WO2021184934A1 - 图像感测装置 - Google Patents

图像感测装置 Download PDF

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Publication number
WO2021184934A1
WO2021184934A1 PCT/CN2021/070762 CN2021070762W WO2021184934A1 WO 2021184934 A1 WO2021184934 A1 WO 2021184934A1 CN 2021070762 W CN2021070762 W CN 2021070762W WO 2021184934 A1 WO2021184934 A1 WO 2021184934A1
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WIPO (PCT)
Prior art keywords
signal
coupled
operational amplifier
voltage
switch
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PCT/CN2021/070762
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English (en)
French (fr)
Inventor
林郁轩
彭子洋
王仲益
洪自立
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神盾股份有限公司
神亚科技股份有限公司
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Priority to US17/908,528 priority Critical patent/US20230123651A1/en
Publication of WO2021184934A1 publication Critical patent/WO2021184934A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/50—Control of the SSIS exposure
    • H04N25/57—Control of the dynamic range
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H04N25/78—Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/50—Control of the SSIS exposure
    • H04N25/57—Control of the dynamic range
    • H04N25/59—Control of the dynamic range by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
    • H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
    • H03F3/087—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light with IC amplifier blocks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
    • H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/50—Analogue/digital converters with intermediate conversion to time interval
    • H03M1/52—Input signal integrated with linear return to datum

Definitions

  • the invention relates to a sensing device, in particular to an image sensing device.
  • a common image sensing device may include a sensing pixel array composed of a plurality of sensing pixels. Each sensing pixel converts incident light into a sensing signal. By analyzing the sensing signal provided by each sensing pixel, it can be obtained The image sensed by the image sensing device. Furthermore, each sensing pixel may include a photodiode, which converts light into an electrical signal. The continuous exposure of the photodiode will cause the voltage value of the sensing signal output by the sensing pixel to continue to decrease. The provided voltage value of the sensing signal can obtain the image sensed by the image sensing device.
  • the size of the sensing pixel will be increased as much as possible to increase the charge generated by the sensing pixel after light exposure, so that there will still be a certain amount of charge under low illumination.
  • increasing the size of the sensing pixel will increase the parasitic capacitance on the sensing pixel, and the capacitive element in the subsequent circuit must be correspondingly increased. Capacitance to prevent the output signal of the subsequent circuit from exceeding the acceptable dynamic range based on the sensing signal.
  • Increasing the capacitance of the capacitive element in the subsequent circuit can solve the problem that the output signal exceeds the acceptable dynamic range.
  • the output voltage of the subsequent circuit will be excessive. Small problems that are not conducive to signal analysis.
  • the invention provides an image sensing device, which can effectively improve the image sensing quality.
  • the image sensing device of the present invention includes a light sensing unit, an amplifying circuit, an analog-to-digital conversion circuit, an input adjustment circuit, and a control circuit.
  • the light sensing unit receives a light signal including image information to generate a sensing signal.
  • the amplifying circuit is coupled to the light sensing unit and amplifies the sensing signal to generate an amplified signal.
  • the amplifying circuit includes a capacitor and an operational amplifier.
  • the negative input terminal of the operational amplifier is coupled to the light sensing unit, the positive input terminal of the operational amplifier is coupled to the first reference voltage, and the capacitor is coupled between the negative input terminal and the output terminal of the operational amplifier.
  • the analog-digital conversion circuit is coupled to the output terminal of the operational amplifier, and converts the sensing signal into a digital signal.
  • the input adjustment circuit is coupled to the negative input terminal of the operational amplifier.
  • the control circuit is coupled to the analog-digital conversion circuit and the input adjustment circuit, determines the voltage change rate of the sensing signal according to the voltage value of the sensing signal during the estimation period, and controls the input adjustment circuit during the exposure period according to the voltage change rate to provide the input adjustment signal to
  • the negative input terminal of the operational amplifier makes the signal value of the amplified signal fall within the preset range during the exposure period.
  • the embodiment of the present invention determines the voltage change rate of the sensing signal according to the voltage value of the sensing signal generated by the light sensing unit during an estimation period, and controls the input adjustment circuit to provide input adjustment during the exposure period according to the voltage change rate.
  • the signal is sent to the negative input terminal of the operational amplifier, so that the signal value of the amplified signal falls within the preset range during the exposure period. In this way, the signal value of the sensing signal can be prevented from being too large, so that the analog-to-digital conversion circuit cannot read the sensing signal correctly due to insufficient dynamic range, and therefore, the image sensing quality can be effectively and greatly improved.
  • Fig. 1 is a schematic diagram of an image sensing device according to an embodiment of the present invention.
  • FIG. 2 is a schematic diagram of an image sensing device according to another embodiment of the invention.
  • FIG. 3 is a schematic diagram of waveforms of a selection control signal, a reset signal, and a sensing signal according to an embodiment of the present invention
  • FIG. 4 is a schematic diagram of an image sensing device according to another embodiment of the present invention.
  • FIG. 5 is a schematic diagram of an image sensing device according to another embodiment of the present invention.
  • FIG. 6 is a schematic diagram of an image sensing device according to another embodiment of the present invention.
  • FIG. 7 is a schematic diagram of waveforms of a selection control signal, a reset signal, and a sensing signal according to another embodiment of the present invention.
  • FIG. 1 is a schematic diagram of an image sensing device according to an embodiment of the present invention, please refer to FIG. 1.
  • the image sensing device may include a light sensing unit 102, an amplifying circuit 104, an analog to digital converter (ADC) 106, an input adjustment circuit 108, and a control circuit 110.
  • the amplifying circuit 104 is coupled to the light sensing unit 102,
  • the control circuit 110 is coupled to the analog-digital conversion circuit 106 and the input adjustment circuit 108.
  • the image sensing device may be, for example, a fingerprint sensor or an X-ray flat panel sensor, but it is not limited thereto.
  • the amplifying circuit 104 includes an operational amplifier A1 and a capacitor C1.
  • the negative input terminal of the operational amplifier A1 is coupled to the light sensing unit 102 and the input adjustment circuit 108, the positive input terminal of the operational amplifier A1 is coupled to the reference voltage VCM, and the operational amplifier
  • the output terminal of A1 is coupled to the analog-to-digital conversion circuit 106, and the capacitor C1 is coupled between the negative input terminal and the output terminal of the operational amplifier A1.
  • the light sensing unit 102 may receive a light signal including image information to generate a sensing signal, wherein as the exposure period of the light sensing unit 102 becomes longer, the voltage value of the sensing signal will correspondingly decrease.
  • the amplifying circuit 104 can amplify the sensing signal to generate an amplified signal to the analog-to-digital conversion circuit 106, and the analog-to-digital conversion circuit 106 can convert the amplified signal into a digital signal and output it to the control circuit 110 for image analysis processing.
  • the control circuit 110 may be, for example, a digital signal processing circuit, but it is not limited thereto.
  • control circuit 110 can learn the signal value of the sensing signal, such as the voltage value of the sensing signal, and the change during the exposure period of the light sensing unit 102 according to the digital signal.
  • the exposure period of the light sensing unit 102 may include an estimation period, and the control circuit 110 may determine the voltage change rate of the sensing signal according to the voltage value of the sensing signal during the estimation period, and then estimate the sensing signal at the end of the exposure period The degree of decrease of the voltage value.
  • the control circuit 110 determines that the voltage value of the sensing signal at the end of the exposure period will cause the signal value of the amplified signal provided by the amplifying circuit 104 to exceed the dynamic range of the analog-to-digital conversion circuit 106, the control circuit 110 can rely on the voltage of the sensing signal During the exposure period of the sensing unit 102, the input adjustment circuit 108 is controlled to provide an input adjustment signal to the negative input terminal of the operational amplifier A1 to change the difference between the positive input terminal and the negative input terminal of the operational amplifier A1.
  • the signal value of the amplified signal provided by the amplifying circuit 104 is adjusted to fall within a preset range without exceeding the dynamic range of the analog-to-digital conversion circuit 106, wherein the preset range is less than or equal to the analog range.
  • the dynamic range of the digital conversion circuit 106 In this way, the signal value of the sensing signal can be prevented from being too large, so that the analog-to-digital conversion circuit 106 cannot read the sensing signal correctly due to the insufficient dynamic range, so that the image sensing quality can be effectively and greatly improved.
  • FIG. 2 is a schematic diagram of an image sensing device according to another embodiment of the invention.
  • the light sensing unit 102 may include a selection switch M1, a photoelectric conversion unit D1, and a parasitic capacitor CS.
  • One end of the selection switch M1 is coupled to the negative input terminal of the budget amplifier A1, and the photoelectric conversion unit D1 is coupled to the selection switch M1.
  • the image sensing device of this embodiment further includes a reset switch SW1, and the reset switch SW1 and the capacitor C1 are connected in parallel between the negative input terminal and the output terminal of the operational amplifier A1.
  • the photoelectric conversion unit D1 can convert an optical signal into an electrical signal (sensing signal).
  • the selection switch M1 and the reset switch SW1 are controlled by the selection control signal SELX and the reset signal RST to enter the conduction during the reset period T1 and reset signal RST, respectively.
  • the voltage VX will be reset to have the same voltage value as the reference voltage VCM at this time.
  • the selection switch M1 and the reset switch SW1 are controlled by the selection control signal SELX and the reset signal RST to enter the off state.
  • the voltage VX on the photoelectric conversion unit D1 will gradually decrease as the exposure time of the photoelectric conversion unit D1 becomes longer.
  • the selection switch M1 is controlled by the selection control signal SELX to enter the on state.
  • the output voltage of the operational amplifier A1 will be equal to the voltage difference dV between the reference voltage VCM and the voltage VX multiplied by the gain value of the operational amplifier A1.
  • the selector switch M1 first enters the conductive state through the control signal SELX during the estimation period, wherein the estimation period TE
  • the estimation period TE may have the same time length as the output period T3, but it is not limited thereto.
  • the amplifying circuit 104 can perform analog-to-digital conversion to the analog-digital conversion circuit 106 according to the reference voltage VCM and the voltage VX output voltage, so that the control circuit 110 knows the voltage change rate of the voltage VX during the estimation period TE. In this way, the control circuit 110 can estimate the drop degree of the voltage VX at the end of the exposure period T2 (for example, the voltage difference dV) according to the voltage change rate of the voltage VX during the estimation period TE.
  • control circuit 110 determines that the voltage difference dV will exceed the dynamic range of the analog-to-digital conversion circuit 106 after being amplified by the amplifying circuit 104, the control circuit 110 can control the input during the exposure period T2 according to the voltage change rate of the voltage VX during the estimation period TE
  • the adjustment circuit 108 provides an input adjustment signal to the negative input terminal of the operational amplifier A1 to adjust the voltage value of the voltage VX so that the voltage VX can meet the dynamic range requirement of the analog-to-digital conversion circuit 106 at the end of the exposure period T2.
  • the voltage VX decreases from the voltage difference dV to dV' at the end of the exposure period T2 (as shown by the dotted line), which can effectively avoid the output of the operational amplifier A1
  • the voltage exceeds the dynamic range of the analog-to-digital conversion circuit 106.
  • the estimation period TE is included in the exposure period T2, but the time length, start point and end point of the estimation period TE are not limited to the embodiment in FIG. 3, and can be designed according to actual conditions.
  • FIG. 4 is a schematic diagram of an image sensing device according to another embodiment of the invention.
  • the input adjustment circuit 108 can be implemented by the current source I1, and the control circuit 110 can control the input adjustment circuit 108 to provide the input adjustment current I1 during the exposure period T2 according to the voltage change rate of the voltage VX during the estimation period TE.
  • the control circuit 110 can control the input adjustment circuit 108 to provide the input adjustment current I1 during the exposure period T2 according to the voltage change rate of the voltage VX during the estimation period TE.
  • the input adjustment signal is not limited to the current signal.
  • the input adjustment circuit 108 may include switches SW2, SW3, and a capacitor C2, wherein one end of the capacitor C2 is coupled On the negative input terminal of the operational amplifier A1, the switch SW2 is coupled between the reference voltage VDAC and the other end of the capacitor C2, and the switch SW3 is coupled between the common connection point of the switch SW2 and the capacitor C2 and ground.
  • the control circuit 110 can output the switch signals ck1 and ck2 to turn on the switches SW2 and SW3 alternately during the exposure period T2 according to the voltage change rate of the voltage VX during the estimation period TE, that is, when the switch SW2 is in the on state , The switch SW3 will be in the off state, and when the switch SW2 is in the off state, the switch SW3 will be in the on state.
  • the input adjustment circuit 108 can generate an input adjustment voltage to the negative input terminal of the operational amplifier A1, thereby adjusting the voltage value of the voltage VX.
  • FIG. 6 is a schematic diagram of an image sensing device according to another embodiment of the invention.
  • the light sensing unit 102 may include a reset switch SW4, a selection switch M1, a transistor M2, a photoelectric conversion unit D1, a parasitic capacitance CS, and a current source I2, wherein one end of the reset switch SW4 is coupled to the reset voltage VRST, the photoelectric conversion unit D1 is coupled between the reset switch SW4 and the ground, and the parasitic capacitance CS is generated between the common contact point of the photoelectric conversion unit D1 and the reset switch SW4 and the ground.
  • the selection switch M1 is coupled between the common contact of the photoelectric conversion unit D1 and the reset switch SW4 and the gate of the transistor M2.
  • One end of the transistor M2 is coupled to the power supply voltage VDD, and the current source I2 is coupled to the other end of the transistor M2 and the ground. between.
  • the reset switch SW4 is controlled by the reset signal SR1 and is turned on, while the selection switch M1 is controlled by the selection control signal SELX and is turned off.
  • the voltage VX will be reset to have the same voltage value as the reset voltage VRST.
  • the reset switch SW1 is controlled by the reset signal RST to enter the off state.
  • the voltage VX on the photoelectric conversion unit D1 will decrease as the exposure time of the photoelectric conversion unit D1 becomes longer.
  • the selection switch M1 is controlled by the selection control signal SELX to enter the on state, and the source follower composed of the transistor M2 and the current source I2 can output the voltage VS to the negative input terminal of the operational amplifier A1 according to the voltage VX.
  • the output voltage of the operational amplifier A1 is equal to the voltage difference dV between the reference voltage VCM and the voltage VS multiplied by the gain value of the operational amplifier A1.
  • the TE can first use the control signal SELX to make the selector switch M1 into the conducting state during the estimation period.
  • the amplifying circuit 104 can perform analog-to-digital conversion to the analog-digital conversion circuit 106 according to the reference voltage VCM and the voltage VS output voltage, so that the control circuit 110 knows the voltage change rate of the voltage VS during the estimation period TE.
  • the control circuit 110 can estimate the drop degree of the voltage VS at the end of the exposure period T2 (for example, the voltage difference dV) according to the voltage change rate of the voltage VS during the estimation period TE.
  • control circuit 110 determines that the voltage difference dV will exceed the dynamic range of the analog-to-digital conversion circuit 106 after being amplified by the amplifying circuit 104, the control circuit 110 can control the voltage change rate of the voltage VS during the estimation period TE during the exposure period T2.
  • the input adjustment circuit 108 provides an input adjustment signal to the negative input terminal of the operational amplifier A1 to adjust the voltage value of the voltage VS so that the voltage VS can meet the dynamic range requirement of the analog-to-digital conversion circuit 106 at the end of the exposure period T2. As shown in FIG.
  • the embodiment of the present invention determines the voltage change rate of the sensing signal according to the voltage value of the sensing signal generated by the light sensing unit during an estimation period, and controls the input adjustment during the exposure period according to the voltage change rate.
  • the circuit provides an input adjustment signal to the negative input terminal of the operational amplifier, so that the signal value of the amplified signal falls within a predetermined range during the exposure period. In this way, the signal value of the sensing signal can be prevented from being too large, so that the analog-to-digital conversion circuit cannot read the sensing signal correctly due to insufficient dynamic range, and therefore, the image sensing quality can be effectively and greatly improved.

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  • Signal Processing (AREA)
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Abstract

本发明提供一种图像感测装置。控制电路依据估测期间内光感测单元所产生的感测信号的电压值确定感测信号的电压变化速率，并依据电压变化速率于曝光期间控制输入调整电路提供输入调整信号至运算放大器的负输入端，以使放大信号的信号值于曝光期间落于预设范围内。

Description

图像感测装置 技术领域
本发明涉及一种感测装置，尤其涉及一种图像感测装置。
背景技术
常见的图像感测装置可包括由多个感测像素构成的感测像素阵列，各个感测像素将入射光转换为感测信号，通过分析各个感测像素所提供的感测信号，即可获得图像感测装置所感测到的图像。进一步来说，各个感测像素可包括光电二极管，其将光转换为电信号，光电二极管的持续曝光将造成感测像素输出的感测信号的电压值持续下降，通过读取各个感测像素所提供的感测信号的电压值即可获得图像感测装置所感测到的图像。
一般而言，为了提高图像感测装置的灵敏度，会尽量提高感测像素的尺寸，以增加感测像素感光后所产生的电荷，如此在低照度下仍会有一定的电荷数。如此虽可有效提高图像感测装置的灵敏度，然由于增加感测像素的尺寸将使得感测像素上的寄生电容也随之变大，而使得后级电路中的电容元件也必须对应地提高其电容量，以避免后级电路依据感测信号输出的信号超出可接受的动态范围。增大后级电路中的电容元件的电容量虽可解决输出信号超出可接受的动态范围的问题，然在感测像素处于低照度的环境时，又会产生后级电路所输出的电压值过小不利于信号解析的问题。
发明内容
本发明提供一种图像感测装置，可有效提高图像感测质量。
本发明的图像感测装置包括光感测单元、放大电路、模拟数字转换电路、输入调整电路以及控制电路。光感测单元接收包括图像信息的光信号，而产生感测信号。放大电路耦接光感测单元，放大感测信号以产生放大信号。放大电路包括电容以及运算放大器。运算放大器的负输入端耦接光感测单元，运算放大器的正输入端耦接第一参考电压，电容耦接于运算放大器的负输入端与输出端之间。模拟数字转换电路耦接运算放大器的输出端，将感测信号 转换为数字信号。输入调整电路耦接运算放大器的负输入端。控制电路耦接模拟数字转换电路与输入调整电路，依据估测期间内的感测信号的电压值确定感测信号的电压变化速率，依据电压变化速率于曝光期间控制输入调整电路提供输入调整信号至运算放大器的负输入端，使放大信号的信号值于曝光期间落于预设范围内。
基于上述，本发明实施例依据一估测期间内光感测单元所产生的感测信号的电压值确定感测信号的电压变化速率，并依据电压变化速率于曝光期间控制输入调整电路提供输入调整信号至运算放大器的负输入端，以使放大信号的信号值于曝光期间落于预设范围内。如此可避免感测信号的信号值过大，使得模拟数字转换电路因动态范围不足而无法正确读取感测信号，因此可有效大幅地提高图像感测质量。
为让本发明的上述特征和优点能更明显易懂，下文特举实施例，并配合附图作详细说明如下。
附图说明
图1是依照本发明的实施例的一种图像感测装置的示意图；
图2是依照本发明另一实施例的一种图像感测装置的示意图；
图3是依照本发明的实施例的选择控制信号、重置信号与感测信号的波形示意图；
图4是依照本发明另一实施例的一种图像感测装置的示意；
图5是依照本发明另一实施例的一种图像感测装置的示意图；
图6是依照本发明另一实施例的一种图像感测装置的示意图；
图7是依照本发明另一实施例的选择控制信号、重置信号与感测信号的波形示意图。
具体实施方式
图1是依照本发明的实施例的一种图像感测装置的示意图，请参照图1。图像感测装置可包括光感测单元102、放大电路104、模拟数字转换电路(Analog to Digital Converter,ADC)106、输入调整电路108以及控制电路110，放大电路104耦接光感测单元102、模拟数字转换电路106以及输入调整电 路108，控制电路110耦接模拟数字转换电路106与输入调整电路108。在一实施例中，图像感测装置可例如为指纹传感器或X光平板传感器，然不以此为限。进一步来说，放大电路104包括运算放大器A1与电容C1，运算放大器A1的负输入端耦接光感测单元102与输入调整电路108，运算放大器A1的正输入端耦接参考电压VCM，运算放大器A1的输出端耦接模拟数字转换电路106，电容C1耦接于运算放大器A1的负输入端与输出端之间。
光感测单元102可接收包括图像信息的光信号而产生感测信号，其中，随着光感测单元102的曝光期间变长，感测信号的电压值将对应地下降。放大电路104可放大感测信号而产生一放大信号至模拟数字转换电路106，模拟数字转换电路106则可将放大信号转换为数字信号后输出给控制电路110以进行图像分析处理。在一实施例中，控制电路110可例如数字信号处理电路，然不以此为限。此外，控制电路110可依据数字信号得知感测信号的信号值，例如感测信号的电压值，在光感测单元102的曝光期间的变化情形。其中光感测单元102的曝光期间可包括估测期间，控制电路110可依据估测期间内感测信号的电压值确定感测信号的电压变化速率，进而估测在曝光期间结束时感测信号的电压值的下降程度。
当控制电路110判断在曝光期间结束时感测信号的电压值将使得放大电路104所提供的放大信号的信号值超出模拟数字转换电路106的动态范围时，控制电路110可依据感测信号的电压变化速率，于感测单元102的曝光期间内控制输入调整电路108提供输入调整信号至运算放大器A1的负输入端，以改变运算放大器A1的正输入端与负输入端间的差值，进而在光感测单元102的曝光期间内，使放大电路104提供的放大信号的信号值被调整至落于预设范围内，而不超出模拟数字转换电路106的动态范围，其中预设范围小于等于模拟数字转换电路106的动态范围。如此可避免感测信号的信号值过大，使得模拟数字转换电路106因动态范围不足，而无法正确读取感测信号，因此可有效大幅地提高图像感测质量。
图2是依照本发明另一实施例的一种图像感测装置的示意图。在本实施例中，光感测单元102可包括选择开关M1、光电转换单元D1以及寄生电容CS，其中选择开关M1的一端耦接预算放大器A1的负输入端，光电转换单元D1耦接于选择开关M1的另一端与电压VBIAS之间，而寄生电容CS产 生于光电转换单元D1与选择开关M1的共同接点与电压VBIAS之间，其中电压VBIAS可例如为接地电压，光电转换单元D1可例如为光电二极管，而选择开关M1可例如以晶体管实施，然不以此为限。此外，本实施例的图像感测装置还包括重置开关SW1，重置开关SW1与电容C1并联于运算放大器A1的负输入端与输出端之间。
光电转换单元D1可将光信号转换为电信号(感测信号)。如图3所示，在光感测单元102被选择而输出感测信号前，选择开关M1在重置期间T1与重置开关SW1分别受控于选择控制信号SELX与重置信号RST而进入导通状态，此时电压VX将被重置为与参考电压VCM具有相同的电压值。而后，在曝光期间T2，选择开关M1与重置开关SW1分别受控于选择控制信号SELX与重置信号RST而进入断开状态。在曝光期间T2，光电转换单元D1上的电压VX将随着光电转换单元D1的曝光时间拉长而逐渐下降。在输出期间T3，选择开关M1受控于选择控制信号SELX进入导通状态，此时运算放大器A1的输出电压将等于参考电压VCM与电压VX的电压差值dV乘以运算放大器A1的增益值。
为避免运算放大器A1的输出电压超出后级之模拟数字转换电路106的动态范围，在一实施例中，选择开关M1于估测期间TE先通过控制信号SELX进入导通状态，其中估测期间TE可例如与输出期间T3具有相同的时间长度，然不以此为限。在估测期间TE，放大电路104可依据参考电压VCM与电压VX输出电压给模拟数字转换电路106进行模拟数字转换，而使控制电路110得知电压VX在估测期间TE的电压变化速率。如此，控制电路110可依据电压VX在估测期间TE的电压变化速率估测出电压VX在曝光期间T2结束时的下降程度(例如电压差值dV)。
若控制电路110判断电压差值dV经由放大电路104放大后将超出模拟数字转换电路106的动态范围，控制电路110可依据电压VX在估测期间TE的电压变化速率，在曝光期间T2内控制输入调整电路108提供输入调整信号至运算放大器A1的负输入端，以调整电压VX的电压值，使电压VX在曝光期间T2结束时可符合模拟数字转换电路106的动态范围需求。如图3所示，经由输入调整电路108的调整，电压VX在曝光期间T2结束时的下降程度由电压差值dV减小为dV’(如虚线所示)，可有效避免运算放大器A1的输出电 压超出模拟数字转换电路106的动态范围。值得注意的是，估测期间TE被包含于曝光期间T2内，然估测期间TE的时间长度、起点以及终点并不限定于图3实施例，而可依据实际情形设计。
图4是依照本发明另一实施例的一种图像感测装置的示意图。在本实施例中，输入调整电路108可由电流源I1来实施，控制电路110可依据电压VX在估测期间TE的电压变化速率，在曝光期间T2内，控制输入调整电路108提供输入调整电流I1至运算放大器A1的负输入端，以调整电压VX的电压值。
值得注意的是，输入调整信号并不以电流信号为限，如图5所示，在图5实施例中，输入调整电路108可包括开关SW2、SW3以及电容C2，其中电容C2的一端耦接运算放大器A1的负输入端，开关SW2耦接于参考电压VDAC与电容C2的另一端之间，开关SW3耦接于开关SW2与电容C2的共同接点与接地之间。控制电路110可依据电压VX在估测期间TE的电压变化速率，在曝光期间T2内，输出开关信号ck1与ck2使开关SW2与SW3交替地导通，亦即，当开关SW2处于导通状态时，开关SW3将处于断开状态，而当开关SW2处于断开状态时，开关SW3将处于导通状态。如此交替地导通开关SW2与SW3，可使输入调整电路108产生输入调整电压至运算放大器A1的负输入端，进而调整电压VX的电压值。
图6是依照本发明另一实施例的一种图像感测装置的示意图。在本实施例中，光感测单元102可包括重置开关SW4、选择开关M1、晶体管M2、光电转换单元D1、寄生电容CS以及电流源I2，其中重置开关SW4的一端耦接重置电压VRST，光电转换单元D1耦接于重置开关SW4与接地之间，寄生电容CS产生于光电转换单元D1与重置开关SW4的共同接点与接地之间。选择开关M1耦接于光电转换单元D1与重置开关SW4的共同接点与晶体管M2的栅极之间，晶体管M2的一端耦接电源电压VDD，电流源I2耦接晶体管M2的另一端与接地之间。
如图7所示，在重置期间T1，重置开关SW4受控于重置信号SR1而处于导通状态，而选择开关M1则受控于选择控制信号SELX而处于断开的状态，此时电压VX将被重置为与重置电压VRST具有相同的电压值。在曝光期间T2，重置开关SW1受控于重置信号RST而进入断开状态。在曝光期间 T2，光电转换单元D1上的电压VX将随着光电转换单元D1的曝光时间拉长而下降。在输出期间T3，选择开关M1受控于选择控制信号SELX进入导通状态，晶体管M2与电流源I2组成的源极随耦器可依据电压VX输出电压VS至运算放大器A1的负输入端。运算放大器A1的输出电压等于参考电压VCM与电压VS的电压差值dV乘以运算放大器A1的增益值。
类似于图2实施例，为避免运算放大器A1的输出电压超出后级的模拟数字转换电路106的动态范围，可于估测期间TE先通过控制信号SELX使选择开关M1进入导通状态，在估测期间TE，放大电路104可依据参考电压VCM与电压VS输出电压给模拟数字转换电路106进行模拟数字转换，而使控制电路110得知电压VS在估测期间TE的电压变化速率。如此，控制电路110可依据电压VS在估测期间TE的电压变化速率估测出电压VS在曝光期间T2结束时的下降程度(例如电压差值dV)。
若控制电路110判断电压差值dV经由放大电路104放大后将超出模拟数字转换电路106的动态范围，控制电路110可依据电压VS在估测期间TE的电压变化速率，在曝光期间T2内，控制输入调整电路108提供输入调整信号至运算放大器A1的负输入端，以调整电压VS的电压值，使电压VS在曝光期间T2结束时可符合模拟数字转换电路106的动态范围需求。如图7所示，经由输入调整电路108的调整，电压VS在曝光期间T2结束时的下降程度由电压差值dV减小为dV’(如虚线所示)，而可有效避免运算放大器A1的输出电压超出模拟数字转换电路106的动态范围。
综上所述，本发明实施例依据一估测期间内光感测单元所产生的感测信号的电压值确定感测信号的电压变化速率，并依据电压变化速率，于曝光期间内控制输入调整电路提供输入调整信号至运算放大器的负输入端，以使放大信号的信号值于曝光期间落于预设范围内。如此可避免感测信号的信号值过大，使得模拟数字转换电路因动态范围不足而无法正确读取感测信号，因此可有效大幅地提高图像感测质量。
虽然本发明已以实施例揭示如上，然其并非用以限定本发明，任何所属技术领域中技术人员，在不脱离本发明的精神和范围内，当可作些许的更改与润饰，故本发明的保护范围当视权利要求所界定的为准。

Claims (10)

  1. 一种图像感测装置，包括：
    光感测单元，接收包括图像信息的光信号，而产生感测信号；
    放大电路，耦接所述光感测单元，放大所述感测信号以产生放大信号，包括：
    电容；以及
    运算放大器，其负输入端耦接所述光感测单元，所述运算放大器的正输入端耦接第一参考电压，所述电容耦接于所述运算放大器的负输入端与输出端之间；
    模拟数字转换电路，耦接所述运算放大器的输出端，将所述感测信号转换为数字信号；
    输入调整电路，耦接所述运算放大器的负输入端；以及
    控制电路，耦接所述模拟数字转换电路与所述输入调整电路，依据估测期间内的所述感测信号的电压值确定所述感测信号的电压变化速率，依据所述电压变化速率于曝光期间控制所述输入调整电路提供输入调整信号至所述运算放大器的负输入端，使所述放大信号的信号值于所述曝光期间落于预设范围内。
  2. 根据权利要求1所述的图像感测装置，其特征在于，所述光感测单元包括：
    选择开关，其一端耦接所述运算放大器的负输入端；
    光电转换单元，耦接于所述选择开关的另一端与接地之间，将所述光信号转换为电信号而产生所述感测信号；以及
    寄生电容，产生于所述光电转换单元与所述选择开关的共同接点与所述接地之间，所述光感测单元于所述共同接点上产生所述感测信号。
  3. 根据权利要求2所述的图像感测装置，其特征在于，还包括：
    重置开关，与所述电容并联于所述运算放大器的负输入端与输出端之间，于重置期间，所述选择开关与所述重置开关为导通状态，于所述曝光期间，所述选择开关与所述重置开关为断开状态，于所述估测期间以及输出期间，所述选择开关为导通状态，所述重置开关为断开状态。
  4. 根据权利要求3所述的图像感测装置，其特征在于，所述估测期间与 所述输出期间具有相同的时间长度。
  5. 根据权利要求1所述的图像感测装置，其特征在于，所述输入调整电路包括：
    电流源，耦接所述控制电路与所述运算放大器的负输入端，所述控制电路依据所述感测信号的电压变化速率于所述曝光期间控制所述电流源提供输入调整电流至所述运算放大器的负输入端。
  6. 根据权利要求1所述的图像感测装置，其特征在于，所述输入调整电路包括：
    电容，其一端耦接所述运算放大器的负输入端；
    第一开关，耦接于所述电容的另一端与第二参考电压之间；以及
    第二开关，耦接于所述电容的另一端与接地之间，所述控制电路依据所述感测信号的电压变化速率于所述曝光期间控制所述第一开关与所述第二开关交替地导通，以提供输入调整电压至所述运算放大器的负输入端。
  7. 根据权利要求1所述的图像感测装置，其特征在于，所述光感测单元包括：
    重置开关，其第一端耦接重置电压；
    选择开关，其第一端耦接所述重置开关的第二端；
    光电转换单元，耦接于所述选择开关的第一端与接地之间，将所述光信号转换为电信号而产生所述感测信号；
    寄生电容，产生于所述光电转换单元与所述选择开关的共同接点与所述接地之间，所述光感测单元于所述光电转换单元与所述选择开关的共同接点上产生所述感测信号；
    晶体管，其第一端耦接电源电压，所述晶体管的第二端耦接所述运算放大器的负输入端，所述晶体管的控制端耦接所述选择开关的第二端；以及
    电流源，耦接于所述晶体管的第二端与接地之间，于重置期间，所述重置开关为导通状态，所述选择开关为断开状态，于所述曝光期间，所述重置开关与所述选择开关为断开状态，于所述估测期间以及输出期间，所述选择开关为导通状态，所述重置开关为断开状态。
  8. 根据权利要求1所述的图像感测装置，其特征在于，所述估测期间与所述输出期间具有相同的时间长度。
  9. 根据权利要求1所述的图像感测装置，其特征在于，所述曝光期间包括所述估测期间。
  10. 根据权利要求1所述的图像感测装置，其特征在于，所述预设范围小于等于所述模拟数字转换电路的动态范围。
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