High-precision ntc thermistor temperature detection circuit for automotive electronic system

Abstract

This invention relates to a high-precision NTC thermistor temperature detection circuit for automotive electronic systems, comprising thermistors Rntc1 and Rntc2, voltage divider resistors Rm1 and Rm2, filter capacitors C1 and C2, an operational amplifier, an analog-to-digital converter, an inverse function compensation code calculation circuit, compensation current sources Ical1 and Ical2. This invention employs a differential temperature detection method, increasing the common-mode interference control capability and reliability of the temperature detection circuit; and further, it adds a function F to the differential temperature detection NTC thermistor, where the output current magnitude is controlled by the variable function F. cal =-K*F ‑1 The compensation currents Ical1 and Ical2, controlled by (T0-T), achieve high linearity compensation of the differential temperature detection voltage Vrt2 with a fixed slope. cal -Vrt1 cal and high linearity temperature detection differential signal Vadd cal This invention performs temperature nonlinearity compensation directly in the detection circuit, eliminating the need for additional software algorithms for data compensation and calibration, thus achieving a higher response speed.

Description

Technical Field

[0001] This invention relates to a high-precision NTC thermistor temperature detection circuit, belonging to the fields of integrated circuits and automotive electronics technology. Background Technology

[0002] NTC thermistors are among the most widely used temperature sensing elements in the electronic systems of new energy vehicles. In the engine cooling system of new energy vehicles, NTC thermistors are commonly used to monitor the coolant temperature to ensure that the engine maintains the optimal operating temperature. In the air conditioning system of automobiles, NTC thermistors are often used to achieve multi-point temperature measurement, supporting multi-zone independent temperature control and evaporator defrosting control. In components such as seat heating and steering systems, NTC thermistors are often used to provide overheat protection, improving driving safety. NTC thermistors are also widely deployed in power battery packs, BMS, inverters, OBC and other systems to monitor the temperature of battery cells and power devices in real time, while providing temperature compensation and overheat protection in autonomous driving ADAS, millimeter-wave radar and lidar to maintain stable system operation.

[0003] The operating environment of automobiles covers a very wide temperature range. In extremely cold northern environments, temperatures can drop as low as -40°C, while the operating temperature near the engine compartment and power devices can exceed 120°C. This wide temperature range and rapid temperature change rate, coupled with vibrations and electromagnetic interference during vehicle operation, directly affect the accuracy of temperature detection. Therefore, temperature detection circuits based on NTC thermistors require high precision and high reliability. The NTC itself must have an R25 resistor accuracy of at least ±1%, a B-value tolerance within ±1%, and an overall temperature error within ±0.5°C. Combined with calibration algorithms to offset nonlinear errors, accurate and reliable detection results can be guaranteed across the entire temperature range.

[0004] Figure 1 This is a schematic diagram of an existing NTC thermistor temperature detection circuit. The existing NTC thermistor temperature detection circuit consists of an NTC thermistor Rv, a precision voltage divider resistor Rm, an operational amplifier, an analog-to-digital converter (ADC), a reference voltage source Vref, and a filter capacitor C1. When the circuit is working normally, the NTC thermistor Rv and the precision voltage divider resistor Rm form a voltage divider circuit. The resistance of the thermistor Rv changes negatively with temperature, causing the voltage Vrt at the voltage divider point to change accordingly. The operational amplifier A is connected in unity-gain configuration to buffer the Vrt signal and output it as Vad. Finally, the analog-to-digital converter (ADC) converts the analog voltage Vad into a digital temperature signal D. tmp This enables digital temperature detection.

[0005] The existing implementation scheme has two significant problems. First, it has poor anti-interference capability. The reference voltage source Vref or other interference can cause instantaneous interference on Vrt, which will directly introduce errors into the digital temperature signal Dtmp. Second, there is the nonlinearity problem of the NTC resistor temperature coefficient. The resistance value of existing NTC thermistors exhibits a very large nonlinear relationship with temperature changes. Therefore, the digital temperature signal Dtmp directly converted by the ADC has a very large nonlinearity. It is necessary to use calibration algorithm software to offset the nonlinear error caused by the resistor in order to ensure accurate and reliable detection results across the entire temperature range. However, the calibration algorithm inevitably introduces a certain delay time, reducing the temperature response speed of the temperature detection circuit. Therefore, providing a low-delay, fast-response, high-precision NTC thermistor temperature detection circuit with high anti-interference characteristics is of significant practical importance. Summary of the Invention

[0006] Based on existing technology, this invention provides a high-precision NTC thermistor temperature detection circuit for automotive electronic systems, improving the speed and accuracy of temperature detection for various functional modules in automobiles.

[0007] The present invention provides a high-precision NTC thermistor temperature detection circuit for automotive electronic systems, comprising: thermistor Rntc1, thermistor Rntc2, voltage divider resistor Rm1, voltage divider resistor Rm2, filter capacitor C1, filter capacitor C2, operational amplifier, analog-to-digital converter, inverse function compensation code calculation circuit, compensation current source Ical1, and compensation current source Ical2. The power supply terminal of the compensation current source Ical1 is connected to the power supply voltage VDD, and the output terminal is connected to the upper end of the thermistor Rntc1. The lower end of the thermistor Rntc1 is connected to the upper end of the voltage divider resistor Rm1 and the upper end of the filter capacitor C1, generating a temperature detection voltage Vrt1 which is connected to the inverting input terminal of the operational amplifier. The lower ends of the voltage divider resistor Rm1 and the lower end of the filter capacitor C1 are grounded. The power supply terminal of the compensation current source Ical2 is connected to the power supply voltage VDD, and the output terminal is connected to the upper end of the thermistor Rntc2. The lower end of the thermistor Rntc2 is connected to the upper end of the voltage divider resistor Rm2 and the upper end of the filter capacitor C2. The temperature detection voltage Vrt2 is connected to the non-inverting input terminal of the operational amplifier, and the lower ends of the voltage divider resistor Rm2 and the lower end of the filter capacitor C2 are grounded. The operational amplifier amplifies the temperature detection voltage difference and outputs a temperature detection differential signal Vadd, which is connected to the analog-to-digital converter (ADC). The ADC converts the temperature detection differential signal Vadd into a digital temperature signal Dtmp, which is connected to the inverse function compensation code calculation circuit. The inverse function compensation code calculation circuit generates a temperature compensation code Dcal based on the magnitude of the digital temperature signal Dtmp, and outputs it to the compensation current sources Ical1 and Ical2 respectively to control their output current magnitude.

[0008] In the above circuit, the thermistor Rntc1, thermistor Rntc2, voltage divider resistor Rm1, voltage divider resistor Rm2, filter capacitor C1, and filter capacitor C2 constitute a differential temperature detection circuit, and the absolute resistance and temperature coefficient of thermistor Rntc1 and thermistor Rntc2 are different.

[0009] Specifically, the inverse function compensation code calculation circuit uses the temperature compensation code Dcal to compensate the temperature detection voltage Vrt1. The compensated temperature detection voltage Vrt1 is obtained by introducing a compensation amount into the compensation current source Ical1. cal It satisfies the following relationship: Vrt1 cal =Vrt0+Ical1* Rntc0*F(T0-T)* F cal The compensation variable function Fcal is set as follows: Fcal=-K* F -1 (T0-T) Furthermore, the nonlinear curve function F(x) and its complementary function F -1 (x) satisfies the product identity: F(x) * F -1 (x) = x, x = T0 - T When the circuit parameters satisfy the normalization condition Ical1*Rntc0=1, the compensated temperature detection voltage Vrt1 cal It can be simplified to: Vrt1 cal =Vrt0-K*(T0-T) Where F(x) represents the nonlinear curve function of the absolute resistance of a single thermistor Rntc1 increasing rapidly with decreasing temperature; T represents the current actual ambient temperature, T0 represents the reference temperature, and at temperature T0, the resistance of the thermistor Rntc1 is Rntc0 and the temperature detection voltage Vrt1 is Vrt0; a compensation variable function F is introduced into the compensation current source Ical1. cal -K represents the fixed slope of the temperature detection voltage Vrt1 obtained under ideal conditions as temperature decreases; F -1 (T0-T) is used to cancel the nonlinear term in F(T0-T) so that the output voltage changes linearly with the temperature difference T0-T; Similarly, the inverse function compensation code calculation circuit uses the temperature compensation code Dcal to compensate the temperature detection voltage Vrt2 to obtain the compensated temperature detection voltage Vrt2. cal .

[0010] When the circuit is working normally, the magnitudes of the currents flowing through thermistors Rntc1 and Rntc2 are both governed by the variable function F. cal = -K*F -1 (T0-T) control, and respectively obtain high linearity compensated temperature detection voltage Vrt1 with fixed slope. cal and compensation temperature detection voltage Vrt2 cal A high linearity compensated differential temperature detection voltage Vrt2 with a fixed slope is obtained through differential processing. cal -Vrt1 cal The high-linearity temperature detection differential signal Vadd is then obtained through differential amplification. cal .

[0011] The advantages of this invention are: First, by employing a differential temperature detection method, the common-mode interference control capability and reliability of the temperature detection circuit are increased; second, an output current that is subject to a variable function F is added to the differential temperature detection NTC thermistor. cal = -K*F -1 The compensation currents Ical1 and Ical2, controlled by (T0-T), achieve high linearity compensation of the differential temperature detection voltage Vrt2 with a fixed slope. cal -Vrt1 cal High linearity temperature detection differential signal Vadd cal .

[0012] This invention performs temperature nonlinearity compensation directly within the detection circuit, eliminating the need for additional software algorithms for data compensation and calibration, thus achieving a higher response speed. The solution presented in this invention can be widely applied in high-precision automotive electronic systems as a temperature detection module. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of an existing NTC thermistor temperature detection circuit.

[0014] Figure 2 This is a schematic diagram of the high-precision NTC thermistor temperature detection circuit of the present invention.

[0015] Figure 3 This is a schematic diagram of the operating curve of the present invention when temperature compensation is not enabled.

[0016] Figure 4 This is a schematic diagram illustrating the implementation effect of the inverse function compensation code circuit of the present invention.

[0017] Figure 5 This is a schematic diagram of the working curve after the temperature compensation of the present invention is turned on. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0019] like Figure 2 As shown, the high-precision NTC thermistor temperature detection circuit for automotive electronic systems includes: thermistor Rntc1, thermistor Rntc2, voltage divider resistor Rm1, voltage divider resistor Rm2, filter capacitor C1, filter capacitor C2, operational amplifier A, analog-to-digital converter ADC, inverse function compensation code calculation circuit, compensation current source Ical1, and compensation current source Ical2.

[0020] The compensation current source Ical1 is connected to the power supply voltage VDD, and its output is connected to the upper end of the thermistor Rntc1. The lower end of the thermistor Rntc1 is simultaneously connected to the upper end of the voltage divider resistor Rm1 and the upper end of the filter capacitor C1, generating a temperature detection voltage Vrt1 which is connected to the inverting input of the operational amplifier. The lower ends of the voltage divider resistor Rm1 and the lower end of the filter capacitor C1 are grounded. The compensation current source Ical2 is connected to the power supply voltage VDD, and its output is connected to the upper end of the thermistor Rntc2. The lower end of the thermistor Rntc2 is simultaneously connected to the upper end of the voltage divider resistor Rm2 and the upper end of the filter capacitor C2, generating a temperature detection voltage Vrt2 which is connected to the non-inverting input of the operational amplifier. At the input, the lower ends of the voltage divider resistor Rm2 and the lower end of the filter capacitor C2 are grounded; the operational amplifier amplifies the temperature detection voltage difference and outputs a temperature detection differential signal Vadd, which is connected to the analog-to-digital converter; the analog-to-digital converter converts the temperature detection differential signal Vadd into a digital temperature signal Dtmp, which is connected to the inverse function compensation code calculation circuit; the inverse function compensation code calculation circuit generates a temperature compensation code Dcal based on the magnitude of the digital temperature signal Dtmp, and outputs it to the compensation current source Ical1 and the compensation current source Ical2 respectively. The temperature compensation code Dcal simultaneously controls the compensation current sources Ical1 and Ical2, changing their output current magnitude.

[0021] Figure 2 The embodiments of the present invention and Figure 1 Compared to the existing solutions, the main improvements are twofold. Firstly, [the following is a separate point:] Figure 1The temperature detection method consisting of a single thermistor Rntc and voltage divider resistor Rm is improved to a differential temperature detection method consisting of thermistors Rntc1 and Rntc2, voltage divider resistors Rm1 and Rm2, filter capacitors C1 and C2, thereby increasing the common-mode interference control capability and reliability of the temperature detection circuit. To achieve differential temperature detection, the absolute resistance and temperature coefficient of thermistors Rntc1 and Rntc2 are usually set to be different. Secondly, an inverse function compensation code calculation circuit, compensation current source Ical1, and compensation current source Ical2 are added. Based on the temperature change, the current compensation signal is used to compensate for the temperature nonlinearity of thermistors Rntc1 and Rntc2, improving the linearity of the temperature change curves of temperature detection voltages Vrt1 and Vrt2. This allows the analog-to-digital converter (ADC) to convert the differential temperature signal Vadd into a high-linearity digital temperature signal Dtmp without the need for further calibration algorithm software, achieving a faster response speed and a high-precision NTC thermistor temperature detection circuit.

[0022] Figure 3 This is a schematic diagram of the operating curve when temperature compensation is not enabled, i.e., the inverse function compensation code calculation circuit is not working. At this time, the compensation current sources Ical1 and Ical2 are fixed currents of different magnitudes. Assuming that under the same temperature conditions, the absolute resistance of thermistor Rntc1 is less than the absolute resistance of thermistor Rntc2, the compensation current Ical1 can be set to be less than the compensation current Ical2, ultimately resulting in the temperature detection voltage Vrt1 being lower than the temperature detection voltage Vrt2. Assuming common-mode interference is received, both temperature detection voltages Vrt1 and Vrt2 generate CM interference of the same magnitude. Because a differential temperature detection method is used, the differential temperature detection voltage Vrt2-Vrt1 at the operational amplifier input will not be affected by common-mode interference, thus improving the anti-interference capability. In addition, the thermistors Rntc1 and Rntc2 exhibit similar trends and nonlinear characteristics with temperature changes. Therefore, the temperature nonlinearity of the differential temperature detection voltage Vrt2-Vrt1 is significantly optimized compared to the linearity of the temperature change curves of temperature detection voltages Vrt1 and Vrt2, thereby reducing the temperature nonlinearity of the temperature detection differential signal Vadd.

[0023] Figure 4This is a schematic diagram illustrating the implementation effect of the inverse function compensation code calculation circuit of the present invention after it is turned on. Assuming the absolute resistance of a single thermistor Rntc1 exhibits a non-linear relationship F(x) that accelerates with decreasing temperature, and if the current Ical1 flowing through the thermistor Rntc1 is kept constant, and assuming the resistance of the thermistor Rntc1 at temperature T0 is Rntc0, and the temperature detection voltage Vrt1 is Vrt0, then the non-linear relationship of the temperature detection voltage Vrt1 accelerating with decreasing temperature can be obtained as: Vrt1 = Vrt0 + Ical1 * Rntc0 * F(T0-T). Ideally, we expect the temperature detection voltage Vrt1 to exhibit a linear relationship Vrt1 = Vrt0 - K * (T0-T) that increases with decreasing temperature, with a fixed slope of -K. If a variable function F is introduced into Ical1 to compensate for F(T0-T),... cal = -K*F -1 (T0-T), then we have: Vrt1cal= Vrt1=Vrt0+Ical1* Rntc0*F(T0-T)* F cal = Vrt0+Ical1* Rntc0*F(T0-T)*( -K *F -1 (T0-T)) = Vrt0-K*(T0-T) It can be seen that targeted current compensation with respect to temperature changes in current Ical1 can compensate for the temperature nonlinearity error of the temperature detection voltage Vrt1; simultaneously, targeted current compensation with compensation currents Ical1 and Ical2 can compensate for the temperature nonlinearity of the temperature detection differential signal Vadd, achieving a high linearity temperature detection differential signal Vadd. cal .

[0024] Figure 5 This is a schematic diagram of the operating curve after temperature compensation is activated in this invention. The thermistors Rntc1 and Rntc2 have different temperature coefficients. The magnitudes of the output currents, namely the compensation currents Ical1 and Ical2 flowing through the thermistors Rntc1 and Rntc2 respectively, are both subject to the variable function F. cal = -K*F -1 (T0-T) control, and respectively obtain the high linearity compensated temperature detection voltage Vrt1cal and the compensated temperature detection voltage Vrt2 with fixed slope. cal A high linearity compensated differential temperature detection voltage Vrt2 with a fixed slope is obtained through differential processing. cal -Vrt1 cal The high-linearity temperature detection differential signal Vadd is then obtained through differential amplification. cal .

[0025] It can be seen that this invention not only employs a differential temperature detection method, increasing the common-mode interference control capability and reliability of the temperature detection circuit; but also adds a function F to the differential temperature detection NTC thermistor, where the output current magnitude is subject to the variable function F. cal = -K*F -1 The compensation currents Ical1 and Ical2, controlled by (T0-T), achieve high linearity compensation of the differential temperature detection voltage Vrt2 with a fixed slope. cal -Vrt1 cal High linearity temperature detection differential signal Vadd cal .

[0026] Figure 2 The circuit shown needs to implement Figure 5 The working effect shown requires, firstly, the inverse function compensation code calculation circuit to accurately calculate how much current the compensation current source Ical1 and compensation current source Ical2 need to compensate on the thermistors Rntc1 and Rntc2 respectively; secondly, compensation current source Ical1 and compensation current source Ical2 need to be able to accurately control the output of different current sizes.

[0027] The core function of the inverse function compensation code calculation circuit is to select the optimal compensation digital quantity for the input temperature data, thus requiring a dedicated digital algorithm circuit. Various implementation methods can be chosen, with neural networks and lookup tables (LUTs) offering the highest accuracy. It's worth noting that all of these implementations require the temperature nonlinearity model of the NTC resistor, i.e., the nonlinear curve relationship F(T). This model necessitates extensive experimental data from NTC resistors, obtained through statistical analysis or by referencing publicly available experimental data. After obtaining the NTC resistor nonlinear curve relationship F(T), the variable function F can be derived using either neural network training or a lookup table (LUT) approach. cal = -K*F -1 (T0-T), the hardware circuit that implements this variable function using a neural network or a lookup table (LUT) is the inverse function compensation code calculation circuit of this invention.

[0028] The compensation current sources Ical1 and Ical2 can be implemented using existing programmable current source array circuits. Typically, a programmable current source array circuit includes a series of common-source, common-gate current sources and control selection switches. The temperature compensation code Dcal, input from an external control circuit, adjusts the output current of the programmable current source array by controlling the on / off state of the selection switches. Clearly, the compensation adjustment accuracy is strongly correlated with the circuit size. To achieve high-precision current-temperature compensation, the temperature compensation code Dcal needs more bits, and the number of current sources within the current source array needs to be increased accordingly.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-precision NTC thermistor temperature detection circuit for automotive electronic systems, characterized in that, include: Thermistor Rntc1, thermistor Rntc2, voltage divider resistor Rm1, voltage divider resistor Rm2, filter capacitor C1, filter capacitor C2, operational amplifier, analog-to-digital converter, inverse function compensation code calculation circuit, compensation current source Ical1 and compensation current source Ical2; The power supply terminal of the compensation current source Ical1 is connected to the power supply voltage VDD, and the output terminal is connected to the upper end of the thermistor Rntc1. The lower end of the thermistor Rntc1 is connected to the upper end of the voltage divider resistor Rm1 and the upper end of the filter capacitor C1, generating a temperature detection voltage Vrt1 which is connected to the inverting input terminal of the operational amplifier. The lower ends of the voltage divider resistor Rm1 and the lower end of the filter capacitor C1 are grounded. The power supply terminal of the compensation current source Ical2 is connected to the power supply voltage VDD, and the output terminal is connected to the upper end of the thermistor Rntc2. The lower end of the thermistor Rntc2 is connected to the upper end of the voltage divider resistor Rm2 and the upper end of the filter capacitor C2. The temperature detection voltage Vrt2 is connected to the non-inverting input terminal of the operational amplifier, and the lower ends of the voltage divider resistor Rm2 and the lower end of the filter capacitor C2 are grounded. The operational amplifier amplifies the temperature detection voltage difference and outputs a temperature detection differential signal Vadd, which is connected to the analog-to-digital converter. The analog-to-digital converter converts the temperature detection differential signal Vadd into a digital temperature signal Dtmp, which is then connected to the inverse function compensation code calculation circuit. The inverse function compensation code calculation circuit generates a temperature compensation code Dcal based on the magnitude of the digital temperature signal Dtmp, and outputs it to the compensation current source Ical1 and the compensation current source Ical2 respectively to control the magnitude of their output current.

2. The high-precision NTC thermistor temperature detection circuit for automotive electronic systems according to claim 1, characterized in that, The thermistors Rntc1 and Rntc2, voltage divider resistors Rm1 and Rm2, filter capacitors C1 and C2 constitute a differential temperature detection circuit, and the absolute resistance and temperature coefficient of the thermistors Rntc1 and Rntc2 are different.

3. The high-precision NTC thermistor temperature detection circuit for automotive electronic systems according to claim 2, characterized in that, The inverse function compensation code calculation circuit uses the temperature compensation code Dcal to compensate the temperature detection voltage Vrt1. The compensated temperature detection voltage Vrt1 is obtained by introducing a compensation amount into the compensation current source Ical1. cal It satisfies the following relationship: Vrt1 cal =Vrt0+Ical1* Rntc0*F(T0-T)* F cal The compensation variable function Fcal is set as follows: Fcal=-K* F -1 (T0-T) Furthermore, the nonlinear curve function F(x) and its complementary function F -1 (x) satisfies the product identity: F(x) * F -1 (x)=x,x= T0-T When the circuit parameters satisfy the normalization condition Ical1*Rntc0=1, the compensated temperature detection voltage Vrt1 cal It can be simplified to: Vrt1 cal =Vrt0 -K*(T0-T) Where F(x) represents the nonlinear curve function of the absolute resistance of a single thermistor Rntc1 increasing rapidly with decreasing temperature; T represents the current actual ambient temperature, T0 represents the reference temperature, and at temperature T0, the resistance of the thermistor Rntc1 is Rntc0 and the temperature detection voltage Vrt1 is Vrt0; a compensation variable function F is introduced into the compensation current source Ical1. cal -K represents the fixed slope of the temperature detection voltage Vrt1 obtained under ideal conditions as temperature decreases; F -1 (T0-T) is used to cancel the nonlinear term in F(T0-T) so that the output voltage changes linearly with the temperature difference T0-T; Similarly, the inverse function compensation code calculation circuit uses the temperature compensation code Dcal to compensate the temperature detection voltage Vrt2 to obtain the compensated temperature detection voltage Vrt2. cal .

4. The high-precision NTC thermistor temperature detection circuit for automotive electronic systems according to claim 3, characterized in that, When the circuit is working normally, the magnitudes of the currents flowing through thermistors Rntc1 and Rntc2 are both governed by the variable function F. cal = -K*F -1 (T0-T) control, and respectively obtain high linearity compensated temperature detection voltage Vrt1 with fixed slope. cal and compensation temperature detection voltage Vrt2 cal A high linearity compensated differential temperature detection voltage Vrt2 with a fixed slope is obtained through differential processing. cal -Vrt1 cal The high-linearity temperature detection differential signal Vadd is then obtained through differential amplification. cal .

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