A new high-speed receiving circuit for contactless transponders

Abstract

The present invention provides a novel high-speed receiving circuit for a contactless transponder, including a resonant circuit composed of an external main coil antenna and an external secondary coil antenna of the transponder, and also including a demodulation circuit, wherein the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder includes a first coil antenna, a second coil antenna, a first capacitor, a second capacitor, a first resistor and a first limiting circuit. The resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder of the present invention introduces a first resistor to prevent the signal voltage amplitude of the second coil antenna from being too high, thereby ensuring the safety of the electrical components connected to the second coil antenna. At the same time, the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder of the present invention introduces a second coil antenna to improve the modulation coefficient of the input signal of the detection circuit, reduce the distortion of the input signal of the detection circuit, and thus reduce the design difficulty of the detection circuit and the hysteresis comparator.

Description

Technical Field

[0001] The invention relates to the technical field of integrated circuits in radio frequency identification technology, and in particular to a novel high-speed receiving circuit for a contactless transponder. Background Art

[0002] Radio Frequency Identification (RFID) is a contactless automatic identification technology. Its basic principle is to use radio frequency signals to transmit data between the reader and the transponder to achieve target identification and information exchange. Among them, ISO IEC 14443 A contactless transponders have the advantages of being erasable, high-speed, and low-cost, and occupy most of the market share. However, these are inseparable from the transponder having a high-quality and high-stability receiving circuit. The receiving circuit is the key circuit for high-speed data transmission between the contactless transponder and the reader, and its performance is directly related to the high-speed communication performance of the transponder. Therefore, the design and research of high-quality and high-stability transponder receiving circuits are of great significance.

[0003] See also Figure 1 , a commonly used contactless transponder receiving circuit structure, its working principle is as follows:

[0004] The transponder's external sensing antenna L2, which is composed of VA and VB, captures the carrier signal emitted by the reader antenna. In order to ensure the safety of the electrical components inside the chip, a limiter circuit Limiter is designed inside the chip to ensure that the electrical components connected to the antenna work within the safe voltage range. When the reader sends a signal, the subcarrier signal is detected by the detection circuit composed of NM1 transistor, NM2 transistor, R1 resistor, C2 capacitor and C3 capacitor, and then input to the negative input terminal of the COMP hysteresis comparator, and the DC bias VREF is provided by the R2 resistor. The detection signal of the DC bias and VREF are compared with the COMP hysteresis comparator to output a digital signal. After the digital signal is interpreted by the digital demodulation circuit, the transponder gives the reader a corresponding answer.

[0005] However, the above contactless transponder receiving circuit still has some shortcomings:

[0006] 1. The limiting circuit inside the transponder will greatly attenuate the effective voltage amplitude of the high-speed signal (848kbps) on the transponder antenna, which increases the difficulty of designing the hysteresis comparator.

[0007] 2. The limiting circuit Limiter inside the transponder will increase the distortion of the high-speed signal on the transponder antenna. The digital demodulation circuit must fully consider the problem of inconsistent pause output of the analog demodulation circuit caused by distortion, which increases the difficulty of designing the digital receiving circuit.

[0008] 3. Due to the attenuation and distortion of the carrier signal on the transponder antenna, it is more difficult to design the detection circuit composed of the NM1 transistor, the NM2 transistor, the R1 resistor, the C2 capacitor and the C3 capacitor.

[0009] In view of the above problems, designing a novel high-speed receiving circuit for contactless transponder has become the object of the present invention. Summary of the invention

[0010] In view of the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a novel contactless transponder high-speed receiving circuit, which has a structure of a resonant circuit composed of an external main coil antenna of the transponder and a demodulation circuit composed of an external secondary coil antenna of the transponder, and can improve the modulation coefficient of the input signal of the detection circuit and increase the safety of the connected electrical components.

[0011] In order to achieve the above technical purpose, the technical solution adopted by the present invention is:

[0012] A novel high-speed receiving circuit for a contactless transponder, the novel high-speed receiving circuit for a contactless transponder comprising a resonant circuit composed of an external main coil antenna and an external secondary coil antenna of the transponder, and also comprising a demodulation circuit, wherein the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder comprises a first coil antenna, a second coil antenna, a first capacitor, a second capacitor, a first resistor and a first limiting circuit, one end of the first coil antenna is connected to one end of the first capacitor, the other end of the first coil antenna is connected to the other end of the first capacitor, one end of the second coil antenna is connected to one end of the first resistor, the other end of the second coil antenna is connected to one end of the second capacitor, the other end of the first resistor is connected to the other end of the second capacitor, two input ends of the first limiting circuit are respectively connected to the two ends of the first coil antenna, and the ground end of the first limiting circuit is connected to the ground end VSS;

[0013] The demodulation circuit includes a third capacitor, a fourth capacitor, a first NMOS transistor, a second NMOS transistor, a second resistor, a third resistor and a first hysteresis comparator, wherein the gate terminal of the first NMOS transistor and the drain terminal of the first NMOS transistor are connected to one end of the second capacitor in the resonance circuit, the gate terminal of the second NMOS transistor and the drain terminal of the second NMOS transistor are connected to the other end of the second capacitor in the resonance circuit, the source terminal of the first NMOS transistor, the source terminal of the second NMOS transistor and one end of the third capacitor are connected to one end of the second resistor, the other end of the third capacitor, one end of the fourth capacitor and one end of the third resistor are connected to the negative input terminal of the hysteresis comparator, the other end of the fourth capacitor and the other end of the second resistor are connected to the ground terminal VSS, the other end of the third resistor and the positive input terminal of the hysteresis comparator are connected to the reference voltage, and one end of the hysteresis comparator is the output terminal.

[0014] The novel high-speed receiving circuit of the contactless transponder of the present invention has the following advantages over the existing technical solutions due to the use of the structure of the resonant circuit and demodulation circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder:

[0015] (1) The resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder of the present invention has not only the first coil antenna but also the second coil antenna. The second coil antenna has no direct connection with the limiting circuit, which ensures that the subcarrier signal of the second coil antenna is not affected by the limiting circuit and prevents the attenuation of the voltage amplitude of the subcarrier signal of the second coil antenna.

[0016] (2) The introduction of the first resistor in the resonant circuit composed of the external primary coil antenna and the external secondary coil antenna of the transponder of the present invention prevents the signal voltage amplitude of the second coil antenna from being too high, thereby ensuring the safety of the electrical components connected to the second coil antenna.

[0017] (3) The area of ​​the second coil antenna in the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder of the present invention is larger than the area of ​​the first coil antenna. The first coil antenna and the second coil antenna are symmetrically designed, which ensures that the second coil antenna is not affected by the first coil antenna and prevents distortion of the subcarrier signal on the second coil antenna.

[0018] (4) The introduction of the second coil antenna in the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder of the present invention improves the modulation coefficient of the input signal of the detection circuit and reduces the distortion of the input signal of the detection circuit, thereby reducing the difficulty of designing the detection circuit and the hysteresis comparator.

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a structural diagram of a traditional contactless transponder receiving circuit.

[0021] Figure 2 This is a structural diagram of a high-speed receiving circuit of a novel contactless transponder specifically implemented in the present invention. DETAILED DESCRIPTION

[0022] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

[0023] See also Figure 2 , which is a structural diagram of a high-speed receiving circuit of a novel contactless transponder specifically implemented in the present invention. Its structural feature is that the novel contactless transponder high-speed receiving circuit includes a resonant circuit composed of an external main coil antenna and an external secondary coil antenna of the transponder, and also includes a demodulation circuit, wherein the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder includes a first coil antenna L1, a second coil antenna L2, a first capacitor C1, a second capacitor C2, a first resistor R1 and a first limiting circuit Limiter, one end VA2 of the first coil antenna L1 is connected to one end of the first capacitor C1, the other end VB2 of the first coil antenna L1 is connected to the other end of the first capacitor C1, one end VA1 of the second coil antenna L2 is connected to one end of the first resistor R1, the other end VB1 of the second coil antenna L2 is connected to one end of the second capacitor C2, the other end of the first resistor R1 is connected to the other end of the second capacitor C2, the two input ends of the first limiting circuit Limiter are respectively connected to the two ends VA2 and VB2 of the first coil antenna L1, and the ground end of the first limiting circuit Limiter is connected to the ground end VSS.

[0024] The demodulation circuit includes a third capacitor C3, a fourth capacitor C4, a first NMOS transistor NM1, a second NMOS transistor NM2, a second resistor R2, a third resistor R3 and a first hysteresis comparator COMP, wherein the gate end of the first NMOS transistor NM1 and the drain end of the first NMOS transistor NM1 are connected to one end of the second capacitor C2 in the resonance circuit, the gate end of the second NMOS transistor NM2 and the drain end of the second NMOS transistor NM2 are connected to the other end of the second capacitor C2 in the resonance circuit, and the first NMOS transistor The source terminal of NM1, the source terminal of the second NMOS transistor NM2, and one end of the third capacitor C3 are connected to one end of the second resistor R2, the other end of the third capacitor C3, one end of the fourth capacitor C4, and one end of the third resistor R3 are connected to the negative input terminal of the hysteresis comparator COMP, the other end of the fourth capacitor C4 and the other end of the second resistor R2 are connected to the ground terminal VSS, the other end of the third resistor R3 and the positive input terminal of the hysteresis comparator COMP are connected to the reference voltage VREF, and the output terminal of the hysteresis comparator COMP is VOUT.

[0025] See also Figure 2 , which is a structural diagram of the contactless transponder high-speed receiving circuit specifically implemented in the present invention. In the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder, the first coil antenna L1 captures the high-frequency carrier signal emitted by the reader antenna, and provides energy to the transponder load through the transponder rectifier circuit and the limiter circuit. In order to prevent the signal on the first coil antenna L1 from affecting the signal on the second coil antenna L2, the first coil antenna L1 and the second coil antenna L2 must be designed symmetrically.

[0026] At the same time, the second coil antenna L2 captures the high-frequency carrier signal emitted by the reader antenna, and detects the subcarrier signal through the detection circuit composed of the first NMOS transistor NM1, the second NMOS transistor NM2, the second resistor R2, the third capacitor C3 and the fourth capacitor C4, and then inputs it into the negative input terminal of the hysteresis comparator COMP, and the third resistor R3 provides a DC bias VREF. The detection signal of the DC bias and the DC bias VREF are compared with the hysteresis comparator COMP to output a digital signal. After the digital signal is interpreted by the demodulation circuit, the transponder gives a corresponding answer to the reader.

[0027] The first resistor R1 is connected in series with the second coil antenna L2. The first resistor R1 can adjust the Q value of the resonant circuit composed of L2 and the second capacitor C2 to prevent the signal voltage amplitude on the second coil antenna L2 from being too high and damaging the electrical components connected to the second coil antenna L2.

[0028] As can be seen from the above, the embodiment of the present invention effectively improves the demodulation efficiency and stability of the receiving circuit through the resonant circuit 101 composed of the external main coil antenna and the external secondary coil antenna of the transponder, and the demodulation circuit 102.

[0029] It should be noted that the above embodiments are only schematic illustrations of the basic concept of the present invention, and the component circuits related to the present invention are not drawn according to the number, shape, device arrangement, and connection method of the component circuits in actual implementation. The type, number, connection method, device arrangement, and device parameters of each circuit in actual implementation can be changed at will.

[0030] The above-described embodiments are only preferred embodiments of the present invention and cannot limit the extension of the technical solution of the present invention. Any modification, equivalent change and obvious replacement of the known technology made by those skilled in the art on the basis of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A novel high-speed receiving circuit for contactless transponders, characterized in that: The novel contactless transponder high-speed receiving circuit includes a resonant circuit composed of an external main coil antenna and an external secondary coil antenna of the transponder, and also includes a demodulation circuit, wherein the resonant circuit composed of the external main coil antenna and the external secondary coil antenna of the transponder includes a first coil antenna, a second coil antenna, a first capacitor, a second capacitor, a first resistor and a first limiting circuit, one end of the first coil antenna is connected to one end of the first capacitor, the other end of the first coil antenna is connected to the other end of the first capacitor, one end of the second coil antenna is connected to one end of the first resistor, the other end of the second coil antenna is connected to one end of the second capacitor, the other end of the first resistor is connected to the other end of the second capacitor, two input ends of the first limiting circuit are respectively connected to the two ends of the first coil antenna, and the ground end of the first limiting circuit is connected to the ground end VSS; The demodulation circuit includes a third capacitor, a fourth capacitor, a first NMOS transistor, a second NMOS transistor, a second resistor, a third resistor and a first hysteresis comparator, wherein the gate terminal of the first NMOS transistor and the drain terminal of the first NMOS transistor are connected to one end of the second capacitor in the resonance circuit, the gate terminal of the second NMOS transistor and the drain terminal of the second NMOS transistor are connected to the other end of the second capacitor in the resonance circuit, the source terminal of the first NMOS transistor, the source terminal of the second NMOS transistor and one end of the third capacitor are connected to one end of the second resistor, the other end of the third capacitor, one end of the fourth capacitor and one end of the third resistor are connected to the negative input terminal of the hysteresis comparator, the other end of the fourth capacitor and the other end of the second resistor are connected to the ground terminal VSS, the other end of the third resistor and the positive input terminal of the hysteresis comparator are connected to the reference voltage, and one end of the hysteresis comparator is an output terminal; The first coil antenna is used to capture the high-frequency carrier signal emitted by the reader antenna and provide energy to the transponder load through the transponder rectification circuit and the amplitude limiting circuit; the first coil antenna and the second coil antenna are symmetrically designed; The second coil antenna is used to capture the high-frequency carrier signal emitted by the reader antenna, and detects the subcarrier signal through a detection circuit composed of a first NMOS transistor, a second NMOS transistor, a second resistor, a third capacitor and a fourth capacitor, and inputs it into the negative input terminal of the hysteresis comparator COMP. The third resistor provides a DC bias VREF. The detection signal of the DC bias and the DC bias VREF are compared with the hysteresis comparator COMP to output a digital signal. After the digital signal is interpreted by the demodulation circuit, the transponder gives a corresponding response to the reader.

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