US20080030606A1

US20080030606A1 - Sensor Apparatus

Info

Publication number: US20080030606A1
Application number: US11/596,069
Authority: US
Inventors: Seiichiro Mizuno; Haruhiro Funakoshi
Original assignee: Hamamatsu Photonics KK
Current assignee: Hamamatsu Photonics KK
Priority date: 2004-05-10
Filing date: 2005-05-02
Publication date: 2008-02-07
Also published as: EP2037675B1; US20110149134A1; DE602005018355D1; US20100308795A1; EP2037675A1; JP4429796B2; US8379128B2; EP1758376A1; EP1758376A4; EP1758376B1; JP2005323210A; US7956917B2; WO2005109864A1

Abstract

The present invention relates to a sensor apparatus having a structure capable of obtaining digital values of signal components with a high accuracy using an A/D conversing circuit with the outputted digital value thereof having a small number of expressive bits. In the sensor apparatus, a voltage value corresponding to the amount of incident light to a photodiode is held by a holding circuit through an integrating circuit and a CDS circuit. Meanwhile, a voltage value corresponding to the amount of incident light to an adjacent photodiode is held by another holding circuit through an integrating circuit and a CDS circuit. The voltage values held by the respective different holding circuits are inputted to a subtracting circuit through different paths. The subtracting circuit outputs a voltage value corresponding to the difference between the two inputted voltage values. In an A/D converting section, the difference voltage outputted from the subtracting circuit is converted into a digital value.

Description

TECHNICAL FIELD

The present invention relates to a sensor apparatus including a plurality of sensor elements.

BACKGROUND ART

In sensor apparatuses including a plurality of sensor elements, voltage values corresponding to the detection result of the amount of sensing by the respective sensor elements are outputted from a signal processing circuit, and further digital values corresponding to the voltage values are outputted from an A/D conversing circuit. Then, one- or two-dimensional distribution of the amount of sensing (e.g. light intensity, temperature, displacement) is obtained based on the digital values corresponding to the amount of sensing for the respective sensor elements. As an example of such a sensor apparatus, there can be cited an image pickup apparatus including a plurality of photodiodes that are arranged one- or two-dimensionally (refer to Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. H9-51476

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

The inventors have studied conventional sensor apparatuses in detail, and as a result, have found problems as follows. That is, the amount of sensing detected by such a sensor apparatus as described above may include not only a signal component that is supposed to be detected but also a noise component (disturbing light component, background light component) that is superimposed on the signal component. When the noise component (disturbing light component, background light component) is significantly indefinite, the A/D conversing circuit requires 10-bit outputted digital values for inputted voltage values with noise components (disturbing light components, background light components) superimposed on signal components, though 8-bit outputted digital values would suffice for, for example, inputted voltage values including signal components only, to A/D-convert the signal components with an accuracy equivalent to the 8-bit case.
When the outputted digital value of the A/D conversing circuit has a large number of bits, the A/D conversing circuit results in a long conversion time, large power consumption, and large circuit scale. It is generally necessary to A/D-convert the detection result of the amount of sensing by all sensor elements within a certain time period, which may require parallel processing using a plurality of A/D conversing circuits, resulting in a larger power consumption and larger circuit scale.
In order to overcome the above-mentioned problems, it is an object of the present invention to provide a sensor apparatus capable of obtaining digital values of signal components with a high accuracy, even in the case of the amount of sensing with noise components (disturbing light components, background light components) superimposed on the signal components, using an A/D conversing circuit with the outputted digital value thereof having a small number of bits.

Means for Solving Problem

A sensor apparatus according to the present invention comprises a sensor array section, a difference operating section, and an A/D converting section. In a first aspect of the sensor apparatus, the sensor array section includes N sensor elements (N represents an integer of 2 or more) and outputs a voltage value V_nin response to the result of sensing by the n-th sensor element (“n” represents any integer of 1 or more but N or less) among the N sensor elements. The difference operating section receives N voltage values V₁to V_Noutputted from the sensor array section and outputs a voltage value U_n(n≠1) corresponding to the difference (V_n−V_n-1) between voltage values V_nand V_n-1. The A/D converting section receives the voltage value U_noutputted from the difference operating section, converts the voltage value U_ninto a digital value, and then outputs the converted digital value.
In the sensor apparatus according to the above-described first aspect, the A/D converting section may converts at least one voltage value among the N voltage values V₁to V_Ninto a digital value, and then outputs the converted digital value.
Also, in a second aspect of the sensor apparatus, the difference operating section may receives N voltage values V₁to V_Noutputted from the sensor array section and outputs a voltage value W_ncorresponding to the difference (V_n−V_n0) between a specific voltage value V_n0and the voltage value V_namong the N voltage values V₁to V_N. In this case, the A/D converting section receives the voltage value W_noutputted from the difference operating section, converts the voltage value W_ninto a digital value, and then outputs the converted digital value.
In the sensor apparatus according to the above-described second aspect, the A/D converting section may converts the specific voltage value V_n0into a digital value, and then outputs the converted digital value.
The sensor apparatus according to the present invention preferably further includes a holding section that receives the N voltage values V₁to V_Noutputted from the sensor array section and once holds the N voltage values V₁to V_N. In this case, the difference operating section outputs the voltage value U_nor W_nbased on the N voltage values V₁to V_Nheld by the holding section.
In the sensor apparatus according to the present invention, each of the N sensor elements preferably includes a photodiode. In this case, the one- or two-dimensional intensity distribution of incident light can be detected. Also, even when the intensity of incident light may include signal components and noise components (disturbing light components, background light components) and the noise components (disturbing light components, background light components) may be significantly indefinite, it is possible to obtain digital values of the signal components with a high accuracy using an A/D conversing circuit with the outputted digital value thereof having a small number of bits.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.

EFFECT OF THE INVENTION

In accordance with the sensor apparatus according to the present invention, it is possible to obtain digital values of signal components with a high accuracy, even in the case of the amount of sensing with noise components (disturbing light components, background light components) superimposed on the signal components, using an A/D conversing circuit with the outputted digital value thereof having a small number of bits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the overall configuration of a sensor apparatus according to a first embodiment of the present invention;
FIG. 2 is a circuit diagram including a photodiode PD_n, an integrating circuit 11 _n, a CDS circuit 12 _n, and a holding circuit 21 _nin the sensor apparatus according to the first embodiment;
FIG. 3 is a timing chart for explaining the operation of a difference operating section and an A/D converting section in the sensor apparatus according to the first embodiment;
FIG. 4 is a view showing the intensity distribution of light to be detected by the sensor apparatus according to the first embodiment;
FIG. 5 is a view showing the overall configuration of a sensor apparatus according to a second embodiment of the present invention; and
FIG. 6 is a circuit diagram of an APS circuit included in each pixel, showing the partial configuration of a sensor apparatus according to a modified example of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

- 1, 2 . . . sensor apparatuses; 10 . . . sensor array section; 11 . . . integrating circuit; 12 . . . CDS circuit; 20 . . . holding section; 30, 30A . . . difference operating sections; 33 . . . subtracting circuit; and 40 . . . A/D converting section.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, embodiments of a sensor apparatus according to the present invention will be explained in detail with reference to FIGS. 1 to 6. In the explanation of the drawings, constituents identical to each other will be referred to with numerals identical to each other without repeating their overlapping descriptions.

First Embodiment

First, a sensor apparatus according to a first embodiment of the present invention will be explained. FIG. 1 is a view showing the overall configuration of the sensor apparatus according to the first embodiment of the present invention. The sensor apparatus 1 shown in FIG. 1 comprises a sensor array section 10, a holding section 20, a difference operating section 30, and an A/D converting section 40.
The sensor array section 10 includes N photodiodes PD₁to PD_N, N integrating circuits 11 ₁to 11 _N, and N CDS circuits 12 ₁to 12 _N. Also, the holding section 20 includes N holding circuits 21 ₁to 21 _N. Each of the photodiodes PD₁to PD_Nhas a common composition, each of the integrating circuits 11 ₁to 11 _Nalso has a common composition, each of the CDS circuits 12 ₁to 12 _Nalso has a common composition, and each of the holding circuits 21 ₁to 21 _Nalso has a common composition. The N photodiodes PD₁to PD_Nare arranged one-dimensionally. The n-th integrating circuit 11 _n, n-th CDS circuit 12 _n, and n-th holding circuit 21 _nare provided correspondingly to the n-th photodiode PD_n. Here, N represents an integer of 2 or more. Also, “n” represents any integer of 1 or more but N or less, unless otherwise specified.
The photodiode PD_ngenerates electric charges corresponding to the amount of incident light and outputs the electric charges to the integrating circuit 11 _n. Each integrating circuit 11 _naccumulates the electric charges outputted from the photodiode PD_ninto a capacitive element and outputs a voltage value corresponding to the amount of accumulated charge to the CDS circuit 12 _n. The CDS circuit 12 _nreceives the voltage value outputted from the integrating circuit 11 _nand outputs a voltage value corresponding to the change of the inputted voltage value after a reference time based on the inputted voltage value at the reference time to the holding circuit 21 _n. That is, the sensor array section 10 includes the N photodiodes PD₁to PD_Nas sensor elements and outputs a voltage value corresponding to the detection result of light by the photodiode PD_n. The holding circuit 21 _nreceives the voltage value outputted from the CDS circuit 12 _nand outputs the voltage value V_nheld therein.
The difference operating section 30 includes switches SW_31,1to SW_31,N, switches SW_32,0to SW_32,N-1, and a subtracting circuit 33. The output terminal of the holding circuit 21 _nis connected to a wiring L1 via the switch SW_31,nand to a wiring L2 via the switch SW_32,n. However, the output terminal of the N-th holding circuit 21 _Nis connected to the wiring L1 via the switch SW_31,Nbut may not be connected to the wiring L2 via a switch. Also, the wiring L2 is connected with the ground potential via the switch SW_32,0. The switches SW_31,nand SW_32,n-1open and close based on the level of a control signal S_n. The subtracting circuit 33 outputs a voltage value corresponding to the difference between voltage values to be inputted through the respective wirings L1 and L2.
The A/D converting section 40 is used together with switches SW₄₁and SW₄₂. The A/D converting section 40 receives one of a voltage value V_FS1to be inputted via the switch SW₄₁and a voltage value V_FS2to be inputted via the switch SW₄₂as a full scale in A/D conversion. Then, the A/D converting section 40 converts the voltage value outputted from the subtracting circuit 33 into a digital value at a resolution of one 2^M-th of the full scale (voltage value V_FS1or V_FS2), and then outputs the converted digital value. It is noted that M represents the number of bits of the outputted digital value. It is preferable that the voltage value V_FS1is greater than V_FS2and the ratio therebetween be a power of two. The switch SW₄₁opens and closes based on the level of a control signal Sel1, while the switch SW₄₂opens and closes based on the level of a control signal Sel2.
FIG. 2 is a circuit diagram including a photodiode PD_n, an integrating circuit 11 _n, a CDS circuit 12 _n, and a holding circuit 21 _nin the sensor apparatus 1 according to the first embodiment. The anode terminal of the photodiode PD_nis grounded, while the cathode terminal thereof is connected to the input terminal of the integrating circuit 11 _n, and the photodiode PD_ngenerates electric charges corresponding to the amount of incident light and outputs the electric charges to the integrating circuit 11 _n.
The integrating circuit 11 _nincludes an amplifier A₁₁, a capacitive element C₁₁, and a switch SW₁₁. The input terminal of the amplifier A₁₁is connected to the cathode terminal of the photodiode PD_n. The capacitive element C₁₁and switch SW₁₁are provided between the input and output terminals of the amplifier A₁₁by being connected parallel with each other. The outputted voltage value of the integrating circuit 11 _nis initialized by closing the switch SW₁₁so that the capacitive element C₁₁is discharged. The integrating circuit 11 _nalso accumulates electric charges outputted from the photodiode PD_ninto the capacitive element C₁₁when the switch SW₁₁is opened, and then outputs a voltage value corresponding to the amount of accumulated charge to the CDS circuit 12 _n.
The CDS circuit 12 _nincludes an amplifier A₁₂, a capacitive element C₁₂, and a switch SW₁₂. The input terminal of the amplifier A₁₂is connected to the amplifier A₁₁in the integrating circuit 11 _nvia the capacitive element C₁₂and is grounded via the switch SW₁₂. The CDS circuit 12 _nreceives the voltage value outputted from the integrating circuit 11 _nand outputs a voltage value corresponding to the change of the inputted voltage value after a reference time (when the switch SW₁₂is opened) based on the inputted voltage value at the reference time from the amplifier A₁₂to the holding circuit 21 _n.
The holding circuit 21 _nincludes an amplifier A₂₁, a capacitive element C₂₁, and a switch SW₂₁. The input terminal of the amplifier A₂₁is connected to the amplifier A₁₂in the CDS circuit 12 _nvia the switch SW₂₁and is grounded via the capacitive element C₂₁. The output terminal of the amplifier A₂₁is connected to the wiring L1 via the switch SW_31,nand to the wiring L2 via the switch SW_32,n. The holding circuit 21 _nholds the voltage value, which is outputted from the CDS circuit 12 _nat a time when the switch SW₂₁is opened, in the capacitive element C₂₁also after the time of the state variation, and then outputs a voltage value V_ncorresponding to the held voltage value from the amplifier A₂₁.
The operation of the photodiode PD_n, integrating circuit 11 _n, CDS circuit 12 _n, and holding circuit 21 _nis as follows.
That is, when the switch SW₁₁in the integrating circuit 11 _nis opened, electric charges outputted from the photodiode PD_nare accumulated into the capacitive element C₁₁, and then a voltage value corresponding to the amount of accumulated charge is outputted from the integrating circuit 11 _n. As the amount of charge accumulated in the capacitive element C₁₁increases gradually, the voltage value outputted from the integrating circuit 11 _nvaries. While the switch SW₁₁in the integrating circuit 11 _nis opened, the switch SW₁₂in the CDS circuit 12 _nis opened at a first time, and then the switch SW₂₁in the holding circuit 21 _nis opened at a second time. The voltage value outputted from the CDS circuit 12 _nafter the first time corresponds to the change of the voltage value outputted from the integrating circuit 11 _nbased on the voltage value outputted from the integrating circuit 11 _nat the first time. Then, the voltage value V_nheld by the holding circuit 21 _nafter the second time corresponds to the voltage value outputted from the CDS circuit 12 _nat the second time.
That is, the voltage value V_nheld by the holding circuit 21 _nafter the second time corresponds to the difference between the voltage values outputted from the integrating circuit 11 _nat the first and second time, and when the time difference between the first and second time is constant, corresponds to the intensity of light incident to the photodiode PD_n. It is noted that the N integrating circuits 11 ₁to 11 _Noperate at the same timing; the N CDS circuits 12 ₁to 12 _Nalso operate at the same timing; and the N holding circuits 21 ₁to 21 _Nalso operate at the same timing. Therefore, a voltage value V_ncorresponding to the amount of incident light to the photodiode PD_nduring a common period of time is to be held by the holding section 20.
Next, the operation of the difference operating section 30 and the A/D converting section 40 in the sensor apparatus 1 according to the first embodiment will be explained. FIG. 3 is a timing chart for explaining the operation of the difference operating section 30 and the A/D converting section 40 in the sensor apparatus 1 according to the first embodiment. FIG. 3 shows a timing chart when the difference operating section 30 and A/D converting section 40 process voltage values V₁to V_Nare held by the holding section 20 as described above. It is noted that not only the above-described operation of the sensor array section 10 and holding section 20 but also the operation of the difference operating section 30 and A/D converting section 40 to be explained hereinafter is performed based on various control signals outputted from a control section (not shown in the figures). FIG. 3 shows the level of each control signal S_nto be inputted to the difference operating section 30, the level of a control signal Sel1 for instructing the switch SW₄₁to open and close, and the level of a control signal Sel2 for instructing the switch SW₄₂to open and close in this order from the top.
As shown in FIG. 3, the control signals S₁to S_Nare made high sequentially. During the time period T_nfrom time t_n,1to time t_n,2, only the control signal S_nis made high among the control signals S₁to S_N. During the time period T₁, the control signal Sel1 is made high, while the control signal Sel2 is made low. Also, from the time period T₂through the time period T_N, the control signal Sel1 is made low, while the control signal Sel2 is made high.
During the time period T₁from time t_1,1to time t_1,2, only the control signal S₁is made high among the control signals S₁to S_N, so that the switches SW_31,1and SW_32,0in the difference operating section 30 are closed. Also, the control signal Sel1 is made high, so that the switch SW₄₁is closed. When the switch SW_31,1is closed, the voltage value V₁held by the holding circuit 21 ₁is inputted to the subtracting circuit 33 through the switch SW_31,1and the wiring L1. Also, when the switch SW_32,0is closed, the ground potential is inputted to the subtracting circuit 33 through the switch SW_32,0and the wiring L2. In the subtracting circuit 33, the ground potential is subtracted from the voltage value V₁, and the subtracted voltage value V₁is outputted. Then, in the A/D converting section 40, the voltage value V₁outputted from the subtracting circuit 33 is converted into an M-bit digital value using the voltage value V_FS1inputted through the switch SW₄₁as a full scale.
During the time period T_nfrom time t_n,1to time t_n,2(n≠1), only the control signal S_nis made high among the control signals S₁to S_N, so that the switches SW_31,nand SW_32,n-1in the difference operating section 30 are closed. Also, the control signal Sel2 is made high, so that the switch SW₄₂is closed. When the switch SW_31,nis closed, the voltage value V_nheld by the holding circuit 21 _nis inputted to the subtracting circuit 33 through the switch SW_31,nand the wiring L1. Also, when the switch SW_32,n-1is closed, the voltage value V_n-1held by the holding circuit 21 _n-1is inputted to the subtracting circuit 33 through the switch SW_32,n-1and the wiring L2. In the subtracting circuit 33, the voltage value V_n-1is subtracted from the voltage value V_n, and a voltage value U_ncorresponding to the subtraction result is outputted. Then, in the A/D converting section 40, the voltage value U_noutputted from the subtracting circuit 33 is converted into an M-bit digital value using the voltage value V_FS2inputted through the switch SW₄₂as a full scale.
That is, during the time period T₁, the A/D converting section 40 converts the voltage value V₁corresponding to the amount of incident light to the first photodiode PD₁into an M-bit digital value using the voltage value V_FS1as a full scale. Also, during each time period T_n(n≠1), the difference operating section 30 calculates a voltage value U_naccording to the difference (V_n−V_n-1) between voltage values V_nand V_n-1that correspond to the amount of incident light to the respective photodiodes PD_nand PD_n-1, and then the A/D converting section 40 converts the voltage value U_ninto an M-bit digital value using the voltage value V_FS2as a full scale.
Therefore, as shown in FIG. 4, even when significant noise components (disturbing light components, background light components) may be superimposed on signal components that are supposed to be detected in the intensity distribution of light to be detected by the sensor apparatus 1, the sensor apparatus 1 can obtain digital values of the signal components with a high accuracy using an A/D conversing circuit with the outputted digital value thereof having a small number of bits of M as the A/D converting section 40.
That is, the maximum value of the difference (V_n−V_n-1) between two adjacent voltage values V_nand V_n-1among the voltage values V₁to V_Noutputted from the respective holding circuits 21 ₁to 21 _Nis smaller than the maximum value of the voltage values V₁to V_N. Hence, the voltage value V_FS2to be used by the A/D converting section 40 as a full scale during the time period T_n(n≠1) is set to the maximum value of the difference (V_n−V_n-1) (or a value somewhat greater than the maximum value) or to the difference between the maximum and minimum values of signal components included in the voltage values V₁to V_N(or a value somewhat greater than the difference). Thus, in the A/D converting section 40, the voltage value V_FS2to be used as a full scale is set appropriately and a voltage value U_ncorresponding to the difference (V_n−V_n-1) is converted into a digital value. Therefore, the digital value to be outputted from the A/D converting section 40 represents signal components with a high accuracy, though having a small number of bits of M.
Meanwhile, the maximum value of the voltage values V₁to V_Noutputted from the respective holding circuits 21 ₁to 21 _Nis larger. Hence, the voltage value V_FS1to be used by the A/D converting section 40 as a full scale during the time period T₁is set to the maximum value of the voltage values V₁to V_N(or a value somewhat greater than the maximum value) that is greater than the voltage value V_FS2. Thus, in the A/D converting section 40, the voltage value V_FS1to be used as a full scale is set appropriately and the voltage value V₁is converted into a digital value. Therefore, the digital value to be outputted from the A/D converting section 40 represents the sum of signal components and noise components (disturbing light components, background light components), though having a small number of bits of M.
As described heretofore, the sensor apparatus 1 according to the first embodiment can obtain digital values of signal components with a high accuracy using an A/D conversing circuit with the outputted digital value thereof having a small number of bits of M as the A/D converting section 40. Therefore, the A/D converting section 40 results in a short conversion time, small power consumption, and small circuit scale. Also, even in the case of performing A/D conversion processing in parallel due to the requirement of performing the A/D conversion processing within a certain time period, the number of A/D converting sections for the parallel processing may be small, which also results in a small power consumption and small circuit scale.

Second Embodiment

Next, a sensor apparatus according to a second embodiment of the present invention will be explained. FIG. 5 is a view showing the overall configuration of the sensor apparatus according to the second embodiment of the present invention. The sensor apparatus 2 shown in FIG. 5 comprises a sensor array section 10, a holding section 20, a difference operating section 30A, and an A/D converting section 40. As compared with the configuration of the sensor apparatus 1 according to the above-described first embodiment (FIGS. 1 and 2), the sensor apparatus 2 according to the second embodiment is different from the first embodiment in that the difference operating section 30A is provided instead of the difference operating section 30.
The difference operating section 30A includes switches SW_31,1to SW_31,N, switches SW_32,0and SW_32,1, and a subtracting circuit 33. The output terminal of the holding circuit 21 _nis connected to a wiring L1 via the switch SW_31,n. The output terminal of the first holding circuit 21 ₁is connected to a wiring L2 via the switch SW_32,1. Also, the wiring L2 is connected with the ground potential via the switch SW_32,0. The switch SW_31,nopens and closes based on the level of a control signal S_n, and the switch SW_32,0opens and closes based on the level of a control signal Sel1, while the switch SW_32,1opens and closes based on the level of a control signal Sel2. The subtracting circuit 33 outputs a voltage value corresponding to the difference between voltage values to be inputted through the respective wirings L1 and L2.
Next, the operation of the difference operating section 30A and the A/D converting section 40 in the sensor apparatus 2 according to the second embodiment will be explained. The timing chart for explaining the operation of the difference operating section 30A and the A/D converting section 40 in the sensor apparatus 2 according to the second embodiment is the same as in FIG. 3.
During the time period T₁from time t_1,1to time t_1,2, only the control signal S₁is made high among the control signals S₁to S_N, so that the switch SW_31,1in the difference operating section 30A is closed. Also, the control signal Sel1 is made high, so that the switches SW_32,0and SW₄₁are closed. When the switch SW_31,1is closed, the voltage value V₁held by the holding circuit 21 ₁is inputted to the subtracting circuit 33 through the switch SW_31,1and the wiring L1. Also, when the switch SW_32,0is closed, the ground potential is inputted to the subtracting circuit 33 through the switch SW_32,0and the wiring L2. In the subtracting circuit 33, the ground potential is subtracted from the voltage value V₁, and the subtracted voltage value V₁is outputted. Then, in the A/D converting section 40, the voltage value V₁outputted from the subtracting circuit 33 is converted into an M-bit digital value using the voltage value V_FS1inputted through the switch SW₄₁as a full scale.
During the time period T_nfrom time t_n,1to time t_n,2(n≠1), only the control signal S_nis made high among the control signals S₁to S_N, so that the switch SW_31,nin the difference operating section 30A is closed. Also, the control signal Sel2 is made high, so that the switch SW₄₂is closed. When the switch SW_31,nis closed, the voltage value V_nheld by the holding circuit 21 _nis inputted to the subtracting circuit 33 through the switch SW_31,nand the wiring L1. Also, when the switch SW_32,1is closed, the voltage value V₁held by the holding circuit 21 ₁is inputted to the subtracting circuit 33 through the switch SW_32,1and the wiring L2. In the subtracting circuit 33, the voltage value V₁is subtracted from the voltage value V_n, and a voltage value W_ncorresponding to the subtraction result is outputted. Then, in the A/D converting section 40, the voltage value W_noutputted from the subtracting circuit 33 is converted into an M-bit digital value using the voltage value V_FS2inputted through the switch SW₄₂as a full scale.
That is, during the time period T₁, the A/D converting section 40 converts the voltage value V₁corresponding to the amount of incident light to the first photodiode PD₁into an M-bit digital value using the voltage value V_FS1as a full scale. Also, during the time period T_n(n≠1), the difference operating section 30A calculates a voltage value W_ncorresponding to the difference (V_n−V₁) between voltage values V_nand V₁that correspond to the amount of incident light to the respective photodiodes PD_nand PD₁, and then the A/D converting section 40 converts the voltage value W_ninto an M-bit digital value using the voltage value V_FS2as a full scale.
Therefore, as shown in FIG. 4, even when significant noise components (disturbing light components, background light components) may be superimposed on signal components that are supposed to be detected in the intensity distribution of light to be detected by the sensor apparatus 2, the sensor apparatus 2 can obtain digital values of the signal components with a high accuracy using an A/D conversing circuit with the outputted digital value thereof having a small number of bits of M as the A/D converting section 40.
That is, the maximum value of the voltage value W_nto be obtained by a difference operation from the voltage values V₁to V_Noutputted from the respective holding circuits 21 ₁to 21 _Nis smaller than the maximum value of the voltage values V₁to V_N. Hence, the voltage value V_FS2to be used by the A/D converting section 40 as a full scale during the time period T_n(n≠1) is set to the maximum value of the voltage value W_n(or a value somewhat greater than the maximum value) or to the difference between the maximum and minimum values of signal components included in the voltage values V₁to V_N(or a value somewhat greater than the difference). Thus, in the A/D converting section 40, the voltage value V_FS2to be used as a full scale is set appropriately and a voltage value W_ncorresponding to the difference (V_n−V₁) is converted into a digital value. Therefore, the digital value to be outputted from the A/D converting section 40 represents signal components with a high accuracy, though having a small number of bits of M.
Meanwhile, the maximum value of the voltage values V₁to V_Noutputted from the respective holding circuits 21 ₁to 21 _Nis larger. Hence, the voltage value V_FS1to be used by the A/D converting section 40 as a full scale during the time period T₁is set to the maximum value of the voltage values V₁to V_N(or a value somewhat greater than the maximum value) that is greater than the voltage value V_FS2. Thus, in the A/D converting section 40, the voltage value V_FS1to be used as a full scale is set appropriately and the voltage value V₁is converted into a digital value. Therefore, the digital value to be outputted from the A/D converting section 40 represents the sum of signal components and noise components (disturbing light components, background light components), though having a small number of bits of M.
As described above, the sensor apparatus 2 according to the second embodiment can obtain digital values of signal components with a high accuracy using an A/D conversing circuit with the outputted digital value thereof having a small number of bits of M as the A/D converting section 40. Therefore, the A/D converting section 40 results in a short conversion time, small power consumption, and small circuit scale. Also, even in the case of performing A/D conversion processing in parallel due to the requirement of performing the A/D conversion processing within a certain time period, the number of A/D converting sections for the parallel processing may be small, which also results in a small power consumption and small circuit scale.
(Exemplary Variation)
The present invention is not restricted to the above-described first and second embodiments, and various modifications may be made. For example, although the sensor apparatuses according to the above-described first and second embodiments are image pickup apparatuses including a plurality of photodiodes that are arranged one-dimensionally, the sensor apparatus according to the present invention may be an image pickup apparatus including a plurality of photodiodes that are arranged two-dimensionally. Further, the sensor apparatus according to the present invention may be an imaging apparatus in which each pixel includes an APS (Active Pixel Sensor) circuit shown in FIG. 6 as well as a plurality of photodiodes and the pixels are arranged one- or two-dimensionally. Also, the sensor apparatus according to the present invention is not restricted to an image pickup apparatus, but may include a plurality of sensor elements for detecting the amount of another sensing parameter (e.g. temperature, displacement).
From the invention thus described, it will be obvious that the embodiments of the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.

INDUSTRIAL APPLICABILITY

The sensor apparatus according to the present invention is applicable to, for example, an image pickup apparatus including a plurality of photodiodes that are arranged one- or two-dimensionally.

Claims

1. A sensor apparatus comprising:

a sensor array section including N sensor elements (N represents an integer of 2 or more) and outputting a voltage value V_nin response to the result of sensing by the n-th sensor element (“n” represents any integer of 1 or more but N or less) among said N sensor elements;

a difference operating section outputting a voltage value U_n(n≠1) corresponding to the difference (V_n−V_n-1) between the voltage values V_nand V_n-1among N voltage values V₁to V_Noutputted from said sensor array section; and

an A/D converting section converting the voltage value U_noutputted from said difference operating section into a digital value.

2. A sensor apparatus according to claim 1, wherein said A/D converting section converts at least one voltage value of the N voltage values V₁to V_Ninto a digital value.

3. A sensor apparatus according to claim 1, further comprising a holding section once holding the N voltage values V₁to V_Noutputted from said sensor array section, and

wherein said difference operating section outputs the voltage value U_nbased on the N voltage values V₁to V_Nheld by said holding section.

4. A sensor apparatus according to claim 1, wherein each of said N sensor elements includes a photodiode.

5. A sensor apparatus comprising:

a sensor array section including N sensor elements (N represents an integer of 2 or more) and adapted to output a voltage value V_nin response to the result of sensing by the n-th sensor element (“n” represents any integer of 1 or more but N or less) among said N sensor elements;

a difference operating section outputting a voltage value W_ncorresponding to the difference (V_n−V_n0) between a specific voltage value V_n0and the voltage value V_namong N voltage values V₁to V_Noutputted from said sensor array section; and

an A/D converting section converting the voltage value W_noutputted from said difference operating section into a digital value.

6. A sensor apparatus according to claim 5, wherein said A/D converting section converts the specific voltage value V_n0into a digital value.

7. A sensor apparatus according to claim 5, further comprising a holding section once holding the N voltage values V₁to V_Noutputted from said sensor array section, and

wherein said difference operating section outputs the voltage value W_nbased on the N voltage values V₁to V_Nheld by said holding section.

8. A sensor apparatus according to claim 5, wherein each of said N sensor elements includes a photodiode.