High frequency tag FSK signal demodulation circuit

Abstract

The utility model relates to the field of RFID technology, specifically is a kind of high-frequency label FSK signal demodulation circuit that can realize high-frequency RFID label long-distance reading, it is characterized by being equipped with envelope detection circuit, active band-pass filter amplification circuit, phase shift circuit, analog multiplier circuit, low-pass filter amplification circuit and comparison decision circuit, wherein, envelope detection circuit receives data from antenna and data is sent into active band-pass filter amplification circuit, and one way output of active band-pass filter amplification circuit will received data send into analog multiplier circuit, and another way of active band-pass filter amplification circuit will received data send into phase shift circuit.

Description

Technical fields:

[0001] This utility model relates to the field of RFID technology, specifically a high-frequency tag FSK signal demodulation circuit that enables long-distance reading of high-frequency RFID tags. Background technology:

[0002] Radio Frequency Identification (RFID) technology is a communication technology that uses radio waves to achieve non-contact automatic identification of target objects and acquire data. Its core components include electronic tags, readers, and a back-end data processing system. Compared with traditional barcode technology, RFID has advantages such as longer reading distance, batch reading, strong environmental adaptability, and data read / write capabilities, and is widely used in logistics management, retail, smart manufacturing, transportation, and other fields.

[0003] Existing high-frequency RFID demodulation circuits mostly use integrated chips (such as PN5180 and ST25R3916). Although they have high integration and short development cycles, they have the following drawbacks: 1) Integrated chips have fixed algorithms, which cannot be adapted to proprietary communication protocols; 2) The tag reading distance is limited, usually between 0.1m and 1.2m. Therefore, it is urgent to solve the problem of insufficient reading distance. Summary of the Invention:

[0004] This invention addresses the shortcomings and deficiencies of existing technologies by proposing a high-frequency tag FSK signal demodulation circuit that is structurally sound, reliable in operation, and capable of enabling long-distance reading of high-frequency RFID tags.

[0005] This utility model achieves its purpose through the following measures:

[0006] A high-frequency tag FSK signal demodulation circuit is characterized by comprising an envelope detection circuit, an active bandpass filter amplifier circuit, a phase shifting circuit, an analog multiplier circuit, a low-pass filter amplifier circuit, and a comparison decision circuit. The envelope detection circuit receives data from an antenna and sends the data to the active bandpass filter amplifier circuit. One output of the active bandpass filter amplifier circuit sends the received data to the analog multiplier circuit, and the other output sends the received data to the phase shifting circuit. The output of the phase shifting circuit is connected to the input of the analog multiplier circuit. The two outputs of the analog multiplier circuit are respectively connected to two low-pass filter amplifier circuits, and the outputs of both low-pass filter amplifier circuits are connected to the comparison decision circuit.

[0007] The present invention includes a detector circuit comprising a capacitor C1, a capacitor C7, a diode D1, and a resistor R3. The capacitor C1 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to one end of the resistor R3, and the other end of the resistor R3 is grounded. The capacitor C7 is connected in parallel with the resistor R3. During operation, the signal received by the antenna includes subcarrier frequency signals of 423.75kHz and 484.28kHz. The subcarrier signal can be extracted by utilizing the unidirectional conductivity of the diode D1 and the charging and discharging process of the detector load RC.

[0008] The active bandpass filter amplifier circuit of this utility model includes a first operational amplifier U1A and a second operational amplifier U1B. A resistor R1 is connected between the inverting input and output of the first operational amplifier U1A. The non-inverting input of the first operational amplifier U1A is connected to resistors R8 and R9 respectively. The other end of resistor R9 is grounded, and the other end of resistor R8 is connected to VDD. Capacitors C3 and C6 are connected in series and then in parallel with resistor R1. Capacitor C4 is connected in series with resistor R4. Resistor R4 is connected between capacitors C3 and C6. One end of resistor R6 is grounded, and the other end is connected between capacitors C3 and C6. The first operational amplifier U1A... The output terminal is connected to capacitor C8. The other end of capacitor C8 is connected in series with resistor R5 and capacitor C9, and then connected to the inverting input terminal of the second operational amplifier U1B. Resistor R2 is connected between the inverting input terminal and the output terminal of the second operational amplifier U1B. Capacitors C5 and C9 are connected in series and then in parallel with resistor R2. One end of resistor R7 is grounded, and the other end is connected between resistor R5 and capacitor C9. The non-inverting input terminal of the second operational amplifier U1B is connected to resistors R10 and R11 respectively. The other end of resistor R10 is connected to VDD, and the other end of resistor R11 is grounded. The active bandpass filter amplifier circuit performs filtering, amplification, and limiting processing on the signal.

[0009] The phase-shifting circuit described in this invention is used to select the frequency and shift the phase of the subcarrier signal. The phase-shifting center frequency is 455kHz, and the subcarrier signals at 423.75kHz and 484.28kHz are shifted by 144° and 35°, respectively.

[0010] The analog multiplier circuit described in this invention is used to multiply the subcarrier signal with the phase-shifted subcarrier signal, converting the frequency signal of the subcarrier signal into an amplitude signal. The analog multiplier can be implemented using the ON Semiconductor MC1496 chip.

[0011] The low-pass filter amplifier circuit of this invention filters out the frequency multiplication component from the amplitude signal after multiplication by the analog multiplier to obtain the FSK analog baseband signal. Furthermore, the low-pass filter amplifier circuit is an active low-pass filter amplifier circuit, equipped with two operational amplifiers and peripheral components. Specifically, it includes a third operational amplifier U3A and a fourth operational amplifier U3B. The output of the third operational amplifier is connected to resistor R27, which is connected in series with resistor R28. The other end of resistor R28 is connected to the inverting input of the fourth operational amplifier. A capacitor C20 is connected between the output and inverting input of the third operational amplifier. Resistors R25 and R26 are connected in series, and the other end of resistor R26 is connected to the inverting input of the third operational amplifier. One end of resistor R23 is connected to resistor R2... Between resistor R25 and resistor R26, the other end of resistor R23 is connected to the output of the third operational amplifier. One end of capacitor C22 is grounded, and the other end is connected between resistors R25 and R26. One end of resistor R29 is connected to VDD, and the other end is connected to the non-inverting input of the third operational amplifier. One end of resistor R30 is grounded, and the other end is connected to the non-inverting input of the third operational amplifier. One end of resistor R24 ​​is connected between resistors R27 and R28, and the other end of resistor R24 ​​is connected to the output of the fourth operational amplifier. One end of capacitor C23 is grounded, and the other end is connected between resistors R27 and R28. One end of resistor R31 is grounded, and the other end is connected to the non-inverting input of the fourth operational amplifier. One end of resistor R32 is grounded, and the other end is connected to the non-inverting input of the fourth operational amplifier.

[0012] In this invention, the output of the comparison decision circuit is connected to the controller MCU, and the output signal is sent to the controller MCU to complete the decoding of the FSK digital baseband signal. The controller MCU can be implemented using an STM32 microcontroller.

[0013] When in operation, this utility model works in conjunction with the radio frequency transmitting circuit of an RFID reader to process and demodulate the high-frequency tag FSK signal, flexibly realizing demodulation and decoding. It can be adapted to private communication protocols and can realize long-distance reading (1m-2m) of high-frequency tags. Compared with the existing technology, it can meet the needs of flexibly implementing firmware algorithms and customizing private protocols, and realize the extension of tag reading distance. Attached image description:

[0014] Appendix Figure 1 This is a structural block diagram of the present invention.

[0015] Appendix Figure 2 This is a schematic diagram of one usage state of this utility model.

[0016] Appendix Figure 3 This is a structural diagram of the envelope detection circuit in this utility model.

[0017] Appendix Figure 4This is a schematic diagram of the active bandpass filter amplifier circuit of this utility model.

[0018] Appendix Figure 5 This is a circuit structure schematic diagram of a phase-shifting circuit in this utility model.

[0019] Appendix Figure 6 This is a circuit diagram illustrating the schematic of an analog multiplier circuit in this utility model. (Attached) Figure 7 This is a schematic diagram of a low-pass filter amplifier circuit in this utility model.

[0020] Appendix Figure 8 This is a schematic diagram of a comparison decision circuit in this utility model.

[0021] Figure labels: 1. Envelope detection circuit; 2. Active bandpass filter amplifier circuit; 3. Phase shifter circuit; 4. Analog multiplier circuit; 5. Low-pass filter amplifier circuit; 6. Comparison decision circuit; 7. Antenna; 8. Controller MCU. Detailed implementation method:

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] As attached Figure 1 As shown, this utility model proposes a high-frequency tag FSK signal demodulation circuit, which includes an envelope detection circuit 1, an active bandpass filter amplifier circuit 2, a phase shifting circuit 3, an analog multiplier circuit 4, a low-pass filter amplifier circuit 5, and a comparison and decision circuit 6. The envelope detection circuit 1 receives data from the antenna 7 and sends the data to the active bandpass filter amplifier circuit 2. One output of the active bandpass filter amplifier circuit 2 sends the received data to the analog multiplier circuit 4, and the other output sends the received data to the phase shifting circuit 3. The output of the phase shifting circuit 3 is connected to the input of the analog multiplier circuit 4. The two outputs of the analog multiplier circuit 4 are respectively connected to two low-pass filter amplifier circuits 5, and the outputs of the two low-pass filter amplifier circuits 5 are both connected to the comparison and decision circuit 6.

[0024] As attached Figure 3 As shown, the present invention includes a detector circuit 1 comprising a capacitor C1, a capacitor C7, a diode D1, and a resistor R3. The capacitor C1 is connected to the positive terminal of the diode D1, the negative terminal of the diode D1 is connected to one end of the resistor R3, the other end of the resistor R3 is grounded, and the capacitor C7 is connected in parallel with the resistor R3. During operation, the signal received by the antenna includes subcarrier frequency signals of 423.75kHz and 484.28kHz. By utilizing the unidirectional conductivity of the diode D1 and the charging and discharging process of the detector load RC, the subcarrier signal can be extracted.

[0025] As attached Figure 4As shown, the active bandpass filter amplifier circuit 2 of this utility model includes a first operational amplifier U1A and a second operational amplifier U1B. A resistor R1 is connected between the inverting input and output of the first operational amplifier U1A. The non-inverting input of the first operational amplifier U1A is connected to resistors R8 and R9 respectively. The other end of resistor R9 is grounded, and the other end of resistor R8 is connected to VDD. Capacitors C3 and C6 are connected in series and then in parallel with resistor R1. Capacitor C4 is connected in series with resistor R4. Resistor R4 is connected between capacitors C3 and C6. One end of resistor R6 is grounded, and the other end is connected between capacitors C3 and C6. The first operational amplifier U1A... The output terminal of 1A is connected to capacitor C8. The other end of capacitor C8 is connected in series with resistor R5 and capacitor C9, and then connected to the inverting input terminal of the second operational amplifier U1B. Resistor R2 is connected between the inverting input terminal and the output terminal of the second operational amplifier U1B. Capacitors C5 and C9 are connected in series and then in parallel with resistor R2. One end of resistor R7 is grounded, and the other end is connected between resistor R5 and capacitor C9. The non-inverting input terminal of the second operational amplifier U1B is connected to resistors R10 and R11 respectively. The other end of resistor R10 is connected to VDD, and the other end of resistor R11 is grounded. The active bandpass filter amplifier circuit performs filtering, amplification, and limiting processing on the signal.

[0026] As attached Figure 5 As shown, the phase-shifting circuit 3 is used to select the frequency and shift the phase of the subcarrier signal. The phase-shifting center frequency is 455kHz, and the subcarrier signals of 423.75kHz and 484.28kHz are shifted by 144° and 35° respectively.

[0027] As attached Figure 6 As shown, the analog multiplier circuit 4 is used to multiply the subcarrier signal with the phase-shifted subcarrier signal, converting the frequency signal of the subcarrier signal into an amplitude signal.

[0028] The low-pass filter amplifier circuit 5 of this invention filters out the frequency multiplication component from the amplitude signal after multiplication by the analog multiplier circuit to obtain the FSK analog baseband signal.

[0029] In this invention, the output of the comparison decision circuit 6 is connected to the controller MCU8, and the output signal is sent to the controller MCU8 to complete the decoding of the FSK digital baseband signal. The controller MCU8 can be implemented using an STM32 microcontroller.

[0030] Example:

[0031] As attached Figure 2As shown, this example provides a high-frequency tag FSK signal demodulation circuit, which is applied in an RFID reader. The RFID reader has a modulation circuit connected to the controller MCU. The output of the modulation circuit is connected to the power amplifier circuit. The output of the power amplifier circuit is connected to the matching circuit. The matching circuit is connected to the antenna. After receiving the signal, the antenna sends it to the high-frequency tag FSK signal demodulation circuit.

[0032] The high-frequency tag FSK signal demodulation circuit described in this example includes an envelope detection circuit 1, an active bandpass filter amplifier circuit 2, a phase shifter circuit 3, an analog multiplier circuit 4, a low-pass filter amplifier circuit 5, a comparison and decision circuit 6, and a controller MCU 8. This circuit receives the high-frequency carrier and tag subcarrier FSK signal from the antenna 7. The envelope of the tag subcarrier signal is extracted by the envelope detection circuit 1, filtered, amplified, and limited by the active bandpass filter amplifier circuit 2, differentially detected by the phase shifter circuit 3 and the analog multiplier circuit 4, filtered to remove the harmonic components and amplified by the active low-pass filter amplifier circuit 5, converted into a digital signal by the comparison and decision circuit 6, and finally decoded by the MCU to demodulate the high-frequency tag FSK signal.

[0033] In this example, the envelope detector circuit 1 receives signals containing subcarrier frequency signals of 423.75kHz and 484.28kHz via antenna 7. The subcarrier signal is extracted using the unidirectional conductivity of the diode and the charging and discharging process of the RC detector load. The active bandpass filter amplifier circuit 2 performs bandpass filtering, amplification, and limiting on the subcarrier signal extracted by the envelope detector circuit 1. Bandpass filtering is used to filter out noise signals other than the subcarrier frequency, while amplification and limiting are used to keep the amplitude of the subcarrier frequency signal entering the analog multiplier constant, so that the output voltage of the analog multiplier can linearly follow the instantaneous frequency change of the input frequency modulated wave and avoid distortion.

[0034] In this example, the phase-shifting circuit 3 performs frequency selection and phase shifting on the subcarrier signal. The phase-shifting center frequency is 455kHz, and the subcarrier signals at 423.75kHz and 484.28kHz are shifted by 144° and 35° respectively. The analog multiplier circuit 4 multiplies the subcarrier signal with the phase-shifted subcarrier signal, converting the frequency signal of the subcarrier signal into an amplitude signal. The low-pass filter amplifier circuit 5 filters out the multiplication factor from the amplitude signal after multiplication by the analog multiplier to obtain the FSK analog baseband signal. The comparison and decision circuit 6 converts the FSK analog baseband signal into an FSK digital baseband signal for MCU decoding. In this example, the controller is used to decode the FSK digital baseband signal.

[0035] Compared with the prior art, this invention can meet the needs of flexibly implementing firmware algorithms and custom private protocols, and realize the extension of tag reading distance.

Claims

1. A high-frequency tag FSK signal demodulation circuit, characterized in that, The circuit includes an envelope detector circuit, an active bandpass filter amplifier circuit, a phase shifter circuit, an analog multiplier circuit, a low-pass filter amplifier circuit, and a comparison and decision circuit. The envelope detector circuit receives data from the antenna and sends the data to the active bandpass filter amplifier circuit. One output of the active bandpass filter amplifier circuit sends the received data to the analog multiplier circuit, and the other output sends the received data to the phase shifter circuit. The output of the phase shifter circuit is connected to the input of the analog multiplier circuit. The two outputs of the analog multiplier circuit are connected to two low-pass filter amplifier circuits, and the outputs of the two low-pass filter amplifier circuits are connected to the comparison and decision circuit.

2. The high-frequency tag FSK signal demodulation circuit according to claim 1, characterized in that, The detection circuit includes capacitor C1, capacitor C7, diode D1, and resistor R3. Capacitor C1 is connected to the positive terminal of diode D1, the negative terminal of diode D1 is connected to one end of resistor R3, and the other end of resistor R3 is grounded. Capacitor C7 is connected in parallel with resistor R3. During operation, the signal received by the antenna includes subcarrier frequency signals of 423.75kHz and 484.28kHz. The subcarrier signal is extracted by utilizing the unidirectional conductivity of diode D1 and the charging and discharging process of the detection load RC.

3. The high-frequency tag FSK signal demodulation circuit according to claim 1, characterized in that, The active bandpass filter amplifier circuit includes a first operational amplifier U1A and a second operational amplifier U1B. A resistor R1 is connected between the inverting input and output of the first operational amplifier U1A. The non-inverting input of the first operational amplifier U1A is connected to resistors R8 and R9 respectively. The other end of resistor R9 is grounded, and the other end of resistor R8 is connected to VDD. Capacitors C3 and C6 are connected in series and then in parallel with resistor R1. Capacitor C4 is connected in series with resistor R4. Resistor R4 is connected between capacitors C3 and C6. One end of resistor R6 is grounded, and the other end is connected between capacitors C3 and C6. The output of the first operational amplifier U1A... The output terminal is connected to capacitor C8. The other end of capacitor C8 is connected in series with resistor R5 and capacitor C9, and then connected to the inverting input terminal of the second operational amplifier U1B. Resistor R2 is connected between the inverting input terminal and the output terminal of the second operational amplifier U1B. Capacitors C5 and C9 are connected in series and then in parallel with resistor R2. One end of resistor R7 is grounded, and the other end is connected between resistor R5 and capacitor C9. The non-inverting input terminal of the second operational amplifier U1B is connected to resistors R10 and R11 respectively. The other end of resistor R10 is connected to VDD, and the other end of resistor R11 is grounded. The active bandpass filter amplifier circuit performs filtering, amplification, and limiting processing on the signal.

4. The high-frequency tag FSK signal demodulation circuit according to claim 1, characterized in that, The analog multiplier is implemented using the MC1496 chip.

5. The high-frequency tag FSK signal demodulation circuit according to claim 1, characterized in that, The low-pass filter amplifier circuit filters out the frequency multiplication component from the amplitude signal after multiplication by the analog multiplier to obtain the FSK analog baseband signal. Furthermore, the low-pass filter amplifier circuit is an active low-pass filter amplifier circuit, equipped with two operational amplifiers and peripheral devices. Specifically, it includes a third operational amplifier U3A and a fourth operational amplifier U3B. The output of the third operational amplifier is connected to resistor R27, which is connected in series with resistor R28. The other end of resistor R28 is connected to the inverting input of the fourth operational amplifier. A capacitor C20 is connected between the output and inverting input of the third operational amplifier. Resistors R25 and R26 are connected in series, and the other end of resistor R26 is connected to the inverting input of the third operational amplifier. One end of resistor R23 is connected to resistors R25 and... Between resistors R26, the other end of resistor R23 is connected to the output of the third operational amplifier. One end of capacitor C22 is grounded, and the other end is connected between resistors R25 and R26. One end of resistor R29 is connected to VDD, and the other end is connected to the non-inverting input of the third operational amplifier. One end of resistor R30 is grounded, and the other end is connected to the non-inverting input of the third operational amplifier. One end of resistor R24 ​​is connected between resistors R27 and R28, and the other end of resistor R24 ​​is connected to the output of the fourth operational amplifier. One end of capacitor C23 is grounded, and the other end is connected between resistors R27 and R28. One end of resistor R31 is grounded, and the other end is connected to the non-inverting input of the fourth operational amplifier. One end of resistor R32 is grounded, and the other end is connected to the non-inverting input of the fourth operational amplifier.

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