JP2010286440A - Infrared imaging sensor module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an offset distribution present in a signal line direction of an image sensor. <P>SOLUTION: The infrared image sensor includes: sensitization pixels 1 disposed in a two-dimensional shape; reference pixels 2 disposed in a row direction in a pixel area; driving lines 3 connected with respective pixels in common for each line; a vertical scanning circuit 7 for selecting one of the driving lines 3; signal lines 8 connected with the respective pixels for each row; a bias line 10 provided with branch points for each row of the pixel area; differential integration circuits 12 for integrating a difference between signals from the signal line 8 and the bias line 10; and a horizontal scanning circuit 14 for selecting one of output signals of the differential integration circuits 12. A correction circuit 20 stores an output signal corresponding to the reference pixel 2 of the output signals selected by the horizontal scanning circuit 14, takes a difference between the output signal and the reference voltage, generates a correction signal for each reference pixel 2, and outputs a correction signal corresponding to the reference pixel 2 connected with the driving line 3 selected by the vertical scanning circuit 7 in a scanning period on and after the next time to the bias line 10. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an infrared imaging element module that detects a temperature change caused by incident infrared rays with a temperature sensor.

In a conventional infrared imaging element module, a pixel area is configured by two-dimensionally arranged photosensitive pixels and reference pixels configured by excluding at least one of a heat insulating structure and an infrared absorbing structure from the photosensitive pixels. The pixels in the pixel area are connected to each other by a drive line for each row and connected to each other by a signal line for each column. In addition, a bias line having the same resistance value as the drive line is provided in parallel with the drive line, and for each column of the pixel area, the difference between the signal from the signal line and the signal from the bias line is integrated for a certain period of time. A differential integration circuit for output is provided. The signal corresponding to the reference pixel from the differential integration circuit is held by the sample hold circuit, compared with the reference voltage, and a bias voltage corresponding to the difference is output to the bias line.
This suppresses an offset distribution due to a voltage drop in the drive line and a temperature drift due to a change in element temperature, thereby preventing a dynamic range over in a subsequent circuit from occurring (for example, see Patent Document 1). ).

JP 2005-214039 A

  In the infrared imaging element module, a voltage drop in the signal line affects the voltage input to the differential integration circuit in addition to the voltage across the pixel. Since the amount of voltage drop in the signal line varies from pixel row to pixel row, the output from the differential integration circuit also varies from pixel row to pixel row. Therefore, there is an offset distribution in the signal line direction due to the resistance of the signal line in the element output from the imaging element.

In a conventional infrared imaging device module, a signal corresponding to a reference pixel from a differential integration circuit is held by a sample and hold circuit, compared with a reference voltage by a bias generation circuit, and a bias voltage corresponding to the difference is applied to a bias line. Is output. Here, when a bias voltage based on the held signal is output to a pixel row including a reference pixel in which a signal is held, an offset distribution due to a voltage drop in the signal line is reduced.
However, when the signal held by the sample and hold circuit is compared and output by the bias generation circuit, the output from the differential integration circuit has already reached the next line due to the time delay caused by the processing in the sample and hold circuit or the bias generation circuit. It has moved to. Therefore, there is a problem that the offset distribution due to the voltage drop in the signal line cannot be reduced.

Further, in the conventional infrared imaging element module, in order to extract a temperature change in the reference pixel, the output of the reference pixel is input to a low-pass filter, and a signal that has passed through the filter is supplied to the bias line as a bias voltage. . Here, since the period of this temperature change is set to several Hz, the band of the filter is set to several Hz.
However, since the offset distribution generated in the signal line direction has a band of several kHz, it does not pass through the filter and remains as it is. For this reason, there is a problem that the occurrence of clipping easily occurs beyond the dynamic range of the subsequent circuit.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an infrared imaging element module capable of reducing the offset distribution existing in the signal line direction of the imaging element.

  An infrared imaging element module according to the present invention is an infrared imaging element module including an infrared imaging element and a correction unit that reduces an offset distribution existing in the signal line direction of the infrared imaging element. A plurality of photosensitive pixels arranged two-dimensionally in the area, a plurality of photosensitive pixels arranged in the column direction within the pixel area, and a reference pixel whose own temperature does not change due to absorption of infrared rays, and one pole of each pixel in the pixel area A drive line commonly connected for each row, a vertical scanning circuit for selecting one of the drive lines and connecting to the power source, a signal line commonly connecting the other pole of each pixel in the pixel area for each column, and a drive line The bias line is arranged in parallel with each other and has a branch point for each column of the pixel area, and is provided for each column of the pixel area, and integrates the difference between the signal from the signal line and the signal from the branch point of the bias line. Then output And a horizontal scanning circuit that selects one of the output signals from the differential integrating circuit, and the correction means corresponds to the reference pixel among the output signals selected by the horizontal scanning circuit. The output signal is stored, and a correction signal is generated for each reference pixel by taking the difference between the output signal and the reference voltage, and the reference connected to the drive line selected by the vertical scanning circuit in the next and subsequent scanning cycles. A correction signal corresponding to the pixel is output to the bias line.

According to the infrared imaging element module according to the present invention, the correcting means stores the output signal corresponding to the reference pixel among the output signals selected by the horizontal scanning circuit, and calculates the difference between the output signal and the reference voltage. Thus, a correction signal is generated for each reference pixel, and a correction signal corresponding to the reference pixel connected to the drive line selected by the vertical scanning circuit is output to the bias line in the next and subsequent scanning cycles.
Therefore, an infrared imaging element module that can reduce the offset distribution existing in the signal line direction of the imaging element can be obtained.

1 is a circuit diagram showing an infrared imaging element module according to Embodiment 1 of the present invention. FIG. (A), (b) is a block diagram which illustrates the photosensitive pixel of the infrared imaging element module which concerns on Embodiment 1 of this invention. It is a circuit diagram which illustrates the differential integration circuit of the infrared imaging element module which concerns on Embodiment 1 of this invention.

  Hereinafter, preferred embodiments of the infrared imaging element module of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing an infrared imaging element module according to Embodiment 1 of the present invention.
In FIG. 1, a plurality of photosensitive pixels 1 are two-dimensionally arranged in the pixel area of the infrared imaging device. Further, a plurality of reference pixels 2 whose own temperature does not change due to infrared absorption are arranged in the column direction in the pixel area. Here, the reference pixels 2 are arranged as one column at the left end of the pixel area.

In FIG. 1, the reference pixels 2 are arranged as one column at the left end of the pixel area. However, the reference pixels 2 are not limited to this and may be arranged in any one column. Further, the reference pixels 2 do not have to be one column, and a plurality of columns may be provided.
Further, in FIG. 1, in order to simplify the description, the pixel area has a 4 × 4 pixel configuration, but the number of pixels is not limited to this.

Each photosensitive pixel 1 has a heat insulation structure and an infrared absorption structure, and is composed of one or a plurality of diodes connected in series. The structure of the photosensitive pixel 1 will be described in detail with reference to FIG.
FIG. 2 is a configuration diagram illustrating the photosensitive pixel 1 of the infrared imaging element module according to Embodiment 1 of the present invention.

  2A and 2B, a PN junction diode 101 serving as a temperature sensor is supported by two long support legs 104 on a hollow portion 103 provided in a silicon substrate 102. The electrode wiring 105 is embedded in the support leg 104. Note that a plurality of PN junction diodes 101 are preferably connected in series in order to increase sensitivity. The hollow portion 103 increases the thermal resistance between the PN junction diode 101 and the silicon substrate 102 to form a heat insulating structure.

  In this example, the PN junction diode 101 is formed on the SOI layer of the SOI substrate, and the buried oxide film under the SOI layer is a part of the structure that supports the hollow structure. In addition, the infrared absorption structure 106 that is in thermal contact with the diode portion has a structure that protrudes above the support leg 104 so that infrared rays incident from above can be efficiently absorbed. In FIG. 2B, in order to make the structure of the lower part easy to understand, the infrared absorption structure in the front part of the drawing is omitted.

  When infrared light is incident on the photosensitive pixel 1, it is absorbed by the infrared absorbing structure 106, the temperature of the photosensitive pixel 1 changes due to the above-described heat insulation structure, and the forward voltage characteristics of the PN junction diode 101 serving as a temperature sensor change. By reading the change amount of the forward voltage characteristic of the PN junction diode 101 with a predetermined detection circuit, an output signal corresponding to the amount of incident infrared rays can be taken out. In the infrared imaging device, a plurality of photosensitive pixels 1 are arranged in a two-dimensional manner, and are accessed in order.

  In such an element, the uniformity of characteristics between pixels is important, but the forward voltage of the diode and its temperature dependence have very little variation between individuals, and for infrared imaging devices, diodes are used as temperature sensors. Is particularly effective in achieving uniform characteristics. In the present invention, the infrared absorption structure may be any structure as long as it absorbs infrared light incident on the element and causes the temperature sensor to rise in temperature, and is not limited to the above structure. Moreover, in this invention, the heat insulation structure should just be a structure which prevents the temperature change of the temperature sensor by infrared absorption, and is not limited to said hollow structure.

  Returning to FIG. 1, the reference pixel 2 has substantially the same configuration as the photosensitive pixel 1 except that it does not have at least one of a heat insulating structure and an infrared absorption structure. The reference pixel 2 may be configured by excluding at least one of the heat insulation structure and the infrared absorption structure from a part of the photosensitive pixels 1 in the pixel area. Thereby, the reference pixel 2 outputs a reference signal corresponding to the temperature change of the entire infrared imaging device. If the sensitivity to infrared absorption falls to a necessary level, either the heat insulating structure or the infrared absorbing structure may be left.

  By outputting the reference signal by the reference pixel 2, it is possible to accurately simulate the response characteristic of the photosensitive pixel 1 with respect to the element temperature, and it is possible to perform highly accurate temperature drift correction. In particular, by eliminating at least one of the heat insulation structure and the infrared absorption structure from a part of the photosensitive pixels 1 in the pixel area, the reference pixel 2 is used to prevent a characteristic shift due to a slight difference in manufacturing conditions. The temperature response characteristic of the photosensitive pixel 1 can be simulated with higher accuracy. Note that a thermistor may be used instead of the reference pixel 2.

  A drive line 3 is connected to one of the poles of the photosensitive pixel 1 and the reference pixel 2 in the pixel area in common for each row. A switch 4 is provided at the end of each drive line 3, and each switch 4 is connected to a power supply 6 via a power supply line 5. Here, when the drive lines 3 are sequentially selected by the vertical scanning circuit 7, the switch 4 is closed, and the voltage from the power source 6 is applied to the photosensitive pixel 1 and the reference pixel 2 through the switch 4 and the drive line 3. The

A signal line 8 is commonly connected to the other pole of the photosensitive pixel 1 and the reference pixel 2 in the pixel area for each column. A first constant current source 9 is connected to the end of each signal line 8.
In FIG. 1, a bias line 10 provided with a branch point for each column of the pixel area is arranged in parallel with the drive line 3 above the pixel area. Connected to each branch point of the bias line 10 is a second constant current source 11 that supplies substantially the same current as the first constant current source 9. Here, the first constant current source 9 and the second constant current source 11 are provided close to each other.

  The bias line 10 has substantially the same resistance value as that of the drive line 3 so as to generate almost the same voltage drop as that of the drive line 3. The bias line 10 only needs to generate a voltage drop substantially the same as that of the drive line 3, and does not necessarily have the same resistance value as that of the drive line 3. Therefore, when the current value of the first constant current source 9 is different from the current value of the second constant current source 11, the drive line 3 and the bias line 10 may have different resistance values accordingly. .

A differential integration circuit 12 is provided for each column of the pixel area. When the voltage across the first constant current source 9 and the voltage across the second constant current source 11 are input to the minus side terminal and the plus side terminal, respectively, the differential integration circuit 12 integrates the difference between the two voltages for a certain period of time. Amplify and output.
The structure of the differential integration circuit 12 will be described in detail with reference to FIG.
FIG. 3 is a circuit diagram illustrating the differential integration circuit 12 of the infrared imaging element module according to Embodiment 1 of the present invention.

  In FIG. 3, the differential integration circuit 12 includes a differential voltage-current conversion amplifier 121 in which the both-ends voltage of the first constant current source 9 and the both-ends voltage of the second constant current source 11 are connected to the input side, and a differential voltage current An integration capacitor 122 connected to the output side of the conversion amplifier 121 and a reset transistor 123 that periodically resets the integration capacitor 122 are provided. The differential voltage-current conversion amplifier 121 is connected without negative feedback, and the product (= time constant) of its output impedance and the capacitance of the integration capacitor 122 is set to be 5 times or more of the integration time. Has been.

A sample and hold circuit 127 including a sample and hold transistor 124, a sample and hold capacitor 125, and a reset transistor 126 is connected to the input terminal of the integration capacitor 122. The integrated output is sampled by the sample hold circuit 127 and output through the buffer 128.
Since the differential integration circuit 12 is configured by using the differential voltage-current conversion amplifier 121 in a state where negative feedback is not performed, the circuit configuration is simplified as compared with a general configuration using an operational amplifier. Can be

Returning to FIG. 1, a switch 13 is provided at the output end of each differential integration circuit 12. Here, when the switches 13 are sequentially selected by the horizontal scanning circuit 14, the output signal from the selected differential integration circuit 12 is output from the output terminal 16 via the output amplifier 15.
Since the bias line 10 has almost the same voltage drop as the drive line 3, the above configuration cancels the voltage drop in the drive line 3 from the output and suppresses the offset distribution due to the drive line 3. it can.

  In this infrared imaging device, the voltage across the first constant current source 9 connected to the reference pixel 2 arranged in the leftmost column of the pixel area is read as a reference signal. This reference signal is read in the same manner as the signal from the normal photosensitive pixel 1. That is, the voltage across the first constant current source 9 connected to the signal line 8 of the reference pixel 2 and the voltage across the second constant current source 11 connected to the bias line 10 are respectively connected to the differential integration circuit 12. It is input to the minus side terminal and the plus side terminal, integrated and amplified. Then, an output signal corresponding to the reference pixel 2 is read for each line of normal image reading by the horizontal scanning circuit 14 and the switch 13, and is output from the output terminal 16 through the output amplifier 15.

Further, among the output signals selected by the horizontal scanning circuit 14, an output signal corresponding to the reference pixel 2 is stored between the output terminal 16 and the input terminal 17 of the infrared imaging device, and this output signal and the reference A correction signal is generated for each reference pixel 2 by taking a difference from the voltage, and a correction signal corresponding to the reference pixel 2 connected to the drive line 3 selected by the vertical scanning circuit 7 in the subsequent scanning cycle is A correction circuit (correction means) 20 that outputs to the bias line 10 is connected.
The correction circuit 20 includes an A / D (Analog to Digital) converter 21, a control circuit (processing means) 22, a line memory 23, a subtractor (subtraction means) 24, a reference power supply 25, and a D / A (Digital to Analog) converter. 26.

  The A / D converter 21 converts the output signal corresponding to the reference pixel 2 out of the output signals selected by the horizontal scanning circuit 14 and outputs the digital signal to the control circuit 22. The control circuit 22 performs an averaging process for each reference pixel 2 based on the output signal from the A / D converter 21 and the average value of the output signal stored in the line memory 23. Here, by averaging the output signal, noise superimposed on the signal can be removed. The line memory 23 stores the average value of the output signal averaged by the control circuit 22 and outputs the average value to the subtractor 24 and the control circuit 22. The line memory 23 may be another memory as long as it has a capacity capable of storing the average value of the output signal.

  A reference power supply 25 is connected to the positive input side of the subtractor 24, and a line memory 23 is connected to the negative input side. The subtractor 24 takes the difference between the average value of the output signal from the line memory 23 and the reference voltage from the reference power supply 25 to generate a correction signal. The D / A converter 26 converts the correction signal generated by the subtracter 24 into an analog signal and outputs it to the bias line 10 via the input terminal 17. Thereby, according to the difference between the output signal from the reference pixel 2 and the reference voltage, the voltage of the bias line 10 can be changed in a direction to reduce the difference.

The correction signal from the correction circuit 20 is output as the difference between the average value of the output signal for each reference pixel 2 and the reference voltage. Here, each reference pixel 2 corresponds to each row of the pixel area. Therefore, the correction circuit 20 outputs a correction signal corresponding to the reference pixel 2 connected to the drive line 3 selected by the vertical scanning circuit 7 to the bias line 10 in the next and subsequent scanning cycles.
The correction signal includes an offset component due to a voltage drop in the signal line 8 and a temperature drift component due to a change in element temperature. Therefore, by outputting the correction signal to the bias line 10, it is possible to reduce an offset distribution due to a voltage drop in the signal line 8 and a temperature drift due to a change in element temperature.

  Note that the reference voltage of the reference power supply 25 may be a certain voltage and is not limited to a specific voltage value. That is, the reference voltage is a reference for automatically correcting the feedback correction signal to a constant voltage. Therefore, the reference voltage may be any voltage as long as it is a certain voltage and is selected so that the output signal from the differential integration circuit 12 falls within the dynamic range of the subsequent circuit.

As described above, according to the first embodiment, the correction unit averages, for each reference pixel, the output signal corresponding to the reference pixel among the output signals selected by the horizontal scanning circuit by the processing unit. The process is executed and the average value of the output signal is stored. Further, the correction means generates a correction signal for each reference pixel by taking the difference between the average value of the stored output signals and the reference voltage by the subtraction means. The correction unit outputs a correction signal corresponding to the reference pixel connected to the drive line selected by the vertical scanning circuit to the bias line in the next and subsequent scanning cycles.
By outputting a correction signal including an offset component due to a voltage drop in the signal line to the bias line, the offset distribution existing in the signal line direction of the image sensor can be reduced.
In addition, since the correction signal includes a temperature drift component due to a change in element temperature, a temperature drift due to a change in element temperature can be reduced.
Further, since the offset distribution existing in the signal line direction of the image sensor is reduced, a sufficient gain can be obtained in the subsequent circuit.

In the first embodiment, the control circuit 22 performs the averaging process for each reference pixel 2 based on the output signal from the A / D converter 21 and the average value of the output signal stored in the line memory 23. Although described as being executed, the present invention is not limited to this.
The control circuit 22 may execute the averaging process only for a predetermined period (predetermined time or predetermined number of times) when the infrared imaging device rises. For example, in order to obtain an offset component due to a voltage drop in the signal line 8, the control circuit 22 averages the output signal for each reference pixel 2 over a predetermined number of times when the infrared image sensor rises, and calculates an average value including the offset component. It is stored in the line memory 23. Then, the control circuit 22 does not execute the averaging process thereafter, and the subtractor 24 takes the difference between the average value of the output signal stored in the line memory 23 and the reference voltage from the reference power supply 25 at the time of rising. Then, a correction signal is generated.
In this case, the processing load on the correction circuit 20 due to the averaging process can be reduced.

Further, the control circuit 22 may execute the averaging process only when requested. For example, the control circuit 22 averages the output signal for each reference pixel 2 over a predetermined period (predetermined time or predetermined number of times) only when requested by an external signal or the like, and the average value including the offset component is stored in the line memory 23. Remember me. Then, the control circuit 22 does not execute the averaging process thereafter, and the subtractor 24 calculates the average value of the output signal stored in the line memory 23 and the reference voltage from the reference power source 25 when requested. A correction signal is generated by taking the difference.
In this case, it is possible to follow the temperature drift due to the change in the element temperature while reducing the processing load of the correction circuit 20 by the averaging process. The request may be arbitrarily given from the outside, or may be given at regular intervals using a timer, for example.

Further, the control circuit 22 may execute the averaging process using the weighted average. For example, the control circuit 22 gives a large weight to the averaging process a predetermined number of times after the infrared image sensor rises, and gradually decreases the weight.
In this case, it is possible to follow a temperature drift due to a change in element temperature while leaving an offset component due to a voltage drop in the signal line 8.

Further, the control circuit 22 stores the output signal from the A / D converter 21 as it is in the line memory 23 without performing the averaging process, and the subtractor 24 calculates the output signal and the reference voltage from the reference power supply 25. A correction signal may be generated by taking the difference.
In this case, even if a sudden temperature change or the like occurs, high followability can be exhibited.

  DESCRIPTION OF SYMBOLS 1 Photosensitive pixel 2 Reference pixel 3 Drive line 5 Power supply line 6 Power supply 7 Vertical scanning circuit 8 Signal line 9 First constant current source 10 Bias line 11 Second constant current source 12 Differential integration Circuit, 14 horizontal scanning circuit, 15 output amplifier, 20 correction circuit (correction means), 22 control circuit (processing means), 24 subtractor (subtraction means), 25 reference power supply.

Claims (6)

An infrared imaging device module comprising: an infrared imaging device; and a correction unit that reduces an offset distribution existing in a signal line direction of the infrared imaging device,
The infrared imaging element is
A plurality of photosensitive pixels arranged two-dimensionally in the pixel area;
A plurality of reference pixels arranged in the column direction in the pixel area, and a reference pixel whose temperature does not change by absorption of infrared rays,
A drive line that commonly connects one pole of each pixel in the pixel area for each row;
A vertical scanning circuit for selecting one of the drive lines and connecting to a power source;
A signal line in which the other pole of each pixel in the pixel area is commonly connected for each column;
A bias line arranged in parallel with the drive line and provided with a branch point for each column of the pixel area;
A differential integration circuit that is provided for each column of the pixel area and integrates and outputs a difference between a signal from the signal line and a signal from a branch point of the bias line;
A horizontal scanning circuit for selecting one of the output signals from the differential integration circuit,
The correction means stores an output signal corresponding to the reference pixel among the output signals selected by the horizontal scanning circuit, and calculates a correction signal for each reference pixel by taking a difference between the output signal and a reference voltage. An infrared imaging element module that generates and outputs a correction signal corresponding to a reference pixel connected to a drive line selected by the vertical scanning circuit to the bias line in a subsequent scanning cycle. The correction means includes
Processing means for performing an averaging process for each reference pixel on an output signal corresponding to the reference pixel among the output signals selected by the horizontal scanning circuit;
The infrared imaging element module according to claim 1, further comprising: a subtracting unit that generates the correction signal by taking a difference between the output signal averaged by the processing unit and the reference voltage.   The infrared imaging element module according to claim 2, wherein the processing unit performs the averaging process only for a predetermined period when the infrared imaging element rises.   3. The infrared imaging element module according to claim 2, wherein the processing means executes the averaging process only when there is a request from the outside.   The infrared imaging element module according to claim 2, wherein the processing unit performs the averaging process using a weighted average. The infrared imaging element is
First constant current means connected to each end of the signal line;
A second constant current source connected to each branch point of the bias line and flowing the same current as the first constant current source;
The infrared imaging element module according to claim 1, wherein the bias line has the same resistance value as that of the drive line.

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