CN104135633A - Image sensor pixel with changeable conversion gain and working method thereof - Google Patents
Image sensor pixel with changeable conversion gain and working method thereof Download PDFInfo
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- CN104135633A CN104135633A CN201410422028.4A CN201410422028A CN104135633A CN 104135633 A CN104135633 A CN 104135633A CN 201410422028 A CN201410422028 A CN 201410422028A CN 104135633 A CN104135633 A CN 104135633A
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Abstract
The invention discloses an image sensor pixel with the changeable conversion gain and a working method thereof. The image sensor pixel comprises a first photodiode, a charge transmission transistor, a first reset transistor, a source following transistor, a selection transistor, a floating active area, a second photodiode, a second reset transistor, a capacitor and a switch transistor which are arranged in a semiconductor substrate. The drain electrode end of the switch transistor is connected with the floating active area, the source electrode end of the switch transistor is connected with one electrode end of the capacitor, the grid electrode end of the switch transistor is connected with the second photodiode, the other electrode end of the capacitor is connected with the floating active area, the source electrode end of the second reset transistor is connected with the second photodiode, and the drain electrode end of the second reset transistor is connected with a power source. The photovoltaic conversion gain for lowering the sensor pixel in the high illumination environment is used for achieving the purpose of delaying the pixel saturation time, the problem that in the prior art, real object information in the outdoor high illumination environment cannot be easily collected is solved, and the quality of images output by an image sensor is improved.
Description
Technical field
The present invention relates to a kind of image sensor pixel, relate in particular to a kind of image sensor pixel and method of work thereof of variable conversion gain.
Background technology
Imageing sensor has been widely used in digital camera, cell phone, medicine equipment, automobile and other application scenarios.Particularly manufacture the fast development of CMOS (CMOS (Complementary Metal Oxide Semiconductor)) image sensor technologies, make people have higher requirement to the output image quality of imageing sensor.
In the prior art, cmos image sensor generally adopts the dot structure of linear photoconductor response function.As shown in Figure 1, be cmos image sensor pixel, in the art also referred to as 4T (four transistors) active pixel.The components and parts of 4T active pixel comprise: photodiode 101, and charge pass transistor 102, reset transistor 103, transistor 104 and row selecting transistor 105 are followed in source, and row bit line 106; VTX is the gate terminal of transistor 102, and VRX is the gate terminal of transistor 103, and VSX is the gate terminal of transistor 105, and FD is floating active area, and Vdd is supply voltage.Photodiode 101 receives the light of extraneous incident, produces photosignal; Turn-on transistor 102, is transferred to the photosignal in photodiode behind FD district, and the FD potential well built-in potential variable signal being detected by transistor 104 reads and preserves through 106.Wherein, the photoelectricity quantity of electric charge in FD district is directly proportional to incident illumination amount, and the variation of the photoelectricity quantity of electric charge is detected and be converted to potential change by transistor 104 in FD potential well, and the amount that photoelectricity charge conversion is electromotive force is called opto-electronic conversion gain; When the photoelectricity quantity of electric charge changes, conversion gain remains unchanged, and the electric potential signal that transistor 104 detects in FD place is also proportional with the quantity of illumination.
The photoelectric respone of such imageing sensor is linear, is called as linear transducer in this area.In environment, linear transducer is difficult for collecting the information in kind of high lighting environment out of doors, thereby has reduced the output image quality of transducer.
Summary of the invention
The object of this invention is to provide a kind of output image quality is high, be applicable to the variable conversion gain of outdoor high lighting environment image sensor pixel and method of work thereof.
The object of the invention is to be achieved through the following technical solutions:
The image sensor pixel of variable conversion gain of the present invention, comprise that the first photodiode, charge pass transistor, the first reset transistor, the source that are placed in semiconductor substrate follow transistor, select transistor, floating active area, it is characterized in that, also comprise the second photodiode, the second reset transistor, electric capacity, the switching transistor that are placed in semiconductor substrate;
The drain electrode end of described switching transistor is connected with described floating active area, and source terminal is extremely connected with one of described electric capacity, and gate terminal is connected with described the second photodiode;
Another of described electric capacity is extremely connected with floating active area;
The source terminal of described the second reset transistor is connected with described the second photodiode, and drain electrode end is connected with power supply.
The method of work of the image sensor pixel of above-mentioned variable conversion gain of the present invention, comprises step:
A, pixel reset operation, do the operation of opening the first reset transistor, charge pass transistor, the second reset transistor, and the electric charge in the first photodiode, the second photodiode is removed;
Before b, pixel exposure finish, do the operation of a floating active area of reset, do the operation of opening the first reset transistor, the electric charge of floating active area is removed, be set to high potential;
After c, floating active area reset operation complete, do the reset signal operation of read pixel;
After the reset signal end of operation of d, read pixel, do the operation of opening charge pass transistor, the photoelectricity electric charge in the first photodiode is transferred to floating active area.
After photoelectricity electric charge in e, the first photodiode is transferred to floating active area, do the photosignal operation of read pixel.
As seen from the above technical solution provided by the invention, the image sensor pixel of the variable conversion gain that the embodiment of the present invention provides and method of work thereof, owing to having connected the second photodiode, the second reset transistor, electric capacity, switching transistor in floating active area, adopt the opto-electronic conversion of sensor pixel while reducing high lighting environment to gain to reach the object that postpones pixel saturation time, solve the information in kind that prior art is difficult for gathering outdoor high lighting environment, thereby promote the image quality of imageing sensor output.Be particularly suitable for outdoor high lighting environment.
Accompanying drawing explanation
Fig. 1 is the circuit diagram of the cmos image sensor pixel of prior art.
Fig. 2 is the circuit diagram of the image sensor pixel of the variable conversion gain that provides of the embodiment of the present invention.
Fig. 3 is the sequencing control schematic diagram of the image sensor pixel work of the variable conversion gain that provides of the embodiment of the present invention.
Fig. 4 is the circuit diagram of the image sensor pixel of the variable conversion gain that provides of the embodiment of the present invention while being operated in low light environment.
Fig. 5 is the circuit diagram of the image sensor pixel of the variable conversion gain that provides of the embodiment of the present invention while being operated in high light environment.
Fig. 6 is the potential well schematic diagram of the image sensor pixel work of the variable conversion gain that provides of the embodiment of the present invention.
Embodiment
To be described in further detail the embodiment of the present invention below.
The image sensor pixel of variable conversion gain of the present invention, its preferably embodiment be:
Comprise that the first photodiode, charge pass transistor, the first reset transistor, the source that are placed in semiconductor substrate follow transistor, select transistor, floating active area, also comprise the second photodiode, the second reset transistor, electric capacity, the switching transistor that are placed in semiconductor substrate;
The drain electrode end of described switching transistor is connected with described floating active area, and source terminal is extremely connected with one of described electric capacity, and gate terminal is connected with described the second photodiode;
Another of described electric capacity is extremely connected with floating active area;
The source terminal of described the second reset transistor is connected with described the second photodiode, and drain electrode end is connected with power supply.
Described the first photodiode is N-type photodiode, and described the second photodiode is N-type photodiode.
Described charge pass transistor, the first reset transistor, the second reset transistor, switching transistor, source are followed transistor and selected transistor is N-type transistor.
Described electric capacity is perhaps transistor capacitance of metal electric.
The threshold voltage of described the second reset transistor is-0.2V～0.3V.
The threshold voltage of described switching transistor is 0V～0.5V.
Described the second photodiode can not be completely depleted.
The capacitance of described electric capacity is 0.5fF～8fF.
The method of work of the image sensor pixel of above-mentioned variable conversion gain of the present invention, its preferably embodiment be:
Comprise step:
A, pixel reset operation, do the operation of opening the first reset transistor, charge pass transistor, the second reset transistor, and the electric charge in the first photodiode, the second photodiode is removed;
Before b, pixel exposure finish, do the operation of a floating active area of reset, do the operation of opening the first reset transistor, the electric charge of floating active area is removed, be set to high potential;
After c, floating active area reset operation complete, do the reset signal operation of read pixel;
After the reset signal end of operation of d, read pixel, do the operation of opening charge pass transistor, the photoelectricity electric charge in the first photodiode is transferred to floating active area.
After photoelectricity electric charge in e, the first photodiode is transferred to floating active area, do the photosignal operation of read pixel.
The image sensor pixel of variable conversion gain of the present invention and method of work thereof, adopt the opto-electronic conversion of sensor pixel while reducing high lighting environment to gain to reach the object that postpones pixel saturation time, solve the information in kind that prior art is difficult for gathering outdoor high lighting environment, thereby promote the image quality of imageing sensor output.Be particularly suitable for outdoor high lighting environment.
The present invention starts with from improving the photoelectric respone character of 4T pixel, luminous sensitivity while reducing high lighting environment, the saturation time that postpones pixel, to reach the object of the detailed information in kind of the how high illumination of transducer collection, thereby promotes the image quality that transducer is exported.When the low light level irradiates, switching transistor conducting, described electric capacity can not join floating active area, and the opto-electronic conversion gain of pixel is high; During strong illumination, switching transistor cuts out, and described electric capacity joins floating active area, and the opto-electronic conversion gain of pixel is low.The saturation time of imageing sensor while effectively having postponed high illumination, more detailed information in kind when transducer collects high illumination, has effectively promoted the image quality that imageing sensor is exported.
Specific embodiment:
On the basis of the image sensor pixel of prior art, special device architecture has been introduced in floating active area, as shown in Figure 2,101～106 image sensor pixel devices that are prior art, VTX, VRX, VSX are respectively 102,103,105 gate terminal; 201 is the second photodiode, and 202 is switching transistor, and 203 is electric capacity, and 204 is the second reset transistor, the gate terminal that PD is 202, and it is one extreme that CD is 203, and Vdd is power supply, the gate terminal that Vct is 204.As shown in Figure 2,201 charge-trapping end is connected with PD, and 204 source terminal is connected with PD, and 204 drain electrode end is connected with Vdd; 202 drain electrode end is connected with FD, and 202 source terminal is connected with CD; Another of 203 is extremely connected with FD.Wherein, 101 and 201 is N-type photodiode, and 102～105,202,204 is N-type transistor; 202 and 204 is low threshold transistor, threshold voltage 0V～0.5V of 202, and 204 threshold voltage is-0.2V～0.3V; Photodiode 101 can exhaust completely, but photodiode 201 can not be completely depleted, and the electromotive force of 201 charge collection region can reach 204 drain electrode end electromotive forces.Described electric capacity 203 can be transistor capacitance, can be also metal capacitance, and the scope of 203 capacitances is 0.5fF～8fF.
The sequencing control schematic diagram of cmos image sensor pixel of the present invention work, as shown in Figure 3.In Fig. 3, show respectively 102,103,204 transistor gate pole tension VTX, VRX, Vct sequencing control figure, SH sequential characterizes the operation of read signal.When described VRX, VTX, Vct are high level, represent to open the operation of respective transistor, during low level, represent to close respective transistor; SH represents the operation of read signal while being high level pulse.In order clearly to explain feature of the present invention, other sequential, as not shown in VSX sequential.
The method of work of pixel of the present invention is expressed as follows:
First, carry out pixel reset operation, do the operation 204 of opening the first reset transistor 103, charge pass transistor 102, the second reset transistor, the electric charge in the first photodiode 101, the second photodiode 201 is removed; As shown in Figure 3,301 for VRX is set to high level operation, opens 103 operation; 302 for VTX is set to high level operation, opens 102 operation; 303 for Vct is set to high level operation, opens 204 operation.
Further, before pixel exposure finishes, do the operation of a floating active area of reset, do the operation of opening the first reset transistor 103, the electric charge of floating active area is removed, be set to high potential; As shown in Figure 3,304 for VRX is set to high level operation, opens 103 operation.
Further, after floating active area reset operation completes, do the reset signal operation of read pixel; As shown in Figure 3,305 high level pulses represent the operation of read reset signal shr.
Further, after the reset signal end of operation of read pixel, do the operation of opening charge pass transistor 102, the photoelectricity electric charge in the first photodiode 101 is transferred to floating active area.As shown in Figure 3,306 for VTX is set to high level operation, opens 102 operation.
Further, after the photoelectricity electric charge in the first photodiode 101 is transferred to floating active area, do the photosignal operation of read pixel; As shown in Figure 3,307 high level pulses represent to read the operation of photosignal shs.
The true picture signal of described image sensor pixel is the difference signal of shs and shr signal.
In order more clearly to explain feature of the present invention, below in conjunction with the embodiment of the present invention, set forth the operation principle of pixel of the present invention.Pixel characteristic of the present invention is, reduces the opto-electronic conversion gain under high light environment, by adjusting the total capacitance value of floating active area, realize, below floating active area electric capacity situation when reading photosignal shs illustrate.Pixel of the present invention is operated under low light environment, and the electric charge that photodiode 201 is collected when end exposure is few, and connected 202 gate terminal electromotive forces are high, and 202 in opening, as shown in Figure 4.In Fig. 4, the state of 402 expressions 202 in opening, CD is communicated with FD, electric capacity 203 actual effects.Be pixel when being subject to the low light level and irradiating, the two poles of the earth of electric capacity 203 are all connected with FD, and now electric capacity 203 can not join the total capacitance of FD.
Pixel of the present invention is operated under high light environment, and the electric charge that photodiode 201 is collected when end exposure is many, and connected 202 gate terminal electromotive forces are low, and 202 in closed condition, as shown in Figure 5.In Fig. 5, the state of 502 expressions 202 in closing, CD is not communicated with FD, and electric capacity 203 is effective.Be pixel while being subject to strong illumination, one of electric capacity 203 is extremely connected with FD, and another extreme CD is independent and keep disconnecting with FD.Now, electric capacity 203 joins the total capacitance of FD.
The pixel operating state of above-mentioned Fig. 4 and Fig. 5, the electric capacity potential well situation of FD as shown in Figure 6.In Fig. 6,601 is the potential well of photodiode 101, and 602 is FD parasitic capacitance potential well, and 603 is the electric capacity potential well of electric capacity 203, and 102 in closed condition, the reset potential that Vreset is FD.The FD electric capacity of the pixel operating state shown in Fig. 4 is only 602 parts, and this electric capacity is Cfd, and now FD electric capacity is low, and the opto-electronic conversion gain of pixel is high, and luminous sensitivity is high; The Cfd that the FD electric capacity of the pixel operating state shown in Fig. 5 is 602 and 603 Ccap two-part and, FD electric capacity is now high, the gain of the opto-electronic conversion of pixel is low, luminous sensitivity is low.The photosensitive pixel signal that pixel of the present invention is expanded is 603 parts, and the semaphore of expansion is directly proportional to Ccap value, and this part signal has been expanded the sensitization dynamic range of pixel, and transducer has gathered the detailed information in kind of how high illumination.Therefore, pixel of the present invention has effectively promoted the image quality of transducer output.
The above; be only the present invention's embodiment preferably, but protection scope of the present invention is not limited to this, is anyly familiar with in technical scope that those skilled in the art disclose in the present invention; the variation that can expect easily or replacement, within all should being encompassed in protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.
Claims (9)
1. the image sensor pixel of a variable conversion gain, it is characterized in that, comprise that the first photodiode, charge pass transistor, the first reset transistor, the source that are placed in semiconductor substrate follow transistor, select transistor, floating active area, it is characterized in that, also comprise the second photodiode, the second reset transistor, electric capacity, the switching transistor that are placed in semiconductor substrate;
The drain electrode end of described switching transistor is connected with described floating active area, and source terminal is extremely connected with one of described electric capacity, and gate terminal is connected with described the second photodiode;
Another of described electric capacity is extremely connected with floating active area;
The source terminal of described the second reset transistor is connected with described the second photodiode, and drain electrode end is connected with power supply.
2. the image sensor pixel of variable conversion gain according to claim 1, is characterized in that, described the first photodiode is N-type photodiode, and described the second photodiode is N-type photodiode.
3. the image sensor pixel of variable conversion gain according to claim 1, it is characterized in that, described charge pass transistor, the first reset transistor, the second reset transistor, switching transistor, source are followed transistor and selected transistor is N-type transistor.
4. the image sensor pixel of variable conversion gain according to claim 1, is characterized in that, described electric capacity is perhaps transistor capacitance of metal electric.
5. the image sensor pixel of variable conversion gain according to claim 1, is characterized in that, the threshold voltage of described the second reset transistor is-0.2V～0.3V.
6. the image sensor pixel of variable conversion gain according to claim 1, is characterized in that, the threshold voltage of described switching transistor is 0V～0.5V.
7. the image sensor pixel of variable conversion gain according to claim 1, is characterized in that, described the second photodiode can not be completely depleted.
8. the image sensor pixel of variable conversion gain according to claim 1, is characterized in that, the capacitance of described electric capacity is 0.5fF～8fF.
9. a method of work for the image sensor pixel of the variable conversion gain described in claim 1 to 8 any one, is characterized in that, comprises step:
A, pixel reset operation, do the operation of opening the first reset transistor, charge pass transistor, the second reset transistor, and the electric charge in the first photodiode, the second photodiode is removed;
Before b, pixel exposure finish, do the operation of a floating active area of reset, do the operation of opening the first reset transistor, the electric charge of floating active area is removed, be set to high potential;
After c, floating active area reset operation complete, do the reset signal operation of read pixel;
After the reset signal end of operation of d, read pixel, do the operation of opening charge pass transistor, the photoelectricity electric charge in the first photodiode is transferred to floating active area.
After photoelectricity electric charge in e, the first photodiode is transferred to floating active area, do the photosignal operation of read pixel.
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| CN112399109A (en) * | 2019-08-15 | 2021-02-23 | 天津大学青岛海洋技术研究院 | Variable conversion gain low noise pixel structure |
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Application publication date: 20141105 |