JP2014185860A - Infrared detection device and method for correcting input/output characteristics of infrared detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared detection device which allows input/output characteristics of an infrared detector to be appropriately corrected by a small number of correction points.SOLUTION: The infrared detection device includes: one or more infrared detectors which generate an output electricity quantity corresponding to input infrared rays; and a correction operation unit 25 which determines a temperature corresponding to the input infrared rays on the basis of the output electricity quantity by correcting input/output characteristics of the infrared detectors by an exponential function.

Description

  The present disclosure relates to an infrared detection device having a function of correcting input / output characteristics, and a method for correcting input / output characteristics of an infrared detector.

  In a Focal Plane Array (FPA) type infrared imaging device, light receiving elements (infrared detectors) corresponding to pixels are two-dimensionally arranged on a plane, and the intensity distribution of infrared rays projected on the surface is converted into an electric signal distribution. And an infrared image is obtained. However, it is usually difficult to make the characteristics uniform between each pixel, and as such, even if the in-plane distribution of the projected infrared intensity is uniform, the output signal has a distribution. . For this reason, in the FPA type infrared imaging device, the output of each pixel is corrected so that the same pixel signal can be obtained for the same incident infrared intensity. Specifically, several infrared rays having known intensities are uniformly incident on the surface, the output is measured, and the pixel output corresponding to the incident light intensity other than the known intensity is corrected by interpolation from the result.

  When performing such correction, since it is necessary to provide infrared sources with known intensities in the apparatus as many as the number of correction points, the apparatus becomes complicated, so that in principle there are few correction points in principle. Interpolation at points is performed. In such a case, a linear interpolation method is usually used assuming the linearity of the pixel element between two points.

However, generally, the incident light-output signal characteristic (hereinafter referred to as input / output characteristic) of the pixel element is not always linear, and in this case, a correction deviation occurs as shown in FIG. . Here, the correction deviation means that the actual incident light intensity or the black body temperature corresponding to the incident light intensity is different from the incident light intensity obtained from the pixel output or the black body temperature corresponding to the incident light intensity. . In Figure 1, the sought image elements, when the output voltage value when the incident infrared radiation intensity of the black body temperature corresponding T ₁ is a V _1, which enters the infrared intensity of black body equivalent temperature T ₂ output voltage value of is V _2. At this time, if the output voltage value of the image element when the target object is imaged is V ₃ , according to the original input / output characteristics, the temperature T ₃ should be correctly detected as the temperature of the target object. In the case of approximation, the temperature T ₃ ′ is erroneously detected as the temperature of the target object. In order to suppress such correction deviation, the correction points are increased and fine linear interpolation is performed, or correction is performed using a correction curve that is closer to the incident light-output signal characteristics of the actual pixel element using polynomial approximation. Can be considered. In this case, however, the number of infrared sources having a known intensity corresponding to the correction point increases.

JP 2012-151661 A

  In view of the above, an infrared detection device that can appropriately correct the input / output characteristics of the infrared detector with a small number of correction points, and a method for correcting the input / output characteristics of the infrared detector are desired.

  The infrared detector is based on the output electric quantity by correcting one or more infrared detectors that generate an output electric quantity corresponding to the input infrared ray, and an input / output characteristic of the infrared detector by an exponential function. A correction calculation unit for obtaining a temperature corresponding to the input infrared rays.

  According to at least one embodiment, there can be obtained an infrared detecting device capable of appropriately correcting the input / output characteristics of the infrared detector with a small number of correction points, and a method for correcting the input / output characteristics of the infrared detector.

It is a figure which shows the correction | amendment deviation by the input / output characteristic of a pixel element. It is a figure for demonstrating the capacitance voltage change by an infrared detection element. It is a figure which shows an example of a structure of the infrared imaging device which is an example of an infrared detection device. 3 is a flowchart illustrating a first embodiment of a method for correcting input / output characteristics in an infrared imaging device. It is a figure which shows an example of a structure of an input / output characteristic calibration data storage part and a correction | amendment calculating part. It is a flowchart which shows the 2nd Example of the correction method of the input-output characteristic in an infrared imaging device. It is a figure which shows an example of a structure of an input / output characteristic calibration data storage part and a correction | amendment calculating part. It is the figure which compared the case where correction | amendment of a prior art was performed, and the case where correction | amendment was performed by the 1st method. It is the figure which compared the case where correction | amendment of a prior art is performed, and the case where correction | amendment is performed by the 2nd method. It is the figure which compared the case where correction | amendment of a prior art was performed, and the case where correction | amendment was performed by the 3rd method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  The cause of the non-linear incident light-output signal characteristics of the pixel element (infrared detector) is various factors such as the non-linearity of the element itself and the non-linearity of the subsequent electrical circuit with respect to the electric signal intensity converted by the pixel. Is included. However, even if ideal linearity is assumed for the element itself, its input / output characteristics are in principle non-linear, and this non-linearity has characteristics approximately expressed by an exponential function. Have been found by the inventors of the present invention. Since this exponential function can be uniquely determined from the correlation between the incident light intensity and the output signal at two points as in the past, the device of the present application can more accurately input / output the pixel element than the two-point linear correction in the prior art. Can be corrected. In addition, since the input / output characteristics can be corrected by a simple exponential function, the apparatus does not become more complicated than necessary.

  The sensitivity R of the infrared detector is defined as “ratio of current value I obtained as output to unit incident light intensity (power)”. Here, the output current dI with respect to the incident light of the incident light intensity W (λ) dλ between the wavelengths λ and λ + dλ is defined from the sensitivity definition, where the wavelength dispersion (spectral characteristic) of the sensitivity is R (λ).

と書ける。したがって、Wの全分光特性に対する出力電流Iは、上式を波長域[0,∞]で積分して、

Can be written. Therefore, the output current I for all spectral characteristics of W is obtained by integrating the above equation in the wavelength range [0, ∞],

となる。ここでR（λ）が、素子駆動バイアス電圧（V_Ig）によって変動するピーク値R_p（V_Ig）と、V_Igによっては変動しない（と仮定した場合の）規格化分光応答特性R₀（λ）によって、

It becomes. Where R (lambda) is the element driving bias voltage peak value varies depending (V _Ig) and R _p (V _Ig), does not vary by V _Ig normalized spectral response (assuming that) R ₀ ( λ)

の形に書けるとする。またW(λ)を、温度Tの黒体放射強度の波長分散特性W（λ,T）

Suppose you can write Also, W (λ) is the wavelength dispersion characteristic W (λ, T) of black body radiation intensity at temperature T

（ｋ：ボルツマン定数、h：プランク定数、c：真空中での光速）によるものとする。光路中での減衰・散乱や、開口径によって決まる比例定数をA（波長に依存しないと仮定）として、上記出力電流Iは、

(K: Boltzmann constant, h: Planck constant, c: speed of light in vacuum). Assuming that the proportionality constant determined by attenuation / scattering in the optical path and the aperture diameter is A (assuming that it does not depend on the wavelength), the output current I is

となる。したがって、暗電流、つまりすべての入射光強度の場合に流れる一定値の電流をId（V_Ig）とすると、温度T₁の黒体からの放射によって赤外線検知器に流れる全電流I_DC（V_Ig）は、

It becomes. Therefore, if Id (V _Ig ) is a dark current, that is, a constant current flowing in the case of all incident light intensities, the total current I _DC (V _Ig) flowing in the infrared detector by radiation from the black body at temperature T ₁ )

と表されることになる。一方、温度T₁の黒体からの放射によって赤外線検知器に流れる全電流と、温度T₂＝T₁+ΔTの黒体からの放射によって赤外線検知器に流れる全電流との差分をΔI_p（V_Ig）とすると、

Will be expressed. On the other hand, the difference between the total current flowing in the infrared detector due to the radiation from the black body at temperature T ₁ and the total current flowing in the infrared detector due to the radiation from the black body at temperature T ₂ = T ₁ + ΔT is ΔI _p ( V _Ig )

となる。ここで、ΔTが十分微小であるとすると、括弧{・}の中は、

It becomes. Here, if ΔT is sufficiently small, the brackets {•} are

と近似できるから、

Can be approximated with

と表すことができる。

It can be expressed as.

Where the ratio of ΔI _p (V _Ig ) to I _DC (V _Ig ),

を考える。ここまでの結果から、この比は、

think of. From the results so far, this ratio is

となる。ここで、

It becomes. here,

である。また上式のうち、

It is. Of the above formula,

は、定義ないしは仮定から、バイアス条件に依存しない定数であり、これを、

Is a constant that does not depend on the bias condition by definition or assumption.

と置く。すると、

Put it. Then

となる。したがって、

It becomes. Therefore,

という関係が得られる。

The relationship is obtained.

Reading circuit in the infrared detector element FPA (R ead O ut I ntegrated C ircuit: ROIC) is common, and a direct injection type. In this case, as shown in FIG. 2, the potential difference V between both ends of the capacitive element 11 is changed by the element current I flowing through the infrared detection element (infrared detector) 10. There is a well-known relational expression Q = CV between the capacitance value C of the capacitive element 11, the accumulated charge Q, and the voltage V between the terminals.

となる。ここで出力信号Sを、蓄積時間Δtでの単位温度差あたりの出力電位差、と定義すると、

It becomes. Here, if the output signal S is defined as an output potential difference per unit temperature difference at the accumulation time Δt,

となるから、先ほどの結果を用いて、

So, using the previous result,

という関係が得られる。ところで、出力信号Sは、その定義「蓄積時間Δtでの単位温度差あたりの出力電位差」から、

The relationship is obtained. By the way, the output signal S is derived from the definition “output potential difference per unit temperature difference at the accumulation time Δt”.

であるから、結局V_DC（T,V_Ig）に関する微分方程式、

_So , after all, the differential equation for V _DC (T, V _Ig ),

が得られる。ところで、ここで考えている赤外線検知器の動作状態では、そのバイアス電圧V_Igは一定であるから、暗電流相当の電圧V_d（V_Ig）は赤外線入射光量（あるいはT）によらず一定である。ここで近似として、右辺の括弧[・]内の第二項を一定値kであると考えると、

Is obtained. By the way, since the bias voltage V _Ig is constant in the operating state of the infrared detector considered here, the voltage V _d (V _Ig ) corresponding to the dark current is constant regardless of the amount of incident infrared light (or T). is there. As an approximation, if we consider the second term in parentheses [·] on the right side to be a constant value k,

となる。良く知られているように、この形の微分方程式の解は指数関数、

It becomes. As is well known, the solution of this form of differential equation is an exponential function,

となる。ここでV_DC0（V_Ig）は変数Tに対する積分定数である。

It becomes. Here, V _DC0 (V _Ig ) is an integral constant for the variable T.

  As can be seen from the above discussion, it can be seen that the input / output characteristics of the infrared detector generally take the form of an exponential function with respect to the black body temperature T corresponding to the incident light intensity. In the process of deriving the input / output characteristics of the infrared detector of equation (2), it is approximated that the amount of change in the infrared radiation intensity with respect to the temperature change of the black body is proportional to ∂W / ∂T. As can be seen from the above, the exponential function relationship of the input / output characteristics of the infrared detector does not reflect the exponential function relationship seen between the black body temperature and the infrared radiation intensity.

Hereinafter, a method for correcting the input / output characteristics of the infrared detector using incident light equivalent to a black body at known temperatures T ₁ and T ₂ (T ₁ <T ₂ ) will be described.
<First method: Method using an arbitrary exponential function>
As described above, the input / output characteristics of the infrared detector are generally expressed as an exponential function with respect to the black body temperature T corresponding to the incident light intensity. Here, this exponential function is expressed using constant coefficients a and b.

とおく。すると、既知温度T₁ならびにT₂の黒体相当の入射光に対する出力電圧がそれぞれV₁ならびにV₂であったとして、

far. Then, assuming that the output voltage for incident light corresponding to a blackbody with known temperatures T ₁ and T ₂ is V ₁ and V ₂ , respectively,

から、赤外線検知器の入出力特性の近似式としての指数関数を一意に決定できる。このとき、任意温度Tの黒体相当の入射光に対する出力電圧がVであるとき、

Thus, the exponential function as an approximate expression of the input / output characteristics of the infrared detector can be uniquely determined. At this time, when the output voltage for incident light equivalent to a black body at an arbitrary temperature T is V,

によって、撮像対象の温度Tを決定できる。

Thus, the temperature T of the imaging target can be determined.

By the way, when the temperature T is expressed as T = T ₁ + DT with T ₁ as a reference, and T ₂ = T ₁ + DT ₀ , the equation (3) is

となる。ここで改めて、

It becomes. Here again,

と置きなおすと、

When I put it again,

となる。従って、

It becomes. Therefore,

として、T=T₁+DTからも撮像対象の温度Tを決定することができる。

As a result, the temperature T to be imaged can also be determined from T = T ₁ + DT.

Similarly, when the temperature T is expressed as T = T ₂ -DT with T ₂ as a reference, and T ₁ = T ₂ -DT ₀ , the equation (3) is

となる。ここで改めて、

It becomes. Here again,

と置きなおすと、

When I put it again,

となる。従って、

It becomes. Therefore,

として、T=T₂-DTからも撮像対象の温度Tを決定することができる。

As a result, the temperature T to be imaged can also be determined from T = T ₂ -DT.

The above two types of methods are merely mathematical operation problems and are in an equivalent relationship with each other, so it is clear that either of these methods may be used.
<Second Method: Method Using Approximation Formula (2)>
Formula (2) above,

において、指数関数の引数の係数は、（１）式から、

The coefficient of the exponential function argument is

となる。この場合のSは、赤外線検知器の出力電圧がV_DC（V_Ig）である場合の値（つまり、V_DC-T曲線における、V_DC＝V_DC（V_Ig）での微係数）である。このSを、既知温度T₁ならびにT₂の黒体相当の入射光に対する出力電圧V₁ならびにV₂に対する平均のS、

It becomes. In this case, S is a value when the output voltage of the infrared detector is V _DC (V _Ig ) (that is, a differential coefficient at V _DC = V _DC (V _Ig ) in the V _DC -T curve). . This S is the average S for the output voltages V ₁ and V ₂ for incident light equivalent to a blackbody with known temperatures T ₁ and T ₂ ,

で近似する。すると、

Approximate. Then

あるいは、

Or

が得られる。このとき、既知温度T₁ならびにT₂の黒体相当の入射光に対する出力電圧V₁ならびにV₂から、（４）式について、

Is obtained. At this time, from the output voltages V ₁ and V ₂ for the incident light corresponding to the black body at the known temperatures T ₁ and T ₂ ,

あるいは、

Or

が得られる（（５）式についても同様であるので、説明は省略する）。したがって、任意温度Tの黒体相当の入射光に対する出力電圧がVであるとき、

(Equivalent to equation (5), description thereof is omitted). Therefore, when the output voltage for incident light equivalent to a black body at an arbitrary temperature T is V,

あるいは、

Or

によって、撮像対象の温度Tを決定できる。あるいは（５）式から、

Thus, the temperature T of the imaging target can be determined. Or from equation (5)

あるいは、

Or

によって、撮像対象の温度Tを決定できる。
＜第３の方法：（２）式の近似式を用いる方法＞
前述のように、（１）式で表されるSは、赤外線検知器の出力電圧がV_DC（V_Ig）である場合の値（つまり、V_DC-T曲線における、V_DC＝V_DC（V_Ig）での微係数）である。ところで、いわゆる平均値の定理により、x-y座標系の任意の滑らかな連続曲線y=f(x)について、変数x変域の区間[x₁,x₂]において、

Thus, the temperature T of the imaging target can be determined.
<Third Method: Method Using Approximation Formula (2)>
As described above, S represented by the equation (1) is a value when the output voltage of the infrared detector is V _DC (V _Ig ) (that is, V _DC = V _DC (V _DC -T curve in the V _DC -T curve). V _Ig )). By the way, according to the so-called mean value theorem, for any smooth continuous curve y = f (x) in the xy coordinate system, in the interval [x ₁ , x ₂ ] of the variable x domain,

を満たす実数cが存在する（ここで、f'(x)は、関数f(x)のxによる一次微分関数を表す）。このことを用いて、当該赤外線検知器の入出力特性上のある点（T_c,V_c）において、

There exists a real number c satisfying (where f ′ (x) represents a first-order differential function of the function f (x) by x). Using this, at a certain point (T _c , V _c ) on the input / output characteristics of the infrared detector,

が成り立つように、（２）式の係数を決定する近似方法が考えられる。このとき、（１）式から、

An approximation method for determining the coefficient of equation (2) is conceivable so that At this time, from equation (1),

となるから、（２）式は、

Therefore, equation (2) becomes

と書ける。既知温度T₁ならびにT₂の黒体相当の入射光に対する出力電圧V₁ならびにV₂から、

Can be written. From the output voltages V ₁ and V ₂ for incident light equivalent to a blackbody with known temperatures T ₁ and T ₂ ,

あるいは、

Or

が得られる。したがって、任意温度Tの黒体相当の入射光に対する出力電圧がVであるとき、

Is obtained. Therefore, when the output voltage for incident light equivalent to a black body at an arbitrary temperature T is V,

あるいは、

Or

によって、撮像対象の温度Tを決定できる。あるいは、温度Tを、T₁を基準としてT=T₁+DTと表し、T₂= T₁+DT₀とすると（６）式は、

Thus, the temperature T of the imaging target can be determined. Alternatively, the temperature T, expressed as T = T ₁ + DT based on the T _1, when the _{T 2 = T 1 + DT 0} (6) Equation,

となる。既知温度T₁ならびにT₂の黒体相当の入射光に対する出力電圧V₁ならびにV₂から、

It becomes. From the output voltages V ₁ and V ₂ for incident light equivalent to a blackbody with known temperatures T ₁ and T ₂ ,

あるいは、

Or

が得られる。したがって、任意温度T=T₁+DTの黒体相当の入射光に対する出力電圧がVであるとき、

Is obtained. Therefore, when the output voltage for incident light equivalent to a black body at an arbitrary temperature T = T ₁ + DT is V,

あるいは、

Or

として、T=T₁+DTからも撮像対象の温度Tを決定することができる。

As a result, the temperature T to be imaged can also be determined from T = T ₁ + DT.

Similarly, when the temperature T is expressed as T = T ₂ −DT with T ₂ as a reference, and T ₂ = T ₁ + DT ₀ , the equation (6) is

となる。既知温度T₁ならびにT₂の黒体相当の入射光に対する出力電圧V₁ならびにV₂から、

It becomes. From the output voltages V ₁ and V ₂ for incident light equivalent to a blackbody with known temperatures T ₁ and T ₂ ,

あるいは、

Or

が得られる。したがって、任意温度T=T₂-DTの黒体相当の入射光に対する出力電圧がVであるとき、

Is obtained. Therefore, when the output voltage for incident light equivalent to a black body at an arbitrary temperature T = T ₂ -DT is V,

あるいは、

Or

として、T=T₂-DTからも撮像対象の温度Tを決定することができる。

As a result, the temperature T to be imaged can also be determined from T = T ₂ -DT.

  FIG. 3 is a diagram illustrating an example of the configuration of an infrared imaging device that is an example of an infrared detection device. In FIG. 3, the boundary between each functional block indicated by each box and another functional block basically indicates a functional boundary. Physical position separation and electrical signal separation are performed. However, it does not always correspond to control logic separation or the like. Each functional block may be one hardware module that is physically separated from other blocks to some extent, or represents one function in a hardware module that is physically integrated with another block. It may be.

  3 includes a pixel circuit array 21, a row selection switch unit 22, a signal extraction & shift register unit 23, an input / output characteristic calibration data storage unit 24, a correction calculation unit 25, a signal output unit 26, and a switch 27. including. The pixel array 21 includes a plurality of pixel circuits arranged on a matrix vertically and horizontally. The pixel circuit at the designated row position is selected by the row selection switch unit 22, and the pixel circuit at the designated column position is further selected by the signal extraction & shift register unit 23. Thereby, imaging data of the pixel can be read out as an output voltage from the pixel circuit at the designated row position and column position.

  Each pixel circuit includes, for example, an infrared detection element 10, a capacitive element 11, and a transistor that operates as a switch 12 as illustrated in FIG. 2. The infrared detecting element 10 has a characteristic that an electric resistance value changes according to the amount of incident light (incident infrared ray), and generates an output electric amount corresponding to the input infrared ray (for example, current flows). An amount of current corresponding to the resistance value of the infrared detection element 10 flows from the capacitive element 11 to the ground GND side via the switch 12 and the infrared detection element 10, and the charge of the capacitive element 11 decreases. A voltage corresponding to the potential difference between both ends of the capacitive element 11 that changes due to the decrease in the electric charge is taken out to the signal extraction & shift register unit 23 as imaging data.

  The signal extraction & shift register unit 23 extracts a column output signal under a constant bias voltage in the selected row as a time-series serial signal. In the serial signal at this time, the output voltage intensity varies depending on the input / output characteristics of each pixel element even if the incident light quantity has the same intensity. The output voltage of each pixel extracted by the signal extraction & shift register unit 23 is supplied to the input / output characteristic calibration data storage unit 24 or the correction calculation unit 25 via the switch 27. The input / output characteristic calibration data storage unit 24 is supplied with an output voltage from the signal extraction & shift register unit 23 in a state where a radiant infrared ray uniform from a black body at a known temperature is incident on the pixel circuit array 21. . As a result, calibration data is stored in the input / output characteristic calibration data storage unit 24.

  At the time of imaging of the target object, the serial signal having a variation from the signal extraction & shift register unit 23 is supplied to the correction calculation unit 25. Based on the calibration data stored in the input / output characteristic calibration data storage unit 24, the correction calculation unit 25 performs a calculation for correcting the input / output characteristics under a predetermined bias condition for each pixel. By this correction calculation, a corrected output voltage in which variations in input / output characteristics are corrected is obtained. At this time, the correction calculation unit 25 corrects the input / output characteristics of the infrared detection element 10 with an exponential function, thereby obtaining a temperature corresponding to the input infrared ray based on the output electric quantity of the infrared detection element 10. The corrected output voltage is a voltage indicating the temperature of the imaging target for each pixel, and is supplied from the correction calculation unit 25 to the signal output unit 26.

  Hereinafter, a method for correcting input / output characteristics in the infrared imaging apparatus shown in FIG. 3 will be described.

  FIG. 4 is a flowchart showing a first embodiment of a method for correcting input / output characteristics in an infrared imaging device. The correction method shown in FIG. 4 will be described with reference to FIGS. In the flowchart, the execution order of the steps is not limited to the order shown in the flowchart, and the execution order of the steps may be changed as long as the operation is not hindered.

First, in step S1, a two-dimensional array (pixel circuit array 21) is set in an operation state in which a desired bias voltage is applied, that is, in a state in which a constant bias voltage V _Ig is applied to the infrared detection element 10 of each pixel. In step S2, the switch 27 is connected to the input / output characteristic calibration data storage unit 24 side. In step S3, the incident uniform infrared radiation in the plane of the object corresponding black body temperature T ₁ of the pixel circuit array 21 (irradiation). In step S4, a pixel output voltage value V ₁ (i, j) is acquired for each pixel of the pixel circuit array 21 in a state where the infrared ray is incident. The output voltage value V ₁ (i, j) is supplied from the signal extraction & shift register unit 23 to the input / output characteristic calibration data storage unit 24.

FIG. 5 is a diagram illustrating an example of the configuration of the input / output characteristic calibration data storage unit 24 and the correction calculation unit 25. The input / output characteristic calibration data storage unit 24 includes an AD conversion unit 31, a storage control unit 32, a read control unit 33, a V ₁ (i, j) storage unit 34, a V ₂ (i, j) storage unit 35, and a temperature storage. Part 36 is included. The correction calculation unit 25 includes a calculation unit 41 and an AD conversion unit 42.

The AD conversion unit 31 converts the analog output voltage supplied from the signal extraction & shift register unit 23 into a digital voltage value. The input / output characteristic calibration data storage unit 24 includes data indicating the pixel position (i, j) of the currently supplied output voltage and data indicating the temperature T ₁ or T ₂ of the currently incident infrared source. Supplied. The storage control unit 32 stores the digital voltage value after AD conversion by the AD conversion unit 31 in the V ₁ (i, j) storage unit 34. At this time, the storage control unit 32 stores the digital voltage value at a memory position corresponding to the pixel position (i, j). Furthermore, the storage control unit 32 stores the current temperature T ₁ of the infrared source in the temperature storage unit 36.

Returning to FIG. 4, in step S < _b > 5, radiant infrared rays that are uniform in a plane from an object corresponding to a black body at temperature T ₂ are incident (irradiated) on the pixel circuit array 21. In step S6, a pixel output voltage value V ₂ (i, j) is acquired for each pixel of the pixel circuit array 21 in a state where the infrared ray is incident. The output voltage value V ₂ (i, j) is supplied from the signal extraction & shift register unit 23 to the input / output characteristic calibration data storage unit 24. In the input / output characteristic calibration data storage unit 24 shown in FIG. 5, the digital voltage value obtained by AD converting the output voltage value V ₂ (i, j) by the AD conversion unit 31 is converted to V ₂ ( i, j) Stored in the storage unit 35. At this time, the storage control unit 32 stores the digital voltage value at a memory position corresponding to the pixel position (i, j). Furthermore, the storage control unit 32 stores the current temperature T ₂ of the infrared source in the temperature storage unit 36.

  Thus, the acquisition of calibration data used for correction is completed. Next, in the normal use state of the infrared imaging device, an operation of performing correction to obtain an infrared image is executed.

In step S7 of FIG. 4, the switch 27 is connected to the correction calculation unit 25 side. Thus, the pixel output V (i, j) from the pixel circuit array 21 is sequentially read out to the correction calculation unit 25 in a state where the constant bias voltage V _Ig is applied to the infrared detection element 10 of each pixel. In the correction calculation unit 25, based on the data stored in the input / output characteristic calibration data storage unit 24, the pixel output V from each pixel is calculated using any one of the above-described first to third methods. The temperature of the imaging target corresponding to (i, j) is obtained.

  Specific examples of temperature calculation include, for example, a correction formula,

を用いた場合について以下に説明する。信号取り出し＆シフトレジスタ部２３から、各画素(i,j)の画素出力電圧V(i,j)が順次出力されてくる。この出力に対応する撮像対象の当該部分の温度T(i,j)は、

The case where is used will be described below. The pixel output voltage V (i, j) of each pixel (i, j) is sequentially output from the signal extraction & shift register unit 23. The temperature T (i, j) of the part to be imaged corresponding to this output is

で求められる。画素(i,j)からの画素出力電圧V(i,j)が補正演算部２５に入力されると、画素位置(i,j)を示すデータに応じて、画素(i,j)に対応した補正データV₁（i,j）、V₂（i,j）、並びにT₁及びT₂が信号取り出し＆シフトレジスタ部２３から読み出される（図４のステップＳ８）。補正演算部２５のＡＤ変換部４２は、画素(i,j)の画素出力電圧V(i,j)をアナログ電圧からデジタル電圧値に変換する。補正演算部２５の演算部４１は、変換後のデジタル電圧値と上記の補正式とを用いて、画素(i,j)の画素出力電圧V(i,j)に対応する撮像対象の当該部分の温度T(i,j)を算出し、信号出力部２６へ出力する（図４のステップＳ９）。ステップＳ８の動作とステップＳ９の動作とが、全画素に対して繰り替えされる（図４のステップＳ１０）。

Is required. When the pixel output voltage V (i, j) from the pixel (i, j) is input to the correction calculation unit 25, it corresponds to the pixel (i, j) according to the data indicating the pixel position (i, j). The corrected data V ₁ (i, j), V ₂ (i, j), and T ₁ and T ₂ are read from the signal extraction & shift register unit 23 (step S8 in FIG. 4). The AD conversion unit 42 of the correction calculation unit 25 converts the pixel output voltage V (i, j) of the pixel (i, j) from an analog voltage to a digital voltage value. The calculation unit 41 of the correction calculation unit 25 uses the converted digital voltage value and the above correction formula, and this part of the imaging target corresponding to the pixel output voltage V (i, j) of the pixel (i, j). The temperature T (i, j) is calculated and output to the signal output unit 26 (step S9 in FIG. 4). The operation in step S8 and the operation in step S9 are repeated for all pixels (step S10 in FIG. 4).

  The signal output unit 26 generates a signal having an intensity corresponding to the above T (i, j), for example, as a contrast signal for television image output according to the configuration of the infrared imaging device, and outputs the generated signal to the display device (step in FIG. 4). S11).

In the second method and the third method described above, in addition to the correction data V ₁ (i, j) and V ₂ (i, j) (and T ₁ and T ₂ ),

の値が必要になる。この値については、予めステップＳ６の段階で計算して信号取り出し＆シフトレジスタ部２３に格納しておいてもよいし、或いはステップＳ９で逐次算出してもよい。また前述の第３の方法では、パラメタcの値が必要になるが、この値は、予め信号取り出し＆シフトレジスタ部２３に保存しておけばよい。

The value of is required. This value may be calculated in advance in step S6 and stored in the signal extraction & shift register unit 23, or may be calculated sequentially in step S9. In the third method described above, the value of the parameter c is required, but this value may be stored in the signal extraction & shift register unit 23 in advance.

  In the above embodiment, the correction calculation unit 25 sequentially executes the correction calculation in order to calculate each T (i, j). On the other hand, instead of sequentially calculating T (i, j), the temperature T (i, j) corresponding to each pixel output voltage V (i, j) is calculated in advance, and the calculated data is It may be stored in the input / output characteristic calibration data storage unit 24 as a table indicating the correspondence between V (i, j) and T (i, j). Such an embodiment is described below.

  FIG. 6 is a flowchart showing a second embodiment of the input / output characteristic correction method in the infrared imaging device. The correction method shown in FIG. 6 will be described with reference to FIGS. In the flowchart, the execution order of the steps is not limited to the order shown in the flowchart, and the execution order of the steps may be changed as long as the operation is not hindered.

First, in step S21, a two-dimensional array (pixel circuit array 21) is set in an operation state in which a desired bias voltage is applied, that is, in a state in which a constant bias voltage V _Ig is applied to the infrared detection element 10 of each pixel. In step S22, the switch 27 is connected to the input / output characteristic calibration data storage unit 24 side. In step S23, radiant infrared rays that are uniform in a plane from an object corresponding to a black body at temperature T ₁ are incident (irradiated) on the pixel circuit array 21. In step S24, a pixel output voltage value V ₁ (i, j) is acquired for each pixel of the pixel circuit array 21 in a state where the infrared ray is incident. The output voltage value V ₁ (i, j) is supplied from the signal extraction & shift register unit 23 to the input / output characteristic calibration data storage unit 24.

  FIG. 7 is a diagram illustrating an example of the configuration of the input / output characteristic calibration data storage unit 24 and the correction calculation unit 25. The input / output characteristic calibration data storage unit 24 includes an AD conversion unit 31, a storage control unit 32, a table calculation unit 51, a voltage / temperature storage unit 52, a table storage unit 53, and a read control / comparison unit 54. The correction calculation unit 25 includes a calculation unit 61 and an AD conversion unit 42.

The AD conversion unit 31 converts the analog output voltage supplied from the signal extraction & shift register unit 23 into a digital voltage value. The input / output characteristic calibration data storage unit 24 includes data indicating the pixel position (i, j) of the currently supplied output voltage and data indicating the temperature T ₁ or T ₂ of the currently incident infrared source. Supplied. The storage control unit 32 stores the digital voltage value after AD conversion by the AD conversion unit 31 in the voltage / temperature storage unit 52. At this time, the storage control unit 32 stores the digital voltage value at a memory position corresponding to the pixel position (i, j). Furthermore, the storage control unit 32 stores the current temperature T ₁ of the infrared source in the voltage / temperature storage unit 52.

Returning to FIG. 4, in step S < _b > 25, radiation infrared rays that are uniform in a plane from an object corresponding to a black body having a temperature T ₂ are incident (irradiated) on the pixel circuit array 21. In step S26, a pixel output voltage value V ₂ (i, j) is acquired for each pixel of the pixel circuit array 21 in a state where the infrared ray is incident. The output voltage value V ₂ (i, j) is supplied from the signal extraction & shift register unit 23 to the input / output characteristic calibration data storage unit 24. In the input / output characteristic calibration data storage unit 24 shown in FIG. 7, a digital voltage value obtained by AD converting the output voltage value V ₂ (i, j) by the AD conversion unit 31 is converted into a voltage / temperature by the storage control unit 32. It is stored in the storage unit 52. At this time, the storage control unit 32 stores the digital voltage value at a memory position corresponding to the pixel position (i, j). Furthermore, the storage control unit 32 stores the current temperature T ₂ of the infrared source in the voltage / temperature storage unit 52.

In step S26, the correction data V ₁ (i, j) and V ₂ (i, j) (and T ₁ and T ₂ ) corresponding to the pixel (i, j) stored in the voltage / temperature storage unit 52 are further displayed. ) And, for example, the following correction formula:

とを用いて、テーブルを作成する。即ち、例えば適当な区間[V(i,j,k)，V(i,j,k)+δV）に対して、

Use and to create a table. That is, for example, for an appropriate interval [V (i, j, k), V (i, j, k) + δV),

を計算することにより、画素(i,j)毎に各区間に対してT(i,j,k)を求める。こうして求めた値が、テーブル記憶部５３に格納される。

By calculating T (i, j, k) for each section for each pixel (i, j). The value thus obtained is stored in the table storage unit 53.

In step S27 in FIG. 6, the switch 27 is connected to the correction calculation unit 25 side. As a result, the pixel output voltage V (i, j) of each pixel (i, j) from the pixel circuit array 21 in the state where the constant bias voltage V _Ig is applied to the infrared detection element 10 of each pixel is corrected. 25 are sequentially supplied.

  In step S28, data is read from the table stored in the table storage unit 53. Specifically, the AD conversion unit 42 of the correction calculation unit 25 converts the pixel output voltage V (i, j) of the pixel (i, j) from an analog voltage to a digital voltage value. The arithmetic unit 61 supplies the pixel output digital voltage value V (i, j) to the read control / comparison unit 54 of the input / output characteristic calibration data storage unit 24. Based on the data indicating the pixel position (i, j) and the digital voltage value V (i, j) of the pixel output, the read control / comparison unit 54 calculates the pixel position from the table stored in the table storage unit 53. The temperature T (i, j) corresponding to (i, j) and the digital voltage value V (i, j) is read out.

In step S29, the temperature T (i, j) of the portion to be imaged corresponding to the pixel output voltage V (i, j) is obtained. That is, from the table stored in the table storage unit 53,
V (i, j, k) ≤ V (i, j) <V (i, j, k) + δV
T (i, j, k) corresponding to k satisfying the above is read out, and this T (i, j, k) is calculated as the temperature T (i of the part to be imaged corresponding to the pixel output voltage V (i, j). , j). The temperature T (i, j) of the part to be imaged is output from the calculation unit 61 to the signal output unit 26. The operation in step S28 and the operation in step S29 are repeated for all pixels (step S30).

  The signal output unit 26 generates a signal having an intensity corresponding to T (i, j), for example, as a contrast signal for television image output according to the configuration of the infrared imaging device, and outputs the generated signal to the display device (step S31).

In the second method and the third method described above, in addition to the correction data V ₁ (i, j) and V ₂ (i, j) (and T ₁ and T ₂ ),

の値が必要になる。この値については、ステップＳ２６の段階で計算してテーブル計算に用いてよい。また前述の第３の方法では、パラメタcの値が必要になるが、この値は、例えば電圧・温度記憶部５２に予め保存しておき、テーブル計算に用いてよい。

The value of is required. This value may be calculated at the stage of step S26 and used for table calculation. In the third method described above, the value of the parameter c is required, but this value may be stored in advance in, for example, the voltage / temperature storage unit 52 and used for table calculation.

FIG. 8 is a diagram comparing the case where correction according to the prior art is performed and the case where correction is performed by the first method. The horizontal axis shows the black body temperature, and the vertical axis shows the difference between the corrected temperature and the original temperature. FIG. 8 shows a case where T ₁ = 20 ° C. and T ₂ = 60 ° C. A deviation between a value corrected by linear interpolation between two points (T ₁ , T ₂ ) by a conventional technique and a true value is shown as a curve 71. Further, a deviation between the value corrected between the two points (T ₁ , T ₂ ) by the above-described first method and the true value is shown as a curve 72. As can be seen from FIG. 8, even in the case of the first method using a relatively simple exponential function, the correction accuracy is improved as compared with the prior art.

FIG. 9 is a diagram comparing a case where correction according to the prior art is performed and a case where correction is performed by the second method. The horizontal axis shows the black body temperature, and the vertical axis shows the difference between the corrected temperature and the original temperature. In FIG. 9, a deviation when linear interpolation is performed by the conventional technique using two points of T ₁ = 20 ° C. and T ₂ = 60 ° C. is shown as a curve 81, and _{2 of} T ₁ = 20 ° C. and T ₂ = 40 ° C. A deviation when a point is used and linear interpolation is performed by the conventional technique is shown as a curve 82. Further, a deviation when two points of T ₁ = 20 ° C. and T ₂ = 40 ° C. are corrected by the above-described second method is shown as a curve 83. As can be seen from the above description, in the second method, the slope of the curve (the value of the signal S) in which the slope of the input / output characteristic curve changes relatively compared to the straight line is changed to the known temperature T ₁ and It is used to approximate the value of the average of S at T _2. Therefore, when the difference between T ₁ and T ₂ is large, the error is relatively large in the second method (for example, see the value of curve 83 in the range of the black body temperature of 20 to 40 ° C.) ). However, in the conventional technique, the value of the correction deviation suddenly increases outside the range, whereas in the second method, the overall change is only moderate, which is advantageous as a whole compared to the conventional technique. Sex is recognized.

FIG. 10 is a diagram comparing the case where correction according to the prior art is performed and the case where correction is performed by the third method. The horizontal axis shows the black body temperature, and the vertical axis shows the difference between the corrected temperature and the original temperature. In FIG. 10, the deviation when linear interpolation is performed by the conventional technique using two points of T ₁ = 20 ° C. and T ₂ = 60 ° C. is shown as a curve 91, and two points of T ₁ = 20 ° C. and T ₂ = 40 ° C. Is shown as a curve 92 when linear interpolation is performed by the conventional technique. Further, a deviation when the two points of T ₁ = 20 ° C. and T ₂ = 40 ° C. are corrected by the above-described third method with c = 0.3 is shown as a curve 93. In the third method, a correction of a deviation equal to or smaller than that of the conventional technique can be realized over a wide range of the black body temperature. That is, in the third method, the advantage as a whole is recognized as compared with the case of the prior art. Note that the constant coefficient c in the third method may be appropriately determined from rough estimation or experience, or an optimal value may be determined using a sample having the same or similar specifications as the infrared imaging device to be used.

  Which of the first method to the third method is selected may be determined as appropriate in consideration of the specifications of the infrared imaging device to be used and various restrictions at the time of implementation. Alternatively, a small correction deviation may be realized with respect to a wide range of pixel output voltages by selectively using a different correction formula depending on the voltage value of the pixel output voltage.

For example, in the second method, as described above, the correction deviation increases as the temperature of the imaging target differs from the temperature T ₁ or T ₂ used for correction. That is, as a correction formula,

或いは、

Or

を用いる場合、式を見ればわかるように、撮像対象の温度がT₁（つまりV＝V₁）では、補正ずれが厳密に０である。しかし撮像対象の温度がT₁から離れるほど、補正ずれを生じる可能性が大きくなる。

As can be seen from the equation, when the temperature of the imaging target is T ₁ (that is, V = V ₁ ), the correction deviation is strictly zero. But as the temperature of the imaging target away from the T _1, it can result in correction deviation increases.

  Similarly, as a correction formula

或いは、

Or

を用いる場合、式を見れば分かるように、撮像対象の温度がT₂（つまりV＝V₂）では、補正ずれが厳密に０である。しかし撮像対象の温度がT₂から離れるほど、補正ずれを生じる可能性が大きくなる。

As can be seen from the equation, when the temperature of the imaging target is T ₂ (that is, V = V ₂ ), the correction deviation is strictly zero. But as the temperature of the imaging target away from the T _2, it can result in correction deviation increases.

In order to compensate for the above-mentioned drawbacks, in, for example, V <V _1,

或いは、

Or

を用い、V₁≦Vでは、

When V ₁ ≤ V,

或いは、

Or

を用いてよい。このように、画素出力電圧Vの値に応じて、使用する補正式を適宜切り替えて補正を行ってもよい。

May be used. As described above, correction may be performed by appropriately switching the correction formula to be used in accordance with the value of the pixel output voltage V.

  Alternatively, in the entire region of the pixel output V, for example

及び、

as well as,

を用いて２つの温度Tを算出し、これら２つの温度Tの平均値を求めて補正結果として用いてもよい。また単純な平均値ではなく、撮像装置の所望の特性を実現するために適切に選ばれた重みづけ平均などの関数を用いて、T_a及びT_bからTを求めて補正結果として用いてもよい。

May be used to calculate two temperatures T, obtain an average value of these two temperatures T, and use it as a correction result. It is also possible to use T as the correction result by obtaining T from T _a and T _b using a function such as a weighted average appropriately selected to realize the desired characteristics of the imaging device, not a simple average value. Good.

  In addition to the above example, in order to further suppress the correction deviation, some correction expressions of the first to third methods may be used in appropriate combination. For the same reason, the constant coefficient c in the third method may be determined and used as an appropriate function of the pixel output V.

  In the description of the above embodiment, an infrared imaging apparatus having a plurality of infrared detectors (infrared detecting elements) has been described as an example, but it goes without saying that the above correction method is effective even in a single infrared detector. Yes.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to the said Example, A various deformation | transformation is possible within the range as described in a claim.

DESCRIPTION OF SYMBOLS 10 Infrared detection element 11 Capacitance element 12 Switch 21 Pixel circuit array 22 Row selection switch part 23 Signal extraction & shift register part 24 Input / output characteristic calibration data storage part 25 Correction calculating part 26 Signal output part 27 Switch

Claims (8)

One or more infrared detectors that generate output electricity in response to the input infrared;
An infrared detection apparatus comprising: a correction calculation unit that obtains a temperature corresponding to the input infrared ray based on the output electric quantity by correcting input / output characteristics of the infrared detector with an exponential function. When the output voltage of the infrared detector with respect to incident light corresponding to a black body with known temperatures T ₁ and T ₂ (T ₂ > T ₁ ) is V ₁ and V ₂ , the infrared detector with respect to arbitrary incident infrared light For output voltage V

To obtain the black body temperature T corresponding to the incident light as DT ₀ = T ₂ -T ₁ ,

For T = T ₁ + DT, the black body temperature T corresponding to the incident light is obtained, or

The infrared detection device according to claim 1, wherein the input / output characteristics of the infrared detector are corrected by obtaining a black body temperature T corresponding to the incident light as T = T ₂ -DT. When the output voltage of the infrared detector with respect to incident light corresponding to a black body with known temperatures T ₁ and T ₂ (T ₂ > T ₁ ) is V ₁ and V ₂ , the infrared detector with respect to arbitrary incident infrared light For output voltage V

As

Or

The infrared detection apparatus according to claim 1, wherein the input / output characteristics of the infrared detector are corrected by obtaining a black body temperature T corresponding to the incident light. When the output voltage of the infrared detector with respect to incident light corresponding to a black body with known temperatures T ₁ and T ₂ (T ₂ > T ₁ ) is V ₁ and V ₂ , the infrared detector with respect to arbitrary incident infrared light Using the parameter c set appropriately for the output voltage V,

As

Or

To obtain the black body temperature T corresponding to the incident light as DT ₀ = T ₂ -T ₁ ,

Or

For T = T ₁ + DT, the black body temperature T corresponding to the incident light is obtained, or

Or

The infrared detection device according to claim 1, wherein the input / output characteristics of the infrared detector are corrected by obtaining a black body temperature T corresponding to the incident light as T = T ₂ -DT. Generates output electricity according to the input infrared by the infrared detector,
A method for correcting input / output characteristics of an infrared detector, comprising: correcting each input / output characteristic of the infrared detector by an exponential function to obtain a temperature corresponding to the input infrared radiation based on the output electric quantity. When the output voltage of the infrared detector with respect to incident light corresponding to a black body with known temperatures T ₁ and T ₂ (T ₂ > T ₁ ) is V ₁ and V ₂ , the infrared detector with respect to arbitrary incident infrared light For output voltage V

To obtain the black body temperature T corresponding to the incident light as DT ₀ = T ₂ -T ₁ ,

For T = T ₁ + DT, the black body temperature T corresponding to the incident light is obtained, or

6. The infrared detector according to claim 5, wherein the input / output characteristics of the infrared detector are corrected by obtaining a black body temperature T corresponding to the incident light as T = T ₂ -DT. I / O characteristics correction method. When the output voltage of the infrared detector with respect to incident light corresponding to a black body with known temperatures T ₁ and T ₂ (T ₂ > T ₁ ) is V ₁ and V ₂ , the infrared detector with respect to arbitrary incident infrared light For output voltage V

As

Or

6. The method for correcting input / output characteristics of an infrared detector according to claim 5, wherein the input / output characteristics of the infrared detector are corrected by obtaining a black body temperature T corresponding to the incident light. When the output voltage of the infrared detector with respect to incident light corresponding to a black body with known temperatures T ₁ and T ₂ (T ₂ > T ₁ ) is V ₁ and V ₂ , the infrared detector with respect to arbitrary incident infrared light Using the parameter c set appropriately for the output voltage V,

As

Or

To obtain the black body temperature T corresponding to the incident light as DT ₀ = T ₂ -T ₁ ,

Or

For T = T ₁ + DT, the black body temperature T corresponding to the incident light is obtained, or

Or

6. The infrared detector according to claim 5, wherein the input / output characteristics of the infrared detector are corrected by obtaining a black body temperature T corresponding to the incident light as T = T ₂ -DT. I / O characteristics correction method.

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