JPH0528334B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal correction circuit for an infrared imaging device.
In particular, the present invention relates to a signal correction circuit for preventing image quality from deteriorating due to variations in the image output of an infrared imaging device.

[Conventional technology]

In infrared imaging devices that have been commonly used, the detector that detects infrared rays contains Hg,
Cd, Te (mercury, cadmium, tellurium), In, Sb
(indium, antimony), but such detectors require cooling to about 77 Kelvin, and liquid nitrogen or argon gas is used as the cooling means.For example,
When using liquid nitrogen as a cooling medium, a large container such as a Viton containing liquid nitrogen is required.
When using a Juul-Thomson cooler, a high-pressure gas cylinder containing argon gas or the like is required, and as a portable infrared imaging device, it is not convenient to carry around the above-mentioned Viton or gas cylinder.

In order to eliminate such drawbacks, an electronic cooling method using a Peltier element as a cooling means has also been proposed.

[Problem that the invention seeks to solve]

The cooling temperature of a photo conductive Hg, Cd, Te detector using the electronic cooling method described above is plotted on the horizontal axis, and the output signal of the detector corresponding to the cooling temperature is plotted on the vertical axis. The detection output characteristics are expressed as shown in FIG. Cooling temperature when the above detector is irradiated with a certain amount of infrared rays (irradiated with infrared power to reach the target temperature)
The output signal of the detector for T ₁ < T ₂ < T ₃ is V ₁ > V ₂
>V ₃ , and as the temperature increases, the output signal of the detector decreases exponentially. for example,
Assuming that the variation in cooling temperature is ±ΔT±1°C at cooling temperature T ₂ as shown in Figure 4, and the output variation of the detector is ±ΔV/V ₂ ±10% or more at output voltage V ₂ , then In order to suppress this output fluctuation to ±1%, it is necessary to control the cooling temperature to the order of 0.1°C. However, in an electronic cooling system that uses a Peltier element to control the cooling temperature, the current flowing through (or supplied to) the Peltier element is determined according to the resistance value (or output) from a temperature sensor such as a thermistor provided on the Peltier element. However, with Peltier elements, the heat generation side depends on the surrounding environment, and the cooling capacity is determined by the temperature difference between the heat generation side and the cooling side, so it can be controlled within a wide temperature range (0℃ to 70℃).
It is extremely difficult to control the temperature to 0.1℃.
Incidentally, there are many demands for an infrared imaging device that can measure a wide temperature range, and thus selecting a temperature range of 0° C. to 70° C. is a common specification.

[Means for solving problems]

The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to suppress output fluctuations due to fluctuations in cooling temperature and stabilize the output of electronically cooled detectors without having to control the cooling temperature with high precision. The signal correction circuit provides a signal correction circuit that can obtain a signal, and the signal correction circuit calculates the cooling temperature by focusing on the fact that the output fluctuation of the detector with respect to the fluctuation of the cooling temperature is linear in a minute temperature range (for example, ±1°C). Without controlling the temperature with high precision (e.g. ±0.1℃), the gain of the amplifier is changed so that the output fluctuation due to the control error is reduced according to the amount of fluctuation in the cooling temperature. This is what I did.

In order to achieve the above object, the present invention provides a cooling means for electronically cooling an infrared detection means, a temperature detection means for detecting the temperature of the cooling means, and a standard for setting the cooling means to a predetermined temperature. Comparing means for comparing the voltage means and the temperature detecting means to extract an error with the reference voltage means, and an output of the comparing means for driving the cooling means and controlling an automatic gain control means connected to the infrared detecting means. This is achieved by providing a signal correction circuit for an infrared imaging device characterized by comprising:

〔Example〕

Hereinafter, one embodiment of the signal correction circuit of the infrared imaging device of the present invention will be described in detail with reference to FIGS. 1 to 3.

FIG. 1 is a signal correction circuit of an infrared imaging device of the present invention, FIG. 2 is a side sectional view of an electronically cooled detector used in the signal correction circuit of an infrared imaging device of the present invention, and FIG.
The figure shows a specific example of an automatic gain amplification circuit. In FIG. 2, a detector 1 used in the present invention is constructed in the same way as a transistor container, and further has a window 4 on the entire surface.
It is housed in a container 2 having a. Inside the container 2, for example, Peltier elements 3a stacked one after another,
3b and 3c are arranged in three stages and placed on the container base 2a, and terminals T ₃ and T ₄ are led out as Bertier terminals outside the container and used as current supply terminals. An infrared detecting element 5 is disposed on the cooling side of the uppermost stage 3a of the three-stage Bertier element at a position corresponding to the window 4 of the container 2, and the detector output is led to terminals _T5 and _T5 . Furthermore, a temperature sensor 6 made of a thermistor or the like is disposed on the cooling side of the Peltier element 3a. The temperature sensor terminals T ₁ and T ₂ are connected to the temperature sensor 6 so that the temperature sensor's power is led out of the container.

A correction circuit is constructed as shown in FIG. 1 using the electronically cooled detector 1 constructed as described above. In FIG. 1, the temperature sensor 6 has a variable resistor _R3 , which is a reference resistance that can be made equal to its resistance value _R5 , and a first
and second resistors R ₁ and R ₂ constitute a bridge. That is, a first resistor R ₁ and a temperature sensor 6 consisting of a thermistor are connected in series, a second resistor R ₂ and a reference resistor R ₃ are also connected in series, and these two series circuits are connected in parallel to each other, and the temperature sensor 6 is connected in series. The sensor 6 and one end of the reference resistor are grounded, the operating voltage V ₀ is applied to the common connection point of the first and second resistors, and the connection point of the first resistor R ₁ and the temperature sensor 6 is connected to the operating amplifier U ₁ . Connect to the negative input terminal and
The connection point of the resistor R ₂ and the reference resistor R ₃ of the operating amplifier U ₁
Connect to the positive input terminal of the One end of the working amplifier U ₁ is a current amplifier U ₂ and an automatic gain control amplifier U ₃
connected to. The control current converted by the current amplifier _U2 is passed through the Peltier elements 3a to 3 which serve as coolers.
In addition to c, the temperature is controlled to a predetermined temperature.

In FIG. 1, three stages of Peltier elements 3a~
The resistance value of 3c is expressed as Rp, and the terminal _T4 of the Peltier element connected between the terminals _T3 and _T4 is grounded and the terminal _T3
is supplied with current from current amplifier U ₂ . Furthermore, the resistance value of the infrared detection element 5 is set to R ₂ and the terminals T ₅ and T ₆
The terminal _T6 is grounded and the detection output is taken out to the terminal _T5 , and the bias voltage _VB is connected to the resistor _R4.
is applied via. The sensing output is applied to the automatic gain control amplifier U ₃ and the differential amplifier U ₁ described above.
A control output is derived to the output terminal T _OUT by adding the output of the automatic gain control amplifier U ₃ to the gain control terminal and controlling the automatic gain control amplifier U 3 . The above automatic gain control amplifier U ₃ is composed of an operational amplifier as shown in Figure 3, and the resistance value VR ₀ of the variable resistor VR connected between the input and output terminals and the resistance value placed between the negative input terminal and ground are R ₀ , the gain G of this operational amplifier _U3 is G=1+VR ₀ /
Since it is expressed as R ₀ , the gain of the operational amplifier U ₃ can be changed by varying the resistance value VR ₀ of the variable resistor VR.

That is, the variable resistor is a field effect transistor, and the output from the differential amplifier is applied to the gate terminal of the field effect transistor to control the gain of the automatic gain control amplifier.

The operation of the correction circuit of the present invention will be explained below. 1st
In the figure, the reference resistance R ₃ is, for example, the cooling temperature T ₂ that you want to set.
If the resistance value R ₃ is set to be equal to the resistance value R _S of the temperature sensor 6 at
The _reference resistor R ₃ outputs the reference voltage V ₂ corresponding to the cooling temperature T ₂ . By applying these two voltages to the differential amplifier U ₁ , the differential voltage V ₂ −V _S is the cooling temperature
The voltage corresponds to the temperature difference ΔT from T ₂ . That is, the output V _c ±ΔV _c corresponding to the temperature error is amplified and obtained at the output terminal of the differential amplifier U ₁ .

The output V _c ±ΔV _c is converted into a control current of I _c ±ΔI _c by a current amplifier U ₂ and applied to the Peltier elements 3a to 3c. Here, it is assumed that the cooling temperature becomes T ₂ when the control current I _c is applied to the Peltier element. In the temperature control system as described above, current flows through the Peltier elements 3a to 3c.
Even if Ic is supplied, the cooling temperature does not immediately correspond to the value of Ic, and the response of the cooling system is slow, so a temperature error ΔT (for example, about ±1° C.) is maintained for a certain period of time.
In the present invention, temperature control is controlled to, for example, about 1°C by the above circuit (not controlled to about 0.1°C), and this error output V _c ±ΔV _c is used to control an electrical circuit system with relatively fast response. Then, the second temperature correction is performed. For this reason, when the infrared detector 5 is irradiated with a predetermined infrared power, a predetermined output signal Vd is generated.
is added to the automatic gain control amplifier U ₃ and the gain is controlled by the error output Vc±ΔVc of the above-mentioned differential amplifier U ₁ .
This gain control is operated to cancel out changes in the output of the detector 5 due to changes in cooling temperature. That is, when the cooling temperature of the Peltier elements 3a to 3c increases, the resistance value of the thermistor 6, which is a temperature sensor, decreases, and the error output of the differential amplifier _U1 increases to + _ΔVc . Corresponding to this increase in error output, the gain of automatic gain control amplifier U ₃ increases by +ΔV/Vd×100%, and detection is performed to compensate for the decrease in the output of detector 5 due to the rise in cooling temperature. The device output increases. On the other hand, when the cooling temperature of the Peltier elements 3a to 3c decreases, the resistance value of the temperature sensor increases and the error output of the differential amplifier _U1 decreases to _-ΔVc . Corresponding to this decrease in the error output, the gain of the automatic gain control amplifier U ₃ decreases by -ΔV/Vd×100%, and the increase in the detector output due to the cooling temperature drop is canceled out, so the gain of the automatic gain control amplifier U ₃ decreases by −ΔV/Vd×100%. Even if the temperature is controlled relatively roughly by the current amplifier U ₂ , the output of the detector can be kept constant relatively quickly.

〔Effect of the invention〕

Since the present invention is configured and operated as described above, a relatively simple cooling temperature control circuit system such as an electronic cooling method is used for the detector of the infrared imaging device, and even if the temperature control is roughly controlled, it can be detected. Since the detector output is electrically and automatically controlled, changes in the detector output due to fluctuations in cooling temperature can be canceled out and kept constant, resulting in a good imaging system with no fluctuations in image quality. Furthermore, since it uses an electronic cooling system, it has the feature that it can provide an infrared imaging device with good operability and portability.

[Brief explanation of the drawing]

FIG. 1 is a signal correction circuit diagram of the infrared imaging device of the present invention, FIG. 2 is a schematic side sectional view showing a detector of the infrared imaging device of the present invention, and FIG. 3 is an automatic signal correction circuit diagram of the infrared imaging device of the present invention. FIG. 4, which is a specific circuit diagram of the gain control circuit, is a curve diagram illustrating the relationship between the detection output and the cooling temperature of the electronically cooled detector. 1...Detector, 2...Container, 2a...Container base, 3a, 3b, 3c...Peltier element, 4...
window, 5...infrared detector, 6...temperature sensor,
U ₁ ... Differential amplifier, U ₂ ... Current amplifier, U ₃ ...
Automatic gain control amplifier.

Claims (1)

[Scope of Claims] 1. A cooling means for electronically cooling the infrared detection means, a temperature detection means for detecting the temperature of the cooling means, a reference voltage means for setting the cooling means to a predetermined temperature, Comparing means for comparing the reference voltage outputted from the reference voltage means and the output voltage of the temperature detecting means to extract an error with the reference voltage; A signal correction circuit for an infrared imaging device, characterized in that it is formed by controlling automatic gain control means connected to a detection means.