WO2019194452A1

WO2019194452A1 - Microbolometer-based infrared detector

Info

Publication number: WO2019194452A1
Application number: PCT/KR2019/003521
Authority: WO
Inventors: 박승현; 이귀로; 이학용; 안기웅
Original assignee: 주식회사 트루윈
Priority date: 2018-04-02
Filing date: 2019-03-26
Publication date: 2019-10-10
Also published as: KR101881461B1

Abstract

Provided is a microbolometer-based infrared detector capable of reducing effects caused by a current component generated according to self heating. An infrared detector, according to one aspect of the present invention, comprises: an active cell having a microbolometer for outputting a detection signal in response to infrared rays; a skimming cell for generating a skimming signal canceling a background component of the detection signal; a detection circuit for detecting the difference between the detection signal and the skimming signal; and a bias voltage generator for modulating the bias voltage of the skimming signal. The bias voltage generator outputs a bias voltage such that a current, which offsets a current increase portion according to a decrease in resistance value due to self heating of the microbolometer in the active cell, flows through the skimming cell for the amount of detection time.

Description

Microbolometer based infrared detector

The present invention relates to a microbolometer-based infrared detector, and more particularly to a microbolometer-based infrared detector that can reduce the effect of the current component generated by the self heating (self heating).

Infrared detectors are generally divided into light-based detectors and hot plate detectors that respond to far-infrared radiation. The hot plate detector generates a temperature image of the target object using the heat sensor array. As such, a device that collects black body radiation emitted from a subject and acquires a temperature image is called a far-infrared thermal imaging system.

Hot plate detectors are known to include bolometers, microbolometers, pyroelectrics and thermocouples. By focusing the far infrared rays of the 8-14 μm band that blackbody radiates on all objects on the microbolometer with a lens, the temperature of the microbolometer rises and falls, and thus the electrical resistance of the microbolometer changes. Thus, by using an array of microbolometer cells, ie a microbolometer array, it is possible to remotely image the temperature distribution of the subject scene.

For the temperature change characteristic of the electrical resistor, it is necessary to measure the current flowing through the electrical resistor after applying the bias voltage, or measure the voltage across the resistor after applying the current bias. At this time, the temperature of the electrical resistor is increased by joule-heating. This phenomenon is called self-heating, which must be corrected as a value independent of the far-infrared radiation to be detected.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) Korean Registered Patent Publication 10-1274026 (Notification date June 12, 2013)

(Patent Document 2) Korean Registered Patent Publication 10-1804860 (Notification Date December 6, 2017)

The problem to be solved by the embodiment of the present invention is to solve the problem of waste of analog dynamic range caused by self-heating.

Another object of the present invention is to provide a micro-bolometer-based infrared detector that can minimize the direct current component and the magnetic heating component input to the integrator.

However, the problems to be solved by the present invention are not limited to the above problems, and may be variously expanded within the scope without departing from the spirit and scope of the present invention.

Infrared detector according to an embodiment of the present invention, the active cell having a micro-bolobiter for outputting a detection signal in response to the infrared; A skimming cell generating a skimming signal that removes a background component of the sense signal; A detection circuit for detecting a difference between the detection signal and the skimming signal; And a bias voltage generator for modulating the bias voltage of the skimming signal.

In one embodiment, the skimming cell may comprise a reference microbolometer and a source follower for controlling the current flowing in the reference microbolometer. The bias voltage output from the bias voltage generator may be input to the gate of the source follower. The bias voltage includes a DC component and a modulation component.

In another embodiment, the skimming cell comprises a first source follower and a second source follower for controlling current flowing through the first reference microbolometer and the second reference microbolometer and the first reference microbolometer and the second reference microbolometer, respectively. It may include. In the first reference microbolometer, a voltage for allowing a DC component current to flow is input to the gate of the first source follower, and a bias voltage output from the bias voltage generator is input to the gate of the second source follower. The bias voltage may include a DC component and a modulation component or may include only a modulation component.

In one embodiment, the bias voltage output from the bias voltage generator has a waveform in which the voltage decreases during the detection time. The waveform may be a linear decrease in voltage.

In an exemplary embodiment, the bias voltage generator may output a bias voltage to allow a current flowing in the skimming cell to cancel a current increase due to a decrease in resistance due to self heating of the microbolometer of the active cell during a detection time. .

According to the embodiment of the present invention, since both the self-heating component and the DC component of the active-current can be canceled, more accurate infrared sensing is possible.

However, the effects of the present invention are not limited to the above effects, and may be variously expanded within the scope without departing from the spirit and scope of the present invention.

1 is a diagram illustrating a signal detection circuit configuration of a microbolometer-based infrared detector according to an exemplary embodiment of the present invention.

FIG. 2 is a graph illustrating changes in current and voltage in the signal detection circuit according to the embodiment of FIG. 1.

3 is a circuit diagram illustrating a signal detection circuit configuration of a microbolometer based infrared detector according to another embodiment of the present invention.

4 is a graph illustrating changes in current and voltage in the signal detection circuit according to the embodiment of FIG. 3.

5 is an example of a bias voltage generator for removing a component due to self heating.

6 is another example of a bias voltage generator for removing components due to self heating.

7 is another example of a bias voltage generator for removing components due to self heating.

8 is a diagram illustrating a signal detection circuit configuration of a conventional microbolometer-based infrared detector.

9 is a diagram illustrating a circuit arrangement of a general microbolometer based infrared detector.

10 is a graph showing changes in current and voltage in a signal detection circuit of a conventional microbolometer based infrared detector.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments to make the disclosure of the present invention complete, and common knowledge in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims.

Although the first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another. Therefore, the first component mentioned below may be a second component within the technical spirit of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprises” and / or “comprising” refers to the presence of one or more other components, steps, operations and / or elements. Or does not exclude additions.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used in a sense that can be commonly understood by those skilled in the art. In addition, terms that are defined in a commonly used dictionary are not ideally or excessively interpreted unless they are specifically defined clearly.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

8 is a block diagram of a signal detection circuit of a conventional microbolometer-based infrared detector, and FIG. 9 is a diagram illustrating a circuit arrangement of the microbolometer-based infrared detector. The microbolometer-based infrared detector may include an active cell array 92, a skimming cell 91, a detection circuit 93, and a reference voltage generator 94.

The active cell array 92 includes a plurality of active cells. Each active cell may include a first source follower 84, a microbolometer 86, and a first switch 85. The active cell outputs a sensing signal in response to infrared rays.

The skimming cell 91 includes a plurality of unit skimming cells and is a cell that does not respond to infrared rays. Each unit skimming cell generates a skimming signal that removes the background component of the sense signal. One unit skimming cell may be shared by cells located in the same row or column of the active cell array. The unit skimming cell may include a second source follower 83 and a reference microbolometer 82. The second microbolometer 82 does not respond to the remote temperature signal and the current Is flowing through the reference microbolometer 82 may have a fixed value independent of the remote temperature signal.

The detection circuit 93 is a circuit for detecting a change in resistance of the active cells, and active cells located in the same column share a channel detection circuit. The infrared energy emitted from the subject is absorbed into the active-cell array through the lens, and the infrared thermal image may be obtained by detecting the current flowing through each of the active cells.

In the signal detection circuit configuration of the conventional microbolometer-based infrared detector of FIG. 8, when the clock Φa closes the switch 85, a Va voltage is applied to both ends of the active cell 86 and an active current Ia flows. The active current contains a large DC component current that is independent of the infrared signal, and in order to remove it, a skimming current (Is) is generated by applying a Vs voltage across the skimming cell 82 which does not respond to infrared rays. . The difference Is-Ia between the two currents is input to the integrator during the time when the switch 85 is closed, that is, the detection time T _read . The integrator may be composed of an OP amplifier 11 and a capacitor (C _int ), and is amplified and converted to a voltage according to a detection time to generate an output voltage Vo as shown in Equation (1). The integrator may include a capacitive trans-impedance amplifier (CTIA).

The power dissipated in the resistor during the detection time is converted into heat to raise the temperature of the active cell. Since the bolometer has a negative temperature coefficient, the resistance value Ra of the bolometer is gradually lowered during the detection time as shown in FIG. Accordingly, as shown in FIG. 10D, the active current Ia also gradually increases during the detection time, and even though unnecessary DC components are removed using the skimming current, the self heating components remain.

As a result, the input current of the integrator is linear over time (Is-Ia = a ₁ t + a ₀ ) and the output voltage is quadratic (Vo = Vref-(1 / Cint) (a ₁ t ² + a _0). t )), which wastes the analog dynamic range ΔV during the integration time, as shown in FIG. In particular, as the ambient temperature increases to a high temperature (eg, 60 degrees Celsius or more), the resistance value of the bolometer decreases exponentially, and the problem caused by self heating may become more serious.

In order to solve this problem, the present invention modulates the bias voltage of the skimming current during the detection time T _read . The bias voltage may be a linear decrease in voltage during the detection time. The bias voltage may allow a current flowing in the skimming cell to offset the increase in current caused by the decrease in the resistance value due to the self heating of the microbolometer of the active cell during the detection time.

First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. 1 is a circuit diagram showing a configuration of a signal detection circuit according to an embodiment of the present invention, Figure 2 is a graph showing the current and voltage changes in the signal detection circuit according to the embodiment of FIG.

In the embodiment of FIG. 1, the bias voltage of the skimming current is modulated during the detection time T _{read in} order to cancel the self-heating component of the active current. That is, the bias voltage generator 18 generates a bias voltage Vrt for removing the component due to self heating, and the generated bias voltage Vr (t) is input to the gate of the second source follower 13. The bias voltage Vr (t) may be a linear decrease in voltage during the detection time as shown in FIG. 1. Then, the voltage across the second source follower 13 changes, so that the voltage Vs across the reference microbolometer 12 also changes as shown in FIG. 2 (c), whereby the reference microbolometer 12 The current Is flowing in also changes as shown in FIG.

If this is expressed as an equation, it is equal to Equation 2. Equation 2 shows the current input to the integrator when the current by the infrared signal is set to zero. In Equation 2, V _s0 is the voltage across the reference microbolometer 12 at the start time of detection time, b represents the slope of Vs ((c) of FIG. 2) during the detection time, and R _a0 at the start time of detection time. Is the resistance value of the microbolometer 16, and c represents the slope of Ra (Fig. 2 (b)) during the detection time.

In

Equation

2, 1 / (R _ao (1-ct)) is approximately (1 + ct) / R _{ao when} ct << 1, so an approximation equation can be obtained as in Equation 2. In the last equation (2), if V _s0 (1 + bt) / Rs ≒ Va (1 + ct) / R _a0, it can be seen that Is-Ia ≒ 0. An example of the output waveform at this time is shown in FIG. In this way, the bias voltage generator 18 applies an appropriate bias voltage Vr (t) such that _Vs0 (1 + bt) / Rs ≒ Va (1 + ct) / R _a0 during the detection time, so that at the input of the integrator, By minimizing all the unnecessary components (DC component and self heating component) except for the desired signal, that is, the current caused by the infrared signal, the analog dynamic range can be prevented from being wasted.

Next, another embodiment of the present invention will be described with reference to FIGS. 3 and 4. 3 is a circuit diagram showing the configuration of a signal detection circuit according to another embodiment of the present invention, Figure 4 is a graph showing the current and voltage changes in the signal detection circuit according to the embodiment of FIG.

In the embodiment of FIG. 3, the first skimming current I _s1 flowing into the first reference microbolometer 12a by dividing the unit skimming cell into two is a DC component current, and the second skimming flowing through the second reference microbolometer 12b −. The current I _s2 generates only the DC component + modulation component or modulation component, so that the sum of the two currents I _s = I _s ₁ + I s ₂ is used as the final skimming current. To this end, Vgsk is applied to the gate of the source follower 13a connected to the first reference microbolometer 12a as in the prior art, and the bias voltage generator ( 18 '), the bias voltage Vr (t) is applied. This configuration makes the design of the bias voltage generator 18 'for generating the skimming-current modulation components more precise and flexible.

The sum of two currents I _s = I _s ₁ + I s ₂ can be expressed as in Equation 3. Equation 3 also shows the current input to the integrator when the current by the infrared signal is set to zero. In Equation 3, V _s2 _, ₀ is the voltage across the second reference microbolometer 12b at the start time of the detection time, and b represents the slope of V _s2 during the detection time.

In the last equation of Equation 3, the parenthesis indicates a DC component and the rest indicates a modulation component. V _s2 _{, 0} / R _s2 may be 0, in which case I _s2 has only a modulation component. An example of this is shown in FIG. 4C.

3, the first skimming current I _s1 flowing in the first reference microbolometer 12a by dividing the unit skimming cell into two is equal to the DC component current and the second reference microbolometer 12b. The second skimming-current I _s2 flowing in) only differs in that it generates only a DC component + a modulation component or a modulation component, and the rest of the operating principle is the same, and the output waveform is also shown as shown in (d) of FIG. 4. do.

Next, some examples of bias voltage generators 18 or 18 'that can be used in the present invention are described. 5 to 7 are some examples of bias voltage generators for removing components due to self heating.

The bias voltage generator 18 of FIG. 5 includes a ramp voltage generator 18a and a reference voltage generator 18b. When the lamp clock Φx drops from the high level to the low level during the detection time T _read , the lamp voltage generator 18a discharges the capacitor 55 while the output voltage Vx is changed from the initial voltage Vi to the reference current. It is reduced by the product of and the detection time (I _ref x t ). That is, it can be expressed as Vx ( t ) = Vi-I _ref t . The reference voltage generator 18b applies the negative feedback of the amplifier 53 to the same structure as the skimming circuit, so that the voltage Vg across the reference resistor Rg 51 can be precisely controlled by the lamp output voltage Vx. In addition, the gate voltage Vr (t) of the P-channel MOSFET 52 required at this time can be obtained from the output of the amplifier 53.

The bias voltage generator 18 of FIG. 6 includes a ramp voltage generator 18a 'and a reference voltage generator 18b. In the embodiment of Fig. 6, the configuration of the lamp voltage generator 18a 'is different from that of Fig. 5, but the operation principle is substantially the same. When the ramp clock Φx drops from the high level to the low level during the detection time T _read , the capacitor 65 discharges and the output voltage Vx is the product of the reference current and the detection time (I _ref ) from the initial voltage Vi. x t ). That is, it can be expressed as Vx ( t ) = Vi-I _ref t . Since the reference voltage generator 18b is the same as the embodiment of FIG. 5, detailed description thereof will be omitted.

The bias voltage generator 18 of FIG. 7 includes a ramp voltage generator 18a '' and a reference voltage generator 18b. The ramp voltage generators of FIGS. 5 and 6 integrate a current source continuously into a capacitor. However, FIG. 7 has a difference in that the step waveform Vx 'is first made discrete and then the ramp waveform Vx is formed using the low pass filter LPF.

Φx = (High): Vx '(t) = Vi ... reset status

Φx = (Low): Vx '(t) = Vi + N * ΔV ... integral state

In the above equation, N is the number of times Φp has transitioned from the high level to the low level. Φpb is the opposite phase of Φp and is formed by a non-overlapped clock. That is, after Φx drops to a low level, as the Φp clock is applied at high speed, charge stored in the sampling capacitor 77 accumulates in the integrating capacitor 75 to generate a stepped waveform Vx '. The staircase waveform changes to the ramp waveform (Vx) as it passes through the LPF with the large time constant. The method as shown in FIG. 7 has an advantage of easily generating sophisticated lamp output by using the ratio of the capacitor and the clock frequency.

The bias voltage generators of FIGS. 5-7 are exemplary, and the present invention is not limited to a specific bias voltage generator. Those skilled in the art will understand that various types of bias voltage generators are configurable.

Although the signal detection circuit of the microbolometer-based infrared detector according to the embodiments of the present invention has been described with reference to the drawings, the above description is exemplary and generally within the scope of the present invention without departing from the technical spirit of the present invention. Obviously, modifications and variations may be appropriately used by those skilled in the art.

Claims

An active cell having a microbolobiter for outputting a detection signal in response to infrared rays;

A skimming cell generating a skimming signal that removes a background component of the sense signal;

A detection circuit for detecting a difference between the detection signal and the skimming signal; And

A bias voltage generator for modulating the bias voltage of the skimming signal

Infrared detector comprising a.
The method of claim 1,

The skimming cell includes a reference microbolometer and a source follower for controlling a current flowing in the reference microbolometer,

And a bias voltage output from the bias voltage generator is input to a gate of the source follower.
The method of claim 1,

The skimming cell includes a first source follower and a second source follower for controlling current flowing through the first reference microbolometer and the second reference microbolometer, and the first reference microbolometer and the second reference microbolometer, respectively.

In the first reference microbolometer, a voltage through which a DC component current flows is input to the gate of the first source follower,

And a bias voltage output from the bias voltage generator is input to a gate of the second source follower.

Infrared detector.
The method of claim 2,

The bias voltage comprises a DC component and a modulation component.
The method of claim 3, wherein

Wherein said bias voltage comprises a DC component and a modulation component or comprises only a modulation component.
The method according to any one of claims 1 to 5,

The bias voltage output from the bias voltage generator is that the voltage during the detection time, the infrared detector.
The method of claim 6,

The bias voltage output from the bias voltage generator is an infrared detector, the voltage decreases linearly during the detection time.
The method according to any one of claims 1 to 5,

And the bias voltage generator outputs a bias voltage for causing a current flowing in the skimming cell to cancel a current increase due to a decrease in resistance caused by self heating of the microbolometer of the active cell during a detection time.