JPS6047546B2 - How to process infrared imaging signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an infrared sensing device, and more particularly to a method of processing an infrared imaging signal using a multi-element infrared sensing device integrated with a shift register.

One type of infrared imaging signal developed in recent years is a photoelectric conversion section in which a plurality of electrically independent infrared sensing elements are arranged and fixed in a straight line on a support substrate, and each element in the group of infrared sensing elements mentioned above. There is a single unit that is combined with an analog shift register that converts electrical signals generated by the photoelectric conversion function into a time series and takes them out to the outside. As the shift register, a charge transfer device (hereinafter abbreviated as CCD) made of silicon is usually used. Therefore, such a unit came to be called an infrared CCD (IRCCD). Naturally, the above IRCCD has a transfer gate (
It has an electrode (hereinafter abbreviated as TG).

In particular, in an IRCCD used for precisely measuring the temperature of an observation target with relatively low contrast, such as a medical device, a gate electrode and a drain region are provided together with the transfer gate to remove unnecessary DC components from the signal. It is growing.
This gate electrode for removing the DC component has the role of removing a portion of the signal level below a certain predetermined level. Regarding the structure of the above IRCCD, the present inventors et al.
This method has been proposed from time to time, but its outline will be explained using the schematic diagram in FIG.

In the figure, 1 is mercury cadmium telluride (HgCdTe)
A group of infrared sensing elements made of multidimensional semiconductors such as D, , D
2, D3...Dn indicates each sensing element. 2 is a shift register section mainly consisting of a CCD made of silicon (Si), B, , B2, B3...
... Bn indicates each bit of the CCD 3, but each transfer electrode is not illustrated.

An input diode 4, an input adjustment gate electrode 5, a temporary signal storage gate electrode 6 having a DC component removal electrode, and a transfer gate electrode 7 are present between the CCD and the detection element group 1. The role of each of these electrodes is as follows.
The input adjustment gate electrode 5 corresponds to an entrance/exit gate to the shift register 2, and has a function of adjusting the amount of signal flowing from the input diode group 4 to the CCD 3.

The charge passing through the gate electrode is temporarily stored in the gate electrode 6.
The transfer gate electrode 7 is temporarily stored at the bottom and then transferred after a predetermined time.
When opened, charges are injected into the CCD 3 through the transfer gate electrode.

At this time, if the potential of the transfer gate electrode 7 is selected so that a depletion layer with a slightly higher potential barrier than under the temporary signal storage gate electrode 6 is formed under it, the temporary signal storage gate electrode 6 can be stored under the temporary signal storage gate electrode 6. A predetermined amount of charge remains,
An amount exceeding this will be injected into the CCD 3.
Next, a predetermined voltage is applied to a gate electrode (not shown) for removing a DC component to discharge the remaining charges to the drain. By using the IRCCD with the above-described configuration and operating as described above, it should be possible to measure the temperature distribution of the observation target with low contrast with sufficient precision. The infrared sensing element has a conductance GD (5Si
The mutual conductance G of the shift register input section consisting of
Since the difference in m cannot be ignored, the infrared imaging signal cannot be faithfully injected under the temporary signal storage gate electrode 6.
As a result, the efficiency of signal transfer to the shift register section may deteriorate, the difference in charge or dark current generated by incident infrared rays due to variations in the characteristics of each sensing element, or the effectiveness of the cold shield for the sensing element array may decrease. Differences in signal levels caused by non-uniformity deteriorate the signal-to-noise ratio for each sensing element, and there is also large variation, making it impossible to obtain a clear signal image.

The present invention provides an IRCCD signal processing method that can obtain a clear signal image by correcting the characteristic variations of each of the above-mentioned sensing elements. A temporary signal storage region for storing a signal and a signal from a memory storing a reversal signal obtained by subtracting a characteristic value specific to each sensing element from a certain reference value and a charge transfer device are disposed via a transfer gate, introducing a photoelectric conversion signal into the temporary signal storage area, while introducing an inversion signal from the memory to a desired bit of the charge transfer device and then into the temporary signal storage area via a transfer gate;
combining the photoelectric conversion signal and the inversion signal, and guiding the effective signal of the combined signal to the charge transfer device via the transfer gate again;
It is designed to sequentially output only valid signals.

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3.

In addition, in each figure, the same reference numerals are given to the parts showing equivalent functions. FIG. 2 is a diagram showing the configuration of the infrared imaging signal processing device of the present invention, FIG. 3 a is a diagram illustrating a reversal signal, and FIG. FIG. 3c is a diagram showing the reversal signal T shown in FIG. 3a.
.

-(μIPO+Ni) and the signal generation amount μ, P, +Ni of each detection element shown in FIG. 3b are combined to explain the signal amount under the temporary signal accumulation region. The memory M shown in FIG.
D.

) is the dominant value of the signal level caused by the non-uniformity of the individual characteristics of (μ, PO+N, ) and the predetermined value T
. A reversal signal based on the difference (TO - (μ, PO + N, )) is stored in advance. Here, N, is a noise component such as dark current of each sensing element, which generally varies depending on each sensing element, μ, represents the photoelectric conversion efficiency of each sensing element, and PO is the noise component from the reference light source. Showing uniform infrared power. That is, this reversal signal to be stored is generated by inputting the output from each sensing element D when uniform infrared power PO is irradiated to each sensing element D1 to Dn through the input diode 4 to the temporary signal storage area 6 and the transfer gate. T
The values (μ, PO+NO and reference The difference from the value T. is sequentially stored.Here, accurate measurement can be achieved by setting T. to a value close to the background signal value when actually measuring the object.Also, μ, PO is each sensing element D
1 is the signal amount when the reference infrared power PO is photoelectrically converted. Next, the operation of an infrared imaging device having such a memory M will be explained.

Each detection element Dl, D2,...Dn (D,) receives infrared rays Pl, P2,...Pp... from the object to be imaged.
...Pn enters each sensing element Di.

Signals μ, Pi photoelectrically converted by each sensing element Di due to this incidence and noise signals N, peculiar to each sensing element due to dark current and leakage current generated during the period of photoelectric conversion by each sensing element Di, occurs. The signal μ of these sums
IP, +N, passes through input diode group 4 and input gate 1
The signal is introduced into the temporary signal storage region 6 corresponding to each sensing element D through the signal G. On the other hand, a reversal signal T corresponding to each sensing element D stored in the memory M. One (μ, PO+N
, through the D/A converter and amplifier M2, are sequentially transferred to the CCD by applying clocks φ1 to φ4 of the CCD through the signal input section 1S and input gates IGl and IG2, and each sensing element D1 of the memory M is Reverse signal T corresponding to
. -(μ, PO+N,) is transferred to the position of the φ3 electrode of a predetermined bit of the CCD, in this embodiment, a voltage is applied to the transfer gate TG and introduced into the temporary signal storage region 6, respectively. At this time, it is necessary to form a deep potential well, that is, a depletion layer, under the gate SG of the temporary signal storage region 6. Through the above operations, each detection element D
, and the signal charges based on the inversion signals corresponding to each sensing element Di are combined under the temporary signal accumulation region 6.

That is, the signal amount at this time is T. + (μ, P “μIPO)
becomes. Here, μ, (PI-PO), i.e., output・ΔP,
corresponds to the difference in the amount of light received by each detection element, that is, the change in signal due to the temperature difference of the object to be imaged, and the noise component N1 is canceled out. The signal accumulation situation in the temporary signal accumulation area 6 at this time is shown in FIG. 3c. The shaded area in Figure 3c is the object to be imaged! This component, ie, .mu.i.DELTA.P, is an effective signal component due to temperature change, and may be introduced into each bit of the CCD and sequentially derived to perform image signal processing.

That is, the composite signal T is stored in the temporary signal storage area 6. +μ
,・ΔP, is the voltage required to create a depletion layer sufficient to accumulate it! is applied to the storage gate and stores the composite signal. In order to introduce only the effective signal component of this composite signal into the CCD, a voltage is applied to the transfer gate TG to form a potential barrier high enough to cause only the effective signal component to overflow to the CCD side. At this time, a potential barrier deeper than the transfer gate m is formed in the temporary signal storage region 6, and approximately T of the composite signal is formed. A potential is applied to TG and SG such that only the DC signal component remains. The effective signal μl·ΔP, thus transferred to the CCD, is sequentially sent to the output gate (1) side by the clock voltage (φ1 to φ4) applied to the CCD, and the output diode 0D
The change in potential due to the signal that has reached 0 is guided to the amplifier MOS and then output from the output terminal 0UT. Here, D and S represent the source and drain of the MOS diode, respectively. Further, φ1 is a voltage application terminal applied to the gate electrode for sequentially sending valid signals to the discharge drain DR. On the other hand, the remaining DC signal component T is the effective signal component sent to the CCD. is discharged to the discharge drain BD by applying a required voltage to the unnecessary signal discharge gate BSG provided around the unnecessary signal discharge gate BSG provided around the unnecessary signal discharge drain BD provided in the temporary signal storage region 6 and to which a predetermined voltage is applied. One cycle of imaging is completed by the operations described above, and the same cycle as above is repeated one after another to perform imaging.

Note that CH indicated by a dotted line in FIG. 2 indicates a charge weir defining a charge path. The above explanation is that the system including the diode ISl gates IGl, IG2 and CCD in the signal input section has good linearity with respect to the amount of signal charge, and the transfer gate T
We have described an ideal case in which the threshold voltages of the parts corresponding to each element of G are uniform, but these characteristics are generally not good, and in this case, the output signal derived as an effective signal has a signal due to them. The output μ,·ΔPi+δTi, to which the value δT due to the distortion component is added is derived.

In this case, in order to improve the accuracy of imaging, a fixed noise removal circuit for removing these δT may be provided in the output section 0UT. If the signal processing method according to the present invention described above is used, the amount of signal handled at the output section of the CCD will be only μi, ΔPI and effective signal components, so the dynamic range of the CCD can be reduced, and the output section of the CCD can be made smaller. At the same time, the signal processing section of the output section, that is, the amplification system, can be made smaller, resulting in high reliability and high quality infrared imaging.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the outline of an IRCCD, FIG. 2 is a diagram showing the configuration of an infrared imaging signal processing device of the present invention, and FIGS. 3 a to 3 c are diagrams explaining the signal processing operation of the present invention. be. 1: Infrared detection element group, 2: Shift register section mainly consisting of CCD made of silicon, 3CCDl6: - signal storage area, M: memory, D1 (external ray detection element, CH: charge dam).

Claims (1)

[Claims] 1. A plurality of infrared sensing elements are provided, and a reversal signal for compensating for characteristic differences obtained by subtracting a signal having a level difference corresponding to the characteristic unique to each sensing element from a predetermined reference value is stored in advance in a memory, and A temporary signal storage area capable of storing an imaging signal obtained by photoelectric conversion from the sensing element and a reverse signal from the memory corresponding to each sensing element, and a charge transfer device are arranged via a transfer gate. The imaging signal is introduced into the temporary signal storage area, while the inversion signal from the memory is introduced into the temporary signal storage area via a transfer gate, which is once guided to a desired bit of the charge transfer device. 1. A method for processing an infrared imaging signal, comprising: combining the signal with an imaging signal, introducing a portion of the combined signal as an effective signal into a charge transfer device via a transfer gate, and sequentially outputting the signal.