JPH1198413A - Infrared ray camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an infrared ray camera with a high S/N provided with a correction means that corrects dispersion in a bias current fed to plural bolometers being components of an image pickup element. SOLUTION: Standard resistors 53-55 are provided in an image pickup element 51, a dispersion in a bias current set by bias current setting means 40-42 is measured by supplying the bias current to the standard resistors 53-55 and the result is stored in a memory 49 in a dispersion correction circuit 45 and corrected by a differential amplifier circuit 46. Thus, the gain of a preamplifier circuit 6 is increased till the effect of the circuit noise after the 1st A/D converter 7 is disregarded and the infrared ray camera with a high S/N is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared camera using a bolometer.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of a conventional infrared camera. In the figure, M is a subject, 1 is an infrared optical system, 2 is an image sensor located on the image forming surface of the infrared optical system 1, 3 is a shutter located between the infrared optical system 1 and the image sensor 2, 4 is a constant voltage source connected to the image sensor 2, 5 is a driver circuit connected to the image sensor 2, 6 is a preamplifier circuit for amplifying the output of the image sensor 2, 7 is a digital signal representing the output of the preamplifier circuit 6. A first A / D conversion circuit for converting the data into a display processing circuit;
Is a timing generation circuit connected to the shutter 3, the driver circuit 5, the first A / D conversion circuit 7, and the display processing circuit 8. The display processing circuit 8 includes an averaging circuit 9, a frame memory 10, and a subtraction circuit 11.

FIG. 8 shows the structure of the image pickup device 2, which has 3.times.3 pixels for simplification of description. 13-2 in the figure
1 is a bolometer, 22 to 36 are transistors, 37 to 3
9 is a capacitor, 40 to 42 are bias current setting means,
43 is a vertical scanning circuit, and 44 is a horizontal scanning circuit. An infrared camera using a bolometer is used to visualize a resistance change due to a temperature rise caused by absorbing infrared rays emitted from a subject.
Reference numerals 121 are formed of a material having a large resistance change rate with respect to temperature, such as polysilicon or vanadium oxide. FIG.
In the above, the case where transistors are used as the bias current setting means 40 to 42 has been described.

Next, the operation will be described. First, a bias voltage Vb and a gate voltage Vg for setting a bias current are applied to the transistors 40 to 42 from the constant voltage source 4. Next, the driver circuit 5 sends a driving clock for selecting a row to the vertical scanning circuit 40 in accordance with the timing generated by the timing generation circuit 12. The vertical scanning circuit 40 is driven by the above clock.
First, the transistors 22 to 24 are turned on for a certain period. As a result, a bias current set by the conduction resistance of the bias current setting means 40 to 42 flows through the bolometers 13 to 15. Next, a sample hold clock is applied from the timing generation circuit 12, and the transistors 31 to 33 are turned on. Thereby, the voltage corresponding to the resistance value of the bolometers 13 to 15 is changed to the capacitors 37 to
39 is stored once. Next, after the transistors 31 to 33 are turned off, the horizontal scanning circuit 44
To 36 are sequentially turned on to output voltages corresponding to the resistance values of the bolometers 13 to 15. Next, the vertical scanning circuit 43
Selects the rows formed by the bolometers 16-18,
In the same procedure as the bolometers 13 to 15, the bolometers 16 to
A voltage corresponding to the resistance value of No. 18 is output. By repeating the above operation, a voltage corresponding to the resistance value of the bolometer constituting the image sensor 2 is output. In this state, the shutter 3 is closed, and the output voltage of each bolometer in a state where uniform infrared rays are incident on the bolometers 13 to 21 is applied to the preamplifier circuit 6.
Then, the signal is converted into a digital signal by the first A / D conversion circuit 7 and then added and averaged for each pixel in the addition circuit 9 and stored in the frame memory 10. This operation is for acquiring offset correction data for removing fixed pattern noise appearing in an image due to variation in the resistance values of the bolometers 13 to 21.

Next, the shutter 3 is opened and the infrared light emitted from the subject M is condensed by the infrared optical system 1, and the bolometers 13 to
21 is formed. As a result, a temperature rise occurs in the bolometers 13 to 21 in accordance with the intensity of the infrared radiation emitted from the subject, and the resistance value of each bolometer changes as compared to before the shutter is opened. This temperature rise is as small as several mK per 1K of the target temperature difference in the 300K background. Bolometer 13
21 are amplified by the preamplifier circuit 6 and converted into digital signals by the first A / D converter circuit 7 in the same manner as when the offset correction data is obtained. The offset correction data recorded in the memory 10 is subtracted for each pixel to remove fixed pattern noise and output.

[0006]

The conventional infrared camera is configured as described above, and the bias current set by the bias current setting means 40 to 42 arranged corresponding to each column is used to set the bias current to the bolometers 13 to 42. Then, a change in the resistance value is read out by flowing the current through the circuit 21. For this reason, the variation in the output of the entire image sensor 2 becomes larger due to the addition of the variation in the bias current in addition to the variation in the resistance values of the bolometers 13 to 21 itself. The gain of the preamplifier circuit 6 cannot be sufficiently increased to suppress the saturation level of the A / D conversion circuit 7 or less, and the first A
The effect of the circuit noise after the / D conversion circuit becomes remarkable, and the S / N at the output of the display processing circuit 8 is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described difficulties, and reduces the amplitude of a signal including a variation by correcting variation in the conduction resistance of transistors 37 to 39, thereby reducing the preamplifier circuit. An object of the present invention is to obtain an infrared camera which can sufficiently gain a gain of 6 and has a sufficient S / N.

[0008]

An infrared camera according to a first aspect of the present invention includes a standard resistor connected to bias current setting means 40 to 42 via a transistor, a preamplifier circuit 6, and a first A / D conversion circuit. 7 is provided with a variation correction circuit connected therebetween.

The infrared camera according to the second aspect of the present invention
As a variation correction circuit, a differential amplifier circuit and a second A /
A D converter, a first switch for selectively connecting the output of the preamplifier to the differential amplifier and the second A / D converter, and a second switch for connecting the second A / D converter. A memory connected to store the variation of the bias current setting means, and a D / A conversion circuit for converting an output of the memory into an analog signal and outputting the analog signal to the differential amplifier circuit.

[0010] The infrared camera according to the third invention comprises:
As the variation correction circuit, a differential amplifier circuit, an attenuation circuit, a first switch for selectively connecting an output of the preamplifier circuit to the differential amplifier circuit and the attenuation circuit, and an output of the attenuation circuit A second A / D conversion circuit for A / D converting the data, a memory connected to the second A / D conversion circuit for storing the variation of the bias current setting means, and converting the output of the memory to an analog signal A D / A conversion circuit, and an amplification circuit provided between the D / A conversion circuit and the differential amplification circuit.

[0011] The infrared camera according to a fourth aspect of the present invention includes:
A standard resistor connected to the bias current setting means 40 to 42 via a transistor; a first switch provided between the preamplifier circuit 6 and the first A / D conversion circuit 7; A switch, a memory connected to the first A / D conversion circuit, for storing the variation of the bias current setting means, and a D for converting an output of the memory into an analog signal.
/ A conversion circuit, and a differential amplifier circuit connected to the first switch and the D / A conversion circuit.

The infrared camera according to a fifth aspect of the present invention comprises:
A standard resistor connected to the bias current setting means 40 to 42 via a transistor; a first switch provided between the preamplifier circuit 6 and the first A / D conversion circuit 7; A switch, the first switch, and the second switch.
And the first A
A memory connected to a D / D conversion circuit for storing the variation of the bias current setting means, a D / A conversion circuit for converting an output of the memory into an analog signal, an amplification circuit connected to the D / A conversion circuit, A differential amplifier connected to the first switch and the amplifier;

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a block diagram showing Embodiment 1 of an infrared camera according to the present invention. In the figure, 1 and 3 to
8 is the same as the conventional device. 45 is a variation correction circuit provided between the preamplifier circuit 6 and the first A / D conversion circuit 7, and 52 is a timing generation circuit. The variation correction circuit 45 includes a differential amplifier circuit 46, a second A / D converter circuit 47, a preamplifier circuit 6, a differential amplifier circuit 46,
Switch 48 connected to the A / D conversion circuit 47
And a memory 49 connected to the second A / D conversion circuit 47
And a D / A conversion circuit 50 connected to the memory 49. FIG. 2 is a connection diagram showing the first embodiment of the image sensor 51, and reference numerals 13 to 42 and 44 are the same as those of the conventional device. 53 to 55 are standard resistors, 56 to 58 are transistors connected to the standard resistors 53 to 55, and 59 is a vertical scanning circuit connected to the transistors 22 to 30 and the transistors 56 to 58. Unlike the bolometers 13 to 21, the standard resistors 53 to 55 do not need to have a large resistance change rate with respect to temperature, and are therefore formed of a material used in a normal semiconductor process, such as titanium nitride or aluminum.

Next, the operation of the infrared camera according to the present invention will be described. In accordance with the timing generated by the timing generation circuit 52, the driver circuit 5 sends a clock to the vertical scanning circuit 43, the horizontal scanning circuit 44, and the transistors 34 to 36, and the transistors 22 to 30 and the transistor 34
To 36 are sequentially turned on, reading is performed in the same procedure as in the conventional apparatus, and voltages corresponding to the standard resistors 53 to 55 and the bolometers 13 to 21 are output. Next, the shutter 3 is closed, and the first switch 48 is connected to the terminals A and B.
And the second A / D conversion circuit 47 is connected to the preamplifier circuit 6
Is converted to a digital signal. The memory 49 stores the image sensor 5 when a bias current flows through the standard resistors 53 to 55.
1 to store the output. Next, the first switch 48 switches between A and C
Switch the connection destination. The D / A conversion circuit 50 is a memory 4
9, the output of the standard resistor 53 is output to the bolometers 13, 16, and 19, the output of the standard resistor 54 is output to the bolometers 14, 17, and 20, and the output of the standard resistor 55 is output to the bolometers 15, 18, and 21. Are output in synchronization with each other as shown in FIG. The differential amplifier circuit 46 amplifies the difference between the output of the D / A conversion circuit 50 and the output of the preamplifier circuit 6 and outputs the result. After that, acquisition of offset correction data and output of an image are performed as in the conventional apparatus.

Embodiment 2 FIG. 4 is a block diagram showing Embodiment 2 of the infrared camera according to the present invention. In the figure, 1, 3 to 8 are the same as the conventional apparatus. Also, 4
6 to 52 are the same as those in the first embodiment. Numeral 60 denotes a variation correction circuit, components 46 to 50 are the same as those in the first embodiment, and 61 is smaller than 1 provided between the first switch 48 and the second A / D conversion circuit 47. An attenuating circuit having a gain, 62 is an amplifying circuit provided between the D / A conversion circuit 50 and the differential amplifying circuit 46 and having a gain greater than 1.

Next, the operation of the infrared camera according to the present invention will be described. The image sensor when the amplitude of the output of the preamplifier circuit 6 is once attenuated by the attenuating circuit 61, A / D converted by the second A / D converting circuit 47, and the bias current flows through the standard resistors 53 to 55. The output of the standard resistor 53 is stored in the memory 49 as in the first embodiment.
The bolometer 1 outputs the output of the standard resistor 54 to 3, 16, and 19.
The bolometer 1 outputs the output of the standard resistor 55 to 4, 17, and 20.
The signals are output from the D / A conversion circuit 50 in synchronization with 5, 18, and 21, respectively, as shown in FIG. Next, the amplifier circuit 6
2 amplifies the output of the D / A conversion circuit 50 by the reciprocal of the attenuation ratio of the attenuation circuit 61 and inputs the result to the differential amplifier circuit 46. Other operations are the same as those in the first embodiment.

Embodiment 3 FIG. 5 is a block diagram showing Embodiment 3 of the infrared camera according to the present invention. In the figure, 1, 3 to 8 are the same as the conventional apparatus. Also, 4
6, 48 to 51 are the same as those in the first embodiment. 63
Is a differential amplifier circuit 46, a first switch 48, and a first A /
The second switch 64 connected to the D conversion circuit 7 is a timing generation circuit.

Next, the operation of the infrared camera according to the present invention will be described. The operation until the output of the image sensor 51 is obtained is the same as in the first embodiment. Next, the shutter 3 is closed to obtain offset correction data, and then the first switch 48 connects the terminals A and B, and the second switch 63 connects the terminals E and D. The first A / D conversion circuit 7 converts the output of the preamplifier circuit 6 into a digital signal, and the memory 49 stores the output of the image sensor 51 when a bias current flows through the standard resistors 53 to 55. Next, the first switch 48
And C, and the second switch 63 switches the connection destination to F and D. The D / A conversion circuit 50 outputs the output of the standard resistor 53 to the bolometers 13 and 1 based on the data stored in the memory 49.
6 and 19, the output of the standard resistor 54 is connected to the bolometers 14, 1
7 and 20, the output of the standard resistor 55 is changed to the bolometers 15, 1
As shown in FIG. The differential amplifier circuit 46 amplifies the difference between the output of the D / A conversion circuit 50 and the output of the preamplifier circuit 6 and outputs the result. After that, acquisition of offset correction data as with the conventional device,
And output an image.

Embodiment 4 FIG. 6 is a block diagram showing Embodiment 4 of the infrared camera according to the present invention. In the figure, 1, 3 to 8 are the same as the conventional apparatus. 46,
48 to 51 and 63 are the same as those in the third embodiment. 6
5 is an attenuation circuit having a gain smaller than 1 provided between the terminal B of the first switch 48 and the terminal E of the second switch 48, and 66 is a circuit between the D / A conversion circuit 50 and the differential amplifier circuit 46. Is an amplifying circuit having a gain greater than 1 provided in.

Next, the operation of the infrared camera according to the present invention will be described. An operation until the output of the image sensor 51 is obtained and a shutter 3 for obtaining offset correction data
The operation up to closing is the same as in the first embodiment. Next, the first switch 48 connects the terminals A and B, and the second switch 63 connects the terminals E and D. The attenuation circuit 65 attenuates the output of the preamplifier circuit 6 once, performs A / D conversion in the second A / D conversion circuit 47, and outputs the image sensor 51 when a bias current flows through the standard resistors 53 to 55. Is stored in the memory 49, and the output of the standard resistor 53 is output to the bolometers 13, 16, and 19, the output of the standard resistor 54 is output to the bolometers 14, 17, and 20, and the output of the standard resistor 55 is output to the bolometer 15, as in the first embodiment. As shown in FIG. 3, the signals are output from the D / A conversion circuit 50 in synchronization with the signals 18 and 21, respectively. Next, the amplification circuit 66 amplifies the output of the D / A conversion circuit 50 by the reciprocal of the attenuation ratio of the attenuation circuit 65 and inputs the result to the differential amplification circuit 46. Next, the first switch 48 switches between A and C, and the second switch 63 switches between F and D. Differential amplifier circuit 4
Reference numeral 6 amplifies and outputs the difference between the output of the D / A conversion circuit 50 and the output of the preamplifier circuit 6. Other operations are described in Embodiment 3.
Is the same as

[0021]

According to the first and second aspects of the present invention, the standard resistors 53 to 55 are provided in the image pickup element 51, and the bias currents set by the bias current setting means 40 to 42 vary in bias current. Since the measurement is made by flowing a current and stored in the memory 49 in the variation correction circuit 45, and the correction is made in the differential amplifier circuit 46, the memory 49 has a small capacity, and the first A / D conversion circuit 7 and thereafter. The gain of the preamplifier circuit 6 can be increased until the influence of the circuit noise can be neglected, and an infrared camera with a high S / N can be obtained.

According to the third aspect of the present invention, the attenuation circuit 61
Since the data about the variation can be acquired after the amplitude is attenuated once, the width of the variation is large,
Even if the input saturation level of the second A / D conversion circuit 47 is exceeded, an infrared camera capable of correcting a variation in bias current set by the bias current setting means 40 to 42 can be obtained.

Further, according to the fourth aspect, the first A / D is switched by switching the first switch 48 and the second switch 63.
Since the correction data for the bias current variation set by the bias current setting means 40 to 42 can be obtained by using the conversion circuit 7, the second A / D conversion circuit becomes unnecessary, and an inexpensive infrared camera can be obtained. There is.

Further, according to the fifth aspect, the first A / D is switched by switching the first switch 48 and the second switch 63.
By using the conversion circuit 7, correction data for the bias current variation set by the bias current setting means 40 to 42 can be obtained, so that the second A / D conversion circuit is not required, and the amplitude is once attenuated by the attenuation circuit 65. After that, data relating to the variation can be obtained, so that even when the variation range is large and exceeds the input saturation level of the second A / D conversion circuit 47, the variation in the bias current set by the bias current setting means 40 to 42 can be reduced. There is an effect that a low-cost infrared camera capable of correction can be obtained.

[Brief description of the drawings]

FIG. 1 is a first embodiment of an infrared camera according to the present invention;
FIG.

FIG. 2 is a first embodiment of an infrared camera according to the present invention;
FIG. 3 is a diagram showing a configuration of an image sensor 51 in FIG.

FIG. 3 is a first embodiment of an infrared camera according to the present invention;
FIG. 3 is an explanatory diagram showing input signals of a differential amplifier circuit in FIG.

FIG. 4 is a second embodiment of the infrared camera according to the present invention;
FIG.

FIG. 5 is a third embodiment of the infrared camera according to the present invention;
FIG.

FIG. 6 is a fourth embodiment of the infrared camera according to the present invention;
FIG.

FIG. 7 is a block diagram showing a conventional infrared camera.

FIG. 8 is a connection diagram showing a configuration of an image sensor 2 in a conventional infrared camera.

[Explanation of symbols]

1 infrared optical system, 4 constant voltage source, 5 driver circuit, 6
Preamplifier circuit, 7 first A / D converter circuit, 8 display processing circuit, 40 bias current setting means, 41 bias current setting means, 42 bias current setting means, 45 variation correction circuit, 46 differential amplifier circuit, 47 The second A /
D conversion circuit, 48 first switch, 49 memory, 5
0 D / A conversion circuit, 51 imaging device, 52 timing generation circuit, 53 standard resistor, 54 standard resistor, 55
Standard resistance, 56 transistors, 57 transistors,
58 transistor, 60 variation correction circuit, 61 attenuation circuit, 62 amplification circuit, 63 second switch, 64
Timing generating circuit, 65 attenuating circuit, 66 amplifying circuit, 67 timing generating circuit.

Claims (5)

[Claims] 1. An infrared optical system, an image sensor located on an image plane of the infrared optical system, a plurality of bolometers formed in the image sensor, and a bias formed in the image sensor and flowing through the bolometer. A plurality of bias current setting means for setting the amount of current; a standard resistor connected to the bias current setting means via a transistor; a constant voltage source for supplying a bias voltage to the image sensor; and a clock supplied to the image sensor. A supply driver circuit, a preamplifier circuit for amplifying the output of the image sensor, a variation correction circuit for correcting variations in the plurality of bias current setting units included in the output of the image sensor, and a variation correction circuit. A first A / D conversion circuit for converting an output into a digital signal; a display processing circuit connected to the first A / D conversion circuit; and a timing generation circuit. An infrared camera characterized by: 2. A variation correction circuit comprising: a differential amplifier circuit, a second A / D converter circuit, and an output of the preamplifier circuit, wherein the output of the preamplifier circuit is the differential amplifier circuit and the second A / D converter circuit. And a memory connected to the second A / D conversion circuit and storing the variation of the bias current setting means, and converting the output of the memory into an analog signal to convert the differential signal to an analog signal. 2. The infrared camera according to claim 1, further comprising a D / A conversion circuit that outputs the signal to an amplification circuit. 3. The variation correction circuit includes a differential amplifier circuit, an attenuation circuit, and a first switch that selectively connects an output of the preamplifier circuit to the differential amplifier circuit and the attenuation circuit. A second A / D converter for A / D converting the output of the attenuation circuit
A D conversion circuit, a memory connected to the second A / D conversion circuit and storing a variation in the bias current setting means;
2. The digital still camera according to claim 1, further comprising a D / A conversion circuit for converting an output of the memory into an analog signal, and an amplification circuit provided between the D / A conversion circuit and the differential amplification circuit. Infrared camera. 4. An infrared optical system, an image sensor positioned on an image plane of the infrared optical system, a plurality of bolometers formed in the image sensor, and a bias formed in the image sensor and flowing through the bolometer. A plurality of bias current setting means for setting the amount of current; a standard resistor connected to the bias current setting means via a transistor; a constant voltage source for supplying a bias voltage to the image sensor; and a clock supplied to the image sensor. A supply driver circuit, a preamplifier circuit for amplifying the output of the image sensor, and a first A connected to the preamplifier circuit via a first switch, a differential amplifier circuit, and a second switch. / D conversion circuit, a memory connected to the first A / D conversion circuit, for storing the variation of the bias current setting means included in the output of the image sensor, and an analog signal output from the memory. And a D / A conversion circuit for converting the signal into a signal and outputting the signal to the differential amplifier circuit. 5. An amplifier circuit is provided between the first switch and the second switch, and an amplifier circuit is provided between the D / A converter circuit and the differential amplifier circuit. The infrared camera according to claim 4, wherein