Temperature-adaptive self-heating effect compensation method and circuit

Abstract

The embodiment of the invention relates to the technical field of sensors, in particular to a temperature-adaptive self-heating effect compensation method and circuit, and the method comprises the steps: generating a negative temperature coefficient voltage which is used for sensing the environment temperature; converting the negative temperature coefficient voltage into a second current; and performing integration on the second current to generate compensation voltage so as to realize self-heating effect compensation. By generating the negative temperature coefficient voltage which has an approximate linear relationship with the temperature, voltage conversion, current integration and the like are further performed, and the compensation voltage which can adaptively change along with the change of the environment temperature is obtained, so that the interference of a self-heating effect is eliminated. The voltage of the micro-bolometer is controlled through the clamping NMOS, and even if the resistance value of the resistor of the micro-bolometer changes, the current can be kept stable. The complexity of the implementation process is low, readjustment is not needed when the environment temperature changes, and the compensation signal can be changed in a self-adaptive mode.

Description

Technical Field

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

[0002] Uncooled infrared image sensors based on microbolometers are widely used in various fields such as automotive, security, and industrial detection due to their advantages in size, weight, power consumption, and cost. The imaging chip is the core component of the uncooled infrared image sensor. The imaging chip mainly includes: infrared photosensitive pixel array, blind pixel array, and readout circuit. Each pixel in the infrared photosensitive pixel array includes a microbolometer that can sense infrared radiation. The microbolometer is thermally insulated from the substrate. When working, the microbolometer resistor receives the infrared radiation emitted by the target to produce a temperature change, causing a change in resistance, and then the resistance change is converted into a digital signal that can be used for imaging through the readout circuit.

[0003] The readout circuit usually reads the resistance value of the microbolometer resistor in a row-by-row manner. However, due to the self-heating effect, the microbolometer will generate Joule heat after power is turned on. The Joule heat temperature rise will cause the resistance value of the microbolometer resistor to change, seriously affecting the readout effect of the imaging chip. Therefore, self-heating effect compensation is required.

[0004] The self-heating effect compensation method mainly generates a compensation signal to eliminate the self-heating interference. The compensation signal is generated in the following ways: compensation based on shielding the microbolometer, by shielding the target infrared radiation, the microbolometer is only affected by the self-heating effect, and a compensation signal that changes linearly with time and is independent of infrared radiation is generated, and then the compensation signal is added to the signal path. However, shielding the microbolometer increases the cost and process complexity.

[0005] Compensation can also be performed by constructing a compensation signal through a CMOS circuit. However, since the severity of the self-heating effect varies with the ambient temperature, the compensation signal needs to be readjusted at different ambient temperatures, which is more troublesome to use. Summary of the invention

[0006] The embodiments of the present application provide a temperature-adaptive self-heating effect compensation method and circuit, which can solve the problem that the self-heating effect compensation process is complex and requires multiple adjustments with temperature changes.

[0007] In a first aspect, an embodiment of the present application provides a temperature-adaptive self-heating effect compensation method, the method comprising:

[0008] generating a negative temperature coefficient voltage, wherein the negative temperature coefficient voltage is used to sense the ambient temperature;

[0009] converting the negative temperature coefficient voltage into a second current;

[0010] The second current is integrated to generate a compensation voltage to achieve self-heating effect compensation.

[0011] In an optional design, it also includes:

[0012] A negative temperature coefficient voltage is generated according to the positive temperature coefficient current, wherein the negative temperature coefficient voltage is negatively correlated with the ambient temperature and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

[0013] In an optional design, it also includes:

[0014] The negative temperature coefficient voltage is converted into a first current in a microbolometer resistor.

[0015] In an optional design, it also includes:

[0016] The first current is copied into a second current.

[0017] In a second aspect, an embodiment of the present application provides a temperature-adaptive self-heating effect compensation circuit, the circuit comprising:

[0018] A negative temperature coefficient generating circuit, used for generating a negative temperature coefficient voltage, wherein the negative temperature coefficient voltage is used for sensing the ambient temperature;

[0019] A voltage-to-current conversion circuit, used for converting the negative temperature coefficient voltage into a second current;

[0020] The integration circuit is used to integrate the second current to generate a compensation voltage to achieve self-heating effect compensation.

[0021] In an optional design, the negative temperature coefficient generating circuit also includes: a transimpedance amplifier, used to generate a negative temperature coefficient voltage based on a positive temperature coefficient current, wherein the negative temperature coefficient voltage is negatively correlated with the ambient temperature, and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

[0022] In an optional design, the transimpedance amplifier includes a first resistor and a first operational amplifier;

[0023] The positive temperature coefficient current is connected to the negative input terminal of the first operational amplifier;

[0024] The first resistor is connected between the negative input terminal and the output terminal of the first operational amplifier;

[0025] The input of the positive input terminal of the first operational amplifier is a preset voltage;

[0026] The output terminal of the first operational amplifier outputs the negative temperature coefficient voltage.

[0027] In an optional design, the voltage-to-current conversion circuit further includes: a second operational amplifier, a microbolometer resistor, and a clamped N-type metal oxide semiconductor MOS transistor;

[0028] The negative temperature coefficient voltage is connected to the positive input terminal of the second operational amplifier;

[0029] The output terminal of the second operational amplifier is connected to the gate of the clamping NMOS transistor;

[0030] The source of the clamp NMOS transistor is connected to the negative input terminal of the second operational amplifier and the microbolometer resistor.

[0031] In an optional design, it is characterized in that

[0032] The clamping NMOS transistor is used to clamp the voltage on the microbolometer resistor to the negative temperature coefficient voltage;

[0033] The second operational amplifier converts the negative temperature coefficient voltage into a first current in the microbolometer resistor.

[0034] In an optional design, the voltage-to-current conversion circuit further includes: a current mirror,

[0035] The input terminal of the current mirror is connected to the drain of the clamped NMOS transistor;

[0036] The output terminal of the current mirror is connected to the integration circuit;

[0037] The current mirror is used to receive an input of a first current, copy the first current into a second current, and output the second current to the integration circuit.

[0038] The present application provides a temperature-adaptive self-heating effect compensation method, including: generating a negative temperature coefficient voltage, the negative temperature coefficient voltage is used to sense the ambient temperature; converting the negative temperature coefficient voltage into a second current; integrating the second current to generate a compensation voltage to achieve self-heating effect compensation. By generating a negative temperature coefficient voltage that has an approximately linear relationship with the temperature, and then performing voltage conversion, current integration, etc., a compensation voltage that can adaptively change with the ambient temperature is obtained to eliminate the interference of the self-heating effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] 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.

[0040] Figure 1 A flow chart of a temperature-adaptive self-heating effect compensation method provided in an embodiment of the present application;

[0041] Figure 2 A temperature-adaptive self-heating effect compensation circuit diagram provided in an embodiment of the present application. DETAILED DESCRIPTION

[0042] 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.

[0043] 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 the specific objects of this class of objects. For example, the terms first, second, etc. may be used to describe electric current in the following embodiments, but electric current should not be limited to these terms. These terms are only used to distinguish different electric currents. 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.

[0044] The following introduces the implementation scenarios involved in the embodiments of the present application and explanations of technical terms.

[0045] The embodiments of the present application relate to an infrared image sensor, in which the resistance of a microbolometer is affected by a self-heating effect, causing a change in resistance value, and therefore self-heating effect compensation is required.

[0046] Assume that the voltage across the microbolometer is V s , the resistance is R s , then the relationship between the current and time during the power-on readout period is:

[0047]

[0048] Where α is the resistance temperature coefficient of the microbolometer, and the relationship between α and the ambient temperature T is:

[0049]

[0050] C th is the heat capacity of the microbolometer, ΔT signal It is the temperature change of the microbolometer caused by the target infrared radiation, that is, the effective signal.

[0051] In formula (1), is the self-heating signal, which has an approximately linear relationship with time. s Applied by the readout circuit and does not vary with ambient temperature; C th Determined by the material properties and does not change with ambient temperature. s and α vary with the ambient temperature, so the self-heating effect varies with the ambient temperature.

[0052] Therefore, the core function of the compensation circuit is to compensate According to formula (2), the resistance temperature coefficient α is inversely proportional to the ambient temperature. Since it is relatively complicated to directly obtain an electrical quantity inversely proportional to the temperature in the circuit, within the typical application temperature range of uncooled infrared (-40℃~85℃ or 233K~358K), α can be fitted with an approximate linear function. Therefore, this application uses a negative temperature coefficient generation circuit to generate a negative temperature voltage that is approximately linearly related to the temperature to achieve self-heating effect compensation.

[0053] Specifically, an embodiment of the present application provides a temperature-adaptive self-heating effect compensation method and circuit, which can achieve compensation for the self-heating effect with low process complexity and can adaptively change the compensation signal without the need for readjustment when the ambient temperature changes.

[0054] The temperature-adaptive self-heating effect compensation method involved in the embodiments of the present application is introduced below through several implementation methods.

[0055] like Figure 1 As shown, Figure 1 A temperature-adaptive self-heating effect compensation method 100 (hereinafter referred to as method 100) is illustrated, and method 100 includes the following steps:

[0056] Step S101 , generating a negative temperature coefficient voltage, wherein the negative temperature coefficient voltage is used to sense the ambient temperature.

[0057] Step S102, converting the negative temperature coefficient voltage into a second current.

[0058] Step S103, integrating the second current to generate a compensation voltage to achieve self-heating effect compensation.

[0059] In an optional implementation, the method further includes:

[0060] A negative temperature coefficient voltage is generated according to the positive temperature coefficient current, wherein the negative temperature coefficient voltage is negatively correlated with the ambient temperature and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

[0061] In an optional implementation, the method further includes:

[0062] The negative temperature coefficient voltage is converted into a first current in a microbolometer resistor.

[0063] In an optional implementation, the method further includes:

[0064] The first current is copied into a second current.

[0065] For ease of understanding, the method 100 is described below in combination with an example. Wherein, V refers to voltage, R refers to resistance, C refers to capacitance, I refers to current,

[0066] like Figure 2 As shown, an embodiment of the present application provides a temperature-adaptive self-heating effect compensation circuit, the circuit comprising:

[0067] A negative temperature coefficient generating circuit, used for generating a negative temperature coefficient voltage, wherein the negative temperature coefficient voltage is used for sensing the ambient temperature;

[0068] A voltage-to-current conversion circuit, used for converting the negative temperature coefficient voltage into a second current;

[0069] The integration circuit is used to integrate the second current to generate a compensation voltage to achieve self-heating effect compensation.

[0070] In an optional embodiment, the negative temperature coefficient generating circuit further includes: a transimpedance amplifier, used to generate a negative temperature coefficient voltage based on a positive temperature coefficient current, wherein the negative temperature coefficient voltage is negatively correlated with the ambient temperature, and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

[0071] In this embodiment, the positive temperature coefficient current is generated by a positive temperature coefficient element. For example, the present application uses a positive temperature coefficient resistor to generate the positive temperature coefficient current. In other embodiments, other positive temperature coefficient elements may also be used to generate the positive temperature coefficient current. The present application does not limit this. The resistance value of the positive temperature coefficient resistor increases with increasing temperature. Under constant voltage, the current passing through the positive temperature coefficient resistor will decrease, so the positive temperature coefficient current decreases with increasing temperature.

[0072] like Figure 2 As shown, the positive temperature coefficient current I 1=aT, a is the current variation coefficient, T is the temperature. When the positive temperature coefficient current passes through the transimpedance amplifier, the current gradually decreases, and the output voltage of the transimpedance amplifier also gradually decreases, that is, the output negative temperature coefficient voltage decreases as the temperature increases. The negative temperature coefficient voltage can change adaptively with the change of ambient temperature. Among them, the negative temperature coefficient voltage V o1 =V ref1 -R 1 I 1 Therefore, the negative temperature coefficient voltage is negatively correlated with the ambient temperature, and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

[0073] In an optional implementation, the transimpedance amplifier includes a first resistor and a first operational amplifier;

[0074] The positive temperature coefficient current is connected to the negative input terminal of the first operational amplifier;

[0075] The first resistor is connected between the negative input terminal and the output terminal of the first operational amplifier;

[0076] The input of the positive input terminal of the first operational amplifier is a preset voltage;

[0077] The output terminal of the first operational amplifier outputs the negative temperature coefficient voltage.

[0078] In this embodiment, the first resistor is R 1 , V ref1 is the voltage at the positive input of the operational amplifier.

[0079] In an optional implementation, the voltage-to-current conversion circuit further includes: a second operational amplifier, a microbolometer resistor, and a clamped N-type metal oxide semiconductor MOS transistor;

[0080] The negative temperature coefficient voltage is connected to the positive input terminal of the second operational amplifier;

[0081] The output terminal of the second operational amplifier is connected to the gate of the clamping NMOS transistor;

[0082] The source of the clamp NMOS transistor is connected to the negative input terminal of the second operational amplifier and the microbolometer resistor.

[0083] In this embodiment, the negative temperature coefficient voltage V o1 is connected to the positive input of the second operational amplifier, the microbolometer resistor is R bol .

[0084] In an optional embodiment, the clamping NMOS transistor is used to clamp the voltage on the microbolometer resistor to the negative temperature coefficient voltage;

[0085] The second operational amplifier converts the negative temperature coefficient voltage into a first current in the microbolometer resistor.

[0086] In this embodiment, the source of the clamped NMOS is connected to the negative input terminal of the second operational amplifier and the microbolometer resistor, and the gate receives a control voltage. When the clamped NMOS is turned on, the voltage on the microbolometer resistor is clamped at a specific level, that is, the negative temperature coefficient voltage V o1 , even if the resistance of the microbolometer resistor changes, the current through the clamping NMOS can remain relatively stable. At this time, the current on the microbolometer resistor is I 1 =V o1 / R bol , that is, the first current.

[0087] In an optional implementation manner, the voltage-to-current conversion circuit further includes: a current mirror,

[0088] The input terminal of the current mirror is connected to the drain of the clamped NMOS transistor;

[0089] The output terminal of the current mirror is connected to the integration circuit;

[0090] The current mirror is used to receive an input of a first current, copy the first current into a second current, and output the second current to the integration circuit.

[0091] In this embodiment, the current mirror converts the first current I 1 The second current I 2 , and finally flows into the integration circuit. The integrator circuit integrates the second current to form a slope compensation voltage to compensate for the self-heating effect.

[0092] Understandably, Figure 2 The 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.

[0093] In summary, the temperature-adaptive self-heating effect compensation method of the embodiment of the present application generates a negative temperature coefficient voltage that is approximately linearly related to the temperature, and then performs voltage conversion, current integration, etc., to obtain a compensation voltage that can adaptively change with changes in ambient temperature, so as to eliminate the interference of the self-heating effect.

[0094] 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.

[0095] 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 temperature-adaptive self-heating effect compensation method, characterized in that: The method comprises: generating a negative temperature coefficient voltage, wherein the negative temperature coefficient voltage is used to sense the ambient temperature; converting the negative temperature coefficient voltage into a second current; The second current is integrated to generate a compensation voltage to achieve self-heating effect compensation.

2. The method according to claim 1, characterized in that Also includes: A negative temperature coefficient voltage is generated according to the positive temperature coefficient current, wherein the negative temperature coefficient voltage is negatively correlated with the ambient temperature and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

3. The method according to claim 1, characterized in that Also includes: The negative temperature coefficient voltage is converted into a first current in a microbolometer resistor.

4. The method according to claim 3, characterized in that Also includes: The first current is copied into a second current.

5. A temperature-adaptive self-heating effect compensation circuit, characterized in that: The circuit comprises: A negative temperature coefficient generating circuit, used for generating a negative temperature coefficient voltage, wherein the negative temperature coefficient voltage is used for sensing the ambient temperature; A voltage-to-current conversion circuit, used for converting the negative temperature coefficient voltage into a second current; The integration circuit is used to integrate the second current to generate a compensation voltage to achieve self-heating effect compensation.

6. The circuit according to claim 5, characterized in that The negative temperature coefficient generating circuit further includes: a transimpedance amplifier, which is used to generate a negative temperature coefficient voltage according to a positive temperature coefficient current, wherein the negative temperature coefficient voltage is negatively correlated with the ambient temperature, and the negative temperature coefficient voltage is linearly correlated with the ambient temperature.

7. The circuit according to claim 6, characterized in that The transimpedance amplifier comprises a first resistor and a first operational amplifier; The positive temperature coefficient current is connected to the negative input terminal of the first operational amplifier; The first resistor is connected between the negative input terminal and the output terminal of the first operational amplifier; The input of the positive input terminal of the first operational amplifier is a preset voltage; The output terminal of the first operational amplifier outputs the negative temperature coefficient voltage.

8. The circuit according to claim 5, characterized in that The voltage-to-current conversion circuit further includes: a second operational amplifier, a microbolometer resistor, and a clamped N-type metal oxide semiconductor MOS transistor; The negative temperature coefficient voltage is connected to the positive input terminal of the second operational amplifier; The output terminal of the second operational amplifier is connected to the gate of the clamping NMOS transistor; The source of the clamp NMOS transistor is connected to the negative input terminal of the second operational amplifier and the microbolometer resistor.

9. The circuit according to claim 8, characterized in that The clamping NMOS transistor is used to clamp the voltage on the microbolometer resistor to the negative temperature coefficient voltage; The second operational amplifier converts the negative temperature coefficient voltage into a first current in the microbolometer resistor.

10. The circuit according to claim 9, characterized in that The voltage-to-current conversion circuit further includes: a current mirror, The input terminal of the current mirror is connected to the drain of the clamped NMOS transistor; The output terminal of the current mirror is connected to the integration circuit; The current mirror is used to receive an input of a first current, copy the first current into a second current, and output the second current to the integration circuit.

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