JP2010283514A - Infrared ray imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep the temperature of a thermoelectric conversion element constant and save power consumption. <P>SOLUTION: An infrared ray imaging device includes: bolometer elements of pixels 15a and 15b which have a sunshade structure; and bolometer elements of pixels 2a and 2b which receive infrared rays incident from the outside. Based on resistance values of the bolometer elements of the pixels 15a and 15b, a current mirror source circuit 14, and a self-heating control circuit 16 control supply of a power source VDD (heat-generating voltage) to the bolometer elements of the pixels 15a, 15b, 2a and 2b in a first period. In a second period exclusive from the first period, the current mirror source circuit 14 and a reading circuit 8 make control so as to apply a reading voltage to the bolometer elements of the pixels 15a, 15b, 2a and 2b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an infrared imaging device, and more particularly to an infrared imaging device including thermoelectric conversion elements such as bolometer elements in a matrix.

  A bolometer-type infrared imaging device detects a voltage output by changing a minute amount of infrared light incident on a bolometer element into a resistance change by a bolometer element having a large resistance temperature characteristic. In this case, the resistance value of the bolometer element fluctuates exponentially even with a change in the operating temperature of the infrared imaging device, so that the output voltage of the infrared imaging device fluctuates significantly. In addition to the resistance value, the sensitivity of the bolometer elements and the in-plane variation of the bolometer elements of the sensor array also vary greatly with changes in the operating temperature, causing output fluctuations. Conventionally, an on-chip readout circuit corresponding to the bolometer characteristics of the operating temperature range is designed to suppress these output fluctuation components and detect only the incident infrared component, and the setting conditions are finely adjusted for each fluctuation of the operating temperature. Therefore, the infrared signal component was detected. For example, in the case of a bolometer material having a temperature coefficient of 100 kΩ at a room temperature (27 ° C.) and a resistance temperature coefficient of −2% / K, the resistance value of the bolometer element is about 410 kΩ to about 410 k in a temperature range of −30 ° C. to 70 ° C. 47 kΩ. In order to suppress fluctuations in the output voltage with respect to the resistance value at which the maximum value / minimum value ratio is 8.7 times, it is necessary for the readout circuit and device to cope with it. For this purpose, the function, chip size, and power consumption of the readout circuit are required. Was getting bigger.

  In order to make it unnecessary to deal with such a large resistance change, the temperature of the chip substrate is controlled by a Peltier element or a heater to detect only the temperature change due to the incident infrared rays of the bolometer element formed on the chip. There is a known technique (see Patent Document 1). The substrate temperature is measured by the resistance value of the bolometer element in the substrate, and the temperature of the bolometer element formed on the chip is kept constant by keeping the temperature of the chip substrate constant by controlling the heater element current according to the substrate temperature. Make it smaller. For example, in the case of the bolometer element described above, by controlling the chip temperature at a constant 70 ° C., it is sufficient that the circuit or device corresponds to the minimum value side of the bolometer resistance value.

  Details of such a circuit are shown in FIG. 5 (see Patent Document 1). In this circuit, the voltage of the bolometer element 102 connected to the constant current source 40 is connected to the non-inverting terminal (+) side of the amplifier 42 via the low-pass filter 41, and the constant voltage source 43 is connected to the inverting terminal (−) of the amplifier. The output terminal of the amplifier 42 is connected to the resistance element 60 that is a heater. The temperature of the chip substrate is controlled by setting the output voltage value of the bolometer element at the target temperature to the voltage of the constant voltage source 43.

  The bolometer element 102 is formed separately from the sensor array 103 as shown in FIG. 6, and is thermally short-circuited with the chip substrate 108. Further, the chip substrate 108 and the package are thermally separated from the ambient temperature of the chip substrate 108 by a material 44 such as silica glass having a low thermal conductivity. The method of heating the chip substrate 108 by the resistance element 60 that is an on-chip heater is less expensive than the method of heating and cooling the substrate using an external circuit such as a Peltier element, and easily controls the substrate temperature. can do.

International Publication No. 98/35212 Pamphlet

  The following analysis is given in the present invention.

  By the way, the bolometer element has a structure that is thermally separated from the substrate for high sensitivity, and there is a temperature difference between the bolometer temperature and the substrate temperature due to self-heating when reading the signal of the bolometer element. To do. In the conventional example, since the temperature of the chip substrate is measured and the heat generation amount of the substrate is controlled, it is difficult to keep the temperature of the bolometer element itself accurately. In addition to the sensor array, a bolometer element for temperature monitoring, a constant current source for the bolometer element, a resistance element for the heater, and an amplifier circuit for current control of the resistance element are required on the chip, which increases the chip area. To do. In this case, since the entire chip having a larger thermal conductivity and heat capacity than the bolometer element generates heat, the power consumption increases as the number of pixels of the sensor array increases and the chip area increases.

  An infrared imaging device according to one aspect (side surface) of the present invention is based on a thermoelectric conversion element group arranged in a two-dimensional matrix and a resistance value of a part of the thermoelectric conversion elements of the thermoelectric conversion element group. And a control circuit for controlling the application of the heat generation voltage to the element group.

  According to the present invention, since the thermoelectric conversion element group generates heat, the temperature of the thermoelectric conversion element can be kept constant and the power consumption can be suppressed.

1 is a circuit diagram of an infrared imaging device according to an embodiment of the present invention. It is a figure which shows typically the access state of the pixel in the infrared imaging device which concerns on the Example of this invention. It is a circuit diagram of the principal part of the infrared imaging device which concerns on the Example of this invention. It is a timing chart showing operation of a self-heating control circuit. It is a circuit diagram of the conventional infrared imaging device. It is a figure which shows the structure of the conventional infrared imaging device.

  The infrared imaging device according to the embodiment of the present invention is based on the thermoelectric conversion element group arranged in a two-dimensional matrix and the resistance value of a part of the thermoelectric conversion element of the thermoelectric conversion element group. And a control circuit for controlling application of the heat generation voltage.

  In the infrared imaging device, the thermoelectric conversion element group includes a first thermoelectric conversion element (bolometer element 3 in the pixels 15a and 15b in FIG. 1) having a light shielding structure and a second light receiving infrared rays incident from the outside. Thermoelectric conversion elements (bolometer elements 3 in the pixels 2a and 2b in FIG. 1), and the control circuit (current mirror source circuit 14 and self-heating control circuit 16 in FIG. 1) is a resistance of the first thermoelectric conversion element. Based on the value, the supply of the heating voltage (VDD in FIG. 1) to the first and second thermoelectric conversion elements is controlled in the first period, and in the second period exclusive to the first period. The first and second thermoelectric conversion elements may be controlled to apply a read voltage (supplied from the current mirror source circuit 14 and the read circuit 8 in FIG. 1).

  In the infrared imaging device, the control circuit compares the resistance value of the first thermoelectric conversion element with a predetermined value, and controls the supply of heat generation voltage to the first and second thermoelectric conversion elements according to the comparison result. It may be.

  In the infrared imaging device, the resistance value of the first thermoelectric conversion element may be obtained from the current value flowing through the first thermoelectric conversion element in the second period.

  In the infrared imaging device, each of the first and second thermoelectric conversion elements includes two or more thermoelectric conversion element sets, and the control circuit exclusively sets each of the thermoelectric conversion element sets in the first and second periods. You may make it control correspondingly.

  The infrared imaging apparatus further includes a readout circuit (8 in FIG. 1) that integrates the current flowing through the second thermoelectric conversion element by the readout voltage in the second period and outputs the received infrared rays as an output voltage. Also good.

  The infrared imaging device further includes a detection circuit (a function of the current mirror source circuit 14 in FIG. 1) that detects a current flowing through the first thermoelectric conversion element by the readout voltage in the second period. A current corrected based on the detection current of the detection circuit may be integrated with the current flowing through the thermoelectric conversion element.

  In the infrared imaging device, the second thermoelectric conversion elements are arranged in a two-dimensional matrix, and the first thermoelectric conversion elements are arranged corresponding to each row of the matrix, and the first and second thermoelectric conversion elements. May be activated in a time-sharing manner for each row of the matrix, and a readout circuit may be provided for each column of the matrix so that each output voltage is scanned and output.

  In the infrared imaging device, the thermoelectric conversion element may be a bolometer element.

  In the above, the two-dimensional matrix may be one-dimensional.

  According to the infrared imaging apparatus as described above, a voltage is applied to the bolometer element, and the temperature of the bolometer element is controlled by heating the bolometer element using self-heating due to the current. Since the heat capacity and thermal conductivity of the bolometer element are very small compared to the chip substrate, it is possible to suppress power consumption for keeping the temperature of the bolometer element constant.

  Also, without using a separate bolometer element for temperature monitoring, a heater element for heating the substrate, and its current control circuit, the bolometer temperature is monitored from the output voltage of the existing circuit, and the bolometer element has a simple circuit configuration with only a power supply and a switch. Control self-heating. Therefore, the circuit area can be reduced.

  Further, in order to keep the temperature of the bolometer element thermally separated from the substrate constant, the temperature of the bolometer element that is also thermally separated and has no sensitivity to incident infrared rays is measured as a resistance value. As a result, the temperature difference between the bolometer element and the substrate and the influence of incident infrared rays are not affected, and the temperature of the bolometer element can be accurately monitored and temperature control can be performed.

  Hereinafter, it will be described in detail with reference to the drawings in accordance with embodiments.

  FIG. 1 is a circuit diagram of an infrared imaging device according to an embodiment of the present invention. 1, the infrared imaging device includes a sensor array 1, a vertical shift register 5, switch circuits 7a, 7b, 9a, 9b, 12, a readout circuit 8, a horizontal shift register 11, a current mirror source circuit 14, and a self-heating control circuit 16. Is provided.

  The sensor array 1 includes pixels 2a, 2b, 15a, and 15b. The pixels 2a, 2b, 15a, and 15b each include a bolometer element 3 and a switch element 4 that opens and closes one end of the bolometer element 3 and the ground. The pixels 2 a and 2 b are a pair of pixels that receive infrared rays incident from the outside, and a large number of pixels 2 a and 2 b are arranged in a two-dimensional matrix in the sensor array 1. The pixels 15a and 15b are a pair of pixels having a light shielding structure, and one pixel is arranged corresponding to each row of the matrix. That is, the sensor array 1 has pixels 15a and 15b having a structure shielded so as not to be sensitive to the incident infrared rays in the two columns at the end of the sensor array 1, and the incident infrared rays in the remaining many columns. It comprises pixels 2a and 2b that receive light.

  In the pixel 2a, the other end of the bolometer element 3 included in the pixel in the column direction is connected to the wiring 6a in common for each column, and then connected to the readout circuit 8 via the switch circuit 7a and the switch circuit 9a. Is connected to a power supply VDD serving as a self-heating power supply. Further, the control ends of the switch elements 4 included in the pixels 2a in the row direction are connected to the wiring 13a in common for each row, and then connected to the vertical shift register 5.

  In the pixel 2b, the other end of the bolometer element 3 included in the pixel in the column direction is connected to the wiring 6b in common for each column, and then connected to the readout circuit 8 through the switch circuit 7b, and the switch circuit 9b. To the power supply VDD. Further, the control ends of the switch elements 4 included in the pixel 2b in the row direction are connected to the wiring 13b in common for each row and then connected to the vertical shift register 5.

  In the pixel 15a, the other end of the bolometer element 3 included in the pixel in the column direction is connected to the wiring 6c common to the column, and then connected to the current mirror source circuit 14 via the switch circuit 7c. It is connected to the power supply VDD via 9c. The control terminal of the switch element 4 included in the pixel 15a is connected to the common wiring 13a for each row and then connected to the vertical shift register 5.

  In the pixel 15b, the other end of the bolometer element 3 included in the pixel in the column direction is connected to the wiring 6d common to the column, and then connected to the current mirror source circuit 14 via the switch circuit 7d. It is connected to the power supply VDD via 9d. The control end of the switch element 4 included in the pixel 15b is connected to the common line 13b for each row and then connected to the vertical shift register 5.

  The vertical shift register 5 receives the vertical shift clock signal CLK2 and the shift signal VIN, and sequentially sets the wirings 13a and 13b to the high level in a time division manner, and selects the row of the sensor array 1 to be read. As will be described later, in order to cause the bolometer element 3 to generate heat, the wirings 13a and 13b in all the rows are alternately set to the high level in a time division manner.

  The current mirror source circuit 14 supplies a canceller voltage Vc related to heat generation control and readout correction to the readout circuit 8 and the self-heating control circuit 16. The read circuit 8 corrects the currents flowing in the wirings 6a and 6b read through the switch circuits 7a and 7b, respectively, with the canceller voltage Vc, and outputs the corrected output voltage Vout through the switch circuit 12. The horizontal shift register 11 receives the horizontal shift clock signal CLK1 and the shift signal HIN, scans the output voltage of each readout circuit 8 and outputs the output signal VOUT, and sequentially turns on the switch circuit 12 in a time division manner. And

  The self-heating control circuit 16 outputs the self-heating switch signals Sa and Sb when the canceller voltage Vc is larger than a predetermined value to exclusively turn on and off the switch circuits 9a and 9b and exclusively switch the switching circuits 9c and 9d. Turn on and off. The self-heating control circuit 16 stops the output of the self-heating switch signals Sa and Sb and turns off the switch circuits 9a, 9b, 9c and 9d when the canceller voltage Vc is smaller than a predetermined value.

  Here, an example is shown in which pixels (pixel pairs) arranged at a ratio of one in two columns are selected. However, the present invention is not limited to this, and the pixel may be configured to be operable in a time division manner at a rate of one in three or more columns.

  FIG. 2 is a diagram schematically illustrating a pixel access state in the infrared imaging apparatus according to the embodiment of the present invention. In FIG. 2, among the columns selected by the switch circuits 7 a to 7 d, the current mirror source circuit 14 and the plurality of readout circuits 8 to which the pixels of one row in which the switch element 4 is selected by the vertical shift register 5 are respectively connected. Signals are read out in parallel. On the other hand, among the switch circuits 9a to 9d during the same period, a column that is not selected by the switch circuits 7a to 7d is selected, and the switch elements 4 of all the pixels in the same column are selected by the vertical shift register 5, so Current is passed to generate heat. In this case, each pair of pixels operates exclusively with switch circuits 7a and 7b that operate exclusively, switch circuits 7c and 7d that operate exclusively, and switch circuits 9a and 9b that operate exclusively. Reading and heat generation are alternately repeated by the switch circuits 9c and 9d.

  As shown in FIG. 2, when the columns are alternately switched and this is repeated twice, the reading process for one row is completed. At the same time, when the readout circuit is not selected, the current can be supplied to the pixels corresponding to half of the sensor array, thereby performing temperature control by self-heating of all bolometer elements.

  FIG. 3 is a circuit diagram of the main part of the infrared imaging device according to the embodiment of the present invention. 3, the same reference numerals as those in FIG. 1 represent the same items.

  The readout circuit 8 includes a bias NMOS transistor MN2 that applies a constant voltage Vs to the pixels 2a and 2b, a bias cancel circuit 19 that removes an offset current other than an incident infrared signal, and a drain and bias cancel circuit of the NMOS transistor MN2. And an integrating circuit 21 connected to 19 outputs.

  The bias cancel circuit 19 includes a DC correction circuit 20 that adjusts the level of the applied canceller voltage Vc, a PMOS transistor MP1, and a resistance element R2. The PMOS transistor MP1 has a source connected to the power supply VDD via the resistor element R2, a gate connected to the output of the DC correction circuit 20, and a drain connected to the drain of the NMOS transistor MN2. The DC correction circuit 20 is a circuit for offsetting the output voltage VOUT in order to effectively output the incident infrared signal component of the light receiving pixel.

  The integrating circuit 21 includes an operational amplifier OP1 and a capacitive element C1. The integrating circuit 21 integrates the current corrected by the bias cancel circuit 19 with respect to the current flowing through the bolometer element 3 by the constant voltage Vs applied to the gate of the NMOS transistor MN2, and outputs the result as the output signal VOUT via the switch circuit 12. .

  The current mirror source circuit 14 includes an NMOS transistor MN1 and a resistance element R1. The current mirror source circuit 14 applies the same constant voltage Vs as that of each light receiving pixel to the pixels 15a and 15b having a light shielding structure that is not sensitive to incident infrared rays. The current mirror source circuit 14 and the plurality of readout circuits 8 are combined to form a current mirror. With this circuit configuration, the resistance change component of the bolometer element caused by the fluctuation of the temperature (reference temperature) other than the signal component of the incident infrared ray is removed.

  The self-heating control circuit 16 includes a comparator CMP1, an inverter circuit INV1, and NOR circuits NOR1 and NOR2. The comparator CMP1 inputs the canceller voltage Vc to the non-inverting input terminal (+), inputs the temperature setting voltage Vst to the inverting input terminal (−), and outputs the comparison result via the inverter circuit INV1 to the NOR circuits NOR1 and NOR2. Output to one input. The NOR circuit NOR1 receives the horizontal switch signal Swa at the other input terminal, and outputs the self-heating switch signal Sa from the output terminal to the control terminals of the switch circuits 9a and 9c. The NOR circuit NOR2 inputs a horizontal switch signal Swb having a phase opposite to that of the horizontal switch signal Swa to the other input terminal, and outputs a self-heating switch signal Sb from the output terminal to the control terminals of the switch circuits 9b and 9d. The temperature setting voltage Vst is set as a value obtained by measuring the canceller voltage Vc when the bolometer element is at the target temperature in advance. Here, it is assumed that the self-heating control circuit 16 performs a desired operation when it is assumed that the temperature coefficient (resistance temperature coefficient) of resistance change of the bolometer element is negative.

  The switch circuits 7a and 7c are turned on / off by a horizontal switch signal Swa, and the switch circuits 7b and 7d are turned on / off by a horizontal switch signal Swb.

  FIG. 4 is a timing chart showing the operation of the self-heating control circuit 16. The self-heating control circuit 16 compares the canceller voltage Vc with the temperature setting voltage Vst corresponding to the target temperature by the comparator CMP1, and if the canceller voltage Vc is higher than the temperature setting voltage Vst, the temperature of the bolometer element is the target temperature. The switch circuits 9a and 9c and the switch circuits 9b and 9d are turned on and off by the self-heating switch signals Sa and Sb obtained by inverting the horizontal switch signals Swa and Swb, respectively. In this case, the power supply VDD is intermittently supplied to the corresponding bolometer element 3, and the bolometer element 3 generates heat and the temperature rises.

  On the other hand, when the canceller voltage Vc is equal to or lower than the temperature setting voltage Vst, it is considered that the temperature of the bolometer element 3 is equal to or higher than the target temperature, and the self-heating switch signals Sa and Sb are fixed at a low level to switch circuits 9a and 9c. The switch circuits 9b and 9d are turned off. In this case, the power supply VDD is not supplied to the corresponding bolometer element 3, and the bolometer element 3 is naturally cooled, and the temperature decreases.

  As described above, the temperature control of the bolometer elements is easily performed by switching the self-heating switch signals Sa and Sb based on the value of the canceller voltage Vc corresponding to the temperature of the bolometer elements 3 of the pixels 15a and 15b. be able to.

  The infrared imaging device of this embodiment directly controls the temperature by causing the bolometer element to generate heat by passing a current through the bolometer element that is thermally separated from the chip. The heat capacity of the bolometer element is very small compared to the chip, and the thermal conductivity of the bolometer element to the chip is much smaller than the thermal conductivity of the chip package. Therefore, power consumption required for heat generation can be suppressed.

  Further, regarding temperature control of the bolometer element, the canceller voltage Vc output from the current mirror source circuit 14 is used, and the power supply VDD and the switch circuits 9a to 9d connected to the power supply VDD are simply configured. Control heat generation. For this reason, a bolometer element for temperature monitoring, a heater element for heating the substrate, and a circuit for controlling the current of the heater element are not necessary, and the circuit area can be reduced.

  Further, in order to keep the temperature of the bolometer element thermally separated from the substrate constant, the temperature of the bolometer element that is also thermally separated and has no sensitivity to incident infrared rays is monitored. Thereby, a temperature difference from the substrate such as a self-heating component of the bolometer element is taken into consideration, and the bolometer temperature without temperature change due to incident infrared rays can be kept constant. Therefore, the signal component of incident infrared rays can be detected with high accuracy.

  It should be noted that the disclosures of the aforementioned patent documents and the like are incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Various combinations and selections of various disclosed elements are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

DESCRIPTION OF SYMBOLS 1 Sensor array 2a, 2b, 15a, 15b Pixel 3 Bolometer element 4 Switch element 5 Vertical shift register 6a, 6b, 6c, 6d, 13a, 13b Wiring 7a, 7b, 7c, 7d, 9a, 9b, 9c, 9d, 12 Switch circuit 8 Read circuit 11 Horizontal shift register 14 Current mirror source circuit 16 Self-heating control circuit 19 Bias cancel circuit 20 DC correction circuit 21 Integration circuit C1 Capacitor element CMP1 Comparator INV1 Inverter circuit MN1, MN2 NMOS transistor MP1 PMOS transistor NOR1, NOR2 NOR Circuit OP1 Operational amplifier R1, R2 Resistive element

Claims (9)

A thermoelectric conversion element group arranged in a two-dimensional matrix;
A control circuit for controlling the application of the heat generation voltage to the thermoelectric conversion element group based on the resistance value of a part of the thermoelectric conversion elements of the thermoelectric conversion element group;
An infrared imaging device comprising: The thermoelectric conversion element group is:
A first thermoelectric conversion element having a light shielding structure;
A second thermoelectric conversion element that receives infrared rays incident from the outside;
Including
The control circuit controls supply of the heating voltage to the first and second thermoelectric conversion elements in a first period based on a resistance value of the first thermoelectric conversion element, 2. The infrared imaging device according to claim 1, wherein the readout voltage is controlled to be applied to the first and second thermoelectric conversion elements in a second period exclusive of the period.   The control circuit compares the resistance value of the first thermoelectric conversion element with a predetermined value, and controls the supply of the heat generation voltage to the first and second thermoelectric conversion elements according to the comparison result. The infrared imaging device according to claim 2.   The infrared imaging device according to claim 3, wherein the resistance value of the first thermoelectric conversion element is obtained from a value of a current flowing through the first thermoelectric conversion element in the second period. Each of the first and second thermoelectric conversion elements includes two or more thermoelectric conversion element sets,
4. The infrared imaging device according to claim 2, wherein the control circuit controls each of the thermoelectric conversion element groups exclusively in correspondence with the first and second periods. 5.   5. The readout circuit according to claim 2, further comprising a readout circuit that integrates a current flowing through the second thermoelectric conversion element by the readout voltage in the second period and outputs received infrared rays as an output voltage. The infrared imaging device according to any one of the above. A detection circuit for detecting a current flowing through the first thermoelectric conversion element by the read voltage in the second period;
The infrared imaging device according to claim 6, wherein the readout circuit integrates a current corrected based on a detection current of the detection circuit with respect to a current flowing through the second thermoelectric conversion element. The second thermoelectric conversion elements are arranged in a two-dimensional matrix,
The first thermoelectric conversion elements are arranged corresponding to the respective rows of the matrix,
The first and second thermoelectric conversion elements are activated in time division for each row of the matrix,
8. The infrared imaging apparatus according to claim 6, wherein the readout circuit is provided for each column of the matrix, and each output voltage is scanned and output.   The infrared imaging device according to claim 1, wherein the thermoelectric conversion element is a bolometer element.

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