Large dynamic range time-of-flight method three-dimensional pixel, control method, pixel array and image sensor
By introducing lateral overflow integrated capacitor technology and complementary phase signal control, the problem of insufficient sensitivity of TOF 3D pixel sensors in strong background light and long-distance measurement is solved, realizing distance measurement with a large dynamic range and enhancing the sensor's measurement capability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2025-12-23
- Publication Date
- 2026-05-05
AI Technical Summary
Existing TOF 3D pixel sensors are prone to saturation under strong background light, which limits the minimum distance measurement and makes it difficult to achieve a large dynamic range distance measurement when measuring at long distances.
By employing lateral overflow integrated capacitor technology, and introducing a lateral overflow gate and a lateral overflow gate capacitor, combined with complementary phase modulation signal control, high and low conversion gain mode switching is achieved, enhancing low light sensitivity and expanding the measurement range.
It increases full-sink capacity and enhances low-light sensitivity at short distances, improves detection sensitivity at long distances, enables distance measurement with a large dynamic range, and supports depth sensing over a wide measurement range.
Smart Images
Figure CN121978712A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of image sensor pixel design technology, and in particular to a method and control method for achieving large dynamic range time-of-flight three-dimensional pixels with large measurement distance using lateral overflow integrated capacitor technology, as well as a pixel array and image sensor. Background Technology
[0002] The measurement range of a Time-of-Flight (TOF) 3D pixel sensor refers to the minimum and maximum distances at which it can effectively detect and measure target objects. It is one of the core indicators determining the sensor's applicable scenarios and performance. A typical 3D 2-tap pixel device structure is shown below. Figure 1 As shown, in three-dimensional operation, the integrated signal is not entirely effective light information. The "background light" in the environment can cause the pixel to saturate prematurely. If the background light is too high, it may cause the depth calculation to fail in severe cases. Therefore, improving the full-well capacity of the pixel is a current design challenge for TOF three-dimensional pixels.
[0003] The current solution to this problem is to add storage diodes SD0 / SD1 and modulation transmission gates TG0 / TG1 between the pinned photodiode (PPD) and the voltage conversion transmission gates TX0 / TX1, such as... Figure 2 As shown, existing methods solve the problem of premature pixel saturation caused by background light by increasing the full-well capacity of pixels, and extend the minimum distance in distance measurement. However, the measurement of the maximum distance still requires pixels to have higher sensitivity to improve measurement accuracy. The pixel structure of existing methods cannot achieve high low-light sensitivity. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and provide a large dynamic range time-of-flight three-dimensional pixel and its control method, pixel array and image sensor. Specifically, the large dynamic range time-of-flight three-dimensional pixel is a time-of-flight three-dimensional pixel device that adopts lateral overflow integrated capacitor technology. It can improve the low light sensitivity of the pixel structure while taking into account the full-well capacity under small distance measurement, expand the measurement distance range of the pixel device, and solve the problem in TOF three-dimensional imaging technology that the intensity of the modulated light reflected back becomes more severe as the measurement distance increases.
[0005] The first objective of this invention is to provide a large dynamic range time-of-flight three-dimensional pixel, comprising a clamping photodiode PPD, one end of which is grounded and the other end is connected to the source of modulation transfer gates TG0 and TG1. The drains of modulation transfer gates TG0 and TG1 are respectively connected to the source of voltage-to-voltage transfer gates TX0 and TX1. A storage node SD0 is connected between modulation transfer gate TG0 and TX0, and a storage node SD1 is connected between modulation transfer gate TG1 and TX1. The drains of voltage-to-voltage transfer gates TX0 and TX1 are respectively connected to charge-to-voltage conversion nodes FD0 and FD1. The charge-to-voltage conversion node FD0 is connected to the gate of a first source follower SF and the source of a lateral overflow gate SG0. The terminals are connected in series. The drain of the lateral overflow gate SG0 is connected to the source of the first reset switch and the non-grounded terminal of the lateral overflow gate capacitor Cs0. The drain of the first reset switch is connected to the drain of the first source follower SF and then to the power supply VDD. The source of the first source follower SF is connected to the drain of the first row gating switch SEL, and the source of the first row gating switch SEL is connected to Col_tap0. The charge-voltage conversion node FD1 is connected to the gate of the second source follower SF and the source of the lateral overflow gate SG1. The drain of the lateral overflow gate SG1 is connected to the source of the second reset switch and the non-grounded terminal of the lateral overflow gate capacitor Cs1. The drain of the second reset switch is connected to the drain of the second source follower SF and then to the power supply VDD. The source of the second source follower SF is connected to the drain of the second row gating switch SEL, and the source of the second row gating switch SEL is connected to Col_tap1.
[0006] Preferably, the non-grounded terminal of the clamping photodiode PPD is connected to the source of the charge leakage gate LG, and the drain of the charge leakage gate LG is connected to the power supply VDD.
[0007] Preferably, the modulation transmission gate TG0, modulation transmission gate TG1, voltage conversion transmission gate TX0, voltage conversion transmission gate TX1, lateral overflow gate SG0, lateral overflow gate SG1, first source follower SF, second source follower SF, first row gating switch SEL, second row gating switch SEL, first reset switch RET, second reset switch RST, and charge leakage gate LG are NMOS transistors.
[0008] Preferably, the lateral overflow gate capacitor Cs0 and the lateral overflow gate capacitor Cs1 are LOFIC capacitors.
[0009] Preferably, the storage node SDO and storage node SD1 are storage diodes.
[0010] The second objective of this invention is to provide a control method for three-dimensional pixels using a large dynamic range time-of-flight method. In the three-dimensional working mode, the pixel array is modulated using a global exposure method. During the exposure, the modulation transmission gate TG0 and modulation transmission gate TG1 use complementary phase modulation signals to modulate and transfer the photogenerated charge in the clamped photodiode PPD. Four phase light signals are obtained through two frames of exposure, thereby synthesizing a complete signal.
[0011] Preferably, during readout, the charge leakage gate LG is turned on, and the signal within the clamping photodiode PPD is guided to the power supply VDD in real time through the leakage process, avoiding interference with the effective imaging signal; during the exposure phase 0 ~ The 1095 rows of pixels are reset through timing control, and after the exposure stage ends, the pixels are read out row by row.
[0012] Preferably, during reading, the transverse transmission gates SG0 and SG1 are first turned off, and the reset levels of the charge-to-voltage conversion nodes FD0 and FD1 are read. Then, the voltage conversion transmission gates TX0 and TX1 are turned on, and the photocharge stored in the storage nodes SD0 and SD1 is transferred to the charge-to-voltage conversion nodes FD0 and FD1 to obtain the corresponding signal levels, thus completing the double-sampling readout operation in high conversion gain mode. The transverse transmission gates SG0 and SG1 are turned on again, connecting the charge-to-voltage conversion nodes FD0 and FD1 and the transverse overflow gate capacitors Cs0 and Cs1. In this state, the signal level in low-gain mode is read first to realize the quantization and acquisition of short-distance strong light signals. Then, the relevant nodes are reset through the first reset switch and the second reset switch to read the corresponding low conversion gain reset level.
[0013] A third objective of this invention is to provide a pixel array comprising the aforementioned large dynamic range time-of-flight three-dimensional pixels.
[0014] A fourth object of the present invention is to provide an image sensor including the pixel array.
[0015] The pixel structure of the present invention is implemented in a global exposure manner. During the exposure, the modulation transmission gate TG0 and the modulation transmission gate TG1 use complementary phase modulation signals to store complementary phase photoacoustic charges in the clamp photodiode PPD into storage nodes SD0 and SD1. After the exposure is completed, the row select switch SEL is activated and enters the signal readout stage.
[0016] In the pixel structure of this invention, storage nodes SD0 and SD1 serve as core charge-to-voltage conversion nodes, and the size of their equivalent capacitance directly determines the value of the high conversion gain.
[0017] The lateral overflow gate capacitors Cs0 and Cs1 play a dual role in this structure: on the one hand, under the condition of high light intensity measured at short distances and after the storage nodes SD0 and SD1 reach full-well capacity, the lateral overflow gate capacitors Cs0 and Cs1 can continue to collect the overflowed saturated charge; on the other hand, by turning on and off the lateral transfer gates SG0 and SG1, the connection between them and the charge-to-voltage conversion nodes FD0 and FD1 can be controlled, thereby realizing the switching between high and low gain states.
[0018] Under low light intensity conditions for long-distance measurement, the pixel reads out the signal only through the charge-to-voltage conversion nodes FD0 and FD1, and operates in a high conversion gain mode, thereby improving the detection sensitivity of the device for long-distance measurement. Under high light intensity conditions for short-distance measurement, the charge-to-voltage conversion nodes FD0 and FD1 are connected in parallel with the lateral overflow gate capacitors Cs0 and Cs1 by turning on the lateral transmission gates SG0 and SG1, thereby reducing the overall conversion gain and realizing effective measurement of short distances in three-dimensional mode.
[0019] Compared with existing methods, the TOF 3D 2-tap pixel based on LOFIC technology of this invention realizes a dual-gain mode signal readout mechanism by introducing lateral overflow gates SG0 and SG1 and lateral overflow gate capacitors Cs0 and Cs1. This structural design not only ensures high sensitivity characteristics under long-distance measurement, but also significantly expands the response range of the pixel under short-distance measurement conditions, providing effective technical support for realizing wide measurement range depth sensing. Attached Figure Description
[0020] Figure 1 It is a typical TOF three-dimensional 2-tap pixel device structure.
[0021] Figure 2 It is a TOF three-dimensional pixel device structure that adds storage diodes SD0 / SD1 to the existing technology.
[0022] Figure 3 This invention relates to a TOF three-dimensional pixel device structure based on LOFIC capacitors.
[0023] Figure 4 This is a timing diagram of the TOF three-dimensional pixel device based on LOFIC capacitors used in this invention. Detailed Implementation
[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0025] See Figure 3As shown, in this embodiment of the invention, a large dynamic range time-of-flight method three-dimensional pixel is provided, including a clamping photodiode PPD. One end of the clamping photodiode PPD is grounded, and the other end is connected to the source of modulation transmission gate TG0 and modulation transmission gate TG1. The drains of modulation transmission gate TG0 and modulation transmission gate TG1 are respectively connected to the source of voltage conversion transmission gate TX0 and voltage conversion transmission gate TX1. A storage node SD0 is connected between modulation transmission gate TG0 and voltage conversion transmission gate TX0, and a storage node SD1 is connected between modulation transmission gate TG1 and voltage conversion transmission gate TX1. The drains of voltage conversion transmission gate TX0 and voltage conversion transmission gate TX1 are respectively connected to charge-to-voltage conversion nodes FD0 and charge-to-voltage conversion nodes FD1. The charge-to-voltage conversion node FD0 is connected to the gate of the first source follower SF and the source of the lateral overflow gate SG0. The drain of the lateral overflow gate SG0 is connected to the source of the first reset switch. The drain of the first reset switch is connected to the drain of the first source follower SF and then to the power supply VDD. The source of the first source follower SF is connected to the drain of the first row gating switch SEL, and the source of the first row gating switch SEL is connected to Col_tap0. The charge-voltage conversion node FD1 is connected to the gate of the second source follower SF and the source of the horizontal overflow gate SG1. The drain of the horizontal overflow gate SG1 is connected to the source of the second reset switch and the non-grounded terminal of the horizontal overflow gate capacitor Cs1. The drain of the second reset switch is connected to the drain of the second source follower SF and then to the power supply VDD. The source of the second source follower SF is connected to the drain of the second row gating switch SEL, and the source of the second row gating switch SEL is connected to Col_tap1, which is the column tap gating signal. It is used to select the pixel taps column by column and synchronously read the charge / signal of the column. It works with the row selection to complete the timing control and data output row by row.
[0026] Among them, the voltage conversion transfer gates TX0 and TX1 are responsible for the directional transfer of the photogenerated charge accumulated in the clamped photodiode PPD to the charge-voltage conversion nodes FD0 and FD1. The lateral overflow gates SG0 and SG1 control the on / off state between the charge-voltage conversion nodes FD0 and FD1 and the lateral overflow gate capacitors Cs0 and Cs1, thereby realizing the switching between the high and low conversion gain modes.
[0027] Among them, the first reset switch RST and the second reset switch RST are used to perform initialization and reset operations on each charge storage node. The first source follower SF, the second source follower SF, the first row gating switch SEL, and the second row gating switch SEL together complete the reading function of the pixel output signal.
[0028] Furthermore, in this embodiment, the non-grounded terminal of the clamping photodiode PPD is connected to the source of the charge leakage gate LG, and the drain of the charge leakage gate LG is connected to the power supply VDD.
[0029] Furthermore, in the embodiments of this application, the modulation transmission gate TG0, modulation transmission gate TG1, voltage conversion transmission gate TX0, voltage conversion transmission gate TX1, lateral overflow gate SG0, lateral overflow gate SG1, storage node SDO, storage node SD1, first source follower SF, second source follower SF, first row gating switch SEL, second row gating switch SEL, first reset switch RET and second reset switch RST, and charge leakage gate LG are NMOS transistors.
[0030] Furthermore, in this embodiment, the lateral overflow gate capacitor Cs0 and the lateral overflow gate capacitor Cs1 are LOFIC capacitors.
[0031] This invention also provides a control method for three-dimensional pixels using a large dynamic range time-of-flight method, with the working timing as follows: Figure 4 As shown, in the three-dimensional working mode, the pixel array is modulated by global exposure. During the exposure, the modulation transmission gate TG0 and modulation transmission gate TG1 use complementary phase modulation signals to modulate and transfer the photogenerated charge in the clamped photodiode PPD. Four phase light signals can be obtained through two frames of exposure, thus synthesizing a complete signal.
[0032] During readout, the charge leakage gate LG is activated, and the signal within the clamping photodiode PPD is guided to the power supply VDD in real time through the leakage process, preventing interference with the effective imaging signal; during the exposure phase 0... ~ The 1095 rows of pixels are reset through timing control, and after the exposure stage ends, the pixels are read out row by row.
[0033] See Figure 4 As shown, during reading, the transverse transmission gates SG0 and SG1 are first turned off, and the reset levels of the charge-to-voltage conversion nodes FD0 and FD1 are read. Then, the voltage conversion transmission gates TX0 and TX1 are turned on, and the optical charge stored in the storage nodes SD0 and SD1 is transferred to the charge-to-voltage conversion nodes FD0 and FD1 to obtain the corresponding signal level, thus completing the double sampling readout operation in high conversion gain mode. The transverse transmission gates SG0 and SG1 are turned on again, connecting the charge-to-voltage conversion nodes FD0 and FD1 and the transverse overflow gate capacitors Cs0 and Cs1. In this state, the signal level in low-gain mode is read first to realize the quantization and acquisition of short-distance strong light signals. Then, the relevant nodes are reset through the first reset switch and the second reset switch to read the corresponding low conversion gain reset level.
[0034] This structure supports Correlated Double Sampling (CDS) to eliminate noise under high conversion gain, and Delta Reset Sampling (DRS) to extract signals under low conversion gain, ensuring accurate signal reconstruction under different measurement distances.
[0035] Based on existing technologies, a lateral overflow integrated capacitor technology for time-of-flight three-dimensional pixel devices is proposed, with the following design structure: Figure 3 As shown, it mainly consists of NMOS transistors M0~M12. PPD is a photodiode, TG0 / TG1 is a modulation transmission gate, and SD0 / SD1 is a storage diode.
[0036] The present invention further provides a pixel array including the large dynamic range time-of-flight method three-dimensional pixels.
[0037] Furthermore, this invention provides an image sensor including the pixel array.
[0038] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and therefore all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.
[0039] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A three-dimensional pixel method based on a large dynamic range time-of-flight method, characterized in that, The system includes a clamping photodiode PPD, with one end grounded and the other end connected to the source of modulation transmission gates TG0 and TG1. The drains of modulation transmission gates TG0 and TG1 are respectively connected to the source of voltage conversion transmission gates TX0 and TX1. A storage node SD0 is connected between modulation transmission gates TG0 and TX0, and a storage node SD1 is connected between modulation transmission gates TG1 and TX1. The drains of voltage conversion transmission gates TX0 and TX1 are respectively connected to charge-to-voltage conversion nodes FD0 and FD1. Charge-to-voltage conversion node FD0 is connected to the gate of the first source follower SF and the source of the lateral overflow gate SG0. The drain of the lateral overflow gate SG0... The first source follower SF is connected to the source of the first reset switch and the non-grounded terminal of the lateral overflow gate capacitor Cs0. The drain of the first reset switch is connected to the drain of the first source follower SF and then to the power supply VDD. The source of the first source follower SF is connected to the drain of the first row gating switch SEL, and the source of the first row gating switch SEL is connected to Col_tap0. The charge-voltage conversion node FD1 is connected to the gate of the second source follower SF and the source of the lateral overflow gate SG1. The drain of the lateral overflow gate SG1 is connected to the source of the second reset switch and the non-grounded terminal of the lateral overflow gate capacitor Cs1. The drain of the second reset switch is connected to the drain of the second source follower SF and then to the power supply VDD. The source of the second source follower SF is connected to the drain of the second row gating switch SEL, and the source of the second row gating switch SEL is connected to Col_tap1.
2. The three-dimensional pixel method of large dynamic range time-of-flight according to claim 1, characterized in that, The non-grounded terminal of the clamping photodiode PPD is connected to the source of the charge leakage gate LG, and the drain of the charge leakage gate LG is connected to the power supply VDD.
3. The three-dimensional pixel method of large dynamic range time-of-flight according to claim 2, characterized in that, The modulation transmission gate TG0, modulation transmission gate TG1, voltage conversion transmission gate TX0, voltage conversion transmission gate TX1, lateral overflow gate SG0, lateral overflow gate SG1, first source follower SF, second source follower SF, first row gating switch SEL, second row gating switch SEL, first reset switch RET and second reset switch RST, and charge leakage gate LG are all NMOS transistors.
4. The three-dimensional pixel method of large dynamic range time-of-flight according to claim 1, characterized in that, The lateral overflow gate capacitors Cs0 and Cs1 are LOFIC capacitors.
5. The three-dimensional pixel method of large dynamic range time-of-flight according to claim 1, characterized in that, The storage nodes SDO and SD1 employ storage diodes.
6. The control method for three-dimensional pixels using the large dynamic range time-of-flight method according to any one of claims 1-5, characterized in that, In the three-dimensional working mode, the pixel array is modulated by global exposure. During the exposure, the modulation transmission gate TG0 and modulation transmission gate TG1 use complementary phase modulation signals to modulate and transfer the photogenerated charge in the clamped photodiode PPD. Four phase light signals are obtained through two frames of exposure, thereby synthesizing a complete signal.
7. The control method for three-dimensional pixels using the large dynamic range time-of-flight method according to claim 6, characterized in that, During readout, the charge leakage gate LG is activated, and the signal within the clamping photodiode PPD is guided to the power supply VDD in real time through the leakage process, avoiding interference with the effective imaging signal; during the exposure phase 0... ~ The 1095 rows of pixels are reset through timing control, and after the exposure stage ends, the pixels are read out row by row.
8. The control method for three-dimensional pixels using the large dynamic range time-of-flight method according to claim 7, characterized in that, During reading, the transverse transmission gates SG0 and SG1 are first turned off, and the reset levels of the charge-to-voltage conversion nodes FD0 and FD1 are read. Then, the voltage conversion transmission gates TX0 and TX1 are turned on, and the optical charge stored in the storage nodes SD0 and SD1 is transferred to the charge-to-voltage conversion nodes FD0 and FD1 to obtain the corresponding signal levels, thus completing the double-sampling readout operation in high conversion gain mode. The transverse transmission gates SG0 and SG1 are turned on again, connecting the charge-to-voltage conversion nodes FD0 and FD1 and the transverse overflow gate capacitors Cs0 and Cs1. In this state, the signal level in low-gain mode is read first to realize the quantization and acquisition of short-distance strong light signals. Then, the relevant nodes are reset through the first reset switch and the second reset switch to read the corresponding low conversion gain reset level.
9. A pixel array, characterized in that, Includes the large dynamic range time-of-flight method three-dimensional pixels as described in any one of claims 1-5.
10. An image sensor, characterized in that, Includes the pixel array of claim 9.