A dual shutter TOF image sensor pixel structure and driving method

Abstract

The invention discloses a dual shutter TOF image sensor pixel structure and driving method, wherein the source of the reset transistor is connected to the negative electrode of the PD, the gate is connected to the RPD signal, and the drain is connected to the VDD signal; the pixel has two readout links, and the structures of the two readout links are symmetrically distributed with the PD as the axis; each readout link comprises: the source of the first shutter transistor is connected to the negative electrode of the PD, the gate is connected to the GS1 signal, and the drain is connected to the SD node; the source of the second shutter transistor is connected to the negative electrode of the PD, the gate is connected to the GS2 signal, and the drain is connected to the FD node; the source of the transmission transistor is connected to the SD node, the gate is connected to the TX signal, and the drain is connected to the FD node; the source of the FD reset transistor is connected to the FD node, the gate is connected to the RFD signal, and the drain is connected to the VDD signal; the gate of the source follower transistor is connected to the FD node, the drain is connected to the VDD signal, and the source is connected to the source of the row selection transistor; the gate of the row selection transistor is connected to the RS signal, and the drain is connected to the output signal line of the first readout link column. It includes the working timing in the single shutter mode and the working timing in the dual shutter mode; it can work in the single shutter mode and the dual shutter mode respectively to adapt to different application scenarios in dynamic detection.

Description

Technical Field

[0001] The present invention relates to a TOF image sensor integrated circuit, and in particular to a dual-shutter TOF image sensor pixel structure and a driving method. Background Art

[0002] TOF image sensors measure the time required for modulated light to travel between the target object and the sensor, calculate the distance information of the target object, and complete 3D imaging. They are widely used in consumer electronics, industrial manufacturing, automotive driving, security monitoring and other fields.

[0003] In dynamic detection applications, considering the speed of moving objects, a TOF image sensor with a global shutter working mode with high shutter efficiency is required. The single-structure TOF image sensor in the prior art is difficult to meet the above requirements.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a dual-shutter TOF image sensor pixel structure and a driving method to solve the above-mentioned technical problems existing in the prior art.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The dual-shutter TOF image sensor pixel structure of the present invention comprises:

[0008] The source of the reset transistor is connected to the negative pole of PD, the gate is connected to the RPD signal, and the drain is connected to the VDD signal;

[0009] The pixel has two readout links, and the structures of the two readout links are symmetrically distributed with PD as the axis;

[0010] Each readout link includes:

[0011] The source of the first shutter transistor is connected to the negative electrode of PD, the gate is connected to the GS1 signal, and the drain is connected to the SD node;

[0012] The source of the second shutter transistor is connected to the negative electrode of PD, the gate is connected to the GS2 signal, and the drain is connected to the FD node;

[0013] The source of the transmission transistor is connected to the SD node, the gate is connected to the TX signal, and the drain is connected to the FD node;

[0014] The source of the FD reset transistor is connected to the FD node, the gate is connected to the RFD signal, and the drain is connected to the VDD signal;

[0015] The gate of the source follower transistor is connected to the FD node, the drain is connected to the VDD signal, and the source is connected to the source of the row selection transistor;

[0016] The gate of the row selection transistor is connected to the RS signal, and the drain is connected to the first readout link column output signal line.

[0017] The driving method of the dual shutter TOF image sensor pixel structure includes a working sequence in a single shutter mode and a working sequence in a dual shutter mode;

[0018] In single shutter mode, a square wave with a duty cycle of 1:4 is used to modulate the optical signal, and the shutter switch performs sampling at four moments:

[0019] In the dual shutter mode, a square wave with a duty cycle of 1:2 is used to modulate the optical signal, and the shutter switch performs two-time sampling.

[0020] Compared with the prior art, the dual-shutter TOF image sensor pixel structure and driving method provided by the present invention can work in single shutter mode and dual shutter mode respectively for high-range detection and high-speed detection to adapt to different application scenarios in dynamic detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A TOF pixel structure according to an embodiment of the present invention;

[0022] Figure 2 The single shutter working mode timing of the embodiment of the present invention;

[0023] Figure 3 The dual shutter working mode timing of the embodiment of the present invention.

[0024] The letter codes in the figure are customary codes in this field. The corresponding Chinese names are as follows. In this article, when they appear alone or together with the Chinese name, they have the same meaning:

[0025] name Chinese name PD Photodiode FD Floating Diffusion Node SD Charge storage nodes Light Modulating optical signals GS1 First shutter signal GS2 Second shutter signal GS3 Third shutter signal GS4 Fourth shutter signal RPD PD reset signal RFD FD reset signal RS row selection signal TX Charge transfer signal VDD Power signal Output Column output signal line DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0027] First, the terms that may be used in this article are explained as follows:

[0028] The term “and / or” means that either or both of them can be realized at the same time. For example, X and / or Y means both “X” or “Y” and “X and Y”.

[0029] The terms "include", "comprises", "contains", "has" or other descriptions with similar semantics should be interpreted as non-exclusive inclusion. For example, including certain technical feature elements (such as raw materials, components, ingredients, carriers, dosage forms, materials, dimensions, parts, components, mechanisms, devices, steps, procedures, methods, reaction conditions, processing conditions, parameters, algorithms, signals, data, products or products, etc.) should be interpreted as including not only certain technical feature elements explicitly listed, but also other technical feature elements known in the art that are not explicitly listed.

[0030] The term "consisting of..." means excluding any technical feature elements not explicitly listed. If this term is used in a claim, it will make the claim closed, so that it does not contain technical feature elements other than the technical feature elements explicitly listed, except for the conventional impurities related to them. If this term only appears in a clause of a claim, it only limits the elements explicitly listed in the clause, and the elements recorded in other clauses are not excluded from the overall claim.

[0031] The contents not described in detail in the examples of the present invention belong to the prior art known to professionals in the field. If no specific conditions are specified in the examples of the present invention, the conditions are carried out according to the conventional conditions in the field or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used in the examples of the present invention, they are all conventional products that can be purchased commercially.

[0032] The dual-shutter TOF image sensor pixel structure of the present invention comprises:

[0033] The source of the reset transistor is connected to the negative pole of PD, the gate is connected to the RPD signal, and the drain is connected to the VDD signal;

[0034] The pixel has two readout links, and the structures of the two readout links are symmetrically distributed with PD as the axis;

[0035] Each readout link includes:

[0036] The source of the first shutter transistor is connected to the negative electrode of PD, the gate is connected to the GS1 signal, and the drain is connected to the SD node;

[0037] The source of the second shutter transistor is connected to the negative electrode of PD, the gate is connected to the GS2 signal, and the drain is connected to the FD node;

[0038] The source of the transmission transistor is connected to the SD node, the gate is connected to the TX signal, and the drain is connected to the FD node;

[0039] The source of the FD reset transistor is connected to the FD node, the gate is connected to the RFD signal, and the drain is connected to the VDD signal;

[0040] The gate of the source follower transistor is connected to the FD node, the drain is connected to the VDD signal, and the source is connected to the source of the row selection transistor;

[0041] The gate of the row selection transistor is connected to the RS signal, and the drain is connected to the first readout link column output signal line.

[0042] The driving method of the dual shutter TOF image sensor pixel structure includes a working sequence in a single shutter mode and a working sequence in a dual shutter mode;

[0043] In single shutter mode, a square wave with a duty cycle of 1:4 is used to modulate the optical signal, and the shutter switch performs sampling at four moments:

[0044] In the dual shutter mode, a square wave with a duty cycle of 1:2 is used to modulate the optical signal, and the shutter switch performs two-time sampling.

[0045] The working sequence in the single shutter mode includes:

[0046] Reset phase:

[0047] The RPD signal, RFD signal and TX signal rise to high level, resetting the PD, FD and SD nodes respectively;

[0048] After that, the RFD and TX signals drop to low level, and after the RPD signal drops to low level, the exposure starts;

[0049] Assume that the modulation light cycle is T. In the exposure stage, the shutter signals of GS1, GS2, GS3, and GS4 sample the charge signal in the PD with a pulse width of T / 4 at the time of 0, T / 4, 2T / 4, and 3T / 4 respectively;

[0050] Readout phase:

[0051] When the RS signal is turned on, the photoelectron signal in the FD is sampled first. The signals sampled by the first readout link GS2 and the second readout link GS4 are recorded as Vsig2 and Vsig4 respectively.

[0052] After that, the RFD pulse is turned on to reset the FD, and the reset signals sampled by the first readout link and the second readout link are Vrst1 and Vrst2 respectively;

[0053] After that, the TX signal is turned on, and the optical signal stored in the SD node is transferred to the FD node. The signals sampled by the first readout link GS1 and the second readout link GS3 are recorded as Vsig1 and Vsig2 respectively;

[0054] Finally, the signal outputs sampled by GS2 and GS4 are calculated as V2=Vrst1-Vsig2 and V4=Vrst2-Vsig4 respectively, which are the results of uncorrelated double sampling; the signal outputs sampled by GS1 and GS2 are calculated as V1=Vrst1-Vsig1 and V3=Vrst2-Vsig2 respectively, which are the results of correlated double sampling.

[0055] In the single shutter mode, readout is performed immediately after one exposure is completed, and high-distance range imaging is achieved by sampling a square wave pulse with a duty cycle of 1:4 at four moments;

[0056] The modulated light flight time is calculated as:

[0057]

[0058] The target object distance information is calculated as:

[0059]

[0060] Where c is the speed of light.

[0061] The working sequence in the dual shutter mode includes:

[0062] Reset phase:

[0063] The RPD signal and the TX signal rise to a high level, resetting the PD and SD nodes respectively;

[0064] After that, the RFD and TX signals drop to low level, and after the RPD signal drops to low level, the exposure starts. In the dual shutter mode, one frame of image completes two exposures. Assuming the modulation light cycle is T, in the first exposure stage, the GS1 and GS3 shutter signals sample the charge signal in the PD at time 0 and T / 2 respectively, with a pulse width of T / 2, and store the light signal in the SD node.

[0065] After the first exposure is completed, the RPD signal and the RFD signal rise to a high level, respectively resetting the PD and FD nodes, and then RFD and RPD drop to a low level, and the second exposure begins;

[0066] In the second exposure stage, the GS2 and GS4 shutter signals sample the charge signal in the PD at time 0 and T / 2 respectively with a pulse width of T / 2, and store the optical signal in the FD node;

[0067] Readout phase:

[0068] When the RS signal is turned on, the photoelectron signal in the FD is sampled first. The signals sampled by the first readout link GS2 and the second readout link GS4 are recorded as Vsig2 and Vsig4 respectively.

[0069] After that, the RFD pulse is turned on to reset the FD, and the reset signals sampled by the first readout link and the second readout link are Vrst1 and Vrst2 respectively;

[0070] After that, the TX signal is turned on, and the optical signal stored in the SD node is transferred to the FD node. The signals sampled by the first readout link GS1 and the second readout link GS3 are recorded as Vsig1 and Vsig2 respectively;

[0071] Finally, the signal outputs sampled by GS2 and GS4 are calculated as V2=Vrst1-Vsig2 and V4=Vrst2-Vsig4 respectively, which are the results of uncorrelated double sampling; the signal outputs sampled by GS1 and GS2 are calculated as V1=Vrst1-Vsig1 and V3=Vrst2-Vsig2 respectively, which are the results of correlated double sampling.

[0072] In the double shutter mode, the readout is performed after two exposures are completed. This mode can be applied to dynamic detection scenarios of high-speed moving objects:

[0073] The flight time of the modulated light for the two exposures is calculated as:

[0074]

[0075]

[0076] The target object distance information of the two exposures is calculated as:

[0077]

[0078]

[0079] Where c is the speed of light.

[0080] In summary, the dual shutter TOF image sensor pixel structure and driving method of the embodiment of the present invention adopts a global shutter working mode, and can work in single shutter mode and dual shutter mode in combination with the design timing. Through the structural design and the corresponding driving timing control scheme, it can work in single shutter mode and dual shutter mode respectively to adapt to different application scenarios in dynamic detection.

[0081] In order to more clearly demonstrate the technical solution and technical effects provided by the present invention, the embodiments of the present invention are described in detail with specific embodiments below.

[0082] Example 1

[0083] like Figure 1 As shown:

[0084] The pixel structure of the dual shutter TOF image sensor, the basic circuit structure is as follows Figure 1 As shown: the source of the reset transistor is connected to the negative electrode of the PD, the gate is connected to the RPD signal, and the drain is connected to the VDD signal; the pixel has two readout links, and the structures of the two readout links are symmetrically distributed. The first readout link is used as an example for explanation. The source of the first shutter transistor is connected to the negative electrode of the PD, the gate is connected to the GS1 signal, and the drain is connected to the SD node; the source of the second shutter transistor is connected to the negative electrode of the PD, the gate is connected to the GS2 signal, and the drain is connected to the FD node; the source of the transmission transistor is connected to the SD node, the gate is connected to the TX signal, and the drain is connected to the FD node; the source of the FD reset transistor is connected to the FD node, the gate is connected to the RFD signal, and the drain is connected to the VDD signal; the gate of the source follower transistor is connected to the FD node, the drain is connected to the VDD signal, and the source is connected to the source of the row selection transistor; the gate of the row selection transistor is connected to the RS signal, and the drain is connected to the output signal line of the first readout link column. The second readout link structure is symmetrically distributed with respect to the PD and the first readout link.

[0085] Figure 2 This is the working sequence of the pixel structure of the present invention in the single shutter mode. In the single shutter mode, a square wave modulated light signal with a duty cycle of 1:4 is used, and the shutter switch performs sampling at four moments. In the reset phase, the RPD signal, the RFD signal and the TX signal rise to a high level to reset the PD, FD and SD nodes respectively; then the RFD and TX signals drop to a low level, and after the RPD signal drops to a low level, exposure begins; assuming that the modulated light period is T, in the exposure phase, the GS1, GS2, GS3 and GS4 shutter signals sample the charge signal in the PD with a pulse width of T / 4 at 0, T / 4, 2T / 4 and 3T / 4 respectively; in the readout phase, the RS signal is turned on, and the photoelectron signal in the FD is first sampled, and the signals sampled by GS2 of the first readout link and GS4 of the second readout link are recorded as Vsig2 and Vsig4 respectively; then the RFD pulse is turned on to reset the FD, and the reset signals sampled by the first readout link and the second readout link are Vrst1 and Vrst2 respectively; then the TX signal is turned on to transfer the optical signal stored in the SD node to the FD node, and the signals sampled by GS1 of the first readout link and GS3 of the second readout link are recorded as Vsig1 and Vsig2 respectively. Finally, the signal output sampled by GS2 and GS4 is calculated as V2 = Vrst1-Vsig2 and V4 = Vrst2-Vsig4, which is the result of non-correlated double sampling; the signal output sampled by GS1 and GS2 is calculated as V1 = Vrst1-Vsig1 and V3 = Vrst2-Vsig2, which is the result of correlated double sampling. In this mode, the readout is performed after one exposure is completed, and high-distance range imaging is achieved by sampling the square wave pulse with a duty cycle of 1:4 at four moments. The modulated light flight time is calculated as:

[0086]

[0087] The target object distance information is calculated as:

[0088]

[0089] Where c is the speed of light.

[0090] Figure 3 This is the working timing of the pixel structure of the present invention in the dual shutter mode. In the dual shutter mode, a square wave modulated light signal with a duty cycle of 1:2 is used, and the shutter switch performs two-time sampling. In the reset stage, the RPD signal and the TX signal rise to a high level to reset the PD and SD nodes respectively; then the RFD and TX signals drop to a low level, and after the RPD signal drops to a low level, the exposure starts; in the dual shutter mode, one frame of image completes two exposures, and the modulated light cycle is set to T. In the first exposure stage, the GS1 and GS3 shutter signals sample the charge signal in the PD at times 0 and T / 2, respectively, with a pulse width of T / 2, and store the light signal to the SD node; after the first exposure, the RPD signal and the RFD signal rise to a high level to reset the PD and FD nodes respectively, and then the RFD and RPD drop to a low level, and the second exposure starts; in the second exposure stage, the GS2 and GS4 shutter signals At time 0 and T / 2, respectively, the charge signal in the PD is sampled with a pulse width of T / 2, and the optical signal is stored in the FD node; in the readout stage, the RS signal is turned on, and the photoelectron signal in the FD is first sampled, and the signals sampled by GS2 of the first readout link and GS4 of the second readout link are recorded as Vsig2 and Vsig4 respectively; then the RFD pulse is turned on to reset the FD, and the reset signals sampled by the first readout link and the second readout link are Vrst1 and Vrst2 respectively; then the TX signal is turned on, and the optical signal stored in the SD node is transferred to the FD node, and the signals sampled by GS1 of the first readout link and GS3 of the second readout link are recorded as Vsig1 and Vsig2 respectively. Finally, the signal outputs sampled by GS2 and GS4 are calculated as V2=Vrst1-Vsig2 and V4=Vrst2-Vsig4, respectively. This output is the result of non-correlated double sampling; the signal outputs sampled by GS1 and GS2 are calculated as V1=Vrst1-Vsig1 and V3=Vrst2-Vsig2, respectively. This output is the result of correlated double sampling. In double shutter mode, the readout is performed after two exposures are completed. This mode can be applied to dynamic detection scenarios of high-speed moving objects. The modulated light flight time of the two exposures is calculated as:

[0091]

[0092]

[0093] The target object distance information of the two exposures is calculated as:

[0094]

[0095]

[0096] Where c is the speed of light.

[0097] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A driving method for a dual-shutter TOF image sensor pixel structure, characterized in that: The dual shutter TOF image sensor pixel structure comprises: The source of the reset transistor is connected to the negative pole of PD, the gate is connected to the RPD signal, and the drain is connected to the VDD signal; The pixel has two readout links, and the structures of the two readout links are symmetrically distributed with PD as the axis; Each readout link includes: The source of the first shutter transistor is connected to the negative electrode of PD, the gate is connected to the GS1 signal, and the drain is connected to the SD node; The source of the second shutter transistor is connected to the negative electrode of PD, the gate is connected to the GS2 signal, and the drain is connected to the FD node; The source of the transmission transistor is connected to the SD node, the gate is connected to the TX signal, and the drain is connected to the FD node; The source of the FD reset transistor is connected to the FD node, the gate is connected to the RFD signal, and the drain is connected to the VDD signal; The gate of the source follower transistor is connected to the FD node, the drain is connected to the VDD signal, and the source is connected to the source of the row selection transistor; The gate of the row selection transistor is connected to the RS signal, and the drain is connected to the first readout link column output output signal line; The driving method of the dual shutter TOF image sensor pixel structure includes a working sequence in a single shutter mode and a working sequence in a dual shutter mode; In single shutter mode, a square wave with a duty cycle of 1:4 is used to modulate the optical signal, and the shutter switch performs sampling at four moments: In the dual shutter mode, a square wave with a duty cycle of 1:2 is used to modulate the optical signal, and the shutter switch performs two-time sampling; The working sequence in the single shutter mode includes: Reset phase: The RPD signal, RFD signal and TX signal rise to high level, resetting the PD, FD and SD nodes respectively; After that, the RFD and TX signals drop to low level, and after the RPD signal drops to low level, the exposure starts; Assume that the modulation light cycle is T. In the exposure stage, the shutter signals of GS1, GS2, GS3, and GS4 sample the charge signal in the PD with a pulse width of T / 4 at the time of 0, T / 4, 2T / 4, and 3T / 4 respectively; Readout phase: When the RS signal is turned on, the photoelectron signal in the FD is sampled first. The signals sampled by the first readout link GS2 and the second readout link GS4 are recorded as Vsig2 and Vsig4 respectively. After that, the RFD pulse is turned on to reset the FD, and the reset signals sampled by the first readout link and the second readout link are Vrst1 and Vrst2 respectively; After that, the TX signal is turned on, and the optical signal stored in the SD node is transferred to the FD node. The signals sampled by the first readout link GS1 and the second readout link GS3 are recorded as Vsig1 and Vsig2 respectively; Finally, the signal outputs sampled by GS2 and GS4 are calculated as V2=Vrst1-Vsig2 and V4=Vrst2-Vsig4 respectively, which are the results of uncorrelated double sampling; the signal outputs sampled by GS1 and GS2 are calculated as V1=Vrst1-Vsig1 and V3=Vrst2-Vsig2 respectively, which are the results of correlated double sampling.

2. The driving method of the dual shutter TOF image sensor pixel structure according to claim 1, characterized in that: In the single shutter mode, readout is performed immediately after one exposure is completed, and high-distance range imaging is achieved by sampling a square wave pulse with a duty cycle of 1:4 at four moments; The modulated light flight time is calculated as: The target object distance information is calculated as: Where c is the speed of light.

3. The driving method of the dual shutter TOF image sensor pixel structure according to claim 2, characterized in that: The working sequence in the dual shutter mode includes: Reset phase: The RPD signal and the TX signal rise to a high level, resetting the PD and SD nodes respectively; After that, the RFD and TX signals drop to low level, and after the RPD signal drops to low level, the exposure starts. In the dual shutter mode, one frame of image completes two exposures. Assuming the modulation light cycle is T, in the first exposure stage, the GS1 and GS3 shutter signals sample the charge signal in the PD at time 0 and T / 2 respectively, with a pulse width of T / 2, and store the light signal in the SD node. After the first exposure is completed, the RPD signal and the RFD signal rise to a high level, respectively resetting the PD and FD nodes, and then RFD and RPD drop to a low level, and the second exposure begins; In the second exposure stage, the GS2 and GS4 shutter signals sample the charge signal in the PD at time 0 and T / 2 respectively with a pulse width of T / 2, and store the optical signal in the FD node; Readout phase: When the RS signal is turned on, the photoelectron signal in the FD is sampled first. The signals sampled by the first readout link GS2 and the second readout link GS4 are recorded as Vsig2 and Vsig4 respectively. After that, the RFD pulse is turned on to reset the FD, and the reset signals sampled by the first readout link and the second readout link are Vrst1 and Vrst2 respectively; After that, the TX signal is turned on, and the optical signal stored in the SD node is transferred to the FD node. The signals sampled by the first readout link GS1 and the second readout link GS3 are recorded as Vsig1 and Vsig2 respectively; Finally, the signal outputs sampled by GS2 and GS4 are calculated as V2=Vrst1-Vsig2 and V4=Vrst2-Vsig4 respectively, which are the results of uncorrelated double sampling; the signal outputs sampled by GS1 and GS2 are calculated as V1=Vrst1-Vsig1 and V3=Vrst2-Vsig2 respectively, which are the results of correlated double sampling.

4. The driving method of the dual shutter TOF image sensor pixel structure according to claim 3, characterized in that: In the double shutter mode, the readout is performed after two exposures are completed. This mode can be applied to dynamic detection scenarios of high-speed moving objects: The flight time of the modulated light for the two exposures is calculated as: The target object distance information of the two exposures is calculated as: Where c is the speed of light.

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