CN112689105B - Low-power-consumption high-dynamic-range image sensor pixel structure and operation method - Google Patents
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Abstract
The invention discloses a low-power-consumption high-dynamic-range image sensor pixel structure and an operation method thereof, wherein the low-power-consumption high-dynamic-range image sensor pixel structure comprises a photodiode (1), a charge transfer transistor (2), a reset transistor (3), a source following transistor (4), a selection transistor (5), a sampling capacitor reset transistor (6), a mode control transistor (7), an extension capacitor C1 and a floating active region FD. The photodiode is connected to the FD through a charge transfer transistor; the drain electrode of the reset transistor is connected with the power line, and the source electrode of the reset transistor is connected with the FD; the grid of the source follower transistor is connected with the FD, the drain of the source follower transistor is connected with the power line, and the source of the source follower transistor is connected with the drain of the selection transistor; the extension capacitor C1 is connected to the FD via a mode control transistor; the drain of the sampling capacitor reset transistor is connected with the source of the selection transistor and the sampling capacitor C2 of the subsequent stage circuit. The invention reduces the power consumption of the image sensor, expands the dynamic range and can be used for monitoring equipment working for a long time in a complex environment.
Description
Technical Field
The invention belongs to the technical field of solid-state image sensors, and further relates to a pixel structure of an image sensor with low power consumption and high dynamic range and an operation method, which can be used for monitoring equipment working for a long time in a complex environment.
Background
An image sensor is a high-end technical element that converts an optical signal into an electrical signal using an optoelectronic device, and is widely used in the field of video monitoring. When the monitoring device operates for a long time in a complex environment, the image sensor is required to have low power consumption and high dynamic range. Currently, a 4-transistor image sensor pixel structure 4T-APS is commonly used in CMOS image sensors. As shown in fig. 1, the 4-tube image sensor pixel structure includes: a photodiode 1, a charge transfer transistor 2, a reset transistor 3, a source follower transistor 4, and a selection transistor 5; tx is the gate terminal of the charge transfer transistor 2, Reset is the gate terminal of the Reset transistor 3, Sel is the gate terminal of the select transistor 5, FD is the floating active region, VDD is the power supply line, Vout is the signal output terminal, ibias is the bias current source. The photodiode 1 receives light incident from the outside and generates photo-generated charges; after the charge transfer transistor is turned on to transfer photo-generated charges in the photodiode 1 to the floating active region FD, the change of the amount of charges in the floating active region FD is detected by the source follower transistor 4 and converted into a change of potential, which is read and stored through the signal output terminal Vout. The photo-generated charge in the photodiode 1 is in direct proportion to the incident light quantity, the change of the charge quantity in the floating active region FD is detected by the source follower transistor 4 and converted into a potential change, and the potential change is in direct proportion to the incident light quantity. Because the amount of photo-charge that can be stored in the floating active region FD of this structure is small, and the source follower transistor 4 is biased by the constant current source ibias, this pixel structure has the disadvantages of small dynamic range and large power consumption, and is difficult to meet the requirement of long-time operation of the monitoring device in a complex environment.
In a patent document "high dynamic range image sensor pixel structure and its operation method" (application No. 201410797654.1, application publication No. CN 104469195 a, published as 2014.12.18) filed by beijing abriko microelectronics technologies, ltd., a high dynamic range image sensor structure is disclosed, which includes a photodiode, a reset transistor, a source follower transistor, a selection transistor, a floating active region, a first charge transfer transistor, a second charge transfer transistor, a third charge transfer transistor, and a transistor capacitance device interposed between the second charge transfer transistor and the third charge transfer transistor. The pixel adopts a double-exposure mode to collect photoelectric signals, photo-generated charges collected in a first long-time exposure mode are transferred to a transistor capacitor device to be stored, photo-generated charges collected in a second short-time exposure mode and photo-generated charges stored in the transistor capacitor device are transferred to a floating active region together, and then photoelectric signal reading operation is carried out. The structure has the following disadvantages: the dynamic range is increased, and simultaneously, the structure of a single pixel is complicated, the area of the pixel is increased, and the power consumption is also increased.
Disclosure of Invention
The present invention is directed to an image sensor pixel structure with low power consumption and high dynamic range and an operating method thereof, which are provided to increase the dynamic range of the pixel and reduce the power consumption of the pixel.
The technical scheme for realizing the purpose of the invention is as follows:
1. an image sensor pixel structure with low power consumption and high dynamic range comprises a charge transfer transistor 2, a reset transistor 3, a source follower transistor 4, a selection transistor 5, a floating active region FD and a photodiode 1 arranged in a semiconductor substrate, and is characterized by further comprising a sampling capacitor reset transistor 6, a mode control transistor 7 and an extension capacitor C1;
the drain electrode of the sampling capacitor reset transistor 6 is connected with the source electrode of the selection transistor 5 and the sampling capacitor C2 of the rear-stage circuit, and the source electrode of the sampling capacitor reset transistor is connected with the ground and used for emptying the rear-stage sampling capacitor C2;
the mode control transistor 7 has a drain connected to the floating active region FD and a source connected to an extension capacitor C1 for controlling an operation mode of the image sensor pixel, and the other end of the extension capacitor C1 is connected to ground.
Further, it is characterized in that the positive electrode of the photodiode 1 is connected to the ground, and the negative electrode is connected to the source of the charge transfer transistor 2; the drain of the charge transfer transistor 2 is connected to the floating active region FD; the drain of the reset transistor 3 is connected to the power supply line VDD, and the source is connected to the floating active region FD; the source follower transistor 4 has a gate connected to the floating active region, a drain connected to the power supply line VDD, and a source connected to the drain of the selection transistor 5.
2. An operating method for the pixel structure of the image sensor is characterized by comprising the following steps:
1) operation mode selection operation of the image sensor: when the illumination intensity of the current use environment is greater than 100Lux, the mode control transistor 7 is switched on, and the image sensor enters a strong light working mode, otherwise, the image sensor enters a weak light working mode;
2) floating active region FD reset operation: when the reset transistor 3 is switched on, the electric potential of the floating active region FD is pulled high, and the reset transistor 3 is switched off after the reset is finished;
3) reset voltage sampling operation: turning on the selection transistor 5, sampling the voltage value of the reset state of the output end by using a sampling capacitor C2 of a post-stage circuit, and turning off the selection transistor 5 after sampling is finished;
4) the sampling capacitor C2 of the latter stage circuit resets: turning on the sampling capacitor reset transistor 6 to empty the sampling capacitor C2 of the subsequent stage circuit, and turning off the sampling capacitor reset transistor 6;
5) photo-generated charge transfer operation: turning on the charge transfer transistor 2, transferring photo-generated charges accumulated in the photodiode 1 to the floating active region FD, and turning off the charge transfer transistor 2 after the photo-generated charges are transferred;
6) signal voltage sampling operation: the selection transistor 5 is turned on, the sampling capacitor C2 of the post-stage circuit is used for sampling the voltage value of the output end after the photo-generated charge is transferred, and the selection transistor 5 is turned off after the sampling is finished;
7) the sampling capacitor C2 of the latter stage circuit resets: the sampling capacitor reset transistor 6 is turned on to empty the sampling capacitor C2 of the subsequent stage circuit, and the sampling capacitor reset transistor 6 is turned off.
Compared with the prior art, the invention has the following advantages:
first, the constant current source in the pixel structure of the existing 4-transistor image sensor is replaced by the sampling capacitor reset transistor, so that the source follower transistor is switched from being always on to being only on during sampling operation, and the power consumption of the pixel circuit is reduced.
Secondly, the invention adds the mode control transistor and the extension capacitor on the basis of the pixel structure of the existing 4-tube image sensor, and controls the on and off of the mode transistor through the illumination intensity, thereby expanding the dynamic range of the image sensor.
Drawings
FIG. 1 is a diagram of a pixel structure of a 4-transistor conventional image sensor;
FIG. 2 is a block diagram of an image sensor pixel according to the present invention;
FIG. 3 is a flow chart illustrating an implementation of the operation of the pixel structure of the image sensor according to the present invention;
FIG. 4 is a timing diagram illustrating the timing of the pixel structure of the image sensor under different illumination conditions;
FIG. 5 is a diagram of a power consumption simulation result of a conventional 4-transistor image sensor pixel circuit and the present invention;
fig. 6 shows the simulation result of the relationship between the dynamic range and the expansion capacitance C1 of the present invention.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
Embodiments of the present invention are described in detail below with reference to the accompanying drawings.
Referring to fig. 2, the image sensor pixel structure of the present invention includes 6 transistors, a photodiode 1, an extension capacitor C1, and a floating active region FD. Wherein the photodiode 1 is arranged in the semiconductor substrate, the anode thereof is connected with the ground wire, and the cathode thereof is connected with the source electrode of the charge transmission transistor 2; the drain of the charge transfer transistor 2 is connected to the floating active region FD; the drain of the reset transistor 3 is connected to the power supply line VDD, and the source is connected to the floating active region FD; the grid electrode of the source following transistor 4 is connected with the floating active region, the drain electrode is connected with a power line VDD, and the source electrode is connected with the drain electrode of the selection transistor 5; the selection transistor 5 is turned on after completion of pixel reset and completion of charge transfer to detect a change in the amount of charge in the floating active region FD, and its source is connected to the drain of the sampling capacitor reset transistor 6 and the sampling capacitor C2 of the subsequent stage circuit; the sampling capacitor reset transistor 6 is conducted after the sampling of the sampling capacitor C2 of the rear-stage circuit is finished, so that the sampling capacitor C2 of the rear-stage circuit is emptied, and the source electrode of the sampling capacitor reset transistor is connected with the ground wire; the mode control transistor 7 is controlled to be turned on and off by the intensity of illumination, the drain thereof is connected to the floating active region FD, and the source thereof is connected to one end of the extension capacitor C1; the other end of the extension capacitor C1 is connected to ground.
In fig. 2, Tx is a gate terminal of the charge transfer transistor 2, Reset is a gate terminal of the Reset transistor 3, Sel is a gate terminal of the selection transistor 5, Rst is a gate terminal of the sampling capacitor Reset transistor 6, DCG is a gate terminal of the mode control transistor 7, Vout is a signal output terminal, C2 is a sampling capacitor of the subsequent stage circuit, and VDD is a power supply line.
Referring to fig. 3 and 4, the operation of the image sensor pixel structure of the present example is as follows:
The working mode of the image sensor is determined by the illumination intensity of the current use environment:
if the illumination intensity of the current using environment is greater than 100Lux, connecting a grid end DCG of the mode control transistor 7 with a power supply voltage, and switching on the mode control transistor 7, so that the ground capacitance of the floating active region FD is increased, more photo-generated electrons can be stored, and the image sensor enters a strong light working mode;
if the current using environment illumination intensity is less than or equal to 100Lux, the gate terminal DCG of the mode control transistor 7 is grounded, the mode control transistor 7 is turned off, and the image sensor enters the low-light operation mode.
The gate terminal Reset of the Reset transistor 3 is connected to the power supply voltage, so that the Reset transistor 3 is turned on, the potential of the floating active region FD is pulled high, and the gate terminal Reset of the Reset transistor 3 is grounded after the Reset is completed, so that the Reset transistor 3 is turned off.
And 3, carrying out reset voltage sampling operation.
The gate terminal Sel of the selection transistor 5 is connected to the power supply voltage, so that the selection transistor 5 is turned on, the voltage value of the reset state of the output terminal Vout is sampled by the sampling capacitor C2 of the subsequent stage circuit, and the gate terminal Sel of the selection transistor 5 is grounded after the sampling is completed, so that the selection transistor 5 is turned off.
And 4, resetting the sampling capacitor C2 of the rear-stage circuit.
And connecting the gate terminal Rst of the sampling capacitor reset transistor 6 with the power supply voltage, so that the sampling capacitor reset transistor 6 is switched on, emptying the sampling capacitor C2 of the later-stage circuit, and grounding the gate terminal of the sampling capacitor reset transistor 6 after the sampling capacitor C2 of the later-stage circuit is emptied, so that the sampling capacitor reset transistor 6 is switched off.
And 5, carrying out photo-generated charge transfer operation.
The gate terminal Tx of the charge transfer transistor 2 is connected to a power supply voltage to turn on the charge transfer transistor 2, the photo-generated charge accumulated in the photodiode 1 is transferred to the floating active region FD, and after the transfer of the photo-generated charge is completed, the gate terminal Tx of the charge transfer transistor 2 is grounded to turn off the charge transfer transistor 2.
And 6, performing signal voltage sampling operation.
The gate terminal Sel of the selection transistor 5 is connected to the power supply voltage so that the selection transistor 5 is turned on, the voltage value of the output terminal Vout after the photo-electric charge transfer is sampled by the sampling capacitor C2 of the subsequent stage circuit, and the gate terminal Sel of the selection transistor 5 is grounded after the sampling is completed so that the selection transistor 5 is turned off.
And 7, resetting the sampling capacitor C2 of the rear-stage circuit.
And connecting the gate terminal Rst of the sampling capacitor reset transistor 6 with the power supply voltage, so that the sampling capacitor reset transistor 6 is switched on, emptying the sampling capacitor C2 of the later-stage circuit, and grounding the gate terminal of the sampling capacitor reset transistor 6 after the sampling capacitor C2 of the later-stage circuit is emptied, so that the sampling capacitor reset transistor 6 is switched off.
The effects of the present invention can be further explained by the following simulation results.
Firstly, simulation conditions:
the simulation experiment in the invention adopts TSMC 0.18um process conditions, and the pixel circuit of the existing 4-tube image sensor and the pixel circuit of the image sensor in the invention are respectively built based on Cadence simulation software. The bias current source ibias in the pixel circuit of the 4-transistor image sensor is 0.5 uA.
Second, simulation content and results:
Claims (5)
1. An image sensor pixel structure with low power consumption and high dynamic range comprises a charge transfer transistor (2), a reset transistor (3), a source follower transistor (4), a selection transistor (5), a floating active region (FD), and a photodiode (1) arranged in a semiconductor substrate, and is characterized by further comprising a sampling capacitor reset transistor (6), a mode control transistor (7), and an extension capacitor C1;
the drain electrode of the sampling capacitor reset transistor (6) is connected with the source electrode of the selection transistor (5) and the sampling capacitor C2 of the rear-stage circuit, and the source electrode of the sampling capacitor reset transistor is connected with the ground and used for emptying the rear-stage sampling capacitor C2;
the mode control transistor (7) is connected with the floating active region FD at the drain electrode and the expansion capacitor C1 at the source electrode, and is used for controlling the working mode of the image sensor pixel, and the other end of the expansion capacitor C1 is connected with the ground;
the structure completes the operations comprising:
operation mode selection operation of the image sensor: when the current using environment illumination intensity is greater than 100Lux, the mode control transistor (7) is switched on, the image sensor enters a strong light working mode, when the environment illumination intensity is less than or equal to 100Lux, the grid terminal DCG of the mode control transistor (7) is grounded, the mode control transistor (7) is switched off, and the image sensor enters a weak light working mode;
floating active region FD reset operation: when the reset transistor (3) is conducted, the potential of the floating active region FD is pulled high, and the reset transistor (3) is turned off after the reset is finished;
reset voltage sampling operation: the selection transistor (5) is turned on, the voltage value of the reset state of the output end is sampled by using a sampling capacitor C2 of a post-stage circuit, and the selection transistor (5) is turned off after the sampling is finished;
the sampling capacitor C2 of the latter stage circuit resets: turning on a sampling capacitor reset transistor (6) to empty a sampling capacitor C2 of a later-stage circuit, and turning off the sampling capacitor reset transistor (6);
photo-generated charge transfer operation: turning on the charge transfer transistor (2), transferring photo-generated charges accumulated in the photodiode (1) to the floating active region FD, and turning off the charge transfer transistor (2) after the photo-generated charges are transferred;
signal voltage sampling operation: the selection transistor (5) is turned on, the sampling capacitor C2 of the post-stage circuit is used for sampling the voltage value of the output end after the photo-generated charges are transferred, and the selection transistor (5) is turned off after the sampling is finished;
the sampling capacitor C2 of the latter stage circuit resets: and (3) opening the sampling capacitor reset transistor (6) to empty the sampling capacitor C2 of the subsequent stage circuit, and then turning off the sampling capacitor reset transistor (6).
2. A structure as claimed in claim 1, characterized in that the photodiode (1) has its anode connected to ground and its cathode connected to the source of the charge transfer transistor (2); the drain of the charge transfer transistor (2) is connected to the floating active region FD; the drain electrode of the reset transistor (3) is connected with a power line, and the source electrode is connected with the floating active region FD; the gate of the source follower transistor (4) is connected to the floating active region, the drain is connected to the power supply line, and the source is connected to the drain of the selection transistor (5).
3. A structure as claimed in claim 1, characterized in that the selection transistor (5) is turned on after the pixel reset is completed and the charge transfer is finished to detect a change in the amount of charge in the floating active region FD.
4. The structure of claim 1, characterized in that the sampling capacitor reset transistor (6) is turned on after the sampling of the sampling capacitor C2 of the subsequent circuit is finished to clear the sampling capacitor C2 of the subsequent circuit.
5. The structure according to claim 1, characterized in that the mode control transistor (7) is controlled to be turned on and off by the intensity of the light.
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| US10313613B2 (en) * | 2017-10-24 | 2019-06-04 | Semiconductor Components Industries, Llc | High dynamic range image sensors with flicker and fixed pattern noise mitigation |
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| CN111033193A (en) * | 2017-08-17 | 2020-04-17 | 脸谱科技有限责任公司 | Detecting high intensity light in a photosensor |
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