A self-heating effect compensation method and circuit based on mechanical baffle

Abstract

The embodiments of the present application relate to the field of sensor technology, and in particular to a self-heating effect compensation method and circuit based on a mechanical baffle, the method comprising: closing the baffle; applying a bias current to a first resistor; a differential circuit detecting the voltage change slope of the first resistor and storing the slope voltage; opening the baffle; an integral circuit constructing a ramp voltage based on the slope voltage; subtracting the ramp voltage when the circuit is read out to achieve compensation for the self-heating effect; and when the circuit temperature changes, re-executing the operation of closing the baffle. The baffle blocks the influence of external infrared radiation, detects the voltage change caused only by the self-heating effect, constructs a ramp voltage representing the self-heating effect, and subtracts the ramp voltage when reading out to achieve compensation for the self-heating effect. When the circuit ambient temperature changes, it is only necessary to re-close the baffle without manual adjustment, and it can work at various ambient temperatures, with low requirements for MEMS process and low cost.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of sensor technology, and in particular to a self-heating effect compensation method and circuit based on a mechanical baffle. Background Art

[0002] Uncooled infrared thermal imagers based on microbolometers have advantages in terms of size, power consumption, and cost, and are widely used in night vision, observation, security, and other fields. A microbolometer is a thermal sensor. Usually, the temperature change of the target scene causes a small temperature change of the microbolometer. For example, if the temperature of the target scene changes by 1K, the temperature of the microbolometer changes by 0.01K. However, the Joule heat of the microbolometer during the power-on readout cycle will cause a temperature change of several K or even tens of K within tens of microseconds, which is the so-called self-heating effect. The large temperature change caused by the self-heating effect superimposes a huge invalid common mode on the weak effective signal. In order to ensure that the effective signal is read correctly without distortion, the self-heating effect needs to be compensated.

[0003] At present, a variety of ways to compensate for the self-heating effect have been proposed, such as using a digital-to-analog converter (DAC) to generate a time-varying bias voltage to keep the readout current constant throughout the readout process to compensate for self-heating. However, the code value of the DAC needs to be precisely adjusted, and the self-heating effect is different at different ambient temperatures. When the temperature changes, it needs to be readjusted, which increases the complexity of the adjustment at different temperatures. In addition, there are also methods that use light-shielded micro-electro-mechanical systems (MEMS) pixels to detect the self-heating effect and eliminate it in the front-end architecture. This method has a good elimination effect and does not require additional adjustments at different temperatures. However, the light-shielded MEMS increases the process complexity and cost and is not suitable for low-cost applications. There is also a method of adding an additional reset. By accurately adjusting the reset time, self-heating elimination can be achieved, but it requires additional manual and precise adjustment of parameters, which consumes a lot of human resources. Summary of the invention

[0004] The embodiments of the present application provide a self-heating effect compensation method and circuit based on a mechanical baffle, which can solve the problem that the self-heating effect compensation needs to be readjusted when the temperature changes.

[0005] In a first aspect, an embodiment of the present application provides a self-heating effect compensation method based on a mechanical baffle, the method comprising:

[0006] A closed baffle, the baffle being used to prevent external infrared radiation from reaching the first resistor;

[0007] applying a bias current to a first resistor, wherein the first resistor is a resistor that senses external infrared radiation;

[0008] The differential circuit detects the voltage change slope of the first resistor and stores the slope voltage;

[0009] Open the baffle;

[0010] The integration circuit constructs a ramp voltage based on the slope voltage;

[0011] The ramp voltage is subtracted when the circuit is read out to achieve compensation for the self-heating effect;

[0012] When the circuit temperature changes, the operation of closing the shutter is performed again.

[0013] In an optional design, applying a bias current to the first resistor includes:

[0014] applying a bias voltage to a second resistor to generate a current, wherein the second resistor is a resistor that is thermally short-circuited with the substrate;

[0015] The current of the second resistor is copied to the first resistor.

[0016] In an optional design, the voltage variation slope is the rate at which the voltage of the first resistor changes with time due to a self-heating effect.

[0017] In an optional design, the slope of the ramp voltage is the same as the voltage change slope of the first resistor.

[0018] In an optional design, the ratio of the resistance-capacitance product of the differential circuit and the integration circuit is 1.

[0019] In a second aspect, an embodiment of the present application provides a self-heating effect compensation circuit based on a mechanical baffle, the circuit comprising:

[0020] a baffle, the baffle being used to prevent external infrared radiation from reaching the first resistor;

[0021] A bias circuit, used for applying a bias current to a first resistor, wherein the first resistor is a resistor for sensing external infrared radiation;

[0022] A differential circuit, used for detecting a voltage change slope of the first resistor and storing a slope voltage;

[0023] an integrating circuit, configured to construct a ramp voltage based on the slope voltage;

[0024] The readout circuit is used for subtracting the ramp voltage when the circuit is read out to compensate for the self-heating effect.

[0025] In an optional design, the bias circuit is further used for:

[0026] applying a bias voltage to a second resistor to generate a current, wherein the second resistor is a resistor that is thermally short-circuited with the substrate;

[0027] The current of the second resistor is copied to the first resistor.

[0028] In an optional design, the voltage variation slope is the rate at which the voltage of the first resistor changes with time due to a self-heating effect.

[0029] In an optional design, the slope of the ramp voltage is the same as the voltage change slope of the first resistor.

[0030] In an optional design, the ratio of the resistance-capacitance product of the differential circuit and the integration circuit is 1.

[0031] The present application provides a self-heating effect compensation method based on a mechanical baffle, comprising: closing the baffle, the baffle is used to prevent external infrared radiation from reaching a first resistor; applying a bias current to the first resistor, the first resistor is a resistor that senses external infrared radiation; a differential circuit detects the voltage change slope of the first resistor and stores the slope voltage; opening the baffle; an integral circuit constructs a ramp voltage based on the slope voltage; subtracts the ramp voltage when the circuit is read out to achieve compensation for the self-heating effect; when the circuit temperature changes, re-execute the operation of closing the baffle. By blocking the influence of external infrared radiation with the baffle, the voltage change caused only by the self-heating effect can be detected, and by constructing a ramp voltage representing the self-heating effect, the ramp voltage is subtracted when reading out to achieve compensation for the self-heating effect. When the circuit ambient temperature changes, it is only necessary to re-close the baffle and then detect the current voltage change slope, without manual adjustment, and it can work at various ambient temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] Figure 1 A commonly used microbolometer readout circuit diagram provided in an embodiment of the present application;

[0034] Figure 2 A schematic diagram of the effect of the self-heating effect of a commonly used microbolometer on the readout provided in an embodiment of the present application;

[0035] Figure 3 An exemplary method flow chart of a self-heating effect compensation method 300 based on a mechanical baffle provided in an embodiment of the present application;

[0036] Figure 4 A compensation voltage generating circuit diagram provided in an embodiment of the present application;

[0037] Figure 5 A bias circuit diagram using a compensation voltage provided in an embodiment of the present application;

[0038] Figure 6 A compensation effect diagram of a self-heating effect compensation method based on a mechanical baffle provided in an embodiment of the present application. DETAILED DESCRIPTION

[0039] The technical solution of the embodiment of the present application will be described below in conjunction with the drawings in the embodiment of the present application.

[0040] The terms used in the following embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to be used as limitations on the present application. As used in the specification and the appended claims of the present application, the singular expressions "one", "a kind", "said", "above", "the" and "this" are intended to also include plural expressions, unless there is a clear contrary indication in the context. It should also be understood that although the terms first, second, etc. may be used to describe a certain class of objects in the following embodiments, the objects should not be limited to these terms. These terms are only used to distinguish specific objects of this class of objects. For example, the terms first, second, etc. may be used to describe resistors in the following embodiments, but resistors should not be limited to these terms. These terms are only used to distinguish different resistors. The same is true for other classes of objects that may be described by the terms first, second, etc. in the following embodiments, which will not be repeated here.

[0041] The following introduces the implementation scenarios involved in the embodiments of the present application and explanations of technical terms.

[0042] The present application embodiment relates to a microbolometer, Figure 1 It is a commonly used microbolometer readout circuit. Figure 1As shown, the microbolometer includes a resistor Rb and a resistor Rs. Rb is a resistor that is thermally "short-circuited" with the substrate. It has a very large thermal conductivity with the substrate. The Joule heat generated by its power supply and the external thermal radiation will be quickly conducted away through the substrate, so it can be considered that the resistance of Rb is only related to the substrate temperature. Rs is a resistor that senses external infrared radiation. The thermal conductivity between it and the substrate is very small, and it has a self-heating effect, that is, when the current passes through Rs, the Joule heat generated will increase its temperature and cause the resistance value to change, thereby affecting the response to infrared radiation. The voltage Veb is used to bias Rb to generate a current Iskim; the voltage Vfid is used to bias Rs to generate a current Is. The difference between the two currents Idiff flows through the transimpedance amplifier, which is used to convert the differential current Idiff into a voltage signal Vafe. The CTIA circuit then integrates and amplifies Vafe to generate the final output signal.

[0043] By designing the bias circuit, the voltage drop of Rs and Rb is equal to Vb. Without considering the self-heating effect, the temperature of Rs is determined by the substrate temperature and external radiation, and the temperature of Rb is only determined by the substrate temperature. Assuming that when the substrate temperature is T0, the resistance of Rb is R0, then:

[0044]

[0045] Where α is the resistance temperature coefficient of Rs, ΔT rad is the temperature change caused by external radiation on Rs. So the output of the transimpedance amplifier is:

[0046]

[0047] Since the sampling rate of the readout circuit is much greater than the rate at which the external radiation changes, ΔT rad can be reasonably considered to be a constant, then V afe The CTIA circuit then changes the V afe The output of the integral amplification is:

[0048]

[0049] It can be found that without considering the self-heating effect, the CTIA output changes linearly with the integration time. The second term in the above formula represents the effective signal that is amplified. However, if the self-heating effect is considered, Rs rises in temperature due to its own Joule heat during the power-on readout cycle, and its temperature expression with time is:

[0050]

[0051] in C this the thermal capacitance of Rs. Therefore, the expressions of its resistance, differential current, Vafe and Vctia over time are:

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] It can be seen that due to the self-heating effect, the relationship between the output of the integral amplifier and time changes from the ideal linear relationship to a quadratic relationship. Figure 2 As shown, Figure 2 The figure shows the effect of self-heating on readout. Although the quadratic term can be eliminated as common-mode interference in a system-level one-point correction, its magnitude is much larger than the effective signal, which poses a challenge to the power supply range of the readout. If the quadratic term is too large, the readout voltage signal will be saturated, resulting in loss of effective signal.

[0058] The embodiments of the present application provide a self-heating effect compensation method based on a mechanical baffle and an electronic device. The method can achieve self-heating effect compensation without manual adjustment, can work at various ambient temperatures, and has low requirements for MEMS process.

[0059] The following describes the self-heating effect compensation method based on a mechanical baffle according to the embodiment of the present application through several implementation methods, wherein V refers to voltage, R refers to resistance, C refers to capacitance, I refers to current, and Φ refers to a switch.

[0060] like Figure 3 As shown, Figure 3 A method 300 for compensating for self-heating effect based on a mechanical baffle (hereinafter referred to as method 300 ) is illustrated. The method 300 includes the following steps:

[0061] Step S301, closing the baffle, wherein the baffle is used to prevent external infrared radiation from reaching the first resistor;

[0062] In this embodiment, the baffle is a mechanical component currently widely used in uncooled infrared thermal imagers. The use of the mechanical baffle can block the influence of external infrared radiation on the resistor, thereby detecting the resistor voltage change caused only by the self-heating effect.

[0063] Step S302, applying a bias current to a first resistor, where the first resistor is a resistor that senses external infrared radiation;

[0064] In this embodiment, the first resistor is Rs, which is a resistor that can sense external infrared radiation. The thermal conductivity between Rs and the substrate is very small and it has a self-heating effect. When a bias current is applied to Rs, the Joule heat generated by the current passing through Rs will increase its temperature, causing the resistance value to change, thereby causing the voltage across Rs to change.

[0065] Step S303, the differential circuit detects the voltage change slope of the first resistor and stores the slope voltage;

[0066] In this embodiment, since the baffle blocks the influence of external infrared radiation on Rs, the voltage change of Rs is entirely caused by the self-heating effect. The voltage change slope at this time can represent the influence of the self-heating effect.

[0067] Step S304, opening the blocking piece;

[0068] In this embodiment, after the slope voltage representing the self-heating effect is obtained, the shutter is opened and normal imaging work is performed.

[0069] Step S305, the integration circuit constructs a ramp voltage based on the slope voltage;

[0070] In this embodiment, the integration circuit constructs a ramp voltage having the same slope as the slope voltage according to the slope voltage, that is, a ramp voltage having the same slope as the self-heating effect, that is, a ramp voltage representing the self-heating effect.

[0071] Step S306, subtracting the ramp voltage when the circuit reads out to achieve compensation for the self-heating effect;

[0072] In this embodiment, subtracting the ramp voltage in the readout circuit is equivalent to subtracting the influence of the self-heating effect, so as to eliminate the self-heating effect.

[0073] Step S307, when the circuit temperature changes, the operation of closing the shutter is performed again.

[0074] In this embodiment, when the temperature of the circuit changes, the self-heating effect will also change accordingly. Therefore, it is necessary to close the shutter again and detect the voltage change slope caused by the self-heating effect again so as to subtract the corresponding slope voltage in subsequent imaging.

[0075] In an optional implementation manner, applying a bias current to the first resistor includes:

[0076] applying a bias voltage to a second resistor to generate a current, wherein the second resistor is a resistor that is thermally short-circuited with the substrate;

[0077] The current of the second resistor is copied to the first resistor.

[0078] In an optional implementation, the voltage change slope is the rate at which the voltage of the first resistor changes with time due to a self-heating effect.

[0079] In an optional implementation, the slope of the ramp voltage is the same as the voltage change slope of the first resistor.

[0080] In an optional implementation, the ratio of the product of the resistance and capacitance of the differential circuit and the integration circuit is 1.

[0081] For ease of understanding, the method 300 is described in detail below with reference to examples.

[0082] The embodiment of the present application further provides a self-heating effect compensation circuit based on a mechanical baffle, the circuit comprising:

[0083] a baffle, the baffle being used to prevent external infrared radiation from reaching the first resistor;

[0084] A bias circuit, used for applying a bias current to a first resistor, wherein the first resistor is a resistor for sensing external infrared radiation;

[0085] A differential circuit, used for detecting a voltage change slope of the first resistor and storing a slope voltage;

[0086] an integrating circuit, configured to construct a ramp voltage based on the slope voltage;

[0087] The readout circuit is used for subtracting the ramp voltage when the circuit is read out to compensate for the self-heating effect.

[0088] In an optional implementation manner, the bias circuit is further used for:

[0089] applying a bias voltage to a second resistor to generate a current, wherein the second resistor is a resistor that is thermally short-circuited with the substrate;

[0090] The current of the second resistor is copied to the first resistor.

[0091] In an optional implementation, the voltage change slope is the rate at which the voltage of the first resistor changes with time due to a self-heating effect.

[0092] In an optional implementation, the slope of the ramp voltage is the same as the voltage change slope of the first resistor.

[0093] In an optional implementation, the ratio of the product of the resistance and capacitance of the differential circuit and the integration circuit is 1.

[0094] Figure 4 A compensation voltage generating circuit diagram provided in an embodiment of the present application, Figure 5A bias circuit diagram using a compensation voltage is provided in an embodiment of the present application, such as Figure 4 and Figure 5 As shown, the second resistor is Rb, which is a resistor that is thermally "short-circuited" with the substrate. When the shutter is closed, the switch Φs is closed, and the bias voltage Vb is applied to Rb. The generated current is copied to the periodically gated Rs. The Joule heat generated when the current passes through Rs will cause a self-heating effect, causing the resistance of Rs to decrease as the power-on time increases. Therefore, the expression for the voltage across Rs changing with time is:

[0095]

[0096] The differential circuit detects the voltage V' output by the source follower S (t) The slope of the time variation is output as:

[0097]

[0098] The value of the slope voltage Vdiv is stored in the on-chip memory. Subsequently, the flap is opened, and the integration circuit constructs the slope voltage Vcomp based on the stored value of Vdiv, which is expressed as:

[0099]

[0100] It can be seen that we only need to set the product ratio of the resistance and capacitance of the differential circuit and the integral circuit That is, the slope of the ramp voltage can be made the same as the slope of the slope voltage, that is, a ramp voltage having the same slope as the self-heating effect can be constructed.

[0101] Figure 6 A compensation effect diagram of a self-heating effect compensation method based on a mechanical baffle provided in an embodiment of the present application shows that before compensation, the output of the circuit changes with time in a quadratic relationship, that is, the self-heating effect occupies a large amount of the output swing. After using the compensation method of the present application, the output of the circuit changes with time in a linear relationship, and the self-heating effect no longer occupies the effective output swing. In addition, in the compensation voltage generating circuit of the present invention, the ratio of the resistor R1 and the capacitor C1 of the differential circuit to the resistor R2 and the capacitor C2 of the integral circuit is offset, which can eliminate the influence of the circuit process angle and ensure the accuracy of compensation.

[0102] Understandably, Figure 1 , Figure 4 , Figure 5The connection modes of the various components listed in the various resistors, power supplies, etc. involved in the present application are schematic descriptions and do not constitute limitations on the embodiments of the present application. In some other implementations, the resistors, power supplies, etc. may also be connected in other ways, which will not be described in detail here. In addition, in actual implementation scenarios, the components involved in the embodiments of the present application may be more or less, and the embodiments of the present application will not be described one by one.

[0103] In summary, the self-heating effect compensation method based on the mechanical baffle in the embodiment of the present application uses the mechanical baffle to block the influence of external infrared radiation, thereby detecting the voltage change slope caused by the self-heating effect, and constructing a ramp voltage with the same slope, and subtracting the ramp voltage from the readout circuit to achieve compensation for the self-heating effect. It can be seen that the method of the embodiment of the present application is simple to operate, has low requirements for MEMS process, and when the ambient temperature changes, it only needs to reclose the baffle, and can work in various ambient temperatures, without manual adjustment, and has low cost.

[0104] Although the optional embodiments of the present application have been described, those skilled in the art, once informed of the basic creative concept, may make additional changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiment and all changes and modifications falling within the scope of the present application.

[0105] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only the specific implementation method of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solutions of the present application should be included in the scope of protection of the present invention.

Claims

1. A self-heating effect compensation method based on a mechanical baffle, characterized in that: The method comprises: A closed baffle, the baffle being used to prevent external infrared radiation from reaching the first resistor; applying a bias current to a first resistor, wherein the first resistor is a resistor that senses external infrared radiation; The differential circuit detects the voltage change slope of the first resistor and stores the slope voltage; Open the baffle; The integration circuit constructs a ramp voltage based on the slope voltage; The ramp voltage is subtracted when the circuit is read out to achieve compensation for the self-heating effect; When the circuit temperature changes, the operation of closing the shutter is performed again.

2. The method according to claim 1, characterized in that The applying a bias current to the first resistor comprises: applying a bias voltage to a second resistor to generate a current, wherein the second resistor is a resistor that is thermally short-circuited with the substrate; The current of the second resistor is copied to the first resistor.

3. The method according to claim 1, characterized in that The voltage change slope is the rate at which the voltage of the first resistor changes over time due to the self-heating effect.

4. The method according to claim 1, characterized in that The slope of the ramp voltage is the same as the voltage change slope of the first resistor.

5. The method according to claim 1, characterized in that The ratio of the product of the resistance and capacitance of the differential circuit and the integration circuit is 1.

6. A self-heating effect compensation circuit based on a mechanical baffle, characterized in that: The circuit comprises: a baffle, the baffle being used to prevent external infrared radiation from reaching the first resistor; A bias circuit, used for applying a bias current to a first resistor, wherein the first resistor is a resistor for sensing external infrared radiation; A differential circuit, used for detecting a voltage change slope of the first resistor and storing a slope voltage; an integrating circuit, configured to construct a ramp voltage based on the slope voltage; The readout circuit is used to subtract the ramp voltage when the circuit is read out to compensate for the self-heating effect.

7. The circuit according to claim 6, characterized in that The bias circuit is also used for: applying a bias voltage to a second resistor to generate a current, wherein the second resistor is a resistor that is thermally short-circuited with the substrate; The current of the second resistor is copied to the first resistor.

8. The circuit according to claim 6, characterized in that The voltage change slope is the rate at which the voltage of the first resistor changes over time due to the self-heating effect.

9. The circuit according to claim 6, characterized in that The slope of the ramp voltage is the same as the voltage variation slope of the first resistor.

10. The circuit according to claim 6, characterized in that The ratio of the product of the resistance and capacitance of the differential circuit and the integration circuit is 1.

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