WO2022140957A1

WO2022140957A1 - Nfc device

Info

Publication number: WO2022140957A1
Application number: PCT/CN2020/140305
Authority: WO
Inventors: 袁广凯
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2022-07-07
Also published as: CN114097180A; CN114097180B

Abstract

Provided is an NFC device. The NFC device comprises a filtering circuit, a matching circuit, data-receiving branches, an NFC controller and an NFC antenna, and further comprises a self-capacitance measurement module, wherein a capacitance measurement end of the self-capacitance measurement module is connected to a positive phase end or a reverse phase end of the NFC antenna, and the self-capacitance measurement module is used for measuring the amount of capacitance change of the NFC antenna. The NFC device of the present application can implement the detection of a target device by using relatively little power consumption.

Description

an NFC device

technical field

The present application relates to the field of NFC communication, in particular to an NFC device.

Background technique

When a near field communication (Near Field Communication, NFC) device is used as an initiator device in NFC communication, it needs to detect the target device based on the NFC antenna, and the target device here is also an NFC device. The current detection method is: set an impedance detection module in the NFC controller (NFC controller, NFCC) of the NFC device, and send a polling signal with a duration of tens of microseconds through the TXP port and TXN port of the NFC controller to detect the TXP The impedance changes between the port and the TXN port. If the impedance change reaches a preset threshold, it is determined that there is a target device in the environment.

However, this target device detection method makes the power consumption of the NFC device relatively large.

SUMMARY OF THE INVENTION

The present application provides an NFC device, which can realize the detection of a target device by the NFC device with relatively small power consumption.

In a first aspect, an embodiment of the present application provides a near field communication NFC device, the NFC device includes: an NFC antenna, a filter circuit for performing signal filtering, a matching circuit for performing impedance matching of the NFC antenna, for A data receiving branch for transmitting data signals received by the NFC antenna, an NFC controller for controlling signal transmission and reception, and the NFC device further comprising: a self-capacitance detection module, wherein the capacitance of the self-capacitance detection module The detection terminal is connected to the positive phase terminal or the reverse phase terminal of the NFC antenna, and the self-capacitance detection module is used to detect the capacitance change of the NFC antenna, and the capacitance change is used to determine whether a target device is close to the NFC antenna.

The NFC device detects the target device by detecting the capacitance change of the NFC antenna by the self-capacitance detection module. Moreover, compared with the prior art, the impedance detection module performs the target device detection and the sending duration each time is tens of microseconds. In the way of polling signal, the self-capacitance detection module has relatively less power consumption.

In a possible implementation manner, the capacitance detection end of the self-capacitance detection module is connected to the non-phase end or the inversion end of the NFC antenna through the matching circuit.

In a possible implementation manner, the capacitance detection end of the self-capacitance detection module is connected to the non-phase end or the inversion end of the NFC antenna through the data receiving branch.

In a possible implementation manner, the capacitance detection end of the self-capacitance detection module is sequentially connected to the non-phase end or the inversion end of the NFC antenna through the data receiving branch and the matching circuit.

In a possible implementation manner, the self-capacitance detection module is located in the NFC controller.

In a possible implementation manner, the capacitance detection end of the self-capacitance detection module is connected to the first end of the first switch, and the second end of the first switch is connected to the non-inverting end or the inverting end of the NFC antenna , the first switch is configured to be turned on when the self-capacitance detection module is working, and turned off when the self-capacitance detection module is not working.

In a possible implementation manner, the NFC device includes a matching circuit and a filter circuit of the NFC antenna, and the ground terminal of the capacitor included in the matching circuit and the filter circuit is grounded through a fourth switch, and the The fourth switch is used to turn off when the self-capacitance detection module works.

In a possible implementation, the self-capacitance detection module includes:

The capacitance detection terminal of the self-capacitance detection module is connected to the power supply voltage terminal through the seventh switch, grounded through the eighth switch, connected to the non-inverting input terminal of the differential amplifier through the ninth switch, and connected to the first terminal of the ninth capacitor through the tenth switch , the second end of the ninth capacitor is grounded;

The first terminal of the ninth capacitor is also connected to the power supply voltage terminal through the eleventh switch, and is grounded through the twelfth switch;

The inverting input terminal of the differential amplifier is connected to the common-mode voltage terminal, and the first output terminal and the second output terminal are used for outputting voltage, and the output voltage is associated with the capacitance change of the NFC antenna;

The non-inverting input terminal of the differential amplifier is also connected to the first output terminal of the differential amplifier through a third resistor, or a tenth capacitor, or a third resistor and a tenth capacitor connected in parallel, and the inverting input terminal is connected through a fourth resistor, Either the eleventh capacitor, or the fourth resistor and the eleventh capacitor connected in parallel are connected to the second output end of the differential amplifier.

In a possible implementation manner, the capacitance value of the ninth capacitor is equal to the first equivalent capacitance value, and the first equivalent capacitance value is an external capacitance of the self-capacitance detection module when no target device approaches the NFC antenna The equivalent capacitance value of the circuit between the capacitance detection terminal and the power supply ground terminal, the voltage of the common mode voltage terminal is 1/2 of the power supply voltage.

In a possible implementation manner, the self-capacitance detection module is specifically configured to: generate a voltage signal based on the capacitance change of the NFC antenna; the NFC device further includes: a judgment module, the input end of which is connected to The output end of the self-capacitance detection module, the judgment module is used to judge whether the amplitude of the first signal output by the self-capacitance detection module exceeds a preset threshold, and if so, judge that a target device is close to the NFC antenna, Otherwise, it is judged that no target device is close to the NFC antenna.

In a possible implementation manner, the NFC controller is configured to determine whether a target device is close to the NFC antenna according to the capacitance change.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a schematic structural diagram of an example of an NFC device;

2 is a schematic diagram of a detection process in a prior art impedance detection method;

FIG. 3 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 4 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 5 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 6 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 7 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 8 is an equivalent circuit diagram of the structure of the NFC device shown in FIG. 7 of the application;

FIG. 9 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 10 is an equivalent circuit diagram of the structure of the NFC device shown in FIG. 9 of the application;

FIG. 11 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 12 is a schematic structural diagram of an embodiment of an NFC device of the present application;

FIG. 13 is an equivalent circuit diagram of the structure of the NFC device shown in FIG. 12 of the application;

14 is a schematic structural diagram of an embodiment of the self-capacitance detection module of the present application;

FIG. 15 is a working timing diagram of the self-capacitance detection circuit shown in FIG. 14 of the application;

FIG. 16 is a schematic structural diagram of an embodiment of an NFC device of the present application.

Detailed ways

The terms used in the embodiments of the present application are only used to explain specific embodiments of the present application, and are not intended to limit the present application.

Generally, the structure of an NFC device is shown in FIG. 1 , including: an NFCC, an NFC antenna, a matching module and a filtering module. The filtering module can be used to filter signals, the matching module can be used to match the impedance of the NFC antenna, and the NFCC can be used to control signal transmission and reception. The signals sent and received by the NFCC are generally signals related to the NFC communication protocol. The NFC communication protocol may be an NCI controller interface (NFC Controller Interface, NCI) or the like. The NFCC generally includes a data interaction module for acquiring the data signal received by the NFC antenna. The first end and the second end of the data interaction module can be respectively connected to the first receiving end RXP and the second receiving end RXN of the NFCC, and then connect the two ends of the NFC antenna through the first data transmission branch and the second data transmission branch respectively. , to obtain the data signal received by the NFC antenna.

Current target device detection is based on the phenomenon that the impedance of the NFC antenna changes when the target device approaches. Specifically, an impedance detection module is set in the NFCC, and the detection process of the impedance detection module includes two stages, as shown in Figure 2, the first stage is the polling phase (Polling Phase), in which the impedance detection module passes the The first output terminal TXP and the second output terminal TXN of the NFCC output polling signals, and the second phase is the listening phase, in which the impedance detection module detects the first output terminal TXP and the second output terminal TXN. The impedance change between the two, when the degree of impedance change exceeds the threshold, it is judged that the target device is detected. In the polling stage, the duration of the polling signal sent by the impedance detection module is tens of microseconds. The polling signal is composed of five types: NFC-ACM, NFC-A, NFC-B, NFC-F and NFC-V. Which types of polling signals are used in actual use can be independently selected. The more types of polling signals are selected, the longer the duration of the polling signals and the more types of NFC target devices that can be detected. For example, three types of polling signals, NFC-A, NFC-B, and NFC-F, are selected in Figure 2. If more types of polling signals are selected, the duration of the polling signal will be longer, and the duration of the polling signal will be longer. The longer the duration is, the more average current the NFCC needs in the detection process, the more power it consumes, and the greater the power consumption of the NFC device.

To this end, the present application proposes an NFC device, which can realize the detection of a target device by the NFC device through relatively small power consumption.

The inventor found that when other NFC devices are close to the NFC antenna in the NFC device, the capacitance of the NFC antenna will increase. Based on this phenomenon, the NFC device in the embodiment of the present application detects the target device by detecting the change in the capacitance of the NFC antenna. Specifically, a self-capacitance detection module for detecting the capacitance change of the NFC antenna is provided in the NFC device, and the capacitance detection end of the self-capacitance detection module is connected to the positive-phase terminal or the reverse-phase terminal of the NFC antenna.

The implementation of the NFC device of the present application will be exemplarily described below through embodiments.

FIG. 3 is a schematic structural diagram of an embodiment of the NFC device of the present application. As shown in FIG. 3 , the NFC device includes: an NFC antenna 21 , a self-capacitance detection module 22 , an NFCC 23 , a matching module 24 , and a filtering module 25 .

The first output terminal TXP and the second output terminal TXN of the NFCC23 are respectively connected to the first terminal P251 and the second terminal P252 of the filtering module 25 respectively, and the third terminal P253 and the fourth terminal P254 of the filtering module 25 are correspondingly connected to the first terminal P251 and the fourth terminal P254 of the matching module 24. One end P241 and the second end P242, the third end P243 of the matching module 24 is connected to the non-inverting end N1 of the NFC antenna 21, and the fourth end P244 of the matching module 24 is connected to the inverting end N2 of the NFC antenna 21;

The first end of the data exchange module 211 in the NFCC23 is connected to the non-inverting end N1 of the NFC antenna 21 through the first receiving end RXP of the NFCC23 and the first data receiving branch in sequence, and the second end of the data exchange module 211 passes through the NFCC23 in turn. The second receiving end RXN and the second data receiving branch 27 are connected to the inverting end N2 of the NFC antenna 21 .

In FIG. 3 , the capacitance detection terminal P1 of the self-capacitance detection module 22 is directly connected to the non-inverting terminal N1 of the NFC antenna 21 to detect the capacitance change in the NFC antenna 21 .

Different from the capacitance detection terminal P1 of the self-capacitance detection module 22 in the NFC device shown in FIG. 3 is directly connected to the non-inverting terminal N1 of the NFC antenna 21, in another embodiment of the NFC device provided in this application, the self-capacitance detection module The capacitance detection terminal P1 of 22 can be directly connected to the inverting terminal N2 of the NFC antenna 21. At this time, the structure of the NFC device can refer to the NFC device shown in FIG. 3, the difference is only that the capacitance detection terminal P1 of the self-capacitance detection module 22 is directly connected. to the inverting terminal N2 of the NFC antenna.

Different from the capacitance detection terminal P1 of the self-capacitance detection module 22 in the NFC device shown in FIG. 3 is directly connected to the non-inverting terminal N1 of the NFC antenna 21, in another embodiment of the NFC device provided in this application, the self-capacitance detection module The capacitance detection terminal P1 of 22 is connected to the normal phase terminal N1 or the reverse phase terminal N2 of the NFC antenna 21 through the matching module 24 . Specifically, the capacitance detection terminal P1 of the self-capacitance detection module 22 may be connected to the first terminal P241 or the second terminal P242 of the matching module 24 . At this time, the structure of the NFC device can refer to the NFC device shown in FIG.

In the NFC device in the above embodiment, the self-capacitance detection module 22 is located outside the NFCC as an example. In another embodiment of the NFC device provided in this application, the self-capacitance detection module 22 in the above embodiment may be located in the NFCC 23, At this time, the capacitance detection terminal P1 of the self-capacitance detection module 22 can be connected to a pin of the NFCC 23, which is connected to the non-inverting terminal N1 of the NFC antenna 21, or to the inverting terminal N2 of the NFC antenna, or to The first end P241 of the matching module 24 is connected to the second end P242 of the matching module 24 .

Different from the capacitance detection terminal P1 of the self-capacitance detection module 22 in the NFC device shown in FIG. 3 is directly connected to the non-inverting terminal N1 of the NFC antenna 21 , in another embodiment of the NFC device provided in this application, see FIG. 4 . It is shown that the capacitance detection terminal P1 of the self-capacitance detection module 22 is connected to the non-inverting terminal N1 of the NFC antenna 21 through the first data receiving branch 26, and the self-capacitance detection module 22 is located outside the NFCC 23. The capacitance detection end P1 is connected to the first end of the first data receiving branch 26 , and the first end is the end where the first data receiving branch 26 is connected to the first data receiving end RXP of the NFCC 23 .

In another embodiment of the NFC device provided in this application, the capacitance detection terminal P1 of the self-capacitance detection module 22 is connected to the inverting terminal N2 of the NFC antenna 21 through the second data receiving branch 27, and the self-capacitance detection module 22 Located outside the NFCC23. At this time, the structure of the NFC device can refer to the NFC device shown in FIG. 4 , the difference is only that the capacitance detection end P1 of the self-capacitance detection module 22 is connected to the first end of the second data receiving branch 27 , and the first end is the first end of the second data receiving branch 27 . The data receiving branch 26 is connected to one end of the second data receiving end RXN of the NFCC 23 .

Different from the self-capacitance detection module 22 in the NFC device shown in FIG. 4 is located outside the NFCC23, in another embodiment of the NFC device provided by the present application, as shown in FIG. 5, the self-capacitance detection module 22 may be located in the NFCC23, The capacitance detection terminal P1 is connected to the first receiving terminal RXP of the NFCC23.

Different from the capacitance detection terminal P1 in the NFC device shown in FIG. 5 is connected to the first receiving terminal RXP of the NFCC23, in another embodiment of the NFC device provided in this application, the self-capacitance detection module 22 is located in the NFCC23, and the capacitance detection module 22 is located in the NFCC23. The terminal P1 is connected to the second receiving terminal RXN of the NFCC23. At this time, the NFC device structure can refer to the NFC device shown in FIG. 5, the difference is only that the capacitance detection terminal P1 is connected to the second receiving terminal RXN of the NFCC23.

For the NFC device in the above embodiment, when the self-capacitance detection module 22 detects that the capacitance of the NFC antenna 21 changes, that is, after detecting the target device, the data interaction module 211 in the NFCC 23 can obtain the data in the target device through the NFC antenna 21 . data, and turn off the self-capacitance detection module 22 at the same time. Specifically, a switch can be set at the capacitance detection terminal P1 of the self-capacitance detection module 22 to be turned on when the self-capacitance detection module 22 needs to detect the target device, so that the self-capacitance detection module 22 works, and the self-capacitance detection module 22 detects After reaching the target device, it is turned off, so that the self-capacitance detection module 22 suspends work, thereby reducing the influence or interference of the self-capacitance detection module 22 on the modules or circuits involved in NFC data interaction such as the data interaction module 211 in the NFC device.

Based on similar reasons, in order to prevent the signals output by other modules from affecting the work of the self-capacitance detection module 22, switches for controlling whether the modules work can also be provided for other modules, which are turned on when the corresponding modules need to work, so that the corresponding modules are turned on. The module is powered on and works, and is turned off when the corresponding module does not need to work, so that the corresponding module suspends work.

Taking the NFC device shown in FIG. 5 as an example, the capacitance detection module 22 and the data interaction module 211 can be respectively set with switches to control whether they work, as shown in FIG. 6 , which is different from the NFC device shown in FIG. A first switch K1 is set between the first input terminal RXP and the capacitance detection terminal P1 of the self-capacitance detection module 22 , and a second switch K2 is set between the first input terminal RXP of the NFCC 23 and the first terminal P1 of the data exchange module 211 , A third switch K3 is set between the second input terminal RXN of the NFCC23 and the second terminal P2 of the data interaction module 211; thus, when the target device detection needs to be performed, the NFC device can control the first switch K1 to be turned on and the second switch to be turned on. K2 and the third switch K3 are turned off, so that the data interaction module 211 suspends work, and the self-capacitance detection module 23 detects whether the capacitance of the NFC antenna 21 changes to detect the target device. Once the self-capacitance detection module 23 detects the target device, the NFC device can The first switch K1 is controlled to be turned off, and the second switch K2 and the third switch K3 are turned on, so that the self-capacitance detection module 23 suspends operation, and the data exchange module 211 reads the data in the target device through the NFC antenna 21 .

Among them, the matching module 24, the filter module 25 and other modules of the NFC device may be provided with capacitors. Therefore, for the self-capacitance detection module 22 in the above embodiment, when the self-capacitance detection module 22 is working, its capacitance detection terminal P1 and The equivalent circuit between the power ground terminals GND often includes not only the capacitance of the NFC antenna, but also the capacitors in the matching module 24 and the filter module 25, that is, the capacitance detection terminal P1 of the self-capacitance detection module 22 and the power supply ground. The equivalent capacitance of the external circuit between the terminals GND is not only the capacitance of the NFC antenna, because only the capacitance of the NFC antenna changes when the target device approaches The equivalent capacitance of the external circuit including the capacitance can still detect the change of the capacitance of the NFC antenna. However, if the capacitance values of the capacitors included in the matching module 24, the filtering module 25 and other modules are relatively large, and the capacitance change of the NFC antenna caused by the proximity of the target device is relatively small, then the matching module 24, the filtering module 25, etc. The capacitance included in the module will cause the detection accuracy of the self-capacitance detection module 22 to decrease with respect to the capacitance variation of the NFC antenna, that is, the detection accuracy of the NFC device with respect to the target device will decrease. For this reason, when the self-capacitance detection module 22 is working, for the capacitors whose one end is grounded in the matching module 24, the filter module 25 and other modules, the connection between the capacitor and the power ground terminal GND can be disconnected, thereby improving the self-capacitance. The detection accuracy of the detection module 22, however, there may be other modules in the NFC device that require the capacitor to be grounded to work properly. For this reason, in another embodiment of the NFC device provided in this application, if the circuit of the NFC device, for example The circuits of the matching module 24, the filter module 25 and other modules include capacitors with ground terminals. The ground terminal of the capacitor refers to the end of the capacitor connected to the power ground terminal GND. Then, it can be set between the ground terminal of the capacitor and the power ground terminal GND. The switch is used to turn off the self-capacitance detection module 22 when it is working, thereby turning off the connection between the ground terminal of the corresponding capacitor and the power supply ground terminal GND, thereby reducing the detection accuracy of the self-capacitance detection module 22 by the capacitance in the NFC circuit. Influence, the switch is also used to conduct when the self-capacitance detection module 22 is suspended and other modules in the NFC device are working, thereby conducting the connection between the corresponding capacitor and the power ground terminal GND, so that the ground terminal of the capacitor is grounded, So as to ensure the normal work of other modules.

For similar reasons, in order to reduce the influence of the capacitance in the NFC device circuit on the detection accuracy of the self-capacitance detection module and ensure the normal operation of other modules, the first output terminal TXP and the second output terminal TXN of the NFCC23 can also be set to ground through the switch respectively. , Correspondingly, when the self-capacitance detection module 22 is working, the NFC device controls the switches corresponding to the first output terminal TXP and the second output terminal TXN to turn off respectively, and the self-capacitance detection module 22 suspends work, and other modules such as the data interaction module 211 work. When the NFC device controls the switches corresponding to the first output terminal TXP and the second output terminal TXN to be turned on respectively, so as to ensure the normal operation of other modules.

The implementation principle of the above-mentioned embodiment is illustrated below through specific examples:

Referring to FIG. 7 , a possible circuit implementation structure of the matching module 24 , the filtering module 25 , the first data receiving branch 26 and the second data receiving branch 27 is given based on the embodiment shown in FIG. 6 , and for the convenience of description , the equivalent circuit structure of the NFC antenna 21 is given.

The matching module 24 is implemented by a symmetrical circuit structure. Specifically, the first terminal P241 of the matching module 24 is connected to the third terminal P243 through the first capacitor C1, the third terminal P243 is grounded through the second capacitor C2, and the second terminal P242 is connected through the third capacitor. C3 is connected to the fourth terminal P244, and the fourth terminal P244 is also grounded through a fourth capacitor C4, wherein the second capacitor C2 and the fourth capacitor C4 both have ground terminals, that is, one terminal is connected to the power supply ground terminal GND.

The filter module 25 is realized by a symmetrical circuit structure. The first end P251 is connected to the third end P253 through the first inductor L1, the third end P253 is also grounded through the fifth capacitor C5, and the second end P252 is connected to the fourth end P254 through the second inductor L2. , the fourth terminal P254 is also grounded through the sixth capacitor C6; the fifth capacitor C5 and the sixth capacitor C6 both have ground terminals.

The first data receiving branch 26 includes a first resistor R1 and a seventh capacitor C7 connected in series, and the second data receiving branch 27 includes a second resistor R2 and an eighth capacitor C8 connected in series.

The equivalent circuit structure of the NFC antenna 21 includes: the non-inverting terminal N1 of the NFC antenna 21 is grounded through the first parasitic capacitance Ca1, the inverting terminal N2 is grounded through the second parasitic capacitance Ca2, and the non-inverting terminal N1 is also grounded through the coil resistance Ra, the first parasitic capacitance Ca2, and the The coil inductance La1 and the second coil inductance La2 are connected to the inverting terminal N2, and the capacitance ΔC is the capacitance change of the NFC antenna when the target device approaches.

When the self-capacitance detection module 22 performs capacitance detection, the capacitance detection terminal P1 can output a driving signal to the external circuit, and then, according to the signal detected by the capacitance detection terminal P1, it can determine the external circuit between the capacitance detection terminal P1 and the power ground terminal GND. The amount of change in the equivalent capacitance of a circuit. Generally, the detection frequency of the self-capacitance detection module is between 10kHZ and 2MHZ. At this time, when the self-capacitance detection module 22 outputs a driving signal to the NFC antenna, the impedance of the NFC antenna is close to 0, that is, Ra is close to 0. It can be considered that When the self-capacitance detection module works, the coil of the NFC antenna is a wire, that is, the coil resistance Ra, the first coil inductance La1 and the second coil inductance La2 are equivalent to one wire; at this time, if the circuit shown in Figure 7 The first switch K1 is closed, the second switch K2 and the third switch K3 are open, and the equivalent circuit is shown in Figure 8, in which only the capacitance ΔC will change when the target device is close to the NFC antenna, so the self-capacitance detection module 22 By detecting the change in the equivalent capacitance of the external circuit between the capacitance detection terminal P1 of the self-capacitance detection module 22 and the power ground terminal GND, the detection of the target device can be realized. In FIG. 7, the external circuit is also the NFCC23 The external circuit between the first receiving terminal RXP and the power supply ground terminal GND, see Figure 8, the equivalent capacitance of the external circuit is the second capacitor C2, the first capacitor C1 and the fifth capacitor C5 connected in series, and the first parasitic capacitor Ca1 , and the parallel capacitance of the four branches of the capacitance ΔC.

In addition, in FIG. 8 , the seventh capacitor C7 is generally a DC blocking capacitor, and the capacitance value is generally much larger than the capacitance values of the first capacitor C1 to the sixth capacitor C6, so that the capacitance detection of the self-capacitance detection module 22 has little influence , however, the first capacitor C1, the fifth capacitor C5, and the second capacitor C2 connected in series will affect the capacitance detection of the self-capacitance detection module 22. Specifically, the equivalent capacitance of these two branches in parallel is assumed to be Ce1, Then the equivalent capacitance Ce1 is connected in parallel with the first parasitic capacitance Ca1 and the capacitance ΔC, so that the capacitance value detected by the self-capacitance detection module 22 becomes smaller, that is, the change in the detected capacitance value becomes smaller, which affects the self-capacitance detection module 22 . detection accuracy.

Therefore, different from the NFC device shown in FIG. 7 , a fourth switch K4 is set in the NFC device shown in FIG. 9 , and the second capacitor C2 , the fourth capacitor C4 , and the fifth capacitor are controlled by the switch state of the fourth switch K4 C5, whether the ground terminal of the sixth capacitor C6 is grounded. Specifically, when the self-capacitance detection module 22 is working, the fourth switch K4 can be controlled to be turned off. At this time, the equivalent circuit of the NFC device shown in FIG. 9 is shown in FIG. 10 , compared to the equivalent circuit shown in FIG. 8 . , the first capacitor C1 , the second capacitor C2 and the fifth capacitor C5 will not affect the capacitance variation detected by the self-capacitance detection module 22 , thereby improving the detection accuracy of the self-capacitance detection module 22 .

While ensuring the detection accuracy of the self-capacitance detection module 22, when the self-capacitance detection module 22 does not need to work and other modules work, for example, when the data exchange module 211 starts to work after the self-capacitance detection module 22 detects the target device, the first The four switches K4 are turned on to ensure the normal operation of the data interaction module 211 .

For similar reasons, in order to reduce the influence of the capacitance in the NFC device circuit on the detection accuracy of the self-capacitance detection module 22 and ensure the normal operation of other modules, as shown in FIG. 11, the first output terminal TXP and the second output terminal of the NFCC23 can also be set. The output terminal TXN is grounded through the fifth switch K5 and the sixth switch K6 respectively. Correspondingly, when the self-capacitance detection module 22 is working, the fifth switch K5 and the sixth switch K6 are turned off, and when the self-capacitance detection module 22 is suspended, the fifth switch K5 and the sixth switch K6 are turned off. The switch K5 and the sixth switch K6 are turned on. Optionally, as shown in FIG. 11 , the grounded branch of the fourth switch K4 may also be set inside the NFCC, so as to facilitate the control of the fourth switch K4. It should be noted that whether the fourth switch K4, the fifth switch K5, and the sixth switch K6 are turned on or off when the self-capacitance detection module 22 is working is related to the actual circuit structure of the NFC device, so as to reduce the parallel connection of the capacitance ΔC. Capacitance is the principle. For example, for the NFC device shown in FIG. 9 and FIG. 11, when the self-capacitance detection module 22 is working, if the fourth switch K4, the fifth switch K5, and the sixth switch K6 are disconnected, the detection of the self-capacitance detection module The accuracy has the smallest impact, but when the fourth switch K4, the fifth switch K5, and the sixth switch K6 are turned on, the self-capacitance detection module can still implement capacitance detection. However, for example, in the NFC device as shown in FIG. 12 , the capacitance detection end of the self-capacitance detection module 22 is connected to the first end P241 of the matching circuit 24 through the first data receiving branch 26 , and then connected to the positive phase of the NFC antenna 21 through the matching circuit. Terminal N1, at this time, the equivalent circuit of Figure 12 is shown in Figure 13. When the fourth switch K4, the fifth switch K5, and the sixth switch K6 are turned off, the capacitance in the circuit affects the detection accuracy of the self-capacitance detection module The minimum, it should be noted that the fifth switch K5 must be turned off to ensure that the self-capacitance detection module can realize the capacitance detection of the NFC antenna.

Optionally, the self-capacitance detection module 23 in the above embodiment can be implemented by, for example, the self-capacitance detection circuit shown in FIG. 14 , and the circuit structure includes:

The capacitance detection terminal P1 of the self-capacitance detection module 22 is connected to the power supply voltage terminal VCC through the seventh switch K7, grounded through the eighth switch K8, connected to the non-inverting input terminal of the differential amplifier A1 through the ninth switch K9, and connected through the tenth switch K10. The first end of the nine capacitors C9, the second end of the ninth capacitor C9 is grounded;

The first end of the ninth capacitor C9 is also connected to the power supply voltage terminal VCC through the eleventh switch K11, and is grounded through the twelfth switch K12;

The inverting input terminal of the differential amplifier A1 is connected to the common mode voltage terminal VCM, the first output terminal and the second output terminal are used for outputting the detected voltage, and the detected voltage is positively related to the capacitance of the NFC antenna.

The non-inverting input terminal of the differential amplifier A1 is also connected to the first output terminal of the differential amplifier A1 through the parallel third resistor R3 and the tenth capacitor C10, and the inverting input terminal is connected to the differential amplifier A1 through the parallel fourth resistor R4 and the eleventh capacitor C11. The second output of amplifier A1.

Optionally, the non-inverting input terminal of the differential amplifier A1 can also be connected to the first output terminal of the differential amplifier A1 only through the third resistor R3 or the tenth capacitor C10; the inverting input terminal of the differential amplifier A1 can also only pass through the fourth resistor. R4 or the eleventh capacitor C11 is connected to the second output terminal of the differential amplifier A1.

The self-capacitance detection circuit shown in Figure 14 is a self-capacitance detection scheme for charge transfer. The capacitance value of the ninth capacitor C9 in this circuit may be equal to the equivalent capacitance of the external circuit between the capacitance detection terminal P1 and the power ground terminal when no target device is approaching. For example, the equivalent capacitance of the external circuit in FIG. 10 is the first parasitic Capacitor Ca1, the voltage of the common mode voltage terminal VCM in this circuit can be Vcc/2.

FIG. 15 is an operation timing diagram of the self-capacitance detection circuit shown in FIG. 14 . In the operation timing diagram, the control switch is turned on when the control signal is at a high level, and the switch is controlled to be turned off when the control signal is at a low level. As shown in Figure 15, each working cycle Tcds of the circuit can be divided into six time periods: in the T1 time period, only the seventh switch K7 and the twelfth switch K12 are turned on, and the other switches are turned off. At this time, The power supply voltage terminal VCC charges the capacitor of the external circuit of the self-capacitance detection module 22 (hereinafter referred to as the external capacitor) through the eighth switch K8, the voltage of the capacitance detection terminal P1 rises to the power supply voltage, and at the same time, both ends of the ninth capacitor C9 are grounded , the ninth capacitor C9 is discharged, the voltage at point N3 in Figure 14 is 0, the non-inverting input terminal of the differential amplifier A1 has no signal, and the output voltage VOUT is 0; in the T2 time period, only the tenth switch K10 is turned on, and the external capacitor and The ninth capacitor C9 is connected in parallel, and the charges of the two are transferred to each other. If the external non-target device is close to the NFC antenna, since the capacitance values of the external capacitor and the ninth capacitor are the same, the voltage of the ninth capacitor C9 is Vcc/2, and the positive phase of the differential amplifier A1 There is no signal at the input terminal, and the output voltage VOUT is 0; in the T3 time period, only the ninth switch K9 and the tenth switch K10 are turned on. If there is no target device close to the NFC antenna, the capacitance value of the external capacitor does not change, and the ninth capacitor C9 The voltage is still Vcc/2, so the voltage of the non-inverting input terminal of the differential amplifier A1 is Vcc/2, which is equal to the voltage of the common-mode voltage terminal VCM connected to the inverting input terminal, and the output voltage VOUT of the differential amplifier A1 is still 0 (Figure 15 The dotted line in the middle), if there is a target device close to the NFC antenna, the NFC antenna will have a capacitance change, and the charge of Q1=△C*(Vcc/2) will be transferred to the non-inverting input of the differential amplifier A1. The output voltage VOUT generates a waveform with the highest voltage U1; in the T4 time period, only the eighth switch K8 and the eleventh switch K11 are turned on, and the power supply voltage terminal VCC charges the ninth capacitor C9 through the eleventh switch K11, and the N3 point When the voltage rises to the power supply voltage, the external capacitor is discharged through the eighth switch K8, and the voltage of the capacitor detection terminal P1 is 0. Since the ninth switch K9 is disconnected, the non-inverting input terminal of the differential amplifier A1 has no signal, and the output voltage VOUT is 0; During the T5 time period, only the tenth switch K10 is turned on, the external capacitor and the ninth capacitor C9 are connected in parallel, and the charges of the two are transferred to each other. If no target device is close to the NFC antenna, the capacitance values of the external capacitor and the ninth capacitor are the same. The capacitor voltage of the ninth capacitor is Vcc/2; in the T6 time period, only the ninth switch K9 and the tenth switch K10 are turned on. If no target device is close to the NFC antenna, the capacitance value of the external capacitor does not change, and the ninth capacitor C9 The voltage of the capacitor is still Vcc/2, so the voltage of the non-inverting input terminal of the differential amplifier A1 is Vcc/2, which is equal to the voltage of the common-mode voltage terminal VCM connected to the inverting input terminal, and the output voltage VOUT of the differential amplifier A1 is still 0 ( The dotted line in Figure 15), if there is a target device close to the NFC antenna, the capacitance of the NFC antenna will change, and the charge of Q2=-△C*1/2Vcc will be transferred to the non-inverting input of the differential amplifier A1, and the differential The output voltage VOUT of amplifier A1 produces a waveform with a minimum voltage of -U1. By demodulating the output voltage VOUT of the differential amplifier A1, the change amount ΔC of the external capacitance can be detected based on the demodulated information, so as to know whether the target device is detected.

The output end of the self-capacitance detection module 22 in the above embodiment can output the first signal generated based on the detected capacitance change of the NFC antenna. For example, when the self-capacitance detection module 22 is implemented by the self-capacitance detection circuit shown in FIG. 14 , The first signal generated from the capacitance detection module 22 is the voltage signal VOUT.

In another embodiment of the NFC device provided in this application, the NFC device in the above embodiment may further include: a judgment module, the input end of the judgment module can be connected with the output end of the self-capacitance detection module 22, and the judgment module is used for receiving From the first signal output by the capacitance detection module 22, it is judged whether the amplitude of the first signal exceeds a preset threshold, and if so, it is judged that a target device is close to the NFC antenna, otherwise, it is judged that no target device is close to the NFC antenna. The specific value of the above-mentioned preset threshold is not limited in the embodiment of the present application, and is related to the first signal generated by the self-capacitance detection module 22 . The judgment module can be set outside the NFCC23, or can be set in the NFCC23. Referring to FIG. 16 , taking the addition of the judgment module 28 to the NFC device shown in FIG. 12 as an example, the judgment module 28 is located in the NFCC.

At present, the NFC device detects the target device by detecting the impedance of the NFC antenna. When sending a polling signal, the driving voltage is generally 2~6V, and the driving circuit impedance is generally 20Ω~50Ω, then the driving current is greater than 100mA, assuming a polling time 30us, the power consumption of one polling is greater than J=2V*100mA*30us=6*10e-6 joules, and in the NFC device of the present invention, the method of detecting the NFC antenna capacitance is used to detect the target device. When the self-capacitance detection module works, The driving voltage can be 2~3.3V, and the load capacitance can be 100~500pF. Assuming that the operating frequency is 100kHz, and one polling time is 200us, then the driving current I=100kHz*2*100pF=20uA, and the power consumption of one polling J= 2V*20uA*200us=8*10e-9 joules. By comparison, it can be seen that the NFC device in the embodiment of the present application detects the target device by detecting the capacitance of the NFC antenna, which has obvious advantages in power consumption.

In the embodiments of the present application, "at least one" refers to one or more, and "multiple" refers to two or more. "And/or", which describes the association relationship of the associated objects, means that there can be three kinds of relationships, for example, A and/or B, which can indicate the existence of A alone, the existence of A and B at the same time, and the existence of B alone. where A and B can be singular or plural. The character "/" generally indicates that the associated objects are an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, and c may represent: a, b, c, a and b, a and c, b and c or a and b and c, where a, b, c may be single, or Can be multiple.

Those of ordinary skill in the art can realize that the modules and algorithm steps described in the embodiments disclosed herein can be implemented by a combination of electronic hardware, computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each particular application, but such implementations should not be considered beyond the scope of this application.

Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described systems, devices and modules may refer to the corresponding processes in the foregoing method embodiments, which will not be repeated here.

In the several embodiments provided in this application, if any function is implemented in the form of a software function module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application can be embodied in the form of a software product in essence, or the part that contributes to the prior art or the part of the technical solution. The computer software product is stored in a storage medium, including Several instructions are used to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, Read-Only Memory (Read-Only Memory; hereinafter referred to as: ROM), Random Access Memory (Random Access Memory; hereinafter referred to as: RAM), magnetic disk or optical disk and other various A medium on which program code can be stored.

The above are only specific embodiments of the present application. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be covered by the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the claims.

Claims

A near field communication NFC device, the NFC device comprising: an NFC antenna, a filter circuit for performing signal filtering, a matching circuit for performing impedance matching of the NFC antenna, and for transmitting data received by the NFC antenna A signal data receiving branch, an NFC controller for controlling signal transmission and reception, characterized in that the NFC device further includes: a self-capacitance detection module, wherein,

The capacitance detection terminal of the self-capacitance detection module is connected to the positive-phase terminal or the reverse-phase terminal of the NFC antenna, and the self-capacitance detection module is used to detect the capacitance change of the NFC antenna, and the capacitance change is used to judge Whether a target device is near the NFC antenna.
The device according to claim 1, wherein the capacitance detection terminal of the self-capacitance detection module is connected to the positive phase terminal or the reverse phase terminal of the NFC antenna through the matching circuit.
The device according to claim 1, wherein the capacitance detection terminal of the self-capacitance detection module is connected to the positive phase terminal or the reverse phase terminal of the NFC antenna through the data receiving branch.
The device according to claim 1, wherein the capacitance detection end of the self-capacitance detection module is sequentially connected to the non-phase end or the inversion end of the NFC antenna through the data receiving branch and the matching circuit .
The device according to any one of claims 1 to 4, wherein the self-capacitance detection module is located in the NFC controller.
The device according to any one of claims 1 to 5, wherein a capacitance detection end of the self-capacitance detection module is connected to a first end of a first switch, and a second end of the first switch is connected to the NFC The positive-phase terminal or the reverse-phase terminal of the antenna, the first switch is configured to be turned on when the self-capacitance detection module is in operation, and turned off when the self-capacitance detection module is not in operation.
The device according to any one of claims 1 to 6, wherein the NFC device includes a matching circuit and a filter circuit of the NFC antenna, and the matching circuit and the filter circuit include a grounding of a capacitor included in the filter circuit. The terminal is grounded through a fourth switch, and the fourth switch is used to turn off the self-capacitance detection module when the self-capacitance detection module works.
The device according to any one of claims 1 to 7, wherein the self-capacitance detection module comprises a seventh switch, an eighth switch, a ninth switch, a tenth switch, an eleventh switch, and a twelfth switch , a differential amplifier and a ninth capacitor, the self-capacitance detection module further includes: a third resistor and/or a tenth capacitor, a fourth resistor and/or an eleventh capacitor, wherein,

The capacitance detection terminal of the self-capacitance detection module is connected to the power supply voltage terminal through the seventh switch, grounded through the eighth switch, connected to the non-inverting input terminal of the differential amplifier through the ninth switch, and connected to the first terminal of the ninth capacitor through the tenth switch , the second end of the ninth capacitor is grounded;

The first end of the ninth capacitor is also connected to the power supply voltage end through the eleventh switch, and is grounded through the twelfth switch;

The inverting input terminal of the differential amplifier is connected to the common-mode voltage terminal, the first output terminal and the second output terminal are used for outputting voltage, and the output voltage is associated with the capacitance change of the NFC antenna;

The non-inverting input terminal of the differential amplifier is also connected to the first output terminal of the differential amplifier through a third resistor, or a tenth capacitor, or a third resistor and a tenth capacitor connected in parallel, and the inverting input terminal is connected through a fourth resistor, Either the eleventh capacitor, or the fourth resistor and the eleventh capacitor connected in parallel are connected to the second output terminal of the differential amplifier.
The device according to claim 8, wherein a capacitance value of the ninth capacitor is equal to a first equivalent capacitance value, and the first equivalent capacitance value is the self-capacitance when no target device approaches the NFC antenna The equivalent capacitance value of the external circuit of the detection module between the capacitance detection terminal and the power supply ground terminal, and the voltage of the common mode voltage terminal is 1/2 of the power supply voltage.
The device according to any one of claims 1 to 9, wherein the self-capacitance detection module is specifically configured to: generate a first signal based on the detected capacitance change of the NFC antenna;

The NFC device further includes: a judgment module, the input end of the judgment module is connected to the output end of the self-capacitance detection module, and the judgment module is used for judging whether the amplitude of the first signal output by the self-capacitance detection module is If the preset threshold is exceeded, if yes, it is determined that a target device is close to the NFC antenna.
The device according to any one of claims 1 to 9, wherein the NFC controller is configured to determine whether a target device is close to the NFC antenna according to the capacitance change.