JPS6040230B2 - infrared imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a parallel scanning infrared imaging device using an array of photoconductive photodetectors arranged in a direction perpendicular to a scanning direction.

FIG. 1 is a diagram showing the configuration of a parallel scanning type infrared imaging device using a secondary photoconductive detector and a one-dimensional scanner.

In the figure, incident infrared light 1 is focused by a light receiving optical system 2 and then scanned by a horizontal scanner 4 that scans in a direction perpendicular to the direction of the infrared detector array 3, and a bias current is supplied from a bias power supply 5. The light enters the infrared detector array 3 that is The electrical signal obtained as the output of the infrared detector array 3 is processed by a signal processing circuit 6 and supplied to an image display 8 as a video signal 7. The image display device 8 displays the captured scene.
In order to display the image, a method is used in which a spot with a brightness corresponding to the size of the video signal 7 is generated at a position corresponding to the angle of incidence of the incident infrared light 1 on the light receiving optical system 2, that is, the angle at which the scanner is facing. It will be done. The orientation of the scanner is transmitted as a synchronization signal 9 from the scanner to the signal processing circuit 6 in the form of an electrical signal, and the video signal 7 also includes this information. FIG. 2 is a diagram showing a parallel scanning method. Each detector in the infrared detector array 3 is arranged in a direction perpendicular to the scanning direction 10, and the field of view 11 is scanned by a horizontal scanner with a number of scanning lines equal to the number of detectors. The output of each detector is amplified by a preamplifier 12 provided for each detector, and then converted by a multiplexer 13 into a serial video signal 7 and supplied to an image display 8. Note that the front amplifier 12 and multiplexer 13 are included in the signal processing circuit 6 in the device shown in FIG. By the way, focusing on two detectors in the infrared detector array, let the sensitivity and power of the first detector be R1 and P1, respectively, and the sensitivity and power of the second detector be R2 and P2, respectively. , the outputs SI and S2 of the first detector and the second detector can be expressed by the following equations, respectively. SI=RIPI
...'11S2=R is 2
...[2' The brightness difference △B of the images displayed on the image display is the gain G of the amplifier provided for each detector.
and a constant K determined by the image display device, it is expressed as follows.

△B=KGSI-KGS2 =KG{P1 (RI-R2) ten (PI-P2) R2} (
3} It is desirable that the brightness difference △B of the image displayed on the image display is determined only by the difference in received light power, and [3}
The second term in {} in the equation represents this effect.

On the other hand, the first term represents the brightness difference caused by the difference in sensitivity between the detectors. The first term can be ignored with respect to the second term.
- [When the condition 41 is satisfied, since IPI - P21 minus PI for an object at room temperature, the sensitivity difference between each detector must be limited to an extremely small value.

However, with the current manufacturing technology of infrared detectors, it is difficult to satisfy the condition of formula '4} for many detectors. Therefore, the displayed image of the conventional device has the drawback that horizontal stripe-like brightness unevenness occurs due to uneven sensitivity of the detector. In order to eliminate this drawback, the present invention provides a circuit that causes infrared light to be incident on the infrared detector array from a reference infrared light source, and uses the infrared detector output at that time to change the bias current for each detector. This system uses the following principle.

The sensitivity R of a photoconductive detector is the sensitivity R per unit bias current.
o and bias current lb, it can be expressed as follows.

R=R.

×lb...{5} Therefore, if you change the bias current, the sensitivity will change accordingly, so even if Ro is different for each detector, if you appropriately set the bias current for each detector, infrared detection R is equal for all detectors in the array, and the {th
It becomes possible to satisfy the condition of formula 4. Hereinafter, this invention will be explained in detail using the drawings. FIG. 3 is a diagram showing an embodiment of the invention.

In the figure, the infrared light incident on the infrared detector array 3 is "incident infrared light 1 incident from the outside or infrared light generated from the reticle 14 provided on the imaging plane in the light receiving optical system 2. Infrared detector row 3 determines which one of them is incident.
It is determined by the orientation of the horizontal scanner 4, which scans in a direction perpendicular to the direction. Immediately before the incident infrared light 1 starts to enter the infrared detector array 3 due to the rotation of the horizontal scanner 4, on the surface of the reticle 14 that the infrared detector array 3 sees, there is a long line in the direction orthogonal to the direction in which the horizontal scanner 4 scans. Two mutually parallel slit-like patterns with sides having different amounts of infrared radiation are provided. These two slit-like patterns can be realized by setting different temperatures or processing them to have different infrared emissivities. The sensitivity correction signal processing circuit 15 adjusts the infrared detector array 3 based on the output of the pre-calendar amplifier 12 provided for each detector corresponding to the two slit-shaped patterns on the reticle 14 surface. detect the difference in sensitivity between each detector. The timing at which the infrared detector array 3 views the slit-like pattern is transmitted to the sensitivity correction signal processing circuit 15 by the synchronization signal 9. The sensitivity correction signal processing circuit 15 generates a bias current 17 for each detector based on the detected sensitivity difference between the detectors.
is adjusted and supplied so that all the detectors satisfy the condition of equation (4).The sensitivity correction signal processing circuit 15 includes a multiplexer inside, and the sensitivity correction signal processing circuit 15 includes a multiplexer, and the The sent signal is converted into a serial format and supplied as a video signal 7 to an image display 8. FIG. FIG.

Each detector in the infrared detector array 3 is scanned by a scanner in a scanning direction 101, but immediately before scanning the field of view 11, two slit-shaped patterns on the reticle, namely a first slit 18 and a second slit 19, are scanned. . Figure 5 shows
FIG. 2 is a block diagram showing an example of the configuration of a sensitivity correction signal processing circuit.

Two digital memories are used to digitize and store the values of bias currents to be supplied to each detector. The multiplex circuit 21 selects one of many detectors based on a detector designation signal 23 given from a detector designation circuit 22 that designates detectors one after another, and selects one of the detectors corresponding to that detector. The front layer amplifier output 24 is output as a video signal 7. The voltage correction circuit 25 detects the difference based on the video signal 7 and the synchronization signal 9 when the sensitivity of the detector designated by the detector designation circuit 22 differs from a preset value, and stores the difference in the digital memory. The memory contents 26 of 20 are modified and sent back to the digital memory 20 as write contents 28 together with a write signal 27. Note that the write signal 27
is a signal for putting the digital memory 20 into the write state, and during the period when this signal is not given, the digital memory 2
The memory contents of 0 remain unchanged. Sample/hold signal 2
9, the sample/hold circuit 30 corresponding to the detector designated by the detector designation circuit 22 performs a digital
It is generated by the detector designation circuit 22 in order to sample and hold the contents of the digital memory 20 converted into an analog quantity by the analog converter 31. Further, after passing through a low-pass filter 32 provided to stabilize the output of the sample-and-hold circuit 30, the sample
The output of the hold circuit 30 becomes the bias current 17.
FIG. 6 is a block diagram showing an example of the configuration of the voltage correction circuit.

The video signal 7 is supplied to two sample-and-hold circuits 34a and 34b after passing through a low-pass filter 33 provided to reduce noise. Based on the synchronization signal 9, the synchronization signal separation circuit 35 generates a first slit synchronization signal 36 when the infrared detector array is looking at the first slit, and a first slit synchronization signal 36 when the infrared detector array is looking at the second slit depending on the orientation of the scanner. A two-slit synchronization signal 37 is generated. Two samples
The hold circuits 34a and 34b sample and hold the video signal 7 based on the first slit synchronization signal 36 and the second slit synchronization signal 37, respectively, and the output thereof is at the first slit level 38 and the second slit level. 39 is generated.

The difference between the first slit level 38 and the second slit level 39 is determined by the sensitivity of each detector in the infrared detector array, and if all the detectors have the same sensitivity, this difference will also be constant. The subtractor 4 calculates the difference between the first slit level 38 and the second slit level 39, and the difference between this difference and a predetermined reference value 41 is calculated again by the subtractor 42, and becomes an error signal 43. After this error signal 43 passes through a coefficient multiplier 44 having a predetermined attenuation coefficient, it is applied to an analog-to-digital converter 45 and becomes a digitized error signal. Digital adder 47 adds memory contents 26 and digitized error signal 46 to generate write contents 28.
Further, the discriminator 48 generates a write signal 27 for correcting the contents of the digital memory when the absolute value of the digitized error signal 46 exceeds a certain value. Figure 7 shows
This is a diagram showing the phase relationship of the main signals in the voltage correction circuit, and shows the relationship among the video signal 7, the first slit synchronization signal 36, the second slit synchronization signal 37, the first slit level 38, and the second slit level 39.

Note that the above explanation is about the case where a one-dimensional scanner is used as the scanner, but the same effect can be obtained by using the same method as above when using a two-dimensional scanner that combines scanners that scan in mutually orthogonal directions instead. is obtained.

Furthermore, in the above explanation, a preset value was used as a reference value for comparison with the difference between the first slit level and the second slit level, but instead of this, the first slit level
By determining the difference between the slit level and the second slit level and using this average value as a reference value, the dynamic range of the error signal can be reduced. In addition, in the above explanation, we explained the method of digitizing all bias current values and storing them in memory, but it is also possible to give a common offset value to all detectors, and then calculate the increment/decrement corresponding to each detector from that value. If the configuration is such that only the bias current is stored in the digital memory, the memory capacity required for setting the bias current can be reduced. As described above, in the infrared imaging device according to the present invention, a highly uniform infrared image can be obtained by having a circuit that automatically corrects sensitivity differences between a plurality of infrared detectors.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a parallel scanning type infrared imaging device using a conventional photoconductive detector and a -dimensional scanner, Figure 2 is a diagram showing the parallel scanning type, and Figure 3 is an embodiment of the ladder invention. FIG. 4 is a diagram showing the relationship between the pattern image on the reticle and the field of view required by the imaging device in the infrared imaging device according to the present invention, and FIG. 5 is an example of the configuration of the sensitivity correction signal processing circuit. 6 is a block diagram showing an example of the configuration of the voltage correction circuit, and FIG. 7 is a diagram showing the phase relationship of the main signals in the voltage correction circuit. In the figure, 1 indicates incident infrared light, 3 is an infrared detector row, 14
15 is a sensitivity correction signal processing circuit, 17 is a bias current, 18 is a first slit, and 19 is a second slit. In the drawings, the same or corresponding parts are designated by the same reference numerals. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. It has a photoconductive infrared detector array linearly arranged in a direction perpendicular to the scanning direction and a light receiving optical system, and a scanner that scans the field of view seen by the infrared detector array two-dimensionally or one-dimensionally. In the infrared imaging device, the infrared detector array is located within the scanning range of the scanner on the imaging plane in the light receiving optical system, and in a position that does not obstruct the field of view of the scene required by the infrared imaging device, in the same direction as the infrared detector row. The above-mentioned 2 reticle is provided with two mutually parallel slit-like patterns having long sides in the direction, each having a different amount of infrared radiation, and an amplifier provided for each detector in the infrared detector row. The bias current applied to each photoconductive infrared detector in the infrared detector array is automatically controlled so that the difference in output corresponding to the two slit images is the same for all detectors. An infrared imaging device featuring: