A temperature detection circuit with adjustable temperature measurement range and a passive sensing tag

Abstract

The present invention discloses a temperature detection circuit and a passive sensing tag with adjustable temperature measurement range. The temperature detection circuit includes a reference circuit for providing a reference current and a reference voltage; a VBE voltage generation circuit for generating a reference voltage related to temperature; an amplification circuit for comparing and amplifying the reference voltage and the reference voltage and generating an amplified voltage signal; a first voltage-controlled oscillator for converting the amplified voltage signal into a periodic signal; a frequency divider for performing frequency division processing on the periodic signal to obtain an enable signal; a second voltage-controlled oscillator for generating a clock signal; and a counter for counting the clock signal according to the enable signal and outputting a temperature value. By adding an amplification circuit, the present invention linearly amplifies the temperature coefficient, improves the measurement resolution and measurement accuracy, reduces the measurement time, and can flexibly change the measurement range, and has the advantages of low power consumption, high integration, and insensitivity to process deviations.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated circuits, and particularly relates to a temperature detection circuit with adjustable temperature measurement range and a passive sensing tag. Background Art

[0002] With the development of communication technologies, the WSN (Wireless Sensor Networks) technology has become increasingly mature and widely applied. A wireless sensor network connects a large number of sensing nodes through wireless communication technologies. Through the WSN technology, remote temperature measurement of environmental objects can be realized without human intervention, which is convenient and fast.

[0003] In recent years, daily body temperature detection and body temperature monitoring of quarantined people have become important means for epidemic prevention and control. However, in traditional temperature measurement methods, it is necessary to manually measure the temperature of individuals in a contact manner one by one, which is likely to cause crowd gathering and increase the risk of cross-infection. Moreover, infrared temperature measurement is vulnerable to environmental temperature. Therefore, there is an urgent need for a wireless temperature sensor with high precision, high resolution, non-contact, and batch body temperature measurement.

[0004] Traditional temperature detection circuits are greatly affected by process factors. Both resistors and capacitors are affected by the process, which will lead to large deviations between the final chips, so they cannot be applied to passive sensing chips.

[0005] The patent document with the publication number CN102175338B proposes a method of using voltage-controlled oscillators with exactly the same structure to eliminate process deviations. However, the resolution of this circuit is much lower than the required 0.1 °C, and there is a problem that the circuit is not easy to adjust for environments with different ranges and different measurement resolutions. Currently, the resolution of the circuit can be improved by the following methods: one is to increase the circuit capacitance ratio coefficient; the second is to increase the quantization division ratio; the third is to increase the clock frequency and the division ratio proportionally.

[0006] However, an overly large capacitance ratio may cause problems in the circuit layout where it is difficult to match the two capacitors, introducing large process deviations, thereby bringing initial errors and affecting the measurement accuracy. Increasing the quantization division ratio will increase the digital noise, resulting in fluctuations in the low bits of the quantization output value, causing an increase in errors, and at the same time slowing down the quantization speed. If considering the stability of the quantization speed and using the method of increasing the clock frequency and the division ratio proportionally, the problems of frequency jitter and increased quantization error caused by a high division ratio still exist. At the same time, a high-speed clock will cause an increase in quantization power consumption. In addition, the above measures all adopt methods of post-processing from quantization, and these methods will reduce the signal-to-noise ratio of temperature quantization. Therefore, none of them can change the adverse effects of the small temperature coefficient of the on-chip temperature-sensitive unit on the measurement accuracy and resolution.

[0007] In addition, for temperature sensors with high precision, most of the existing solutions use an Analog-to-Digital converter (ADC) to implement, which has problems such as complex structure and high circuit power consumption, and does not solve the problem of the small temperature coefficient of the temperature-sensitive unit, which is not conducive to application in passive sensing tags; and the ADC structure temperature sensor needs to increase the quantization bits to improve the measurement accuracy, and thus the influence of noise is also increasing.

[0008] In summary, the existing temperature detection circuit has a small temperature coefficient, and the circuit is complex and not easy to integrate, with high power consumption, and the resolution and measurement accuracy also need to be further improved, and it cannot meet the high-precision measurement requirements in various temperature ranges. Summary of the Invention

[0009] In order to solve the above problems existing in the prior art, the present invention provides a temperature detection circuit with adjustable temperature measurement range and a passive sensing tag. The technical problems to be solved by the present invention are realized through the following technical solutions:

[0010] In a first aspect, the present invention provides a temperature detection circuit with an adjustable temperature measurement range, which is characterized by including:

[0011] A reference circuit for providing a reference current and a reference voltage;

[0012] V BE A voltage generation circuit connected to the reference circuit for generating a reference voltage related to temperature;

[0013] An amplification circuit connected to the reference circuit and the voltage generation circuit for comparing and amplifying the reference voltage and the reference voltage, and generating an amplified voltage signal;

[0014] A first voltage-controlled oscillator connected to the amplification circuit for converting the amplified voltage signal into a periodic signal;

[0015] A frequency divider connected to the first voltage-controlled oscillator for performing frequency division processing on the periodic signal to obtain an enable signal;

[0016] A second voltage-controlled oscillator connected to the reference circuit for generating a clock signal;

[0017] A counter connected to the frequency divider and the second voltage-controlled oscillator for counting the clock signal according to the enable signal and outputting a temperature value.

[0018] In an embodiment of the present invention, the amplification circuit includes a first operational amplifier, a first resistor, a second operational amplifier, and a second resistor, wherein,

[0019] The positive input terminal of the first operational amplifier is connected to the output terminal of the voltage generation circuit. The negative input terminal of the first operational amplifier is connected to its output terminal and is connected to the negative input terminal of the second operational amplifier through the first resistor.

[0020] The positive input terminal of the second operational amplifier is connected to the output terminal of the reference circuit. The output terminal of the second operational amplifier is connected to its negative input terminal through the second resistor.

[0021] The output terminal of the second operational amplifier also serves as the output terminal of the entire amplification circuit to output an amplified voltage signal.

[0022] In an embodiment of the present invention, the first voltage-controlled oscillator and the second voltage-controlled oscillator have the same structure.

[0023] In a second aspect, the present invention further provides a passive sensing tag. The passive sensing tag is integrated with a temperature detection circuit and a baseband. The temperature detection circuit is the temperature detection circuit with adjustable temperature measurement range described in the above embodiment.

[0024] After receiving an instruction sent by a reader, the temperature detection circuit performs temperature detection.

[0025] The baseband calibrates the measurement result of the temperature detection circuit to improve the detection accuracy.

[0026] Advantages of the present invention:

[0027] 1. By adding an amplification circuit to the existing temperature measurement circuit, the present invention can amplify the temperature coefficient, thereby improving the resolution accuracy and measurement accuracy. At the same time, the present invention can also flexibly change the measurement range by changing the reference voltage of the reference circuit, and has the advantages of low power consumption, high integration and insensitivity to process deviations, and can meet the high-precision measurement requirements of various temperature ranges.

[0028] 2. The present invention can adjust the amplification factor of the amplification circuit by adjusting the ratio of resistor R2 to resistor R1 in the amplification circuit, thereby flexibly changing the measurement resolution of the temperature sensor to meet the measurement requirements in various environments.

[0029] 3. Since the present invention adds an amplifier circuit, it can improve the resolution accuracy without increasing the division ratio, or reduce a certain division ratio to achieve the same resolution accuracy. This method can greatly reduce the temperature sampling time and can be applied to some specific environments with requirements for speed. Compared with the method of improving the division ratio or the oscillator frequency to improve the resolution, the present invention is less affected by the cycle jitter of the voltage-controlled oscillator or the quantization output caused by the digital noise of the frequency divider and counter, and reduces the fluctuation of the quantization output.

[0030] 4. The temperature detection circuit with adjustable temperature measurement range provided by the present invention is designed with low power consumption. The current consumed causes a negligible temperature rise in the chip, reducing the influence of its own circuit on the temperature sensing circuit test.

[0031] 5. Since the present invention has good linearity, a single-point calibration method can be adopted to make the measurement accuracy of the circuit less than 0.1 °C, meeting the accuracy requirements for temperature measurement.

[0032] The present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic structural diagram of a temperature detection circuit with adjustable temperature measurement range provided by an embodiment of the present invention;

[0034] Figure 2 is a detailed circuit diagram of an amplifier circuit provided by an embodiment of the present invention;

[0035] Figure 3 is a schematic structural diagram of a passive sensing tag provided by an embodiment of the present invention;

[0036] Figure 4 is a curve graph of the counter output varying with temperature in a simulation experiment;

[0037] Figure 5 is a curve graph of the slope of the counter output curve varying with temperature in a simulation experiment;

[0038] Figure 6 is a simulation curve graph of the overall power consumption of the circuit varying with temperature in a simulation experiment;

[0039] Figure 7 is a comparison graph of the fitted curve and the actual temperature measurement curve after single-point calibration in a simulation experiment;

[0040] Figure 8 is a quantization error curve of the output values of the fitted curve and the actual temperature measurement curve after single-point calibration in a simulation experiment;

[0041] Figure 9 is a temperature quantization error curve of the fitted curve and the actual temperature measurement curve after single-point calibration in a simulation experiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0043] Embodiment 1

[0044] Please refer to Figure 1 , Figure 1It is a schematic structural diagram of a temperature detection circuit with an adjustable temperature measurement range provided by an embodiment of the present invention, which includes:

[0045] A reference circuit 1 for providing a reference current and a reference voltage;

[0046] V BE A voltage generation circuit 2 connected to the reference circuit 1 for generating a reference voltage related to temperature;

[0047] An amplification circuit 3 connected to the reference circuit 1 and the voltage generation circuit 2 for comparing and amplifying the reference voltage and the reference voltage, and generating an amplified voltage signal;

[0048] A first voltage-controlled oscillator 4 connected to the amplification circuit 3 for converting the amplified voltage signal into a periodic signal;

[0049] A frequency divider 5 connected to the first voltage-controlled oscillator 4 for performing frequency division processing on the periodic signal to obtain an enable signal;

[0050] A second voltage-controlled oscillator 6 connected to the reference circuit 1 for generating a clock signal;

[0051] A counter 7 connected to the frequency divider 5 and the second voltage-controlled oscillator 6 for counting the clock signal according to the enable signal and outputting a temperature value.

[0052] Specifically, in this embodiment, the reference circuit 1 adopts an existing conventional circuit structure, which is mainly used to provide the reference current of the circuit I REF , and at the same time provides a reference voltage for the amplification circuit 3 and the second voltage-controlled oscillator 6 V REF . The voltage generation circuit 2 mainly generates a reference voltage with a negative temperature coefficient through a triode V BE , so it is also called V BE a generation circuit, which also adopts an existing circuit structure.

[0053] Furthermore, the amplification circuit 3 is mainly used to amplify the slight change of the reference voltage V BE with temperature to generate an amplified voltage signal V amp .

[0054] Optionally, as an implementation manner of the present invention, the amplification circuit may adopt the circuit structure shown in Figure 2 , which specifically includes a first operational amplifier A1, a first resistor R1, a second operational amplifier A2, and a second resistor R2, where

[0055] The positive input terminal of the first operational amplifier A1 is connected to the output terminal of the voltage generation circuit 2. The negative input terminal of the first operational amplifier A1 is connected to its output terminal and is connected to the negative input terminal of the second operational amplifier A2 through the first resistor R1;

[0056] The positive input terminal of the second operational amplifier A2 is connected to the output terminal of the reference circuit 1. The output terminal of the second operational amplifier A2 is connected to its negative input terminal through the second resistor R2;

[0057] The output terminal of the second operational amplifier A2 also serves as the output terminal of the entire amplifier circuit 3 to output an amplified voltage signal.

[0058] Specifically, the first operational amplifier A1 is used to form a unity-gain buffer with a gain of 1. Its positive terminal is connected to the temperature reference voltage V BE , and its negative terminal is connected to the output terminal. The positive terminal of the second operational amplifier A2 is connected to the reference voltage V REF , and it forms an inverting amplifier with the first resistor R1 and the second resistor R2. Assuming its gain is A , then there is , that is, the amplification factor of the amplifier circuit is A , where R 1 and R 2 are the resistance values of the first resistor R1 and the second resistor R2 respectively.

[0059] The amplifier circuit compares the reference voltage V BE signal with the reference voltage V REF signal, amplifies the change amount of the V BE signal by A times, and outputs an amplified voltage signal V amp as the control voltage of the first voltage-controlled oscillator 4.

[0060] It can be understood that other amplifier circuit structures can also be used in this embodiment to implement the circuit function, and this embodiment does not limit this.

[0061] Furthermore, the first voltage-controlled oscillator 4 converts the amplified voltage signal V amp into a periodic signal T_tem .

[0062] The frequency divider 5 divides the periodic signal T_tem by 2 n times to generate an enable signal T_TEM , which serves as the control signal of the counter. Among them, nIt represents the frequency division bit number. Meanwhile, the second voltage-controlled oscillator 6 converts the reference voltage generated by the reference circuit V REF into a clock signal T_con , and uses it as the counting signal of the counter.

[0063] The counter 7 uses the enable signal T_TEM and the clock signal T_con to perform counting, and outputs a temperature-related value N as the output of the overall circuit.

[0064] The working principle of the temperature detection circuit with adjustable temperature measurement range provided in this embodiment is as follows: After power-on, the reference circuit 1 provides a reference current I REF for the voltage generation circuit 2, thereby generating a voltage with a negative temperature coefficient V BE , and at the same time provides a reference voltage V REF for the second voltage-controlled oscillator 6 and the amplifier circuit 3. Thus, the second voltage-controlled oscillator 6 generates a clock signal T_con for the counter; the amplifier circuit 3 compares the V BE signal with the V REF signal, amplifies the change amount of the V BE signal by A times, and the output voltage is V amp , which is used as the control voltage of the first voltage-controlled oscillator 4. The output of the first voltage-controlled oscillator 4 is divided by the frequency divider 5 to generate an enable signal T_TEM for the counter 7; when T_TEM becomes high level, the counter 7 starts to count T_con , and when T_TEM becomes low level, the counter 7 stops counting, and outputs the count value N. Then, N at this time is the value of the temperature.

[0065] In this embodiment, the first voltage-controlled oscillator 4 and the second voltage-controlled oscillator 6 have the same structure, which mainly includes a comparator, a cascaded inverter, a charge and discharge circuit, etc. The detailed circuit diagram can refer to the existing related technologies, and this embodiment will not introduce it here.

[0066] Thus, the period of the oscillator output signal is approximately:

[0067] (1)

[0068] Among them, C represents the charging capacitor in the oscillator, V represents the input voltage of the oscillator,I Represents the charging current of the capacitor.

[0069] Then the enable signal T_tem and the clock signal T_con The periods of can be expressed as:

[0070] (2)

[0071] (3)

[0072] The output of the counter is:

[0073] (4)

[0074] Wherein, C 1 and C 2 are the capacitance values of the charging capacitors in the first voltage-controlled oscillator and the second voltage-controlled oscillator respectively, n is the number of 2-divider dividers.

[0075] Here, it can be considered that V REF has a very small temperature coefficient and is approximately independent of temperature change. V amp is the temperature-related amplified voltage, and its first derivative satisfies:

[0076] (5)

[0077] Wherein, A is the amplification factor of the amplifier circuit, V BE is the reference voltage output by the temperature-related voltage generation circuit, and its value is the base-emitter voltage difference of the PNP transistor, and its expression is:

[0078] (6)

[0079] Wherein, V T represents the thermal voltage, I C represents the collector current, I S represents the saturation current.

[0080] It can be seen that the counter output value is inversely proportional to the reference voltage V BE , and the other parameters are regarded as independent of temperature. In addition, the counter output value is independent of both the power supply and the reference current changes.

[0081] Taking the derivative of the output value N with respect to temperature can obtain the output temperature coefficient of the temperature sensor, and its expression is:

[0082] (7)

[0083] Assume V REF is 666 mV, n is 12, C 1 = C 2, and V BE The temperature coefficient of is basically constant, about -1.9 mV / °C. Substituting it into equation (7), we can get:

[0084] (8)

[0085] Therefore, to make the measurement resolution of the temperature sensor 0.1 °C, it only needs to satisfy that the resistance value of resistor R2 is 1.71 times that of resistor R1, that is, the amplification factor of the amplifier A = 1.71. In this embodiment, it is rounded up to A = 2.

[0086] It can be understood that if a higher precision is desired for the temperature detection circuit, only the amplification factor of the amplifier needs to be changed, that is, the value of the output N of the counter changes with temperature increases to distinguish smaller temperature changes and increase the temperature measurement accuracy.

[0087] It can be seen that the temperature detection circuit with adjustable temperature measurement range provided in this embodiment adjusts the ratio of resistor R2 to resistor R1 in the amplification circuit to adjust the amplification factor of the amplification circuit, so that the measurement resolution of the temperature sensor can be flexibly changed, and the measurement requirements in various environments can be met.

[0088] Of course, if high-precision measurement is desired in other temperature ranges (non-body temperature range segments), the V REF voltage generated by adjusting the reference circuit can also be used to detect this temperature range under the condition of the same precision to meet the needs of different environments, greatly improving the application flexibility of the temperature sensor.

[0089] The present invention can increase the temperature coefficient by adding an amplification circuit to the existing temperature measurement circuit, thereby improving the resolution accuracy and measurement accuracy; at the same time, the present invention can also flexibly change the measurement range by changing the reference voltage of the reference circuit, and has the advantages of low power consumption, high integration, and insensitivity to process deviations, and can meet the high-precision measurement requirements of various temperature ranges.

[0090] Furthermore, since the amplifier circuit is added in the present invention, the resolution accuracy can be improved without increasing the frequency division ratio, or a certain frequency division ratio can be reduced to achieve the same resolution accuracy. This method can greatly reduce the temperature sampling time and can be applied to some specific environments with requirements for speed. Compared with the method of improving the resolution by increasing the frequency division ratio or the oscillator frequency, the present invention is less affected by the cycle jitter of the voltage-controlled oscillator or the quantization output caused by the digital noise of the frequency divider and counter, reducing the fluctuation of the quantization output.

[0091] In addition, the temperature detection circuit provided by the present invention is designed with low power consumption, and the current consumed by it can be ignored in terms of the temperature rise generated by the chip, reducing the influence of its own circuit on the test of the temperature sensing circuit.

[0092] Embodiment 2

[0093] Based on the above embodiment, this embodiment provides a passive sensing tag. Please refer to Figure 3 , Figure 3 which is a schematic structural diagram of the passive sensing tag provided by the embodiment of the present invention. Among them, the passive sensing tag is integrated with a temperature detection circuit and a baseband, and the temperature detection circuit is the temperature detection circuit with adjustable temperature measurement range provided in the above Embodiment 1.

[0094] After receiving the instruction sent by the reader, the temperature detection circuit performs temperature detection;

[0095] The baseband calibrates the measurement result of the temperature detection circuit to improve the detection accuracy.

[0096] Since the temperature coefficient ∂N / ∂T of the circuit of the present invention changes very little and the linearity of the output N is very good, a single-point calibration method can be adopted to make the measurement accuracy of the circuit less than 0.1 °C, meeting the accuracy required for temperature measurement.

[0097] When adopting the single-point calibration method, it can be assumed that at temperature T0, the output count value of the temperature sensor is N0. If the output digital quantity of the designed temperature sensor represents 0.1 °C per word and the output of the temperature sensor is N1, then the corresponding actual temperature at this time is:

[0098]

[0099] For the convenience of temperature calibration, a more appropriate temperature such as 37 °C is generally adopted. By sending an instruction to the tag through the reader, after being processed by the tag baseband, the processed data will be uploaded to the tag, and finally the terminal device performs operations and displays the specific temperature value finally detected.

[0100] Embodiment 3

[0101] The effects of the present invention can be further illustrated by the following simulation experiments:

[0102] 1. Simulation Conditions

[0103] The present invention adopts the TSMC 0.18μm process, with a power supply voltage of 1V. In the temperature range of 35°C to 42°C, simulation is carried out at every 0.1°C temperature under the TT process corner.

[0104] 2. Simulation Contents

[0105] 2.1) The present invention simulates the overall circuit at the TT process corner in the temperature range of 35°C to 42°C. The curve of the counter output N changing with temperature is as Figure 4 shown, and its curve slope is as Figure 5 shown. It can be seen from Figure 4 that the linearity of the counter output N with respect to temperature is very good, and it can be seen from Figure 5 that the accuracy of the simulation can reach 0.01°C, far exceeding the required 0.1°C accuracy of the body temperature sensor, reflecting the advantage that the present invention can flexibly adjust the temperature sensor accuracy by adjusting the amplification factor of the amplifier.

[0106] 2.2) The present invention simulates the overall circuit at the TT process corner in the temperature range of 35°C to 42°C. The curve of the overall circuit power consumption changing with temperature is as Figure 6 shown. It can be seen from Figure 6 that the circuit power consumption is small, being 1.89 μW.

[0107] 2.3) The present invention simulates the overall circuit at the TT process corner in the temperature range of 35°C to 42°C. The comparison diagram of the fitted curve and the actual temperature measurement curve after single-point calibration is as Figure 7 shown. Figure 7 It can be seen that there will be errors between the two curves at both ends. Through Figure 7 it can be seen that at the temperature edges at both ends, the maximum error is ΔN = 5.

[0108] 2.4) The present invention simulates the overall circuit at the TT process corner in the temperature range of 35°C to 42°C. The quantization error curve of the output values of the fitted curve and the actual temperature measurement curve after single-point calibration is as Figure 8 shown. Figure 8 It can be seen that in the entire temperature measurement range, the maximum difference between the two curves is 5, having a very small quantization output error.

[0109] 2.5) The present invention simulates the overall circuit at the TT process corner in the temperature range of 35°C to 42°C. The temperature quantization error curve of the fitted curve and the actual temperature measurement curve after single-point calibration is as Figure 9As shown, it can be seen that in the entire temperature measurement range, the actual temperature error precision of the two curves is less than 0.05 °C, that is, the resolution of the circuit is 0.01 degrees Celsius and the error precision is 0.05 °C, indicating that the body temperature sensor of the present invention has a quite high temperature measurement precision.

[0110] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A temperature detection circuit with adjustable temperature measurement range, characterized in that Comprising: A reference circuit (1) for providing a reference current and a reference voltage; V BE A voltage generation circuit (2), connected to the reference circuit (1), for generating a temperature-related reference voltage; An amplifier circuit (3) connected to the reference circuit (1) and the voltage generation circuit (2), for comparing and amplifying the reference voltage and the reference voltage, and generating an amplified voltage signal; the amplifier circuit (3) includes a first operational amplifier A1, a first resistor R1, a second operational amplifier A2, and a second resistor R2, wherein, The positive input terminal of the first operational amplifier A1 is connected to the output terminal of the voltage generation circuit (2), the negative input terminal of the first operational amplifier A1 is connected to the output terminal, and is connected to the negative input terminal of the second operational amplifier A2 through the first resistor R1; The positive input terminal of the second operational amplifier A2 is connected to the output terminal of the reference circuit (1), and the output terminal of the second operational amplifier A2 is connected to its negative input terminal through the second resistor R2; The output terminal of the second operational amplifier A2 also serves as the output terminal of the entire amplifier circuit (3) to output an amplified voltage signal; the first operational amplifier A1 is used to form a unity-gain buffer with a gain of 1, and its positive terminal is connected to the temperature reference voltage V BE , and its negative terminal is connected to the output terminal; the positive terminal of the second operational amplifier A2 is connected to the reference voltage V REF , and it forms an inverting amplifier with the first resistor R1 and the second resistor R2; A first voltage-controlled oscillator (4) connected to the amplifier circuit (3) for converting the amplified voltage signal into a periodic signal; A frequency divider (5) connected to the first voltage-controlled oscillator (4) for frequency-dividing the periodic signal to obtain an enable signal; A second voltage-controlled oscillator (6) connected to the reference circuit (1) for generating a clock signal; A counter (7) connected to the frequency divider (5) and the second voltage-controlled oscillator (6) for counting the clock signal according to the enable signal and outputting a temperature value.

2. The temperature detection circuit with adjustable temperature measurement range according to claim 1, wherein The first voltage-controlled oscillator (4) and the second voltage-controlled oscillator (6) have the same structure.

3. A passive sensing tag, characterized in that, The passive sensing tag is integrated with a temperature detection circuit and a baseband, and the temperature detection circuit is the temperature detection circuit with adjustable temperature measurement range according to any one of claims 1-2; After receiving the instruction sent by the reader, the temperature detection circuit performs temperature detection; The baseband calibrates the measurement result of the temperature detection circuit to improve the detection accuracy.

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