supply changes; the current compensation part 312b is connected to the current detection part 312a, and is used to generate a compensation current Ifix when the current of the corresponding power supply changes, so as to convert the compensation current Ifix into a compensation amount through the load output part 311b and compensate it to the ramp voltage Vramp. Wherein, when the first pixel does not correspond to the clamping power supply CLAMPVDD, the above-mentioned corresponding power supply refers to the pixel power supply PIXVDD, and when the first pixel corresponds to the clamping power supply CLAMPVDD, the above-mentioned corresponding power supply refers to the pixel power supply PIXVDD or the clamping power supply CLAMPVDD. In one implementation, the pixel array 100 corresponds to a ramp unit 311, and the compensation unit 312 includes a plurality of current detection parts 312a and a current compensation part 312b, each current detection part 312a corresponds one-to-one to each pixel column in the pixel array 100, and the current compensation part 312b corresponds to the ramp unit 311; in other implementations, each pixel column may share a current detection part 312a, that is, the compensation unit 312 includes a current detection part 312a and a current compensation part 312b, the current detection part 312a corresponds to the pixel array 100, and the current compensation part 312b corresponds to the ramp unit 311.

[0087] In one implementation, the current detection part 312a includes a first transistor MP1, the current compensation part 312b includes N second current branches, and the second current branches include second transistors (e.g., MP21-MP2n) and second switches (e.g., S21-S2n); wherein the control end of the first transistor MP1 is connected to the control end of each second transistor, the first end is connected to its control end and realizes current change detection, and the second end is connected to the working power supply AVDD; the first end of each second transistor is connected to the load output part 311b via each second switch, and the second end is connected to the working power supply AVDD, and N is an integer greater than or equal to 1. In the application, the first transistor MP1 and each second transistor (e.g., MP21-MP2n) are PMOS tubes, and in this case, the control end in the above text refers to the gate, the first end refers to the drain, and the second end refers to the source.

[0088] In the above implementation, the number of the second current branches may be 1 or greater than 1; and when the number of the second current branches is greater than 1, the width-to-length ratios of the second MOS tubes in each second current branch may be the same or different. In applications, in order to reduce the circuit area, each second switch is usually implemented by a MOS tube; in addition, the opening and closing control of each second switch is usually completed by a master controller used in conjunction with the image sensor 10. When the corresponding power supply refers to the clamping power supply CLAMPVDD, the first end of the first transistor MP1 is connected to its control end and generates the clamping power supply CLAMPVDD; the working power supply AVDD generates the clamping power supply CLAMPVDD after passing through the first transistor MP1 to power the corresponding clamping circuit 200, and generates the power supply current Iclampvdd when the switch transistor M6 in the corresponding clamping circuit 200 is turned on, so that the current change detection of the clamping power supply CLAMPVDD can be realized. The second transistor and the first transistor MP1 form a current mirror structure, and obtain a compensation current Ifix by mirroring the power supply current Iclampvdd, wherein Ifix=k*Iclampvdd, k is a correction coefficient. When the number of second current branches is 1, the correction coefficient k can be designed by designing the width-to-length ratio of the second transistor. When the number of second current branches is greater than 1, the correction coefficient k can be designed by designing the opening and closing of each second switch and / or the width-to-length ratio of each second transistor.

[0089] In fact, for a specific application scenario, the correction coefficient k is a fixed quantity; that is, when a change in the current of the clamping power supply CLAMPVDD is detected, the current compensation part 312b generates a fixed amount of compensation current Ifix relative to Iclampvdd, thereby generating a relatively fixed compensation amount ΔV (ΔV=Ifix*R1), and the ramp voltage Vramp is raised as a whole by ΔV. By reasonably designing the correction coefficient k, ΔV=Vrise, so that the influence of the dispersion phenomenon on the second pixel is offset by the differential amplification of the comparator module 320, and the correction coefficient k can be given according to actual needs and circuit configuration. Of course, in other implementations, the correction coefficient k can also be variable, for example, it can be set according to the magnitude of the current change of the detected pixel power supply PIXVDD, so as to be fed back to the ramp generation module to achieve ramp voltage compensation, thereby achieving signal quantization through the compensated ramp voltage. When the corresponding power source refers to the pixel power source PIXVDD, the current detection part 312a also includes a third transistor (not shown in the figure), the control end is connected to the detection enable signal, the first end is connected to the first end of the first transistor MP1, and the second end is connected to the corresponding column line; the current change of the pixel power source PIXVDD will be reflected in the branch where the third transistor is located, so that the current change detection of the pixel power source PIXVDD can be realized, and the second transistor and the first transistor MP1 form a current mirror structure and finally obtain the compensation amount through the current mirror. The principle is the same as above and will not be repeated here. In the application, the third transistor is an NMOS tube. At this time, the control end in the above text refers to the gate, the first end refers to the drain, and the second end refers to the source; of course, in other implementations, it is also feasible for the third transistor to be a PMOS tube.

[0090] The comparator module 320 has a first input terminal (eg, a negative phase input terminal) connected to the pixel voltage Vpix, and a second input terminal (eg, a positive phase input terminal) connected to the ramp voltage Vramp, and generates a quantization result by comparing the pixel voltage Vpix and the ramp voltage Vramp.

[0091] Accordingly, the present embodiment further provides a quantization compensation method for an image sensor, comprising: in the image sensor 10, the first pixel and the second pixel are provided with pixel power through the same power line; when the pixel voltage of the second pixel is quantized based on the ramp voltage, a compensation amount is generated according to the current change of the pixel power supply in the first pixel and compensated to the ramp voltage, so as to obtain the quantization result of the second pixel based on the compensated ramp voltage, thereby correcting the quantization result of the second pixel; wherein, the image sensor 10 is implemented using the structure described above.

[0092] The first pixel and the second pixel are usually located in the same pixel row in the pixel array 100. In fact, in the pixel array 100, the pixels 110 in the same pixel row are usually provided with pixel power through the same power line. In addition, the light intensity of the area where the first pixel is located is greater than the light intensity of the area where the second pixel is located.

[0093] In one embodiment, the compensation amount can be directly generated according to the current change of the pixel power supply in the first pixel, such as directly detecting whether the current of the pixel power supply in the first pixel changes, and generating the compensation amount when the current change of the pixel power supply is detected. Of course, in other embodiments, the compensation amount can also be indirectly generated according to the current change of the pixel power supply in the first pixel; in the case where the image sensor 10 includes the clamping circuit 200, the first pixel also corresponds to the clamping power supply, and the current change of the pixel power supply in the first pixel will cause the current change of the clamping power supply. At this time, the compensation amount is generated according to the current change of the clamping power supply, such as detecting whether the current of the clamping power supply changes, and generating the compensation amount when the current change of the clamping power supply is detected.

[0094] Among them, when the current of the clamped power supply changes, a compensation current is generated based on the power supply current of the branch where the clamped power supply is located and converted to obtain a compensation amount. The compensation current satisfies the formula Ifix=k*Iclampvdd, Ifix is ​​the compensation current, k is the correction coefficient, and Iclampvdd is the power supply current.

[0095] Next, please combine Figure 6 , see Fig.10 and Fig.11 , the dispersion compensation scheme of the image sensor 10 in this embodiment is further analyzed and explained.

[0096] Based on the dispersion compensation solution of this embodiment, the second pixel (eg, the pixel in the weak illumination area) is compensated, and the compensation result is as follows: Fig.10 As shown, vinn0 is the voltage waveform input to the vinn terminal when the second pixel is not affected by the diffusion phenomenon (generated by the first pixel, such as the pixel in the strong light area), vinn1 is the voltage waveform input to the vinn terminal when the second pixel is affected by the diffusion phenomenon, vinp0 is the original waveform of the ramp voltage Vramp, and vinp1 is the compensated waveform of the ramp voltage Vramp;

[0097] It can be seen from the figure that when the second pixel is affected by the dispersion phenomenon and the signal voltage Vsig is raised, if the ramp voltage Vramp is not compensated, the quantization of the signal voltage Vsig will end at time t1, at which time Tsig-Trst will become smaller, making the image corresponding to the second pixel darker overall;

[0098] However, if the ramp voltage Vramp is compensated, the ramp voltage Vramp will also rise, and the quantization of the signal voltage Vsig will end at time t2, which is almost the same as the quantization end time when the second pixel is not affected by the dispersion phenomenon. Tsig is corrected back to its original level. At this time, Tsig-Trst is almost unchanged, which can improve the image quality.

[0099] The influence of the above dispersion compensation scheme on the first pixel (eg, the pixel in the strong light area, i.e., the pixel producing the dispersion phenomenon) is as follows: Fig.11 As shown, in one case, since the level of the signal voltage Vsig of the first pixel is very low and exceeds the quantization range of the comparator module 320, the comparator module 320 will only flip after the ramp voltage Vramp ends, which is reflected in the full-scale output in the quantization result; although the ramp voltage Vramp is raised as a whole after compensation, there is still no intersection between the signal voltage Vsig and the ramp voltage Vramp, and the quantization result is still full-scale output, which has no effect on the quantization result of the first pixel.

[0100] It can be seen that the above-mentioned dispersion compensation scheme can compensate for the quantization results of the pixels in the weak light area near the strong light area without affecting the quantization results of the pixels in the strong light area, weaken or even offset the impact of the dispersion phenomenon, and improve the image quality.

[0101] In summary, the utility model of a ramp generation module, a quantization control circuit and an image sensor introduces the current change of the pixel power supply in the strong light area pixel into the ramp voltage. In this way, when the pixel voltage of the weak light area pixel is quantized based on the ramp voltage, the differential amplification of the comparator module can weaken or even offset the influence of the diffusion phenomenon on the weak light area pixel, thereby improving the image quality. Therefore, the utility model effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0102] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the technology may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed in the present invention shall still be covered by the claims of the present invention.

Claims

1. A ramp generation module, characterized in that: It includes a slope unit and a compensation unit; The ramp unit is used to generate a ramp voltage; The compensation unit is connected to the ramp unit, and is used to generate a compensation amount according to the current change of the pixel power supply in the first pixel and compensate it to the ramp voltage, so as to obtain the quantization result of the second pixel based on the compensated ramp voltage; wherein, the first pixel and the second pixel are provided with pixel power through the same power line.

2. The ramp generation module according to claim 1, characterized in that: The light intensity of the area where the first pixel is located is greater than the light intensity of the area where the second pixel is located.

3. The ramp generation module according to claim 1, characterized in that: The first pixel also corresponds to a clamping power supply, and a current change of the pixel power supply in the first pixel causes a current change of the clamping power supply.

4. The ramp generating module according to any one of claims 1 to 3, characterized in that: The slope unit includes a slope current part and a load output part, and the compensation unit includes a current detection part and a current compensation part; The ramp current part is used to generate a ramp current, and the load output part is connected to the ramp current part and is used to convert the ramp current into the ramp voltage; The current detection part is used to detect whether the current of the corresponding power supply changes, and the current compensation part is connected to the current detection part, and is used to generate a compensation current when the current of the corresponding power supply changes, so as to convert the compensation current into the compensation amount through the load output part and compensate it to the ramp voltage; When the first pixel does not correspond to a clamped power supply, the corresponding power supply refers to a pixel power supply; when the first pixel corresponds to a clamped power supply, the corresponding power supply refers to a pixel power supply or a clamped power supply.

5. The ramp generating module according to claim 4, characterized in that: The ramp current part includes M first current branches, the first current branch includes a current source and a first switch, and the load output part includes a load resistor; the M first current branches are connected in parallel to a first reference potential via the load resistor, and in any first current branch, the current source and the first switch are connected in series between a working power supply and a parallel node, wherein M is an integer greater than 1; or, the load output part also includes a filter capacitor connected in parallel to both ends of the load resistor.

6. The ramp generation module according to claim 4, characterized in that: The current detection part includes a first transistor, the current compensation part includes N second current branches, the second current branches include a second transistor and a second switch; the control end of the first transistor is connected to the control end of each of the second transistors, the first end is connected to its control end and realizes current change detection, and the second end is connected to the working power supply, wherein, when the corresponding power supply refers to a clamping power supply, the first end of the first transistor is connected to its control end and generates a clamping power supply; the first end of each of the second transistors is connected to the load output part via each of the second switches, and the second end is connected to the working power supply; wherein N is an integer greater than or equal to 1.

7. A quantization control circuit, characterized in that: It comprises a ramp generation module and a comparator module as described in any one of claims 1 to 6; The ramp generating module is used to provide the ramp voltage; The first input terminal of the comparator module is connected to the pixel voltage, and the second input terminal is connected to the ramp voltage. The quantization result is generated by comparing the pixel voltage with the ramp voltage.

8. An image sensor, characterized in that: comprising a pixel array and a plurality of quantization control circuits as claimed in claim 7; The pixel array includes a plurality of pixels arranged in an array in rows and columns, and the pixels are used to generate pixel voltages; Each of the quantization control circuits corresponds to each pixel in the pixel array, and is used for quantizing the pixel voltage of each of the pixels according to the ramp voltage.

9. The image sensor according to claim 8, characterized in that: The comparator module corresponds one-to-one to the pixel columns in the pixel array, the slope unit of the slope generating module corresponds to the pixel array, and when the compensation unit of the slope generating module includes a current detection part and a current compensation part, the current detection part corresponds to the pixel array or corresponds one-to-one to the pixel columns in the pixel array, and the current compensation part corresponds to the slope unit.

10. The image sensor according to claim 8, characterized in that The pixel includes a photosensitive element, a transfer transistor, a reset transistor and a source follower transistor; the control end of the transfer transistor is connected to a transmission control signal, the first end is connected to a floating diffusion node, and the second end is connected to a second reference potential via the photosensitive element; the control end of the reset transistor is connected to a reset control signal, the first end is connected to a pixel power supply, and the second end is connected to a floating diffusion node; the control end of the source follower transistor is connected to a floating diffusion node, the first end is connected to a pixel power supply, and the second end is connected to a corresponding column line; wherein the corresponding column line is connected to a third reference potential via a corresponding tail current source; or, the pixel also includes a row selection transistor, which is connected between the second end of the source follower transistor and the corresponding column line, and the control end is connected to a row selection signal.

11. The image sensor according to any one of claims 8 to 10, characterized in that: The image sensor further includes a plurality of clamping circuits, each of which corresponds to each pixel column in the pixel array and is used to start voltage clamping when the voltage of the corresponding column line drops to a set value; And / or, the clamping circuit includes a clamping transistor and a switching transistor; the control end of the clamping transistor is connected to a reference voltage, the first end is connected to a clamping power supply, and the second end is connected to the first end of the switching transistor; the control end of the switching transistor is connected to a clamping enable signal, and the second end is connected to a corresponding column line.

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