JP2008219613A - Non-cooled infrared camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain reduction in the frequency of image interruption when acquiring offset correction data. <P>SOLUTION: There are provided: an imaging device 2 including valid pixels of a two-dimensional array constituted of thermal type infrared detectors and reference pixel which is installed while being paired with the valid pixels and whose sensitivity to incident infrared rays is extremely low while having electrical characteristics equal with the valid pixels; a shutter 3 which closes an aperture part to make infrared rays of almost uniform intensity incident on the valid pixels and the reference pixels; an imaging reference pixel memory 11 for storing the output of the reference pixels during imaging of an object in the state of opening the shutter; and a subtraction circuit 18 which applies correction of an output offset level difference from the respective valid pixels to respective data in the imaging reference pixel memory 11 for improving correction accuracy. Offset correction is performed on the basis of output offset data of the reference pixels acquired in the state of opening the shutter 3 during imaging while performing imaging by using the valid pixels, the frequency of image interruption is extremely reduced and fixed pattern noise is reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an infrared camera, and more particularly to an uncooled infrared camera using a thermal infrared detector operating at room temperature such as a bolometer method or an SOI diode method.

  The conventional uncooled infrared camera is installed at a position where a reference infrared ray having a substantially uniform intensity can be incident on each of the two-dimensionally arranged thermal type infrared detector and the two-dimensionally arranged thermal type infrared detector. And when the fixed pattern noise increases during camera start-up or imaging, the shutter is temporarily closed to obtain correction data corresponding to variations in the output offset level of each infrared detector, and the shutter is opened again. Offset correction is performed by subtracting the acquired correction data for each output of each infrared detector and outputting it, thereby reducing fixed pattern noise (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 3261617 JP 2005-214039 A

  However, when the offset correction data is acquired, the shutter is closed, and the image is interrupted even while the image is being captured. Especially for surveillance cameras for the purpose of finding intruders and for obstacle detection ahead while driving In the application as a vehicle-mounted camera, the problem is how to reduce the frequency of the image interruption.

  The present invention has been made to solve such a problem, and an object of the present invention is to obtain an uncooled infrared camera in which the frequency of image interruption during imaging by acquiring offset correction data is extremely low.

  The present invention provides an imaging device including a plurality of effective pixels and a plurality of reference pixels, an opening, and the effective pixels and the reference pixels that constitute the imaging device by closing the opening. A shutter installed at a position where infrared rays having a substantially uniform intensity can be incident on each of them; an effective pixel memory at the time of calibration for storing the output of each effective pixel in the closed state of the shutter; and the shutter at the time of subject imaging Any one of the reference pixel memory at the time of imaging that stores the output of each reference pixel in the open state, the effective pixel memory at the time of calibration and the reference pixel memory at the time of imaging is stored in the open state of the shutter at the time of imaging the subject. An uncooled infrared camera including a subtraction correction circuit that performs offset correction by subtracting from the output of each effective pixel.

  The present invention provides an imaging device including a plurality of effective pixels and a plurality of reference pixels, an opening, and the effective pixels and the reference pixels that constitute the imaging device by closing the opening. A shutter installed at a position where infrared rays having a substantially uniform intensity can be incident on each of them; an effective pixel memory at the time of calibration for storing the output of each effective pixel in the closed state of the shutter; and the shutter at the time of subject imaging Any one of the reference pixel memory at the time of imaging that stores the output of each reference pixel in the open state, the effective pixel memory at the time of calibration and the reference pixel memory at the time of imaging is stored in the open state of the shutter at the time of imaging the subject. Reference pixel acquired during imaging because it is an uncooled infrared camera having a subtraction correction circuit that performs offset correction by subtracting from the output of each effective pixel Data can be corrected to the effective pixel output with, it can be extremely less frequently interrupted image being captured by the offset correction data acquisition.

Embodiment 1 FIG.
The uncooled infrared camera according to the first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an uncooled infrared camera according to the first embodiment. In FIG. 1, 1 is an infrared optical system that collects infrared rays emitted from a subject during imaging and forms an infrared image on the imaging device 2, 2 is an imaging device positioned on the imaging plane of the infrared optical system 1, Reference numeral 3 denotes an opening, and a shutter installed at a position where infrared rays having a substantially uniform intensity can be incident on the infrared incident surface of the image sensor 2 by closing the opening, and 4 is an element bonded to the image sensor 2. The device package 4 has a structure as shown in, for example, Japanese Patent Publication No. 9-506712, and has a high transmittance for infrared rays, and is surrounded by the device package 4 and the image pickup device 2. The created space is maintained in a vacuum. Reference numeral 5 denotes a driver circuit connected to the image sensor 2, 6 denotes a DC power source connected to the image sensor 2, 7 denotes a control signal connected to each part of the driver circuit 5, the shutter 3 and the electric circuit constituting the uncooled infrared camera. A generation circuit, 8 is an amplification circuit connected to the image sensor 2, 9 is an A / D conversion circuit connected to the amplification circuit 8, and 10 is a frame of the output from the A / D conversion path 9 a desired number of times for each pixel. A frame integration circuit that performs integration calculation, 11 is a reference pixel memory during imaging that stores an output of a reference pixel in the imaging device 2 when the shutter 3 is open when imaging a subject, and 12 is an imaging when the shutter 3 is closed during calibration. A calibration effective pixel memory for storing the output of the effective pixel in the element 2, and a correction memo for storing either one of the reference pixel memory for imaging 11 or the calibration effective pixel memory 12 , 14 are connected to the correction memory 13 and the A / D conversion circuit 9, and offset correction is performed by subtracting the data in the correction memory 13 from the output of the effective pixels output from the A / D conversion circuit 9 at the time of subject imaging. A subtracting correction circuit 15 performs a display processing circuit for converting the output from the subtracting correction circuit 14 into a desired output format and outputting it as an image signal.

In FIG. 1,
(Dopt0 (m)) bar: data in the calibration effective pixel memory 12 acquired with the shutter 3 closed,
(Dref1 (n)) bar: data in the reference pixel memory 11 at the time of imaging acquired with the shutter 3 open,
Dopt1 (m): data of effective pixels during imaging,
Dref1 (n): Reference pixel data during imaging.

Further, as shown in FIG. 1, the data stored in the correction memory 13 is
(I) The period from the execution of the shutter close calibration to the execution of the shutter open calibration is a (Dopt0 (m)) bar.
(Ii) (Dref1 (n)) bar (*) until the shutter closing calibration is executed after the shutter opening calibration is executed.

Further, as shown in FIG. 1, the image data output by the display processing circuit 15 is
(I) After the shutter closing calibration is executed and until the shutter opening calibration is executed, it is Dopt1 (m)-((Dopt0 (m)) bar).
(Ii) The period from the execution of the shutter opening calibration to the execution of the shutter closing calibration is Dopt1 (m)-((Dref1 (n)) bar) (*).

Further, m and n are as follows, where m is a code attached to the effective pixel and n is a code attached to the reference pixel.
m = 52, 53, 54, 55
n = 56, 57, 58, 59

However, for the data marked with (*), the combinations of m and n are as follows.
(M, n) = (52, 56), (53, 57), (54, 58), (55, 59)

  FIG. 2 is a diagram illustrating the configuration of the image sensor 2. In FIG. 2, reference numeral 40 denotes a vertical scanning circuit to which a vertical driving clock signal is input, 41 denotes a horizontal scanning circuit to which a horizontal driving clock signal is input, and 42 and 43. Is a vertical scanning transistor connected to the vertical scanning circuit 40, 44 to 47 are horizontal scanning transistors connected to the horizontal scanning circuit 41, 48 to 51 are constant current sources, and 52 to 55 are two-dimensionally arranged on the surface of the image sensor 2. Effective pixels composed of thermal infrared detectors arranged in an array, 56 to 59 are reference pixels arranged one-on-one in the vicinity of the effective pixels 52 to 55, and 60 and 61 are vertical scans. The horizontal signal lines 62 to 65 are connected to the vertical scanning circuit 40 through the transistors 42 and 43 and are connected to the effective pixels 52 to 55 and the reference pixels 56 to 59. Effective pixels 52 to 55 is connected to the horizontal scanning circuit 41 via the transistor 44 - 47 is connected to the vertical signal line to the reference pixels 56 to 59 and constant-Nagarehara 48-51. For simplification of the figure, in FIG. 2, the effective pixel 52 and the reference pixel 56, the effective pixel 53 and the reference pixel 57, the effective pixel 54 and the reference pixel 58, and the effective pixel 55 and the reference pixel 59 are combined as one set. Although only four sets of 2 pixels in the horizontal direction × 2 pixels in the vertical direction are illustrated, in practice, in order to obtain a practical resolution, generally more than about 320 pixels in the horizontal direction × 240 pixels in the vertical direction (= 76,800 pixels or more).

  The effective pixels 52 to 55 are thermal infrared detectors utilizing the temperature dependence of the forward voltage of the diode, and have a structure shown in, for example, Japanese Patent Application Laid-Open No. 2005-214039. . On the other hand, the reference pixels 56 to 59 are the same as the effective pixels 52 to 55 except that the pixel structure shown in Patent Document 2 is configured by excluding both or either of the hollow heat insulation structure and the infrared absorption structure. It has a structure. Differences in structure between the effective pixels 52 to 55 and the reference pixels 56 to 59 will be schematically described with reference to FIGS. 3 and 4. FIG. 3 is a structural schematic diagram of the effective pixels 52 to 55, in which 62 is a semiconductor substrate, 63 is a hollow heat insulating structure (hollow portion) formed by a recess formed in the semiconductor substrate 62 by etching, and 64 is hollow heat insulating. A structure support disposed on the semiconductor substrate 62 so as to cover the structure 63, 65 and 66 are electrode wirings provided on the structure support 64, and 67 is an electrode wiring 65 and 66 and a PN junction diode 68 described later. An insulating protective layer provided on the upper portion, 68 is a PN junction diode provided between the electrode wirings 65 and 66, and 69 is an infrared absorbing structure (infrared absorbing member) provided on the insulating protective layer 67. On the other hand, FIG. 4 is a schematic diagram of the structure of the reference pixels 56 to 59. As can be seen from comparison with the effective pixels 52 to 55, both the hollow heat insulating structure 63 and the infrared absorption structure 69 of the effective pixels 52 to 55 (or It has the structure which excluded any one). Since other configurations are the same as those of the effective pixels 52 to 55, the same reference numerals are given and description thereof is omitted here. The structure of the reference pixels 56 to 59 is also described in, for example, Japanese Patent Application Laid-Open Nos. 2003-198942 and 2005-64999. With the above structure, the electrical characteristics such as the output offset level of the reference pixels 52 to 55 and the temperature change rate of the output offset level are substantially the same as those of the effective pixels 56 to 59 except that the sensitivity to incident infrared rays is extremely low. It has become. The vertical scanning transistors 42 and 43, the horizontal scanning transistors 44 to 47, and the constant current sources 48 to 51 have the same characteristics.

  Next, the operation of the uncooled infrared camera according to the first embodiment will be described with reference to FIG. 1, FIG. 2, and FIG. In the description of the first embodiment, data to be stored in each of the imaging reference pixel memory 11, the calibration effective pixel memory 12, and the correction memory 13 in each stage of the operation, and the display processing circuit 15 output the data. The relationship between the image data is as described above with reference to FIG. After starting the uncooled infrared camera (step S100), a shutter close calibration signal is input to the control signal generation circuit 7 (step S101), and the shutter 3 is closed by a signal generated by the control signal generation circuit 7 based on the input. Infrared rays having spatially uniform intensity emitted from the shutter 3 are made incident on the effective pixels 52 to 55 and the reference pixels 56 to 59 of the image sensor 2 through the element package 4 (step S102). Next, a vertical drive clock is supplied from the control signal generation circuit 7 to the vertical scanning circuit 40 of the image sensor 2 and a horizontal driving clock is supplied to the horizontal scanning circuit 41 via the driver circuit 5. The image pickup device 2 makes the vertical scanning transistor 42 conductive by the operation of the vertical scanning circuit 40, and outputs each element current determined by the characteristics of the constant current sources 48 to 51 from the DC power source 6 through the horizontal signal line 60 and the effective pixels 52 and 52. 53 and the reference pixels 56 and 57. In addition, the image pickup device 2 performs horizontal scanning of the potentials of the vertical signal lines 62 to 65 (that is, output voltages of the effective pixels 52 and 53 and the reference pixels 56 and 57) while each element current is supplied by the operation of the horizontal scanning circuit 41. The transistors 44 to 47 are sequentially turned on and sequentially output to the amplifier circuit 8. Next, the vertical scanning transistor 43 is turned on and the same operation is repeated to read out the output voltages of the effective pixels 54 and 55 and the reference pixels 58 and 59. In this way, the output voltages of all effective pixels and reference pixels are continuously read (step S103).

  As described above, the output voltages of the effective pixels 52 to 55 and the reference pixels 56 to 59 in a state where infrared rays of uniform intensity are incident are amplified by the amplifier circuit 8, and then the A / D conversion circuit 9. After conversion into a digital signal, the frame integration circuit 10 performs integration processing for each pixel a desired number of times (step S104), and the output data (Dopt0 (m)) bars of the effective pixels 52 to 55 are stored in the calibration effective pixel memory 12. After being stored (step S105), it is also stored in the correction memory 13 as output offset variation data of the effective pixels 52 to 55 (step S106). Note that the process from step S101 to S106 is the shutter closing calibration operation.

  Next, the shutter 3 is opened, and infrared rays emitted from the subject are collected by the infrared optical system 1 and transmitted through the element package 4. Then, the effective pixels 52 to 55 and the reference pixels 56 to 59 are positioned on the image sensor 2. An image is formed on the surface (step S107). As a result, a minute temperature rise of about several mK corresponding to the intensity of the radiant infrared ray incident from the subject occurs in each of the effective pixels 52 to 55, and the PN junction diode 68 (FIG. 3) included in each of the effective pixels 52 to 55. The forward voltage value of the reference) changes for each of the effective pixels 52 to 55. On the other hand, in the reference pixels 56 to 59 that do not have the hollow heat insulating structure 63 and the infrared absorption structure 69, the amount of radiation infrared radiation is small, and the absorbed heat is released to the semiconductor substrate 62 side. Is very small compared to the effective pixels 52 to 55. In this state, the output voltages Dopt1 (m) and Dref1 (n) of the effective pixels 52 to 55 and the reference pixels 56 to 59 are read out in the same manner as in step S103 and input to the subtraction correction circuit 14. In the subtraction correction circuit 14, for the output data Dopt1 (m) corresponding to the effective pixels 52 to 56 in the shutter open state at the time of subject imaging, the data (Dop0 (m)) bar of the correction memory 13 is set for each pixel. By subtracting, the output offset variation superimposed on the output data is subtracted and corrected (step S108), converted into a desired output format in the display processing circuit 15, and image signal (Dopt1 (m)). -(Dopt0 (m)) bar) (step S109).

  During imaging, the signals of both the effective pixels 52 to 55 and the reference pixels 56 to 59 are continuously output from the imaging device 2, but the output signals of the reference pixels 56 to 59 in a desired period after the shutter 3 is opened are used as the frame integration circuit 10. Then, the desired number of times of averaging processing is performed, and the obtained data (Dref1 (n)) bar is stored in the reference pixel memory 11 during imaging. When imaging is performed for a long time, the above averaging process regarding the outputs of the reference pixels 56 to 59 is repeated, and imaging is performed while appropriately updating the contents of the imaging reference pixel memory 11 (step S110).

  As the number of pixels of the image pickup device 2, for simplification of the figure, only four sets are shown in FIG. 2, but in order to obtain a practical resolution, the number of sets of about 320 horizontal × 240 vertical is generally used. In addition, since the effective pixel and the reference pixel have a size of about 50 μm in the horizontal direction and about 25 μm in the vertical direction per pair, there is a distance of about 10 to 20 mm corresponding to the diagonal at the maximum between the effective pixels. . For this reason, during imaging, self-heating of an electronic circuit inside the uncooled infrared camera, the influence of ambient temperature change, and the like occur in the effective pixels 52 to 55 due to infrared rays radiated from the subject in the surface of the imaging device 2. There may be a change in the relative temperature distribution exceeding a temperature rise of several mK, which becomes a difference in output offset level between effective pixels, and appears as fixed pattern noise on the image.

  Further, as described above, there is a diagonal distance of about 10 to 20 mm between the effective pixels of the image sensor 2, and therefore the temperature change rate of the output offset level of the effective pixels 52 to 55 is different due to a manufacturing error. Exists. For this reason, even when the temperature of the image sensor 2 changes uniformly in the plane, a difference occurs in the output offset level between the effective pixels 52 to 55, and this appears in the image as fixed pattern noise.

  On the other hand, the reference pixels 56 to 59 are arranged adjacent to the effective pixels 52 to 55, respectively, and have substantially the same electrical characteristics as the effective pixels 52 to 55 except that the sensitivity to incident infrared rays is extremely low. Therefore, the output offset levels of the reference pixels 56 to 59 are effective pixels even if the above-described relative temperature change or uniform temperature change occurs in the image pickup device 2 during image pickup. It changes in the same way as 52-55. For this reason, the output offset levels of the reference pixels 56 to 59 are substantially equal to the output offset levels of the effective pixels 52 to 55 in a state where the radiant infrared rays from the subject are not incident.

  Using the change in the output offset level of the reference pixels 56 to 59 as described above, it is determined whether or not the fixed pattern noise has increased to reach an unacceptable level from the viewpoint of image quality (step S112). In step S112 (YES in step S112), a shutter open calibration signal is input to the control signal generation circuit 7 (step S113), and the data in the correction memory 13 is updated to the latest data in the reference pixel memory 11 (Dref1 (n )) The pattern is replaced with a bar, and the fixed pattern noise is reduced without image interruption while the imaging is continued with the shutter 3 opened (step S114). Note that the steps S112, YES, S113, and S114 are shutter opening calibration operations.

  The relative in-plane temperature distribution and the uniform temperature change in the image sensor 2 are further increased while the imaging is continued after the shutter opening calibration is performed, and the difference in the output offset level between the effective pixels 52 to 55 is increased. If the fixed pattern noise becomes noticeable, the shutter opening calibration operation is performed again, and correction is performed using the data (Dref1 (n)) bar of the latest imaging reference pixel memory 11 (step S111). YES → YES of step S112 → step S113 → step S114). If there is no problem with the inconvenience due to the image interruption, the shutter close calibration operation is appropriately selected in step S112 (NO in step S112), and the process returns to step S101 to return the data (Dopt0 (Dot0 ( m)) The bar may be updated to continue imaging.

  As described above, according to the first embodiment, the infrared optical system 1 that collects infrared rays emitted from a subject during imaging and forms an image on the imaging device 2, the plurality of effective pixels 52 to 55, and the plurality of pixels. Infrared light having substantially uniform intensity is applied to each of the imaging element 2 having the reference pixels 56 to 59 and the effective pixels 52 to 55 and the reference pixels 56 to 59 constituting the imaging element 2 by closing the opening. A shutter 3 installed at a position where it can be incident, a control signal generation circuit 7 that outputs a control signal for each part in the uncooled infrared camera, and an effective pixel at the time of calibration that stores the outputs of the effective pixels 52 to 55 in the shutter closed state The memory 12, the imaging reference pixel memory 11 that stores the outputs of the reference pixels 56 to 59 in the shutter open state at the time of subject imaging, the calibration effective pixel memory 12, and the imaging reference pixel memory 11 A subtraction correction circuit 14 that performs offset correction by subtracting the data from the output of each of the effective pixels 52 to 55 at the time of subject imaging, and a display processing circuit 15 that outputs the offset-corrected data as an image signal. Since it is a non-cooling infrared camera, the data of either the calibration effective pixel memory 12 or the imaging reference pixel memory 11 is subtracted from the outputs of the effective pixels 52 to 55 in the open state of the shutter 3 during imaging of the subject. When the offset correction is performed and the change in the output offset level of the reference pixels 56 to 59 is used to increase the fixed pattern noise and reach an unacceptable level from the viewpoint of image quality, the shutter open calibration signal Is input to the control signal generation circuit 7 and the data in the correction memory 13 is referred to at the latest imaging time. By replacing the contents of the elementary memory 11 and correcting the effective pixel output using the reference pixel data acquired during imaging, it is possible to continue the imaging while the shutter 3 is opened. Since the fixed pattern noise is reduced without causing interruption, the frequency of image interruption during imaging due to acquisition of offset correction data can be extremely reduced.

Embodiment 2. FIG.
FIG. 6 is a block diagram of an uncooled infrared camera according to Embodiment 2 of the present invention. In the figure, 16 is a reference pixel memory at the time of calibration that stores the output of the reference pixel of the image sensor 2 when the shutter 3 is closed at the time of calibration, and 17 is connected to the effective pixel memory 12 at the time of calibration and the reference pixel memory 16 at the time of calibration. The calibration difference value memory 18 for storing the result of subtracting the calibration effective pixel memory 12 data from the calibration reference pixel memory 16 data is stored in the imaging reference pixel memory 11 and the calibration difference value memory 17. A subtracting circuit connected to subtract the data in the calibration difference value memory 17 from the data in the reference pixel memory 11 during imaging. In the second embodiment, the correction memory 13 is connected to the calibration effective pixel memory 12 and the subtraction circuit 18 and stores either one of the outputs. Details of the stored data will be described later. Other configurations are the same as those in FIGS. 1 to 4, and are therefore denoted by the same reference numerals, and the description thereof is omitted here.

  As described above, the uncooled infrared camera according to the second embodiment condenses the infrared rays emitted from the subject during imaging and forms an image on the image sensor 2, the plurality of effective pixels, and the plurality of effective pixels. And a shutter 3 installed at a position where infrared rays having substantially uniform intensity can be incident on each of the effective pixel and the reference pixel constituting the image sensor 2 by closing the opening. A control signal generation circuit 7 that outputs a control signal for each part in the uncooled infrared camera, a calibration effective pixel memory 12 that stores the output of each effective pixel in the shutter closed state, and each effective pixel in the shutter closed state Calibration reference pixel memory 16 for storing the output, calibration difference value memory 17 for storing the difference between the calibration reference pixel memory 16 and the calibration effective pixel memory 12, and a shutter for shooting the subject. An imaging reference pixel memory 11 that stores the output of each reference pixel in the open state, a subtraction circuit 18 that corrects data by subtracting data in the calibration difference value memory 17 from data in the imaging reference pixel memory 11, and calibration A subtraction correction circuit 14 that performs offset correction by subtracting one of the data output from the effective pixel memory 12 and the subtraction circuit 18 from the output of each effective pixel at the time of subject imaging, and the offset corrected data as an image And a display processing circuit 15 that outputs the signal.

In FIG. 6,
(Dopt0 (m)) bar: data in the calibration effective pixel memory 12 acquired with the shutter 3 closed,
(Dref0 (n)) bar: data in the calibration reference pixel memory 16 acquired with the shutter 3 closed,
(Dref1 (n)) bar: data in the reference pixel memory 11 at the time of imaging acquired with the shutter 3 open,
Dopt1 (m): data of effective pixels during imaging,
Dref1 (n): Reference pixel data during imaging.

Further, as shown in FIG. 6, the data stored in the correction memory 13 is
(I) The period from the execution of the shutter close calibration to the execution of the shutter open calibration is a (Dopt0 (m)) bar.
(Ii) After the shutter opening calibration is executed and until the shutter closing calibration is executed, ((Dref1 (n)) bar) − {((Dref0 (n)) bar) − ((Dopt0 (m) ) Bar)} (*).

Furthermore, as shown in FIG. 6, the image data output by the display processing circuit 15 is
(I) After the shutter closing calibration is executed and until the shutter opening calibration is executed, it is Dopt1 (m)-((Dopt0 (m)) bar).
(Ii) After the shutter opening calibration is executed and until the shutter closing calibration is executed, Dopt1 (m) − [((Dref1 (n)) bar) − {((Dref0 (n)) bar) − ((Dopt0 (m)) bar)}] (*).

Further, m and n are as follows, where m is a code attached to the effective pixel and n is a code attached to the reference pixel.
m = 52, 53, 54, 55
n = 56, 57, 58, 59

However, for the data marked with (*), the combinations of m and n are as follows.
(M, n) = (52, 56), (53, 57), (54, 58), (55, 59)

  Next, the operation of the uncooled infrared camera according to the second embodiment will be described with reference to FIGS. In the description of the second embodiment, the imaging reference pixel memory 11, the calibration effective pixel memory 12, the correction memory 13, the data stored in the calibration reference pixel memory 16, and the display processing circuit 15 in each stage of the operation. The relationship of the image data output from is as described above. Since the operation from step S100 to S104 after the start of the uncooled infrared camera is the same as that of the first embodiment, the description thereof is omitted here.

  Next, in the second embodiment, in the process of the shutter close calibration operation, the outputs (Dopt0) of the effective pixels 52 to 55 that have been subjected to frame integration by the frame integration circuit 10 for the desired number of times by closing the shutter 3 are performed. (M)) The bar is stored in the calibration effective pixel memory 12, and the output (Dref0 (n)) bar of the reference pixels 56 to 59 is stored in the calibration reference pixel memory 16 (step S200). (((Dref0 (n)) bar) − ((Dopt0 (m)) bar)) is stored in the calibration difference value memory 17 (step S201). Thereafter, the same operation as step S106 described in the first embodiment is performed (step S106). In the second embodiment, the steps S101 to S104, S200, S201, and S106 are shutter closing calibration operations.

  Next, since the operation from step S107 to step S111 is the same as that in the first embodiment, the operation is the same as in the first embodiment. Next, an increase in fixed pattern noise is recognized during imaging (YES in step S112), and when the shutter open calibration signal is input to the control signal generation circuit 7 (step S113), the subtraction circuit 18 determines the latest. By subtracting the data (((Dref0 (n)) bar) − ((Dopt0 (m)) bar)) in the calibration difference value memory 17 from the data (Dref1 (n) bar) in the reference pixel memory 11 during imaging. The correction corresponding to the output offset difference between the effective pixel and the reference pixel constituting the pair is applied to the data of the reference pixel memory 11 at the time of imaging, and the data obtained as a result ((Dref1 (n) bar) − ( ((Dref0 (n)) bar)-((Dopt0 (m)) bar)) is replaced with the data of the correction memory 13, and the shutter 3 remains open. Without causing interruptions image is performed to reduce the fixed pattern noise (YES in step S112, S113, S202).

  Each of the reference pixels 56 to 59 is ideally the same in electrical characteristics as the effective pixels 52 to 55 except that the sensitivity to incident infrared rays is extremely low as compared with the effective pixels 52 to 55 that constitute a pair. However, there are actually slight differences in characteristics such as the output offset level and the temperature change rate of the output offset level between the effective pixels 52 to 55 and the reference pixels 56 to 59 due to manufacturing errors. To do. For this reason, there is a slight difference in output offset level between each of the effective pixels 52 to 55 and each of the reference pixels 56 to 59 (A in FIG. 8), and the relative in-plane temperature within the image sensor 2. When the temperatures of the effective pixels 52 to 55 and the reference pixels 56 to 59 constituting the pair change due to a change in distribution or a uniform temperature change in the image sensor 2, the difference in output offset level (B in FIG. 8). Will also increase. The difference A in FIG. 8 is stored in the calibration difference value memory 17 in step S201 of the shutter closing calibration, and is corrected in step S202 of the shutter opening calibration, but from the difference A in FIG. This is the fixed pattern noise after the shutter opening calibration is performed. The fixed pattern noise increases as the amount of temperature change from when the shutter close calibration is performed at the location of the imaging device 2 where the effective pixels 52 to 55 and the reference pixels 56 to 59 that constitute a pair are located. If the fixed pattern noise cannot be sufficiently reduced by the shutter opening calibration in steps S113 and S202, the shutter closing calibration signal is input to the control signal generation circuit 7 again as necessary, and steps S101 to S101 are performed. Steps S104, S200, S201, and S106 are executed to update the data in the calibration effective pixel memory 12, the calibration reference pixel memory 16, and the calibration difference value memory 17, and each effective pixel at the time of executing the shutter closing calibration. Imaging is continued by correcting the output offset level difference between 52-55 and each of the reference pixels 56-59. Other operations are the same as those in the first embodiment.

  As described above, according to the second embodiment, the same effects as those of the first embodiment can be obtained. Further, in the second embodiment, at the time of start-up and at a necessary time during imaging, it is appropriately selected. In the shutter closing calibration to be executed, the output offset level of each effective pixel is stored in the reference pixel memory 12 during calibration, and the output offset level of each reference pixel is stored in the reference pixel memory 16 during calibration. The difference of the output offset level existing between the pixels is stored in the calibration difference value memory 17, and the correction corresponding to the output offset difference between the effective pixel and the reference pixel forming a pair in the subtraction circuit 18 is referred to at the time of imaging. Since it is applied to the data in the pixel memory 11 and corrected and stored in the correction memory 13, each effective pixel and each The influence on the image of the output offset level difference caused by the difference in electrical characteristics with the illumination pixel can be eliminated, and the fixed pattern noise can be reduced without causing the image interruption while continuing the imaging with the shutter 3 opened. Not only can be performed, but also the effect of improving the image quality by improving the accuracy of reducing the fixed pattern noise can be obtained.

Embodiment 3 FIG.
FIG. 9 is a block diagram of an uncooled infrared camera according to the third embodiment. In FIG. 9, reference numeral 19 denotes an image sensor having reference pixels arranged in a line. FIG. 10 shows a configuration of the image sensor 19, in which 70 to 75 are effective pixels, and 76 to 78 are reference pixels arranged in a line in the horizontal direction. In the third embodiment, as described above, the image pickup device 19 includes the effective pixels 70 to 75 arranged two-dimensionally and the row direction or the column direction around the outside of the two-dimensional arrangement of the effective pixels 70 to 75. Reference pixels 76 to 78 are provided in common for each array. That is, in the present third embodiment, the reference pixel 76 for the effective pixels 70 and 73 arranged in the column direction, the reference pixel 77 for the effective pixels 71 and 74, and the effective pixels 72 and 75, respectively. The reference pixels 78 form a pair with each other. This point is different from the second embodiment. For simplification of the drawing, FIG. 10 shows only the effective pixels 70 to 75 in the horizontal direction by 3 pixels × 2 in the vertical direction, and the reference pixels in the horizontal direction only for 3 pixels. In order to obtain a practical resolution, generally, effective pixels have about 320 pixels in the horizontal direction × 240 pixels in the vertical direction, and reference pixels have about 320 pixels in the horizontal direction.

  In FIG. 9, reference numeral 20 denotes a reference pixel memory during calibration for storing the reference pixel output in the closed state of the shutter 3 during calibration, and reference numeral 21 denotes an output of the reference pixel in the open state of the shutter 3 during subject imaging. A reference pixel memory 22 at the time of image capture, 22 is a difference value memory at the time of calibration for storing a difference obtained by subtracting data of the effective pixel memory 12 at the time of calibration from the data of the reference pixel memory 20 at the time of calibration, It is a subtraction circuit that subtracts the data in the calibration difference value memory 22 from the data. The reference pixel memory 20 at the time of calibration and the reference pixel memory 21 at the time of imaging have a smaller number of reference pixels 76 to 78 than the first and second embodiments described above, and therefore the reference pixel memory 16 at the time of calibration and the reference pixels at the time of imaging. The memory 11 may have a smaller capacity. In the third embodiment, the correction memory 13 is connected to the calibration effective pixel memory 12 and the subtraction circuit 23, and any one of these outputs is stored. Details of the stored data will be described later. Since other configurations are the same as those in FIGS. 6 and 2, the same reference numerals are given and description thereof is omitted here. Further, the configuration of the effective pixels is the same as the configuration of FIG. 3, and the configuration of the reference pixels is the same as the configuration of FIG. 4, so these drawings will be referred to.

  As described above, the uncooled infrared camera according to the third embodiment collects infrared light emitted from the subject during imaging and forms an image on the image sensor 2 and a plurality of two-dimensionally arranged infrared optical systems. The image pickup device 2 including the effective pixels 70 to 75 and the plurality of reference pixels 76 to 78 arranged in common with respect to the respective arrays in the column direction of the effective pixels 70 to 75, and an opening The shutter 3 installed at a position where infrared rays with substantially uniform intensity can be incident on each of the effective pixels 70 to 75 and the reference pixels 76 to 78 constituting the image pickup device 2, and an uncooled infrared camera. A control signal generation circuit 7 that outputs a control signal for each part, a calibration effective pixel memory 12 that stores an output of each effective pixel 70 to 75 in the shutter closed state, and an output of each effective pixel 70 to 75 in the shutter closed state The reference pixel memory 20 for calibration, the difference value memory 22 for calibration for storing the difference between the reference pixel memory 20 for calibration and the effective pixel memory 12 for calibration, and the reference pixels 76 to in the shutter open state at the time of subject imaging An imaging reference pixel memory 21 that stores the output of 78, a subtraction circuit 23 that subtracts and corrects the data in the calibration difference value memory 22 from the data in the imaging reference pixel memory 21, and a calibration effective pixel memory 12; A subtraction correction circuit 14 that performs offset correction by subtracting one of the data output from the subtraction circuit 23 from the output of each of the effective pixels 70 to 75 at the time of subject imaging, and outputs the offset-corrected data as an image signal. The display processing circuit 15 is provided.

In FIG. 9,
(Dopt0 (m)) bar: data in the calibration effective pixel memory 12 acquired with the shutter 3 closed,
(Dref0 (k)) bar: data in the calibration reference pixel memory 20 acquired with the shutter 3 closed,
(Dref1 (k)) bar: data in the reference pixel memory 11 at the time of imaging acquired with the shutter 3 opened,
Dopt1 (m): data of effective pixels during imaging,
Dref1 (k): Reference pixel data during imaging.

Further, as shown in FIG. 9, the data stored in the correction memory 13 is
(I) The period from the execution of the shutter close calibration to the execution of the shutter open calibration is a (Dopt0 (m)) bar.
(Ii) After the shutter opening calibration is executed and until the shutter closing calibration is executed, ((Dref1 (k)) bar)-{((Dref0 (k)) bar)-((Dopt0 (m) ) Bar)} (*).

Furthermore, as shown in FIG. 9, the image data output by the display processing circuit 15 is
(I) After the shutter closing calibration is executed and until the shutter opening calibration is executed, it is Dopt1 (m)-((Dopt0 (m)) bar).
(Ii) After the shutter opening calibration is executed and until the shutter closing calibration is executed, Dopt1 (m) − [((Dref1 (k)) bar) − {((Dref0 (k)) bar) − ((Dopt0 (m)) bar)}] (*).

In addition, m and k are as follows, m is a code attached to the effective pixel, and k is a code attached to the reference pixel.
m = 70, 71, 72, 73, 74, 75
k = 76, 77, 78

However, for the data marked with (*), the combinations of m and k are as follows.
(M, k) = (72, 78), (71, 77), (70, 76),
(75, 78), (74, 77), (73, 76)

  In the third embodiment, the reference pixel memory 20 at the time of calibration is output offset data of the reference pixels 76 to 78 at the time of executing the shutter closing calibration, and the reference pixel memory 21 at the time of imaging is referred to in the shutter open state at the time of imaging. The output offset data for the pixels 76 to 78 and the calibration effective pixel memory 12 store the output offset data for the valid pixels 70 to 75 when the shutter close calibration is executed. Further, the calibration difference value memory 22 stores the difference between the data in the calibration effective pixel memory 12 and the data in the calibration reference pixel memory 20 positioned corresponding to the same column for each effective pixel by the number of effective pixels. It is remembered. In the subtraction circuit 23, the difference between the data in the calibration difference value memory 22 and the data in the imaging reference pixel memory 21 corresponding to the same column is calculated, and the above-mentioned (*) is added to the correction memory 13. Data corresponding to the number of effective pixels indicated by a combination of m and k is stored. Since other operations are the same as those in the second embodiment, the reference pixel memory 11 at the time of imaging is the reference pixel memory 21 at the time of imaging, the reference pixel memory 16 at the time of calibration is reference pixel memory 20 at the time of calibration, and the difference at the time of calibration. The value memory 17 is replaced with the calibration difference value memory 22, the subtraction circuit 18 is replaced with the subtraction circuit 23, n is replaced with k, and the description and FIG. 7 are referred to, and the detailed description is omitted here. The relationship between the reference pixel memory 21 at the time of imaging, the effective pixel memory 12 at the time of calibration, the correction memory 13, the data stored in the reference pixel memory 20 at the time of calibration, and the image data output from the display processing circuit 15 at each stage of the operation. Is as described above.

  As described above, in the third embodiment, the same effect as in the first and second embodiments described above can be obtained, and in addition, in the third embodiment, the reference pixels 76 to 78 are effective. Since the pixels 70 to 75 are arranged outside the two-dimensional array, the aperture ratios of the effective pixels 70 to 75 are improved as compared with the first and second embodiments, and the shutter 3 is arranged like the first and second embodiments. It is possible to reduce the fixed pattern noise without causing image interruption while continuing the imaging while being opened, and to improve the sensitivity as an uncooled infrared camera. In the third embodiment, the reference pixels 78 to 76 are located farther from the constant current sources 48 to 51 outside the two-dimensionally arranged effective pixels (below the two-dimensional arrangement of the effective pixels 70 to 75 in FIG. 10). ) Shows the case of being arranged in the horizontal direction, but it may be arranged on the side close to the constant current sources 48 to 51 (above the two-dimensional array of effective pixels 70 to 75 in FIG. 10). Furthermore, although the case where the reference pixels 76 to 78 are arranged in the horizontal direction on the opposite side of the horizontal scanning circuit 41 is shown, the vertical scanning circuit 40 side or the vertical side outside the two-dimensional array of the effective pixels 70 to 75 is shown. The same effect can be obtained by arranging the scanning circuit 40 vertically on the opposite side of the scanning circuit 40.

  In the description of the first, second, and third embodiments, it is assumed that the shutter closing calibration is executed by closing the shutter 3 installed between the infrared optical system 1 and the imaging elements 2 and 19. As described above, the position of the shutter 3 may be in front of the infrared optical system 1, or other means other than the shutter may be used as long as infrared light having a uniform intensity can be incident on each effective pixel and each reference pixel. . In the above description, the shutter closing calibration signal and the shutter opening calibration signal are input from the outside of the uncooled infrared camera. However, the first shutter closing calibration signal after the activation is automatically sent from the control signal generation circuit 7. It is good also as a structure supplied to.

It is a block diagram which shows the structure of the non-cooling infrared camera by Embodiment 1 of this invention. It is a figure which shows the structure of the image pick-up element 2 in the non-cooling infrared camera by Embodiment 1 and 2 of this invention. It is the structure schematic diagram of the effective pixels 52-55 in the non-cooling infrared camera by Embodiment 1 and 2 of this invention, and the effective pixels 70-75 in Embodiment 3 of this invention. It is the structure schematic diagram of the reference pixels 56-59 in the non-cooling infrared camera by Embodiment 1 and 2 of this invention, and the reference pixels 76-78 in Embodiment 3 of this invention. It is a flowchart which shows operation | movement of the non-cooling infrared camera by Embodiment 1 of this invention. It is a block diagram which shows the structure of the non-cooling infrared camera by Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the non-cooling infrared camera by Embodiment 2 of this invention. It is a figure which shows the difference of the temperature change of the output offset level of the effective pixel and reference pixel in the non-cooling infrared camera by Embodiment 2 and 3 of this invention. It is a block diagram which shows the structure of the non-cooling infrared camera by Embodiment 3 of this invention. It is a figure which shows the structure of the image pick-up element 19 in the non-cooling infrared camera by Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Infrared optical system, 2 Image sensor, 3 Shutter, 4 element package, 5 Driver circuit, 6 DC power supply, 7 Control signal generation circuit, 8 Amplification circuit, 9 A / D conversion circuit, 10 Frame integration circuit, 11 At the time of imaging Reference pixel memory, 12 Valid pixel memory during calibration, 13 Correction memory, 14 Subtraction correction circuit, 15 Display processing circuit, 16 Reference pixel memory during calibration, 17 Difference value memory during calibration, 18 Subtraction circuit, 19 Imaging device, 20 During calibration Reference pixel memory, 21 Reference pixel memory at imaging, 22 Calibration difference value memory, 23 Subtraction circuit, 52, 53, 54, 55 Effective pixel, 56, 57, 58, 59 Reference pixel, 63 Hollow heat insulation structure, 69 Infrared absorption Structure, 70, 71, 72, 73, 74, 75 effective pixels, 76, 77, 78 reference pixels.

Claims (5)

An image sensor comprising a plurality of effective pixels and a plurality of reference pixels;
A shutter that has an opening, and is disposed at a position where infrared light having a substantially uniform intensity can be incident on each of the effective pixel and the reference pixel constituting the image sensor by closing the opening; ,
Calibration effective pixel memory for storing the output of each effective pixel in the closed state of the shutter;
An imaging reference pixel memory for storing the output of each reference pixel in the open state of the shutter at the time of subject imaging;
A subtraction correction circuit that performs offset correction by subtracting one of the data of the effective pixel memory during calibration and the reference pixel memory during imaging from the output of each effective pixel in the open state of the shutter during imaging of the subject; An uncooled infrared camera characterized by comprising: An image sensor comprising a plurality of effective pixels and a plurality of reference pixels;
A shutter that has an opening, and is disposed at a position where infrared light having a substantially uniform intensity can be incident on each of the effective pixel and the reference pixel constituting the image sensor by closing the opening; ,
Calibration effective pixel memory for storing the output of each effective pixel in the closed state of the shutter;
A reference pixel memory during calibration for storing the output of each reference pixel in the closed state of the shutter;
A calibration difference value memory for storing a difference between the calibration reference pixel memory and the calibration effective pixel memory;
An imaging reference pixel memory for storing the output of each reference pixel in the open state of the shutter at the time of subject imaging;
A subtraction circuit for adding a correction for subtracting the data in the calibration difference value memory from the data in the imaging reference pixel memory;
Subtraction correction for performing offset correction by subtracting either the data of the effective pixel memory at the time of calibration or the output from the subtraction circuit from the output of each effective pixel in the open state of the shutter at the time of photographing the subject. An uncooled infrared camera comprising a circuit. The effective pixel is composed of a thermal infrared detector having a hollow heat insulating structure and an infrared absorption structure,
The non-cooled infrared camera according to claim 1 or 2, wherein the reference pixel has a configuration in which both or one of the hollow heat insulating structure and the infrared absorbing structure is excluded from the effective pixel. . The image sensor is
Effective pixels arranged in two dimensions;
The uncooled infrared camera according to any one of claims 1 to 3, further comprising a reference pixel disposed adjacent to each effective pixel in a one-to-one manner. The image sensor is
Effective pixels arranged in two dimensions;
4. The non-pixel according to claim 1, further comprising: a reference pixel that is commonly arranged with respect to the array in the row or column direction around the two-dimensional array of the effective pixels. Cooling infrared camera.

Images