JPH10293067A - Infrared imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an infrared imaging apparatus which can be made small and lightweight, whose power consumption can be made low and whose sensitivity can be made constant over a wide ambient temperature range. SOLUTION: Infrared rays from an optical system 1 are converted into a change in the resistance of an infrared detecting element 2. When a current is made to flow to the infrared detecting element 2 from a read circuit 3, it is read out as a voltage change so as to be processed by an imaged-signal processing circuit 4. On the basis of the signal of a temperature sensor 7, a constant-temperature control circuit 5 changes the temperature of the infrared detecting element 2 into a constant temperature near an ambient temperature, and a current control circuit 6 controls the current of the read circuit 3 according to the ambient temperature or the like so as to cancel a sensitivity change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared imaging apparatus, and more particularly to a bolometer type non-cooled infrared imaging apparatus which uses a normal temperature infrared detecting element and detects a temperature change of a subject as a resistance change of the infrared detecting element. About.

[0002]

2. Description of the Related Art Conventionally, an infrared imaging device of this kind has been designed to keep the sensitivity of an infrared detecting element constant at a specific temperature regardless of the environmental temperature so as to keep the sensitivity constant, or to sacrifice a change in sensitivity. A method of keeping the temperature constant near the ambient temperature has been adopted.

[0003]

The structure in which the temperature of the infrared detecting element is kept constant at a specific temperature regardless of the ambient temperature, as in the former prior art, is large between the environmental temperature and the specific temperature. When there is a temperature difference, a large-scale temperature controller is required, and the use environment and the like are limited to a limited range due to the capability of the temperature controller.

[0004] In the latter prior art, in which only the temperature of the infrared detecting element is kept constant near the ambient temperature, the resistance of the infrared detecting element changes depending on the environmental temperature. If the same voltage (current) is always applied to detect the resistance, there is a problem that the detected current (voltage) fluctuates according to the environmental temperature and the sensitivity changes.

SUMMARY OF THE INVENTION An object of the present invention is to provide an infrared imaging device which can realize small size, light weight, low power consumption, and can keep sensitivity constant over a wide range of use environment temperature.

[0006]

Means for detecting the environmental temperature with a temperature sensor and for keeping the infrared detecting element constant at or near the environmental temperature (5 in FIG. 1), and a voltage applied to the infrared detecting element based on the environmental temperature signal Means for controlling (current) amount (FIG. 1)
6) is provided.

That is, an infrared imaging apparatus according to the present invention is an imaging apparatus for detecting the resistance of an infrared detecting element to perform imaging.
Constant temperature means for keeping the infrared detecting element at a temperature close to the environmental temperature, resistance detecting means for reading the resistance of the infrared detecting element by applying voltage or current, and infrared detecting element according to the environmental temperature or the constant temperature And control means for correcting the current or the voltage applied to the device. Further, the resistance detecting means for detecting the resistance value of the infrared detecting element includes a capacitance means for accumulating a fixed electric charge and then discharging the electric charge via the infrared detecting element for a predetermined time, and The voltage at the end of discharge is read. Further, a constant current means using a transistor is provided in a discharge path of the electric charge of the capacitance means, and a bias of a control electrode of the transistor is controlled according to the environmental temperature or the constant temperature.

More specifically, the infrared imaging apparatus of the present invention comprises an infrared detecting element, a thermostat circuit for thermostatting the infrared detecting element to an environmental temperature, a capacitor and a switch for charging the capacitor with a constant charge. A readout circuit that includes a transistor that discharges the charge of the capacitor to the infrared detection element for a certain period of time and outputs a voltage after discharging the charge of the capacitor; and correcting the base voltage of the transistor according to the ambient temperature or the constant temperature to detect the infrared ray. A control circuit for controlling a value of a current flowing through the sensing element.

According to the present invention, since the temperature of the infrared detecting element is kept constant near the ambient temperature, a small-scale temperature controller can be used in the constant temperature section, and it can be used with low power consumption and in a wide environmental temperature range. A possible infrared imaging device can be configured.

Further, since the voltage (current) applied to the infrared detecting element is controlled based on the environmental temperature signal, it is possible to eliminate a change in the sensitivity of the infrared imaging apparatus due to the environmental temperature change.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the infrared imaging apparatus according to the present invention will be described. FIG. 1 is a block diagram showing a basic configuration of the present embodiment.

In the basic configuration of the infrared imaging apparatus according to the present embodiment, an optical system 1 for collecting infrared light, an infrared detecting element 2 to which the collected infrared light is irradiated, and a voltage or current applied to the infrared detecting element 2 And a reading circuit 3 for reading a resistance change based on the amount of infrared rays as a current or a voltage, and an imaging signal processing circuit 4 for imaging the read output, and further detects an environmental temperature and a constant temperature. Temperature sensor 7
And controlled by the output of the temperature sensor 7, respectively.
The apparatus includes a control circuit 5 for controlling the temperature of the infrared detecting element 2 to a temperature close to the sensitivity temperature, and a control circuit 6 for controlling the quantity of electricity for controlling the reading sensitivity of the infrared detecting element 2.

In FIG. 1, infrared light condensed by an optical system 1 causes a change in resistance of an infrared detecting element 2, and the readout circuit 3
Thus, a change in current or voltage is read out, processed by the imaging signal processing circuit 4, and output as a video signal.

On the other hand, the temperature sensor 7 detects the use environment temperature and the constant temperature, and supplies them to the constant temperature control circuit 5 and the control circuit 6.

The constant temperature control circuit 5 performs feedback control based on a signal from the temperature sensor 7 based on a signal corresponding to, for example, a difference between the environmental temperature and the constant temperature of the infrared detecting element. The temperature is controlled to be constant near the temperature.

The control circuit 6 controls the voltage or current applied to detect the resistance of the infrared detecting element 2 based on the signal of the temperature sensor 7 so that the sensitivity of the infrared imaging device does not change with the environmental temperature.

With the above configuration and operation, the temperature of the infrared detecting element 2 is controlled by the control of the constant temperature control circuit 5 based on the output of the temperature sensor. It is stabilized at a temperature near the ambient temperature.

On the other hand, the reading circuit 3 of the infrared detecting element 2
The control circuit 6 outputs a current or the like including a correction amount corresponding to the environmental temperature, and cancels a sensitivity variation based on a resistance change of the infrared detecting element 2 due to the environmental temperature, thereby changing a resistance of the infrared detecting element 2 to a voltage value or the like. Read as

Therefore, the output of the readout circuit 3 and the video signal obtained from the imaging signal processing circuit 4 become a signal having a constant sensitivity regardless of a change in environmental temperature, and a high-precision infrared imaging device can be constructed.

[0020]

Next, an embodiment of the present invention will be described. FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, an infrared detecting element 2 is a detecting element whose resistance value changes by infrared rays using a metal or a semiconductor utilizing a Peltier effect or the like, for example, and a readout circuit 3 includes a charge storage element (C) such as a switch SW and a capacitor. ) And a transistor Tr.

[0021] In the operation of Figure 2, in the reading circuit 3, first, to charge the capacitor (C) the switch SW is turned on to until the power supply voltage V _C. Next, switch S
Switch the W constant time off state, the electric charge of the capacitor (C) discharges through the transistor Tr, a constant current is supplied in accordance with the base voltage V _B of the transistor in the infrared sensing element 2 (the resistance value R). Since the voltage between the terminals of the capacitor (C) after the current has flowed through the resistor for a certain period of time changes according to the magnitude of the resistance value R, the infrared detection element 2 is determined from the voltage between the terminals after the discharge of the capacitor (C). Can be detected, from which the amount of infrared radiation can be detected.

Here, the voltage of the capacitor (C) after the predetermined time is determined by the charge amount after discharging. When the capacitance of the capacitor (C) is C and the charge is Q, the voltage between the terminals of the capacitor is represented by Q / C. When the discharge current is I and the discharge period (constant time) τ, the discharge charge is , I × τ.

The voltage between the terminals of the infrared detecting element (resistance value R) is V _B ,
Assuming that the voltage between the emitters is V _BE , it becomes (V _B -V _BE ), and the discharge current I is represented by I = (V _B -V _BE ) / R.

Therefore, the capacitor (C) after the discharge period τ
The voltage V, the voltage of the discharge charge amount from the charging voltage V _C τ (V _B
−V _BE ) / C · R is subtracted, and is expressed as V = V _C −τ (V _B −V _BE ) / C · R (1)

From the equation (1), the voltage change dV with respect to the resistance value of the infrared detecting element is given by dV = {τ (V _B −V _BE ) / C · R} · β (2) where β = It is expressed by dR / R as a resistance change rate with respect to a subject temperature as an infrared imaging device.

On the other hand, the resistance value R of the infrared detecting element is changed by the environmental temperature change dT as follows: R = R ₀ (1 + α · dT) (3) R ₀ : resistance value at the reference temperature T ₀ I do.

The V _{BE of} the transistor also has a temperature characteristic. V _BE = V _BEO (1 + ∂V _BE · dT) (4) V _BEO : V _{BE at the} reference temperature T ₀ ∂V _BE : V It can be approximated by the temperature derivative of _BE .

Therefore, from the equations (3) and (4), when the environmental temperature changes, the sensitivity of the infrared imaging device expressed by the equation (2) changes.

Therefore, the ambient temperature is detected by the temperature sensor 7, the temperature of the infrared detecting element is kept constant at the temperature T by the constant temperature control circuit 5, and the sensitivity dV of the equation (2) does not change from the reference temperature T _0. controls the base voltage V _B of the transistor Tr of the read circuit 3 by the control circuit 6 as.

Hereinafter, a control method in the control circuit 6 will be described.

First, considering the condition that the sensitivity dV is constant irrespective of the environmental temperature in the equation (2), the above-mentioned current (V _B) flowing through the infrared detecting element at the temperature T is considered.
−V _BE ) / R is given by ΔV _B −V from the above equations (3) and (4).
_Since it can be expressed as _BEO (1+ {V _BE · dT)} / R ₀ (1 + α · dT), the sensitivity dV is constant regardless of the ambient temperature.
That is, as a condition that does not change from the case of the reference temperature T ₀ , {V _B −V _BEO (1 + ΔV _BE · dT)} / R ₀ (1 + α · dT) = (V _BO −V _BEO ) / R ₀ It is necessary to satisfy (5).

Then, when the base voltage V _{B of the} transistor is obtained from the equation (5), the following equation is obtained: V _B = ｛α (V _BO −V _BEO ) + ∂V _BE · V _BEO ｝ dT + V _BO (6) .

[0033] (6) As can be seen from the equation, the condition of the base voltage V _B of sensitivity dV is constant irrespective of the environmental temperature is represented by a linear function of the temperature deviation dT from the temperature T ₀ as a reference.

Therefore, for example, the output current proportional to the environmental temperature T from the control circuit 6 as a bias circuit is controlled so that the sensitivity dV to the temperature deviation dT becomes equal at two environmental temperatures in advance, and the base voltage is reduced. By calibrating, it is possible to cancel the sensitivity change based on the environmental temperature change of the infrared imaging device.

In the embodiment described above, the read circuit 3 has been described as a circuit composed of a switch, a capacitor and a bipolar transistor. However, it is obvious that an electronic switch or a unipolar transistor can be used. Further, as a means for detecting the resistance value of the infrared detecting element,
Although the description has been given of the example in which the detection means based on the principle of detecting the voltage drop by discharging the charge of the capacitor via the infrared detection element is used, the change in the resistance value of the infrared detection element is directly measured and detected by another method. Needless to say, the configuration may be made as follows.

[0036]

According to the infrared imaging apparatus of the present invention, since the temperature of the infrared detecting element is kept constant near the ambient temperature, the size of the temperature keeping device and the temperature control circuit can be small, and the power consumption is low. Therefore, it is possible to configure a small, lightweight, and low power consumption infrared imaging device.

Furthermore, since the sensitivity of the infrared imaging device does not change with the environmental temperature, a high-performance infrared imaging device that can be used over a wide environmental temperature range can be constructed.

[0038]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 optical system 2 infrared detecting element 3 readout circuit 4 imaging signal processing circuit 5 constant temperature control circuit 6 control circuit 7 temperature sensor

Claims (4)

[Claims] 1. An imaging apparatus for detecting a change in resistance of an infrared detection element and imaging the same, wherein the thermostat means keeps the temperature of the infrared detection element at a temperature near an environmental temperature, and detects a change in resistance of the infrared detection element by voltage or current. And a control means for correcting the voltage or current applied to the infrared detecting element in accordance with the environmental temperature or the constant temperature, so that the sensitivity of the infrared detecting element is constant with respect to the environmental temperature. An infrared imaging device characterized in that: 2. The resistance detection means detects a change in resistance according to a discharge result of a capacitance means for discharging stored electric charge via the infrared detecting element. A constant current means is provided in a discharge path of the electric charge of the capacitance means. Wherein the control means corrects the current of the constant current means.
An infrared imaging device as described in the above. 3. The infrared imaging apparatus according to claim 2, wherein a transistor is used as said constant current means, and a bias of a control electrode of said transistor is corrected by said control means. 4. An infrared detecting element, a thermostat circuit for keeping the infrared detecting element at an ambient temperature, a capacitor, a switch for charging the capacitor with a constant charge, and charging the capacitor with the charge for a predetermined time. An infrared imaging apparatus comprising: a readout circuit that includes a discharging transistor and outputs a voltage after discharging the charge of the capacitor; and a control circuit that corrects a base voltage of the transistor according to an environmental temperature or a constant temperature. .