A non-contact card chip automatic temperature protection circuit

Abstract

The present invention provides a non-contact card chip automatic temperature protection circuit. The non-contact card chip automatic temperature protection circuit includes a temperature detection circuit and a resonance circuit. Among them, the temperature detection circuit includes a temperature detection module and a voltage conversion module; the resonance circuit is composed of a variable capacitor in parallel with a resonant capacitor and a parallel antenna; since a variable capacitor is added to the resonance circuit, after the output voltage of the temperature detection circuit rises, the output voltage controls the capacitance value of the variable capacitor to increase, and the resonance frequency of the resonance circuit decreases; when the resonance frequency of the resonance circuit deviates from 13.56 MHz, the energy received by the non-contact card will decrease, and then the temperature of the non-contact card chip will drop. Therefore, this automatic temperature protection circuit can effectively protect the non-contact smart card chip exposed in a large field strength from being damaged by high temperature. Compared with traditional smart cards, it improves the field strength range applicable to the non-contact card chip and enhances the performance stability and use reliability of the non-contact card chip.

Description

Technical Field

[0001] The present invention relates to the technical field of contactless cards, and particularly to an automatic temperature protection circuit for a contactless card chip. Background Art

[0002] In the application of 13.56 MHz high-frequency smart cards, passive cards obtain energy from a card reader through inductive coupling. The amount of energy obtained directly determines the core performance of the card, such as the operating frequency and response time. The greater the energy, the better the card performance; the smaller the energy, the worse the card performance. In the design of smart card chips, usually more energy is obtained by adjusting the resonant frequency, improving the efficiency of the rectifier circuit, etc. However, too much energy will also cause certain damage to the chip.

[0003] See Figure 1 Shown in [figure reference] is a block diagram of a common analog front-end circuit for a contactless smart card chip, which mainly includes three parts: a resonant circuit, a rectifier circuit, and a limiting circuit. The resonant circuit couples the energy concentrated near 13.56 MHz emitted by the card reader into the card; the rectifier circuit converts the coupled AC power into usable DC power; and the limiting circuit bypasses the excess current Ipass and limits the rectified output voltage VRF to protect the chip safety.

[0004] In order to improve the energy acquisition efficiency, there are mainly two methods in the design of smart card chips: The first method is to adjust the frequency of the resonant circuit to be the same as that of the card reader, that is, to adjust the frequency of the resonant circuit to 13.56 MHz; the second method is to improve the rectification efficiency of the rectifier circuit. However, in the case of a very large emission field strength of the card reader, a card with a high energy acquisition efficiency will generate heat due to too much energy. As Figure 1 shown in [figure reference], in a large field strength, the excess energy will be bypassed by the limiting circuit in the form of current. Usually when the field strength is greater than 7 A / m, the bypass current Ipass may reach more than 60 mA, and the card will heat up due to excessive power.

[0005] Too high a temperature will reduce the working performance and reliability of the card chip, and even damage the package of the card. Therefore, how to avoid the heating phenomenon under strong fields while improving the energy acquisition efficiency of the card has become one of the difficulties in the design of smart card chips. Summary of the Invention

[0006] In view of the deficiencies in the above-mentioned existing technologies, the objective of the present invention is to provide a non-contact card chip automatic temperature protection circuit, which includes a temperature detection circuit and a resonance circuit. Among them, a variable capacitor is added to the resonance circuit. After the output voltage of the temperature detection circuit rises, the output voltage controls the capacitance value of the variable capacitor to increase, and the resonance frequency of the resonance circuit decreases; when the resonance frequency of the resonance circuit deviates from 13.56 MHz, the energy received by the non-contact card will decrease, and the temperature of the non-contact card chip will drop, thereby achieving the purpose of protecting the chip.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A non-contact card chip automatic temperature protection circuit, the non-contact card chip automatic temperature protection circuit includes a temperature detection circuit and a resonance circuit. Among them, the temperature detection circuit includes a temperature detection module and a voltage conversion module; the resonance circuit is composed of a variable capacitor in parallel with a resonance capacitor and a parallel antenna;

[0009] The temperature detection module includes a first resistor, a second resistor, a third resistor, a fourth resistor, and a first triode. The first resistor is connected to the second resistor, the second resistor is connected to the third resistor, the third resistor is connected to the first triode, the first triode is connected to the fourth resistor, and the fourth resistor is connected to the first resistor;

[0010] The voltage conversion module includes a first NMOS transistor, a second NMOS transistor, a first PMOS transistor, a second PMOS transistor, a third PMOS transistor, a fifth resistor, a current source IB, and a reference voltage VREF. Among them, the total current flowing through the first PMOS transistor and the second PMOS transistor is the current source IB. The gate terminal of the first NMOS transistor is connected to the chip voltage signal Vtemp at the output terminal of the temperature detection module, the gate terminal of the second NMOS transistor is connected to the reference voltage VREF, and the ratio of the first PMOS transistor, the second PMOS transistor, and the third PMOS transistor is 1:1:1;

[0011] The voltage conversion module converts the chip temperature voltage signal into a control signal, and the variable capacitor in the resonance circuit is connected to the control signal at the output terminal of the temperature detection circuit.

[0012] Due to the circuit structure of the temperature detection circuit and the resonance circuit adopted by the non-contact card chip automatic temperature protection circuit of the present invention, and a variable capacitor is added to the resonance circuit, the beneficial effects obtained are that this automatic temperature protection circuit can effectively protect the non-contact smart card chip exposed to a large field strength from being damaged by high temperature. Compared with traditional smart cards, the field strength range applicable to the non-contact card chip is increased, and the performance stability and use reliability of the non-contact card chip are enhanced. Description of the Drawings

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0014] Figure 1 is a block diagram of an analog front-end circuit of an existing non-contact card chip.

[0015] Figure 2 is a block diagram of an analog front-end circuit of an automatic temperature protection circuit for a non-contact card chip according to a specific embodiment of the present invention.

[0016] Figure 3 is the automatic temperature protection circuit diagram of a non-contact card chip according to a specific embodiment of the present invention.

[0017] Figure 4 is a graph showing the relationship between the voltage value of the control signal VC and the temperature according to a specific embodiment of the present invention.

[0018] Figure 5 is a graph showing the relationship between the capacitance value of the variable capacitor Cvar and the voltage value of the control signal VC according to a specific embodiment of the present invention.

[0019] Figure 6 is a graph showing the relationship between the capacitance value of the variable capacitor Cvar and the temperature according to a specific embodiment of the present invention.

[0020] Figure 7 is the resonance frequency f osc of the specific embodiment of the present invention versus temperature graph. Specific Embodiments

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0022] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0023] Refer to Figure 2 , which is a block diagram of an analog front-end circuit of an automatic temperature protection circuit according to a specific embodiment of the present invention. Figure 2In the specific embodiments shown, the automatic temperature protection circuit design scheme for the contactless card chip in the present invention is within the dashed box. The automatic temperature protection circuit for the contactless card chip includes a temperature detection circuit and a resonant circuit. Among them, the resonant circuit consists of a variable capacitor Cvar, a resonant capacitor Cant, and an antenna Lant connected in parallel; the temperature detection circuit is powered by the system voltage VDD, monitors the chip temperature in real time, and generates a control signal VC. The variable capacitor Cvar in the resonant circuit is controlled by the control signal VC. When the voltage of the control signal VC rises, the capacitance value of the variable capacitor Cvar increases; when the voltage of the control signal VC decreases, the capacitance value of the variable capacitor Cvar decreases.

[0024] In the specific embodiments of the present invention, the resonant frequency of the card antenna network LC f osc is as follows:

[0025] f osc = (1)

[0026] When the contactless card chip is operating normally, the antenna Lant, the resonant capacitor Cant, and the variable capacitor Cvar resonate in the optimal state at a frequency of 13.56 MHz, and the contactless card obtains the maximum energy. When the energy is too large and the temperature of the contactless card chip exceeds a certain threshold and continues to rise, the voltage of the control signal VC output by the temperature detection circuit rises. The control signal VC controls the capacitance value of the variable capacitor Cvar to increase, and the resonant frequency of the card antenna network LC decreases. When the resonant frequency deviates from the resonant frequency of 13.56 MHz, the energy received by the contactless card will decrease, and the temperature of the contactless card chip will drop, thus achieving the purpose of protecting the chip.

[0027] See Figure 3 , the automatic temperature protection circuit diagram for the contactless card chip in the specific embodiments of the present invention. The automatic temperature protection circuit for the contactless card chip includes a temperature detection circuit and a resonant circuit. Among them, the temperature detection circuit includes a temperature detection module and a voltage conversion module; the resonant circuit consists of a variable capacitor Cvar, a resonant capacitor Cant, and an antenna Lant connected in parallel; the temperature detection module converts the chip temperature into a chip temperature voltage signal Vtemp, and the voltage conversion module is connected to the output end of the temperature detection module and converts the chip temperature voltage signal Vtemp into a control signal VC suitable for the variable capacitor Cvar to use; the variable capacitor Cvar is connected to the output end of the temperature detection circuit and is controlled by the control signal VC to change the capacitance value of the variable capacitor Cvar, thereby changing the resonant frequency of the resonant circuit.

[0028] See Figure 3, in this specific embodiment, the temperature detection module includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a first triode Q1. The first resistor R1 is connected to the second resistor R2, the second resistor R2 is connected to the third resistor R3, the third resistor R3 is connected to the first triode Q1, the first triode Q1 is connected to the fourth resistor R4, and the fourth resistor R4 is connected to the first resistor R1. Among them, the system power supply VDD = 1.5V; the first resistor R1 = 40Kohm, the second resistor R2 = 60Kohm, the third resistor R3 = 2Kohm, and the fourth resistor R4 = 5Kohm are set. At room temperature, the voltage difference VBE between the base and the emitter of the first triode Q1 is 0.7V. Then, the voltage of the chip temperature voltage signal Vtemp of the temperature detection module is calculated as follows:

[0029] Vtemp = VDD - [VDD * (R1 / (R1 + R2) - VBE] / R3 * R4 (2)

[0030] It can be obtained that Vtemp = 1.0V at room temperature. From the temperature characteristics of the triode, it can be known that the VBE voltage value is inversely proportional to the temperature, that is, the higher the temperature, the smaller the VBE voltage value; the lower the temperature, the higher the VBE voltage value.

[0031] According to formula (2), the voltage value of the chip temperature voltage signal Vtemp is directly proportional to the VBE voltage value. It can be known that the voltage value of the chip temperature voltage signal Vtemp is inversely proportional to the temperature, that is, the higher the temperature, the smaller the voltage value of the chip temperature voltage signal Vtemp; the lower the temperature, the larger the voltage value of the chip temperature voltage signal Vtemp. Usually, within the temperature change range of 27 to 100 degrees, the output voltage value range of the chip temperature voltage signal Vtemp is 1.0V to 0.4V.

[0032] See Figure 3, in this specific embodiment, the voltage conversion module includes a first NMOS transistor MN1, a second NMOS transistor MN2, a first PMOS transistor MP1, a second PMOS transistor MP2, a third PMOS transistor MP3, a fifth resistor R5, a current source IB, and a reference voltage VREF, where VREF is set to 0.7V; the ratio of the first PMOS transistor MP1, the second PMOS transistor MP2, and the third PMOS transistor MP3 is 1:1:1; the total current flowing through the first PMOS transistor and the second PMOS transistor is the current source IB, IB = 100uA, and R5 = 7Kohm; the gate terminal of the first NMOS transistor MN1 is connected to the chip voltage signal Vtemp at the output terminal of the temperature detection module, and the gate terminal of the second NMOS transistor MN2 is connected to the reference voltage VREF; when the voltage value of the chip voltage signal Vtemp rises, according to the characteristics of the differential circuit composed of the first NMOS transistor MN1 and the second NMOS transistor MN2, the current in the first PMOS transistor MP1 increases, the current in the second PMOS transistor MP2 decreases, and the output current of the third PMOS transistor MP3 decreases, thereby controlling the voltage value of the signal VC to decrease; conversely, when the voltage value of the chip voltage signal Vtemp decreases, the voltage value of the control signal VC increases. In the range of normal temperature from 27 to 100 degrees, the voltage value of the chip voltage signal Vtemp decreases from 1.0V to 0.4V, and the voltage value of the control signal VC increases from 0V to 0.7V.

[0033] In summary, the characteristics of the temperature detection circuit are obtained as follows: when the temperature rises from 27 degrees to 100 degrees, the voltage value of the control signal VC output by the temperature detection circuit rises from 0V to 0.7V, as Figure 4 shown.

[0034] The variable capacitor Cvar is controlled by the control signal VC, and the capacitance value of the variable capacitor Cvar is affected by the voltage value of the control signal VC. When the voltage value of the control signal VC is less than 250mV, the capacitance value of the variable capacitor Cvar is small. When the voltage value of the control signal VC is greater than 250mV, the capacitance value of the variable capacitor Cvar rises relatively fast, as Figure 5 shown.

[0035] According to Figure 4 and Figure 5 the relationship between the capacitance value of the variable capacitor Cvar and the temperature can be obtained, as Figure 6 shown.

[0036] When the temperature is less than 60 degrees, the capacitance value of the variable capacitor Cvar is less than 0.01pF. When the temperature is greater than 60 degrees, the variable capacitor Cvar gradually rises with the temperature. According to the resonance frequency formula (1) of the card antenna network LC, the relationship between the resonance frequency fosc and the temperature change can be obtained, as Figure 7 shown.

[0037] When the temperature is less than 60 degrees, the LC resonance of the card antenna network is around 13.56 MHz. When the temperature is greater than 60 degrees, the resonance frequency fosc gradually decreases with the temperature. And the more the resonance frequency deviates from 13.56 MHz, the lower the energy coupled by the card from the card reader. Therefore, once the card temperature is greater than 60 degrees, the energy coupled by the card automatically decreases, then Figure 2 the bypass current Ipass in Figure 2 decreases, and the chip power decreases, thus achieving the purpose of reducing the temperature and protecting the chip.

[0038] Actual measurements show that for the card adopting the present invention in a strong magnetic field greater than 7 A / m, the bypass current Ipass can always be less than 40 mA, and the card temperature is maintained below 60 degrees, greatly improving the magnetic field range applicable to the card and enhancing the performance stability and reliability of the card.

[0039] The above has introduced in detail a non-contact card chip automatic temperature protection circuit provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

[0040] It should be noted that the embodiments in this specification are all described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0041] It also should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements but also other elements inherent to these process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0042] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An automatic temperature protection circuit for a contactless card chip, characterized in that The non-contact card chip automatic temperature protection circuit includes a temperature detection circuit and a resonance circuit. The output end of the temperature detection circuit is connected to the resonance circuit. The temperature detection circuit includes a temperature detection module and a voltage conversion module. The temperature detection module is used to detect the chip temperature and convert the temperature into a chip temperature voltage signal. The chip temperature voltage signal is inversely proportional to the temperature. The output end of the temperature detection module is connected to the voltage conversion module. The voltage conversion module is used to convert the chip temperature voltage signal into a control signal. The voltage value of the control signal is inversely proportional to the chip temperature voltage signal. The resonance circuit includes an antenna, a resonance capacitor, and a variable capacitor connected in parallel. The variable capacitor is connected to the control signal at the output end of the temperature detection circuit. The voltage value of the control signal is used to control the capacitance value of the variable capacitor to adjust the resonance frequency of the resonance circuit.

2. The non-contact card chip automatic temperature protection circuit according to claim 1, wherein The temperature detection module includes a first resistor, a second resistor, a third resistor, a fourth resistor, and a first triode. The first resistor is connected to the second resistor, the second resistor is connected to the third resistor, the third resistor is connected to the first triode, the first triode is connected to the fourth resistor, and the fourth resistor is connected to the first resistor.

3. The non-contact card chip automatic temperature protection circuit according to claim 2, wherein The voltage conversion module includes a first NMOS transistor, a second NMOS transistor, a first PMOS transistor, a second PMOS transistor, a third PMOS transistor, and a fifth resistor. The gate terminal of the first NMOS transistor is connected to the chip temperature voltage signal at the output end of the temperature detection module. The gate terminal of the second NMOS transistor is connected to a reference voltage. The first NMOS transistor and the first PMOS transistor are connected in series. The second NMOS transistor and the second PMOS transistor are connected in series. The source terminal of the first PMOS transistor is connected to the fourth resistor. The source terminal of the second PMOS transistor is connected to the source terminal of the third PMOS transistor. The drain terminal of the third PMOS transistor is connected to the fifth resistor.

4. The non-contact card chip automatic temperature protection circuit according to claim 3, characterized in that, The ratio among the first PMOS transistor, the second PMOS transistor, and the third PMOS transistor is 1:1:

1.

5. The non-contact card chip automatic temperature protection circuit according to claim 1, wherein the capacitance value of the variable capacitor is inversely proportional to the resonance frequency of the resonance circuit, characterized in that, When the temperature is less than the preset temperature, the resonance frequency of the resonance circuit is within the preset frequency range. When the temperature is greater than the preset temperature, the resonance frequency of the resonance circuit exceeds the preset frequency range to reduce the chip temperature.

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