A low power tire pressure monitoring circuit and method

Abstract

The application discloses a low-power-consumption tire pressure monitoring circuit and method, and relates to the technical field of tire pressure monitoring, in particular to a low-power-consumption tire pressure monitoring circuit and method. The circuit comprises a normal-open power supply domain, a power-off power supply domain 1 and a power-off power supply domain 2; the power-off power supply domain 2 comprises a CPU and an acceleration sensor; the normal-open power supply domain comprises a counter, a main state machine and a register; the power-off power supply domain 1 comprises a pressure sensor, a secondary state machine, a programmable gain amplifier, a comparator, a DAC, an ADC and a threshold value detection and alarm circuit; the CPU stores a mode flag into the register before sleeping; the main state machine periodically wakes up the power-off power supply domain 1, turns on the power supply and performs air pressure measurement; the secondary state machine compares the air pressure measurement result with a threshold value range at least once, and performs alarm processing or adjusts the counting period of the counter according to the comparison result. The application can independently and automatically complete the periodic sampling and monitoring of the tire air pressure in the completely sleeping state of the CPU without software intervention through a special hardware processing circuit, and effectively reduces the power consumption.

Description

Technical Field

[0001] This invention relates to the field of semiconductor circuit design technology, and specifically to a low-power tire pressure monitoring circuit and method. Background Technology

[0002] Tire Pressure Monitoring System (TPMS) is a critical safety device during vehicle operation. It ensures driving safety by monitoring the tire pressure in real time. When a tire experiences abnormal pressure or sudden loss of pressure, the TPMS immediately issues an alarm signal and transmits it to the vehicle's main control circuitry to assist in implementing safety measures such as vehicle attitude control and steering adjustment. Typically, the tire pressure sensor is installed at the tire valve, and the sensor chip transmits the monitoring data to the main control system wirelessly.

[0003] Because the entire monitoring and communication device rotates with the tire, its size and weight are strictly limited, resulting in a small battery capacity. Under these conditions, achieving low-power design becomes both a key focus and a challenge for TPMS systems. To ensure the effectiveness of tire pressure monitoring, the tire pressure chip needs to periodically collect air pressure data; simultaneously, to cope with emergencies such as tire blowouts and provide sufficient system response time, the TPMS is generally required to complete the entire process from data measurement to alarm signal transmission within 300 milliseconds. If the measurement cycle is too long, the system's real-time requirements cannot be met; while if the cycle is too short, chip power consumption will increase significantly, shortening battery life. Therefore, how to effectively reduce system power consumption while meeting the requirements of air pressure monitoring accuracy and alarm response time has become a key issue in TPMS design and optimization. Summary of the Invention

[0004] To address the aforementioned issues, this invention aims to propose a low-power tire pressure monitoring circuit and method. Through a dedicated hardware processing circuit, it can independently and automatically complete the periodic sampling and monitoring of tire pressure without software intervention while the system CPU is in complete sleep mode, effectively reducing power consumption.

[0005] This was achieved through the following technical solutions: First, a low-power tire pressure monitoring circuit is proposed, including a normally-on power domain, a power-off power domain 1, and a power-off power domain 2. Power-off power domain 2 includes a CPU and an accelerometer. The normally-on power domain includes a counter, a main state machine, and a register. Power-off power domain 1 includes a pressure sensor, a sub-state machine, a programmable gain amplifier, a comparator, a DAC, an ADC, and a threshold detection and alarm circuit. Before the CPU goes to sleep, it converts the output of the accelerometer into a mode flag and stores it in the register. The mode flag is used to indicate the counting cycle. The main state machine periodically wakes up power-off power domain 1 according to the counting cycle and performs air pressure measurement by the pressure sensor. The sub-state machine uses the comparator to perform an initial comparison between the air pressure measurement result amplified by the programmable gain amplifier and the preset threshold range in the register. If the initial comparison does not exceed the threshold range, a measurement completion flag signal is generated and the power supply of PD1 domain is turned off. If the initial comparison exceeds the threshold range, the sub-state machine controls the ADC to collect a second air pressure data and performs a second comparison between the second air pressure data and the threshold range. Based on the result of the second comparison, an alarm is executed or the counting cycle of the counter is adjusted.

[0006] Preferably, the threshold range includes interval I, interval II, and a slope threshold. During the initial comparison, the amplified pressure measurement result is compared with interval I. If interval I is not met, a second pressure measurement is performed using an ADC and compared with interval II for the second time. Through multiple threshold comparisons, a graded determination of the degree of pressure anomaly is achieved, avoiding misjudgments or missed judgments caused by a single threshold.

[0007] Preferably, if the second comparison does not exceed interval II, it is determined that the system has entered the fluctuation range, and the counter's counting period is adjusted. If the second comparison exceeds interval II, the sub-state machine controls the ADC to perform at least two consecutive pressure data acquisitions, and calculates the pressure change slope based on the difference between the at least two acquired data and the time interval. When the pressure change slope exceeds the slope threshold, an alarm signal is output to indicate rapid leakage; when the pressure change slope does not exceed the slope threshold, an alarm signal is output to indicate slow leakage. Continuous ADC acquisition and slope calculation are only initiated when interval II is exceeded, and measurement resources are only used when alarm judgment is required, effectively suppressing the increase in average power consumption.

[0008] Preferably, when the comparator determines that the output voltage of the programmable gain amplifier has not exceeded the interval I, the secondary state machine disables the ADC startup and returns a measurement completion flag signal to the main state machine; the main state machine shuts off the power supply to the power-down domain based on the measurement completion flag signal.

[0009] Preferably, interval I is from Vlimit_h to Vlimit_l, and interval II is from limit_l to limit_h, where limit_l < Vlimit_l < Vlimit_h < limit_h. Clearly defining the boundaries of each interval effectively establishes a multi-level monitoring system encompassing stability, fluctuations, and alarms.

[0010] Preferably, the counter adopts a cascaded structure, and the counter includes a pre-counter and a post-counter; the overflow signal of the pre-counter is used as the clock input of the post-counter.

[0011] Preferably, the normally open power domain further includes a low-frequency clock for driving the counter; the power-down power domain 1 further includes a high-frequency clock for driving the sub-state machine; wherein, when the normally open power domain is in the counting state, the low-frequency clock provides a clock signal of a first frequency to the counter and the main state machine; after the post-counter is full, the clock signal of the main state machine is switched to a clock signal of a second frequency; wherein, the second frequency is not lower than the first frequency.

[0012] Preferably, the configuration parameters stored in the register include: each mode flag, each measurement cycle value corresponding to different modes, and a threshold range. The mode flag is used to indicate whether the tire is in parking mode or rolling mode. The main state machine is used to select the corresponding measurement cycle value based on the mode flag and load it into the counter. By pre-setting the data of each mode and its measurement cycle in the register, the hardware circuit can automatically adapt to monitoring under different operating conditions without CPU intervention.

[0013] Secondly, a low-power tire pressure monitoring method is proposed, which uses the aforementioned low-power tire pressure monitoring circuit. This method includes the following steps: S1. After the system is powered on, the CPU writes the configuration parameters into the register of the normally open power domain. Then the CPU enters sleep mode, the power-off power domain is powered off, and the normally open power domain continues to operate while powered on. S2. The main state machine of the normally open power domain loads the corresponding measurement cycle value into the counter based on the mode flag in the register. The counter counts under the drive of a low-frequency clock. S3. When the counter reaches the preset measurement cycle, the main state machine controls the power-down domain to power on, enabling the high-frequency clock, programmable gain amplifier and DAC to perform air pressure measurement. S4. Through the sub-state machine of the power-down domain, the comparator is used to make an initial comparison between the output voltage of the programmable gain amplifier and the preset interval I. If the initial comparison does not exceed the interval I, the air pressure is determined to be in the stable range, a measurement completion flag is generated, and the power supply of the PD1 domain is turned off. S5. If the initial comparison exceeds interval I, the sub-state machine controls the ADC to collect the second air pressure data and compares the second air pressure data with the preset interval II for the second time. Based on the result of the second comparison, the preset alarm processing or measurement cycle adjustment operation is executed.

[0014] Preferably, in step S5, performing a preset alarm processing or measurement cycle adjustment operation based on the comparison result includes: if the second air pressure data is within interval II, an air pressure warning signal is generated, the main state machine reloads the counter's cycle to a shorter cycle than the current rolling cycle, and returns to the counting state after turning off the power supply of power domain 1; if the second air pressure data exceeds interval II, the alarm judgment stage is entered, the sub-state machine controls the ADC to continuously collect at least two air pressure data, calculates the corresponding air pressure change slope, and issues a leak warning or tire blowout warning based on the comparison result of the air pressure change slope and a preset slope threshold, while generating a wake-up signal to wake up the CPU.

[0015] The beneficial effects of this invention compared to the prior art are: Compared to traditional solutions that rely on CPU-driven program execution to control tire pressure measurement, this invention achieves significant optimization in power consumption and performance through dedicated hardware circuitry. During the main working cycle of tire pressure monitoring, the CPU remains in a sleep state, with only the counter running and other circuits only briefly activated when necessary. Secondly, in most cases, during tire pressure measurement, only a low-to-medium precision DAC provides the threshold voltage, and tire pressure monitoring is performed via a voltage comparator and PGA output voltage. This design significantly reduces the startup frequency of the high-precision ADC, further reducing the power consumption of the dedicated hardware circuitry, thereby effectively lowering the average power consumption of the TPMS and significantly extending battery life. Furthermore, since the measurement and threshold judgment logic are entirely implemented by hardware circuitry without executing software code, the delay in signal acquisition and processing is significantly shortened, improving alarm response speed. This feature is particularly important for monitoring emergency situations such as tire blowouts, providing the vehicle system with more time for emergency response and thus enhancing driving safety. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the TPMS chip structure; Figure 2 This is a schematic diagram of the architecture of a low-power tire pressure monitoring circuit. Figure 3 A schematic diagram illustrating the workflow of a low-power tire pressure monitoring method; Figure 4 This is a schematic diagram of air pressure ranges and thresholds. Detailed Implementation

[0017] The technical solutions of the present invention will now be described in detail with reference to the accompanying drawings.

[0018] like Figure 1 The diagram shown is a schematic of a TPMS chip structure; as shown Figure 2 The diagram shown is a schematic of the architecture of a low-power tire pressure monitoring circuit; combined with Figure 1 and Figure 2 As shown, the low-power tire pressure monitoring circuit includes a normally-on power domain, a power-off power domain 1, and a power-off power domain 2. Unlike traditional general-purpose computing architectures, this circuit can independently and automatically complete the periodic sampling and monitoring of tire pressure without software intervention when the system CPU is in complete sleep mode. This achieves a breakthrough reduction in power consumption, effectively reducing overall power consumption and improving driving range, and significantly improving the tire pressure safety monitoring effect of the vehicle system during driving.

[0019] Combination Figure 1 As shown, in terms of circuit architecture, a dual-power-domain structure is adopted to optimize system power consumption. The dedicated hardware circuit is divided into an Always-on power domain and a Powerdown power domain 1, which can be referred to as the AON domain and PD1 domain, respectively. The AON domain can independently control the power supply of the PD1 domain. The PD1 domain is responsible for barometric pressure measurement and has the function of waking up the CPU. The accelerometer and the CPU belong to the Powerdown power domain 2 (PD2 domain). Before the CPU enters sleep mode, the CPU can convert the output of the accelerometer into a mode flag signal and configure it in the register of the AON domain, so that the data can be retained after the CPU is powered off.

[0020] Combination Figure 2 As shown, the AON domain integrates a low-frequency clock, a counter, a main state machine, and registers. The registers store the configuration parameters specified by the CPU when the chip is powered on and retain the data even after power failure. The low-frequency clock drives the counter, providing a fixed-frequency clock source (e.g., 1kHz) to the counter and a clock signal that can dynamically switch between different frequencies (e.g., 1kHz and 32kHz) to the main state machine. The counter adopts a cascaded structure, including a pre-counter and a post-counter; the overflow signal of the pre-counter serves as the clock input of the post-counter, thus helping to reduce power consumption and circuit area when achieving larger count values. When the low-frequency clock is in the counting state in the normally open power domain, it provides a first-frequency clock signal to the counter and the main state machine; after the post-counter reaches its full count, it switches the clock signal of the main state machine to a second-frequency clock signal (e.g., from 1kHz to 32kHz); wherein the second frequency is not lower than the first frequency.

[0021] The configuration parameters stored in the register include: each mode flag (i.e., mode flag signal), the measurement cycle value corresponding to each mode, and the threshold range; the mode flag can indicate whether the tire is in parking mode or rolling mode, and also indicate the counting cycle; the main state machine is used to select the corresponding counting cycle value (measurement cycle) according to the mode flag and load it into the counter, and can periodically wake up the power-down power domain 1 to perform air pressure measurement of the pressure sensor. By pre-setting the data of each mode and its measurement cycle in the register, the hardware circuit can automatically adapt to monitoring under different operating conditions without CPU intervention.

[0022] The components in power-down domain 1 include: a high-frequency clock, a pressure sensor, a sub-state machine (i.e., the sub-state machine circuit), a programmable gain amplifier (PGA), a comparator (COMP, i.e., a voltage comparator), a DAC (digital-to-analog converter), an ADC (analog-to-digital converter), and a threshold detection and alarm circuit. The high-frequency clock drives the sub-state machine, the pressure sensor measures air pressure, and the programmable gain amplifier amplifies the air pressure measurement result. The threshold detection and alarm circuit compares the amplified air pressure measurement result with a preset threshold range in a register using a comparator. When an abnormal air pressure is detected, an alarm signal is generated and the CPU is activated. The sub-state machine controls the operation of other components in power-down domain 1.

[0023] If the initial comparison does not exceed the threshold range, a measurement completion flag signal is generated and the PD1 domain power is turned off; if the initial comparison exceeds the threshold range, the sub-state machine controls the ADC to collect the second air pressure data and compares the second air pressure data with the threshold range for the second time. Based on the result of the second comparison, an alarm is executed or the counter's counting cycle is adjusted.

[0024] The threshold range includes interval I, interval II, and slope threshold; combined with Figure 4As shown, interval I is from Vlimit_h to Vlimit_l, and interval II is from limit_l to limit_h, where limit_l < Vlimit_l < Vlimit_h < limit_h. During the initial comparison, the amplified pressure measurement result is compared with interval I. If the conditions of interval I are not met, the sub-state machine performs a second pressure measurement using the ADC and compares it with interval II for the second time. If the second comparison does not exceed interval II, it is determined that the system has entered a fluctuation range, and the counter's counting period is adjusted. If the second comparison exceeds interval II, the sub-state machine controls the ADC to perform at least two consecutive pressure data acquisitions and calculates the pressure change slope based on the difference between the at least two acquisitions and the time interval. When the pressure change slope exceeds the slope threshold, the sub-state machine controls the threshold detection and alarm circuit to output an alarm signal to indicate rapid leakage. When the pressure change slope does not exceed the slope threshold, the threshold detection and alarm circuit outputs an alarm signal to indicate slow leakage. By comparing multiple thresholds, the system achieves graded judgment of the degree of air pressure anomaly, avoiding misjudgment or missed judgment caused by a single threshold. Furthermore, continuous ADC acquisition and slope calculation are only initiated when the pressure exceeds interval II, and measurement resources are only used when alarm judgment is required, effectively suppressing the increase in average power consumption.

[0025] During the comparison by the comparator, if it is determined that the output voltage of the programmable gain amplifier does not exceed the range I, the sub-state machine disables the ADC startup and returns a measurement completion flag signal to the main state machine; the main state machine shuts off the power supply to the power-down domain based on the measurement completion flag signal.

[0026] In this embodiment, the functions of each module and methods for reducing power consumption in barometric pressure measurement will be explained in detail below, in conjunction with the workflow of the hardware circuit. Figure 3 As shown, the entire barometric pressure monitoring process can be divided into five orderly execution stages: Stage 1 (system initialization and CPU sleep), Stage 2 (low power counting state), Stage 3 (measurement preparation and PD1 domain power-on), Stage 4 (barometric pressure measurement and threshold judgment), and Stage 5 (state recovery and alarm handling).

[0027] In Phase 1, after the TPMS chip powers on, the CPU writes the configuration parameters into the registers in the AON domain before powering off. The configuration parameters mainly include the following: a mode flag, used to indicate whether the dedicated hardware circuitry is currently in parking mode or rolling mode; different measurement (technical) cycles Tstop, Trl, and Trs. Tstop is the measurement cycle in parking mode, Trl and Trs are the measurement cycles in rolling mode, and Trl > Trs; measurement threshold ranges Vlimit_l and Vlimit_h; alarm threshold ranges limit_l and limit_h; and a pressure change slope limit limit_k.

[0028] Figure 4 The threshold setting strategy of the circuit of this invention is demonstrated: within the measurement threshold range is the stable interval, where the air pressure is within a reasonable range; between the measurement threshold and the alarm threshold is the fluctuation interval, where the air pressure may fluctuate (e.g., the tire goes over a pothole or the tire pressure drops slightly), and in this state, the dedicated hardware circuit will use a higher frequency and higher precision measurement method; outside the alarm threshold is the alarm interval, where air pressure entering this interval will trigger the hardware circuit to wake up the CPU and send an alarm signal. After the CPU enters a power-down state, the entire system enters Powerdown mode. The PD domain 2 circuit is then powered down, and only the AON domain circuit remains powered on, with the dedicated hardware circuit independently performing air pressure monitoring.

[0029] In Phase Two, under Powerdown state, the main state machine first determines whether the tire is in rolling mode based on the mode flag and loads the corresponding parameters from the AON register accordingly. If it is in rolling mode, the counter loads the rolling count period Trl (which can be set to less than 1 second); if it is in parking mode, it loads the parking count period Tstop (which can be tens of minutes or longer). The pre-counter counts at a low-frequency clock of 1kHz, during which the main state machine is in counting state. The system will maintain this state until the post-counter reaches the set count period.

[0030] In Phase Three, once the post-counter reaches the set value corresponding to the counting cycle, the low-frequency clock switches to 32kHz and supplies it to the main state machine circuit to accelerate the processing of the PD1 domain power-on timing and the synchronization of the PD1 domain signals. The main state machine switches to the measurement state, at which point the counter continues counting to maintain the periodicity of the barometric pressure measurement. In the measurement state, the AON domain sequentially enables the high-frequency clock, PGA, and DAC, and then waits for the PD1 domain to return a measurement completion flag signal or alarm signal.

[0031] Phase four is the key step in achieving low-power operation, where the logic control is completed by the PD1 domain sub-state machine under a high-frequency clock. Due to the significant increase in power consumption under a high-frequency clock, this circuit prioritizes the use of a voltage comparator for air pressure monitoring and reduces the number of ADC startups to minimize the operating time and power consumption of the PD1 domain circuit.

[0032] First, the voltage comparator compares the PGA's output voltage Va1 with preset thresholds Vlimit_h and Vlimit_l provided by the DAC. Since these thresholds are only used for the first-stage detection, a DAC of appropriate accuracy (DAC accuracy is lower than ADC accuracy) can be used to further reduce power consumption. Generally, at the same resolution, DAC power consumption is lower than ADC. If Va1 does not exceed the range set by Vlimit_h and Vlimit_l, it indicates that the tire pressure is in a stable range, and in this case, there is no need to enable ADC measurement, thus saving power.

[0033] If Va1 exceeds the threshold range, the PD1 domain sub-state machine controls the ADC to activate and perform a second tire pressure acquisition. The ADC accuracy should be higher than the DAC, typically 14 to 16 bits. The tire pressure data Dp1 acquired by the ADC will be compared with limit_l and limit_h: if Dp1 does not exceed the threshold, it is determined that the tire pressure has entered the fluctuation range, and the counter period is adjusted to Trs to increase the measurement frequency and achieve more frequent tire pressure monitoring; if Dp1 still exceeds the threshold, the alarm judgment stage is entered.

[0034] Then, during the alarm judgment phase, the ADC performs a third air pressure acquisition, obtaining data Dp2. Since the entire measurement process is performed under the control of the sub-state machine, and the time interval Δt between the two acquisitions is a fixed value, the air pressure change slope K = (Dp2 - Dp1) / Δt can be calculated. The slope K is compared with the preset threshold limit_k: if K is greater than limit_k, it is determined to be a rapid leak; otherwise, it is a slow leak.

[0035] In Phase 5, after completing the alarm judgment, the circuit performs corresponding operations based on the threshold comparison results: If the air pressure is in the stable range, the secondary state machine generates a measurement completion flag signal; upon receiving this signal, the primary state machine immediately shuts down the high-frequency clock and the PD1 domain power supply, and returns to Phase 1 to continue counting. If the air pressure is in the fluctuating range, the secondary state machine generates an air pressure warning signal; upon receiving this signal, the primary state machine reloads the counter period to TRS to increase the measurement frequency, then shuts down the PD1 domain power supply and returns to Phase 1 to continue counting. If the air pressure exceeds the alarm threshold, the secondary state machine determines the leak type based on the slope K, and issues a leak warning or tire blowout warning signal accordingly, while simultaneously sending a wake-up signal to wake up the CPU. At this time, the primary state machine maintains the PD1 domain power-on state. After the CPU powers on, it receives the alarm signal, and the preset software program executes the subsequent alarm processing procedure.

[0036] Secondly, a low-power tire pressure monitoring method is proposed, which uses the aforementioned low-power tire pressure monitoring circuit. This method includes the following steps: S1. After the system is powered on, the CPU writes the configuration parameters into the register of the normally open power domain. Then the CPU enters sleep mode, the power-off power domain is powered off, and the normally open power domain continues to operate while powered on. S2. The main state machine of the normally open power domain loads the corresponding measurement cycle value into the counter based on the mode flag in the register. The counter counts under the drive of a low-frequency clock. S3. When the counter reaches the preset measurement cycle, the main state machine controls the power-down domain to power on, enabling the high-frequency clock, programmable gain amplifier and DAC to perform air pressure measurement. S4. Through the sub-state machine of the power-down domain, the comparator is used to make an initial comparison between the output voltage of the programmable gain amplifier and the preset interval I. If the initial comparison does not exceed the interval I, the air pressure is determined to be in the stable range, a measurement completion flag is generated, and the power supply of the PD1 domain is turned off. S5. If the initial comparison exceeds interval I, the sub-state machine controls the ADC to collect a second air pressure data, and compares the second air pressure data with the preset interval II for a second time. Based on the result of the second comparison, a preset alarm processing or measurement cycle adjustment operation is executed. The preset alarm processing or measurement cycle adjustment operation based on the comparison result includes: if the second air pressure data is within interval II, a air pressure warning signal is generated, the main state machine reloads the counter's period to a shorter period relative to the current rolling period, and returns to the counting state after turning off the power to power domain 1; if the second air pressure data exceeds interval II, the alarm judgment stage is entered, the sub-state machine controls the ADC to continuously collect at least two air pressure data, calculates the corresponding air pressure change slope, and issues a leak warning or tire blowout warning based on the comparison result of the air pressure change slope with a preset slope threshold, while simultaneously generating a wake-up signal to wake up the CPU. The specific implementation method and beneficial effects of this method can be referred to the description of the aforementioned low-power tire pressure monitoring circuit, and will not be repeated here.

[0037] In summary, this invention employs a hierarchical measurement mechanism controlled by a state machine. It prioritizes the use of low-power comparators and DACs for initial air pressure assessment, activating a high-precision ADC only when pressure exceeds a preset threshold, thereby minimizing the operating time of high-power modules. Simultaneously, the cascaded counter design and dynamically switchable clock strategy further optimize power consumption during the counting and measurement preparation phases. This solution significantly reduces the average power consumption of the TPMS, extends battery life, and substantially improves alarm response speed due to its fully hardware-based processing logic. It is particularly suitable for rapid leak or tire blowout monitoring scenarios with stringent real-time requirements, representing a significant advancement.

[0038] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A low-power tire pressure monitoring circuit, characterized in that, It includes a normally open power domain, a power-down power domain 1, and a power-down power domain 2; power-down power domain 2 includes the CPU and an accelerometer; the normally open power domain includes a counter, a main state machine, and registers; power-down power domain 1 includes a pressure sensor, a sub-state machine, a programmable gain amplifier, a comparator, a DAC, an ADC, and a threshold detection and alarm circuit. Before the CPU goes to sleep, it converts the output of the accelerometer into a mode flag and stores it in a register. The mode flag is used to indicate the counting cycle. The main state machine periodically wakes up the power-down power domain 1 according to the counting cycle and performs air pressure measurement of the pressure sensor. The sub-state machine uses a comparator to initially compare the amplified air pressure measurement result from the programmable gain amplifier with a preset threshold range in the register. If the initial comparison does not exceed the threshold range, a measurement completion flag signal is generated and the PD1 domain power is turned off. If the initial comparison exceeds the threshold range, the sub-state machine controls the ADC to collect the second air pressure data and compares the second air pressure data with the threshold range for the second time. Based on the result of the second comparison, an alarm is executed or the counter's counting cycle is adjusted.

2. The low-power tire pressure monitoring circuit according to claim 1, characterized in that, The threshold range includes interval I, interval II, and slope threshold. During the initial comparison, the amplified air pressure measurement result is compared with interval I. If the result does not meet the requirements of interval I, a second air pressure measurement is performed using the ADC and compared with interval II for the second time.

3. The low-power tire pressure monitoring circuit according to claim 2, characterized in that, If the second comparison does not exceed interval II, it is determined that the system has entered the fluctuation range and the counter's counting period is adjusted. When the second comparison exceeds interval II, the sub-state machine controls the ADC to perform at least two consecutive air pressure data acquisitions and calculates the air pressure change slope based on the difference between the at least two acquired data and the time interval. When the air pressure change slope exceeds the slope threshold, an alarm signal is output to indicate rapid air leakage. When the air pressure change slope does not exceed the slope threshold, an alarm signal is output to indicate slow air leakage.

4. The low-power tire pressure monitoring circuit according to claim 2, characterized in that, When the comparator determines that the output voltage of the programmable gain amplifier has not exceeded the range I, the secondary state machine disables the ADC startup and returns a measurement completion flag signal to the main state machine; the main state machine shuts off the power supply to the power-down domain based on the measurement completion flag signal.

5. A low-power tire pressure monitoring circuit according to claim 2, characterized in that, Interval I is from Vlimit_h to Vlimit_l, and interval II is from limit_l to limit_h, where limit_l < Vlimit_l < Vlimit_h < limit_h.

6. A low-power tire pressure monitoring circuit according to claim 1, characterized in that, The counter adopts a cascaded structure, which includes a pre-counter and a post-counter; the overflow signal of the pre-counter is used as the clock input of the post-counter.

7. A low-power tire pressure monitoring circuit according to claim 6, characterized in that, The normally open power domain also includes a low-frequency clock, which is used to drive the counter; the power-down power domain 1 also includes a high-frequency clock, which is used to drive the sub-state machine. When the low-frequency clock is in the counting state in the normally open power domain, it provides a clock signal of the first frequency to the counter and the main state machine; after the post-counter is full, it switches the clock signal of the main state machine to a clock signal of the second frequency; wherein the second frequency is not lower than the first frequency.

8. A low-power tire pressure monitoring circuit according to claim 1, characterized in that, The configuration parameters stored in the register include: each mode flag, each measurement cycle value corresponding to different modes, and the threshold range. The mode flag is used to indicate whether the tire is in parking mode or rolling mode. The main state machine is used to select the corresponding measurement cycle value based on the mode flag and load it into the counter.

9. A low-power tire pressure monitoring method, operating using a low-power tire pressure monitoring circuit as described in any one of claims 1 to 8, characterized in that, The method includes the following steps: S1. After the system is powered on, the CPU writes the configuration parameters into the register of the normally open power domain. Then the CPU enters sleep mode, the power-off power domain is powered off, and the normally open power domain continues to operate while powered on. S2. The main state machine of the normally open power domain loads the corresponding measurement cycle value into the counter based on the mode flag in the register. The counter counts under the drive of a low-frequency clock. S3. When the counter reaches the preset measurement cycle, the main state machine controls the power-down domain to power on, enabling the high-frequency clock, programmable gain amplifier and DAC to perform air pressure measurement. S4. Through the sub-state machine of the power-down domain, the comparator is used to make an initial comparison between the output voltage of the programmable gain amplifier and the preset interval I. If the initial comparison does not exceed the interval I, the air pressure is determined to be in the stable range, a measurement completion flag is generated, and the power supply of the PD1 domain is turned off. S5. If the initial comparison exceeds interval I, the sub-state machine controls the ADC to collect the second air pressure data and compares the second air pressure data with the preset interval II for the second time. Based on the result of the second comparison, the preset alarm processing or measurement cycle adjustment operation is executed.

10. A low-power tire pressure monitoring method according to claim 9, characterized in that, In step S5, performing preset alarm processing or measurement cycle adjustment operations based on the comparison results includes: If the second air pressure data is within interval II, an air pressure warning signal is generated. The main state machine reloads the counter's period to a shorter period than the current rolling period and returns to the counting state after powering off power to domain 1. If the second air pressure data exceeds interval II, the alarm judgment stage is entered. The secondary state machine controls the ADC to continuously collect at least two air pressure data, calculates the corresponding air pressure change slope, and issues a leak warning or tire blowout warning based on the comparison result between the air pressure change slope and the preset slope threshold. At the same time, a wake-up signal is generated to wake up the CPU.

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