JP4207831B2 - Infrared detector - Google Patents

Description

  The present invention relates to an infrared detection apparatus that images a temperature distribution of a subject using a plurality of infrared detection elements that convert incident infrared light into an electrical signal, and more specifically, a technique for imaging a temperature distribution of a subject with high accuracy. Related to.

  Conventionally, a plurality of infrared detectors arranged in a two-dimensional matrix of m rows in the vertical direction and n columns in the horizontal direction, a vertical scanner that scans and selects the infrared detectors for extracting output signals in units of rows, and infrared detectors There is known an infrared detection apparatus having a plurality of N-type MOSFETs arranged for each element column and including a horizontal scanner that scans and selects an infrared detection element for extracting an output signal in units of columns (for example, a patent) References 1 and 2).

In the infrared detecting device having such a configuration, the gate of the N-type MOSFET corresponding to the column including the infrared detecting element is selected simultaneously with selecting the row including the infrared element from which the output signal is extracted by the vertical scanner. By inputting a pulse signal to the terminal, an output signal of each infrared detecting element arranged in a two-dimensional matrix is taken out and the temperature distribution of the subject is imaged.
JP-A-8-105794 Japanese Patent Laid-Open No. 7-087399

  However, in the configuration of the conventional infrared detection device, when the infrared detection element is an element having a high output impedance such as a thermopile (thermocouple), a pulse signal is applied to the gate terminal of the N-type MOSFET constituting the horizontal scanner. As shown in FIGS. 5 (a) and 5 (b), step-like changes in the pulse signal when the pulse signal is applied are caused by switching noise as the gate-drain capacitance Cgd of the N-type MOSFET. It is superimposed on the output signal of the infrared detection element via the gate-source capacitance Cgs, and the detection signal of the infrared detection element cannot be extracted with high accuracy.

  In order to solve the above problem, as a first method, as shown in FIG. 6, a horizontal scanner is constituted by an N-type MOSFET and a P-type MOSFET connected in parallel, and N-type MOSFET is connected to the gate terminal of the P-type MOSFET. A method has been proposed to cancel switching noise superimposed via the gate-drain capacitance and the gate-source capacitance of the N-type MOSFET by applying an inverted signal of the pulse signal applied to the gate terminal of the MOSFET. ing.

  Further, in order to solve the above problem, as a second method, as shown in FIG. 7, an inverted signal of the pulse signal is applied to the gate terminal with respect to the drain terminal and the source terminal of the N-type MOSFET constituting the horizontal scanner. A method has also been proposed in which switching noise is canceled by connecting an N-type MOSFET having a capacitance formed between the gate terminal by short-circuiting the drain terminal and the source terminal.

  However, according to the first and second methods, a phase (time) difference occurs between the pulse signal before inversion and the pulse signal after inversion due to the influence of the signal delay by the inverter that inverts the pulse signal. In addition, the switching noise cannot be canceled satisfactorily, and as a result, the output signal of the infrared detection element cannot be read out at high speed.

  According to the first and second methods, an inverter for inverting the pulse signal, a P-type MOSFET connected in parallel for each N-type MOSFET constituting the horizontal direction, and an N-type MOSFET constituting the horizontal direction Since circuit elements such as N-type MOSFETs for forming capacitors connected to the drain terminal and the source terminal are added, the circuit scale of the infrared detection device is increased.

  The present invention has been made to solve the above-described problems, and its object is to reduce the switching noise generated when scanning the infrared detection element without increasing the circuit scale and to increase the temperature distribution of the subject. An object of the present invention is to provide an infrared detection device capable of accurately capturing an image.

  In order to solve the above-described problems, an infrared detection apparatus according to the present invention includes an infrared detection unit having a plurality of infrared detection elements arranged in a two-dimensional matrix in the vertical direction and the horizontal direction, and each infrared detection element. It has a first switch connected and a vertical direction selection signal is input to the control terminal. By switching the first switch to be selected according to the vertical direction selection signal, the output signal of the infrared detection element is selected in the vertical direction. And a second switch connected to each column of the plurality of infrared detection elements and having a horizontal selection signal input to the control terminal, and the second switch to be selected is switched according to the horizontal selection signal. Therefore, the horizontal direction in which the output signal of the infrared detection element selected by the vertical decoder is selected by scanning in the horizontal direction and the output signal of the infrared detection element is output. A second terminal of the second capacitor is connected to the first terminal of the second switch, and the second terminal of the second switch selected immediately before is connected to the other terminal of the second capacitor. The control terminal is connected.

  In order to solve the above-described problem, an infrared detection device according to the present invention is connected to an infrared detection unit having a plurality of infrared detection elements arranged one-dimensionally, and to each of the infrared detection elements, and is connected to a gate terminal. It has a first MOSFET switch to which a selection signal is input, and switches the first MOSFET switch to be selected according to the selection signal, thereby scanning and selecting the output signal of the infrared detection element and outputting the output signal of the infrared detection element A first MOSFET switch, at least one of the drain terminal and the source terminal of the first MOSFET switch is connected to one terminal of the capacitive element, and the other terminal of the capacitive element is immediately before the first MOSFET switch is selected. The gate terminal of the selected first MOSFET switch is connected.

  According to the infrared detection device of the present invention, since switching noise is canceled when output as an output signal, the switching noise generated when scanning the infrared detection element is reduced without increasing the circuit scale, and the subject Can be imaged with high accuracy.

  Hereinafter, a configuration of an infrared detection device according to an embodiment of the present invention will be described with reference to the drawings.

[Configuration of infrared detector]
First, the configuration of an infrared detection device according to an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a circuit diagram showing a configuration of an infrared detection apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an infrared detection apparatus according to an embodiment of the present invention mainly includes a two-dimensional infrared detection element unit 2, a counter 3, a vertical decoder 4, a horizontal decoder 5, and a horizontal scanner 6. Prepare as an element.

  The two-dimensional infrared detection element unit 2 is formed by a plurality of pixels arranged in a two-dimensional matrix of vertical m rows and horizontal n columns. Each pixel includes an infrared detection element 11 and an infrared detection element 11. And an N-type MOSFET switch Mmn (m = 1 to m, n = 1 to n) functioning as a vertical scanner. In FIG. 1, the infrared detection element 11 is assumed to be a thermopile (thermocouple), and the infrared detection element 11 is illustrated as a series circuit of a resistor and a voltage source, which is an equivalent circuit of a thermopile.

  Further, the drain (infrared detector) of the N-type MOSFET switch Mm1 (m = 1 to m) of each pixel in the first column in the horizontal direction, which is a column in which the selection in the horizontal direction is switched simultaneously with the selection in the vertical direction. 11 side) terminal is connected to an N-type MOSFET-Mm1a (m = 1 to m) having a transistor size that is 1/2 that of the N-type MOSFET switch Mm1. The gate terminal of the N-type MOSFET-Mm1a is connected to the gate terminal of the N-type MOSFET switch Mm1 in the row selected immediately before the row is selected.

  That is, the gate terminal of the N-type MOSFET-M11a connected to the drain terminal of the N-type MOSFET switch M11 in the first vertical column is the gate terminal of the N-type MOSFET switch Mm1 in the m-th row and the N-type MOSFET in the second row. The gate terminal of the N-type MOSFET-M21a connected to the drain terminal of the switch M21 is connected to the gate terminal of the N-type MOSFET switch M21 in the first row, and the same applies to the N-type MOSFET switch Mm1 in the m-th row. The gate terminal of the N-type MOSFET-Mm1a connected to the drain terminal is connected to the gate terminal of the N-type MOSFET switch M (m-1) 1 in the (m-1) th row.

  The counter 3 counts the addresses corresponding to the number of pixels constituting the two-dimensional infrared detection element unit 2 based on the reference clock signal CLK, and inputs the count value to the vertical direction decoder 4 and the horizontal direction decoder 5. The vertical decoder 4 is connected in the row direction of the two-dimensional infrared detection element unit 2, and after decoding the count value input from the counter 3, as a vertical direction selection signal Ym (m = 1 to m) for each row. Input to an N-type MOSFET switch Mmn which is a vertical scanner. The horizontal decoder 5 decodes the count value input from the counter 3 and then inputs it to the horizontal scanner 6 as a horizontal direction selection signal Xn (n = 1 to n) for each column.

  The horizontal scanner 6 outputs the output signal Vn (n = 1 to n) of the pixel selected for scanning as the output signal Vout of the infrared detecting device. In this embodiment, the horizontal scanner 6 is provided for each column of the two-dimensional infrared detector elements 2, and the N-type MOSFET switch Mn to which the horizontal selection signal Xn from the horizontal decoder 5 is input to the gate terminal. (N = 1 to n). The input (drain) terminal of the N-type MOSFET switch Mn is connected to the drain terminal and the source terminal of an N-type MOSFET-Mna (n = 1 to n) having a transistor size ½ that of the N-type MOSFET switch Mn. Has been.

  The gate terminal of the N-type MOSFET-Mna is connected to the gate terminal of the N-type MOSFET switch Mn that is selected immediately before the N-type MOSFET switch Mn is selected. That is, the gate terminal of the N-type MOSFET-M1a connected to the input terminal of the N-type MOSFET switch M1 in the first column in the horizontal direction is the gate terminal of the N-type MOSFET switch Mn in the n-th column. The gate terminal of the N-type MOSFET-2a connected to the input terminal of the N-type MOSFET switch M2 is connected to the gate terminal of the N-type MOSFET switch M1 in the first column. The gate terminal of the N-type MOSFET-Mna connected to the input terminal of the type MOSFET switch Mn is connected to the gate terminal of the N-type MOSFET switch M (n-1) in the (n-1) th column.

  The N-type MOSFET switch Mmn, the N-type MOSFET switch Mn, the N-type MOSFET-Mm1a, and the N-type MOSFET-Mna are respectively a first MOSFET switch, a second MOSFET switch, and a first capacitor according to the present invention. It functions as an element and a second capacitor element.

[Basic operation of infrared detector]
Next, the basic operation of the infrared detection device will be described with reference to FIG.

  FIG. 2 is a time chart showing the operation of the infrared detecting device.

  In the infrared detecting device, when the vertical direction selection signal Y1 becomes H (high) level as shown in the timing of t = t1 in FIG. 2, the N-type MOSFET switch M1n is turned on, and the pixel 1n (n = 1 to n). Output signal Vn (n = 1 to n) is input to the horizontal scanner 6. At the same time, when the horizontal direction selection signal X1 becomes H level, the N-type MOSFET switch M1 is turned on, and the output signal of the pixel 11 is scanned and selected as the output signal Vout of the infrared detector. Thereafter, as the horizontal direction selection signals X2 to Xn sequentially become H level, the output signal of the pixel 1n (n = 2 to n) is selected as the output signal Vout following the output signal of the pixel 11. . Next, as the vertical direction selection signal Y2 becomes H level and the horizontal direction selection signal Xn (n = 1 to n) sequentially becomes H level, the output signal of the pixel 2n (n = 1 to n). Is selected as the output signal Vout. Thereafter, the same operation is performed, so that the output signals of the pixels 1n, 2n,..., Mn (n = 1 to n) are sequentially selected as the output signal Vout, and when one cycle ends, the output signal of the pixel 11 The scan selection from is repeated again.

  The infrared detecting device having such a configuration operates as described below when the vertical direction selection signal Ym and the horizontal direction selection signal Xn rise and fall to detect infrared rays without increasing the circuit scale. Switching noise generated when scanning the element 11 is selected can be reduced, and the temperature distribution of the subject can be imaged with high accuracy. Hereinafter, with reference to FIG. 3 and FIG. 4, the operation of the infrared detecting device at the time of rising and falling of the vertical direction selection signal Ym and the horizontal direction selection signal Xn will be described in detail.

[Operation at rising and falling of vertical direction selection signal and horizontal direction selection signal]
(Operations when the horizontal direction selection signal rises and falls)
First, as an example of the operation of the infrared detecting device at the time of falling of the horizontal direction selection signal X2 (= at the time of rising of the horizontal direction selection signal X3) shown in FIG. 3, infrared rays at the time of rising and falling of the horizontal direction selection signal Xn. The operation of the detection device will be described.

  Assuming that the pixels 2n (n = 1 to n) in the second vertical direction are selected when the vertical direction selection signal Y2 becomes H level, the horizontal direction selection signal X2 falls and the horizontal direction is selected at the same time. When the direction selection signal X3 rises, the N-type MOSFET switch M2 in the second column in the horizontal direction is turned off, and at the same time, the N-type MOSFET switch M3 in the third column is turned on. At this time, the step change of the rising edge of the horizontal direction selection signal X3 rises via the gate-drain capacitance Cgd3 and the gate-source capacitance Cgs3 of the N-type MOSFET switch M3 in the third column shown in FIG. It is superimposed on the output signal Vout of the infrared detector as direction switching noise.

  Further, the stepwise change in the falling edge of the horizontal direction selection signal X2 is caused in the output signal Vout as falling edge switching noise via the gate-source capacitance Cgs2 of the N-type MOSFET switch M2 in the second column shown in FIG. Superimposed. At this time, the reason why the switching noise via the gate-drain terminal capacitance Cgd2 is not superimposed on the output signal Vout is that the drain-source is open because the N-type MOSFET switch M2 in the second column is in the OFF state. This is because it is in a (non-conducting) state.

  Further, the step change of the falling edge of the horizontal direction selection signal X2 is connected between the gate terminal of the N-type MOSFET switch M2 in the second column and the drain terminal of the N-type MOSFET switch M3 in the third column. Is superimposed on the output signal Vout as switching noise in the falling direction via the gate-drain capacitance Cgd3a and the gate-source capacitance Cgs3a of the N-type MOSFET-M3a shown in FIG.

That is, the switching noise caused by the capacitors Cgd3 and Cgs3 is superimposed on the output signal Vout as the rising direction switching noise, and the switching noise caused by the capacitors Cgs2 and Cgd3a and Cgs3a is superimposed on the falling direction switching noise. However, as described above, in this infrared detection device, all of the three MOSFETs are of the same conductivity type. The transistor sizes of the N-type MOSFET switches M2 and M3 are equal to each other, and the transistor size of the N-type MOSFET-M3a is 1/2 the size of the N-type MOSFET switches M2 and M3. Furthermore, since the gate-drain capacitance and the gate-source capacitance of the MOSFET are generally equal, the relationship between the gate-drain capacitance and the gate-source capacitance of the three MOSFET switches is expressed by the following formula 1. become.

  Therefore, in this infrared detection device, even if the rising direction switching noise and the falling direction switching noise are superimposed as described above, the switching noise is canceled when output as the output signal Vout as shown in FIG. , There will be no switching noise at all. Here, the operation at the time of falling of the horizontal direction selection signal X2, that is, the operation at the time of rising of the horizontal direction selection signal X3 has been described as an example, but the same operation is performed for other horizontal direction selection signals, Since the switching noise is completely cancelled, there is no switching noise when the horizontal scanning is selected.

(Operations when the vertical direction selection signal rises and falls)
Next, as an example of the operation of the infrared detecting device at the time of falling of the vertical direction selection signal Y1 (= at the time of rising of the vertical direction selecting signal Y2), the operation of the infrared detecting device at the time of rising and falling of the vertical direction selection signal Ym Will be described. When the vertical direction selection signal Y2 rises at the same time as the vertical direction selection signal Y1 falls, the horizontal direction selection signal X1 rises at the same time as the horizontal direction selection signal Xn falls in the horizontal direction, and the vertical scanning selection is performed. At the time of switching, the first column in the horizontal direction is always selected. Therefore, regarding the switching noise at the time of selecting the vertical scanning, the N-type MOSFET switch Mm1 connected to the pixel m1 (m = 1 to m) in the first column in the horizontal direction. It is only necessary to consider (m = 1 to m).

  If the vertical direction selection signal Y2 rises simultaneously with the fall of the vertical direction selection signal Y1, the N-type MOSFET switch M11 in the first row in the vertical direction is turned off and the N-type MOSFET switch M21 in the second row at the same time. Turns on. At this time, the stepwise change in the vertical direction selection signal Y2 is caused as rising direction switching noise via the gate-drain capacitance Cgd21 and the gate-source capacitance Cgs21 of the N-type MOSFET switch M21 in the second row. Superposed on V1 output.

  Further, the step-like change in the fall of the vertical direction selection signal Y1 is superimposed on the output V1 as the fall direction switching noise via the gate-source capacitance Cgs11 of the N-type MOSFET switch M11 in the first row. At this time, the reason why the switching noise via the gate-drain terminal capacitance Cgd11 is not superimposed on the V1 output is that the drain-source is open because the N-type MOSFET switch M11 in the first row is off ( This is because it is in a non-conductive state.

  Further, the falling step-like change of the vertical direction selection signal Y1 is N-type connected between the gate terminal of the N-type MOSFET switch M11 in the first row and the drain terminal of the N-type MOSFET switch M21 in the second row. Through the gate-drain capacitance Cgd21a and the gate-source capacitance Cgs21a of the MOSFET-M21a, it is superimposed on the V1 output as switching noise in the falling direction.

That is, the switching noise caused by the capacitors Cgd21 and Cgs21 is superimposed on the V1 output as the rising direction switching noise, and the switching noise caused by the capacitors Cgs11 and Cgd21a and Cgs21a is superimposed on the falling direction switching noise. However, as described above, in this infrared detection device, all of the three MOSFETs are of the same conductivity type. The transistor sizes of the N-type MOSFET switches M11 and M21 are the same, and the transistor size of the N-type MOSFET-M21a is half the size of the N-type MOSFET switches M11 and M21. Further, as described above, since the gate-drain capacitance and the gate-source capacitance of the MOSFET are equal, the relationship between the gate-drain capacitance and the gate-source capacitance of the three MOSFET switches is expressed by the following Equation 2. It becomes a relationship.

  Therefore, in this infrared detection device, even when the rising direction switching noise and the falling direction switching noise are superimposed as described above, the switching noise is canceled when output as the V1 output, and there is no switching noise. become. Here, the operation at the time of falling of the vertical direction selection signal Y1, that is, the operation at the time of rising of the vertical direction selection signal Y2 has been described as an example, but the same operation is performed for other vertical direction selection signals. Since the switching noise is completely cancelled, there is no switching noise even when the vertical scanning is selected.

  As is apparent from the above description, according to the infrared detecting device according to an embodiment of the present invention, an N-type MOSFET is connected to each drain terminal of the N-type MOSFET switch Mn (n = 1 to n) for horizontal direction selection. A drain terminal and a source terminal of an N-type MOSFET having a transistor size ½ of the switch Mn are connected, and are selected immediately before an N-type MOSFET switch to which the gate terminal of the N-type MOSFET is connected is selected. Connect to the gate terminal of the N-type MOSFET switch. According to such a configuration, it is possible to reduce the switching noise generated when the horizontal scanning is selected as described above and minimize the increase in circuit elements, and to capture the temperature distribution of the subject with high accuracy. it can.

  In addition, according to the infrared detection device according to an embodiment of the present invention, the vertical direction connected to each pixel in the first horizontal column, which is a column in which the selection in the horizontal direction is switched at the same time as the selection in the vertical direction is switched. A drain terminal and a source terminal of an N-type MOSFET having a transistor size 1/2 that of the N-type MOSFET switch Mm1 are connected to each drain terminal of the N-type MOSFET switch Mm1 (m = 1 to m) for selection. The gate terminal of the N-type MOSFET is connected to the gate terminal of the N-type MOSFET switch in the selected row immediately before a row of the connected N-type MOSFET switch is selected. According to such a configuration, it is possible to reduce the switching noise generated when the vertical direction is selected as described above while minimizing an increase in the number of circuits, and to image the temperature distribution of the subject with high accuracy. .

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. For example, although the thermopile is assumed as the infrared detecting element 11 in the above embodiment, the present invention is not limited to the thermopile. Moreover, in the said embodiment, although the infrared detection element 11 was arranged in two dimensions, this invention is not limited to this form, For example, you may arrange the infrared detection element 11 in one dimension. When the infrared detection elements 11 are arranged one-dimensionally, the infrared detection element unit 2 is composed of one row of pixels 1n (n = 1 to n), and functions as the vertical direction decoder 4 and the vertical direction scanner. The N-type MOSFET switch is omitted. As described above, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

It is a circuit diagram which shows the structure of the infrared rays detection apparatus used as one Embodiment of this invention. It is a time chart figure which shows operation | movement of the infrared rays detection apparatus shown in FIG. It is a figure for demonstrating operation | movement of the infrared rays detection apparatus at the time of the rise and fall of a horizontal direction selection signal. It is a figure for demonstrating a mode that the rising direction switching noise and the falling direction switching noise cancel. It is a figure for demonstrating operation | movement of the infrared detection apparatus until now. It is a figure which shows an example of the conventional cancellation method of the switching noise.

Explanation of symbols

2: Two-dimensional infrared detection element unit 3: Counter 4: Vertical decoder 5: Horizontal decoder 6: Horizontal scanner Mmn: N-type MOSFET switch (vertical scanner)
Mn, Mna, Mm1a: N-type MOSFET switch Xn: Horizontal direction selection signal Ym: Vertical direction selection signal

Claims (7)

An infrared detection unit having a plurality of infrared detection elements arranged in a two-dimensional matrix in the vertical and horizontal directions;
An output of the infrared detection element is provided by switching a first switch connected to each infrared detection element and having a control terminal to which a vertical direction selection signal is input, and selecting according to the vertical direction selection signal. A vertical scanner that scans and selects signals vertically;
A second switch connected to each column of the plurality of infrared detection elements and having a control terminal input with a horizontal direction selection signal, and switching a second switch to be selected in accordance with the horizontal direction selection signal makes it possible to change the vertical direction. A horizontal scanner that scans and selects the output signal of the infrared detection element selected by the decoder in the horizontal direction and outputs the output signal of the infrared detection element;
One terminal of a second capacitive element is connected to the first terminal of the second switch, and the control terminal of the second switch selected immediately before is connected to the other terminal of the second capacitive element. It is,
The second switch is configured by a MOSFET, and the second capacitive element is configured by a third MOSFET switch having the same conductivity type as the second switch, and a drain terminal and a source terminal of the third MOSFET switch, An infrared detecting device using a short circuit as the one terminal and a gate terminal as the other terminal .   The total capacitance value of the second capacitance element is half the total capacitance value of the control terminal-first terminal capacitance and the control terminal-second terminal capacitance of the second switch. The infrared detection device according to claim 1. Among the first switches, a first terminal of a first switch connected to each infrared detection element arranged in a row in which selection in the horizontal direction switches simultaneously with selection in the vertical direction. The one terminal of the first capacitive element is connected, and the control terminal of the first switch selected immediately before is connected to the other terminal of the first capacitive element. The infrared detection device according to claim 1 or 2. The total capacitance value of the first capacitance element is ½ of the total capacitance value of the control terminal-first terminal capacitance and the control terminal-second terminal capacitance of the first switch. The infrared detection device according to claim 3. The first switch is constituted by a MOSFET, and the first capacitive element is constituted by a fourth MOSFET switch having the same conductivity type as the first switch, and a drain terminal and a source terminal of the fourth MOSFET switch, The infrared detection device according to claim 3, wherein a short circuit is used as the one terminal and a gate terminal is used as the other terminal. An infrared detection unit having a plurality of infrared detection elements arranged in a one-dimensional manner;
A first MOSFET switch connected to each of the infrared detection elements and having a selection signal input to a gate terminal is provided. By switching the first MOSFET switch that is selected according to the selection signal, the output signal of the infrared detection element is changed. A scanner that selects scanning and outputs an output signal of the infrared detection element;
One terminal of a capacitive element is connected to at least one of the drain terminal and the source terminal of the first MOSFET switch, and the other terminal of the capacitive element is selected immediately before the first MOSFET switch is selected. The gate terminal of the first MOSFET switch connected,
The capacitive element is constituted by a second MOSFET switch having the same conductivity type as the first MOSFET switch, and the drain terminal and the source terminal of the second MOSFET switch are short-circuited as the one terminal and the gate terminal. Is used as the other terminal . The total capacitance value of the capacitive element is half the total capacitance value of the gate-drain capacitance and the gate-source capacitance of the first MOSFET switch. Infrared detector.

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