BLE modulation frequency automatic calibration method for backscatter communication

Abstract

The invention discloses a BLE modulation frequency automatic calibration method for backscatter communication. A digital Gaussian filter, a modulation voltage-controlled oscillator in signal connection with the digital Gaussian filter and a voltage-controlled oscillator in signal connection with the modulation voltage-controlled oscillator are included. Wherein the voltage-controlled oscillator comprises a phase-locked loop, and the phase-locked loop locks the frequency to fIF through a reference clock input by a crystal oscillator; the voltage of the voltage-controlled oscillator is a first control voltage, the voltage of the modulation voltage-controlled oscillator is a second control voltage, and the first control voltage is connected with the second control voltage. According to the invention, the problem that the BLE modulation center frequency and the modulation index are unstable in the backscattering technology is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits and wireless communications, and in particular to a BLE modulation frequency automatic calibration method for backscatter communication. Background Art

[0002] Since the release of Bluetooth 4.0 in 2010, BLE (Bluetooth Low Energy) has rapidly become a core communication protocol for the Internet of Things (IoT), wearable devices, and sensor networks. Backscatter technology, a key low-power communication technology in the IoT, is crucial for expanding its application scenarios and enhancing its value. BLE backscatter modulation utilizes GFSK modulation of an intermediate frequency (IF) switching signal to modulate the reflected RF signal. Several IF modulation schemes have been developed for BLE backscatter, but these solutions have limitations.

[0003] Example 1: Traditional BLE backscatter technology suffers from unstable center frequency and modulation index of the reflected signal. This technology uses a digital Gaussian filter to process the baseband signal. The generated digital Gaussian filter signal controls the current source array of a current-starved oscillator, thereby controlling the oscillator's output frequency and achieving the output of a GFSK intermediate frequency (IF) signal. Due to its open-loop design, this solution is subject to the following issues: ① The center frequency of the output GFSK IF signal may deviate from the intended channel due to factors such as circuit manufacturing process variations, unstable power supply voltage, and variations in circuit operating temperature; ② Instability in the modulation index, resulting in poor signal quality; and ③ Limited operating time, which limits the packet length.

[0004] Example 2: Traditional BLE backscatter technology suffers from low integration and excessive size. Its backscatter switch signals are generated by FPGA programming, requiring additional hardware resources. Resistors and capacitors also use off-chip discrete components, which cannot meet miniaturization requirements and has limited applicability.

[0005] Example 3: Traditional BLE backscatter technology suffers from low spectrum efficiency. This solution uses components such as a PLL and an XOR gate to generate an FSK intermediate frequency signal, which provides a certain degree of frequency stability. However, due to the FSK modulation scheme, the peak sidelobes of the reflected signal are relatively low. Furthermore, the modulation method used in this solution limits the transmission rate to below 0.5 Mbps, and the output contains an image interference component near the channel, which affects signal demodulation.

[0006] In summary, the current BLE IF modulation technology used for backscattering suffers from the following drawbacks: ① The modulation frequency is severely affected by PVT, causing the reflected signal to deviate from the BLE channel, resulting in an unstable modulation index, short communication time, and limited packet length. ② The system has low integration and requires excessive hardware resources, resulting in a large overall size, high cost, and limited applicability. ③ The modulated signal has a low peak-to-sidelobe ratio and suffers from image interference, resulting in low spectrum utilization. The disadvantages of existing BLE backscattering technology include: the use of a current-starved oscillator to generate the GFSK IF signal, resulting in an output signal frequency that is significantly affected by factors such as process angle, voltage fluctuations, and operating temperature. This makes it impossible to stably reflect the input RF signal to the predetermined channel and maintain a stable modulation index. Furthermore, as the operating environment of the circuit changes, the signal frequency will continue to shift, limiting the circuit's operating time and the length of the modulated packet. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a method for automatically calibrating the BLE modulation frequency for backscatter communication, which is used to solve the problem of instability of the BLE modulation center frequency and modulation index in backscatter technology. In order to achieve the above-mentioned purpose and other advantages of the present invention, a method for automatically calibrating the BLE modulation frequency for backscatter communication is provided, comprising: A digital Gaussian filter, a modulated voltage-controlled oscillator signal-connected to the digital Gaussian filter, and a voltage-controlled oscillator signal-connected to the modulated voltage-controlled oscillator; The voltage controlled oscillator includes a phase locked loop, which locks the frequency to f through the reference clock input by the crystal oscillator. IF ; The voltage of the voltage-controlled oscillator is a first control voltage, the voltage of the modulated voltage-controlled oscillator is a second control voltage, and the first control voltage is connected to the second control voltage.

[0008] Preferably, the digital Gaussian filter is used to generate a digital Gaussian filtered baseband signal, and the digital Gaussian filtered baseband signal is used to control the capacitive load of the modulated voltage-controlled oscillator.

[0009] A method for automatically calibrating the BLE modulation frequency for backscatter communication includes the following steps: S1. Send the signal to be sent to the digital Gaussian filter for processing to obtain a digital Gaussian filtered baseband signal; S2, the voltage controlled oscillator locks the frequency to f through the phase locked loop IF , so that the intermediate frequency of the output signal of the modulated voltage controlled oscillator is also f IF ; S3, the capacitive load of the modulated voltage controlled oscillator is controlled by the digital Gaussian filter signal, and the output signal frequency is f IF ±f offset GFSK intermediate frequency modulation.

[0010] Compared with the prior art, the present invention has the following advantages: the chip area occupied by the BLE modulation frequency automatic calibration circuit for backscatter communication is only 0.14mm2, and the power consumption is 15.8μW when the data rate is 1Mb / s. Figure 3 The spectrum diagram of the reflected signal shows that the modulation scheme achieves an 11.1dB peak-to-sidelobe ratio optimization. Figure 4 In order to test the function of wearable devices using backscatter technology, this invention was applied to the mobile phone, and the BLE data packet named "EEIS" reflected by this invention was successfully received, and long-term stable reception was achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A modulation circuit diagram of a BLE modulation frequency automatic calibration method for backscatter communication according to the present invention; Figure 2 A diagram showing spectrum measurement results of the BLE modulation frequency automatic calibration method for backscatter communication according to the present invention; Figure 3 A flowchart of the BLE modulation frequency automatic calibration method for backscatter communication according to the present invention is applied to functional testing and performance testing of wearable devices; Figure 4 This is a diagram showing an application case of a specific implementation of the BLE modulation frequency automatic calibration method for backscatter communication according to the present invention. DETAILED DESCRIPTION

[0012] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0013] Reference Figure 1 , a BLE modulation frequency automatic calibration method for backscatter communication, comprising: a digital Gaussian filter, a modulated voltage-controlled oscillator signal-connected to the digital Gaussian filter, and a voltage-controlled oscillator signal-connected to the modulated voltage-controlled oscillator; The voltage controlled oscillator includes a phase locked loop, which locks the frequency to f through the reference clock input by the crystal oscillator. IF; The voltage of the voltage-controlled oscillator is the first control voltage, the voltage of the modulating voltage-controlled oscillator is the second control voltage, and the first control voltage is connected to the second control voltage. By adopting a phase-locked loop-assisted voltage-controlled oscillator modulation scheme: since the frequency of the voltage-controlled oscillator of the phase-locked loop is controlled by the loop, its output signal will track the phase of the reference signal, so it has a stable frequency. By connecting the first control voltage of the voltage-controlled oscillator in the phase-locked loop with the second control voltage of the modulating voltage-controlled oscillator and matching the circuit and layout, the PVT environment and control voltage of the two voltage-controlled oscillators are the same, so that their output frequencies are also the same when the capacitive load is the same, thereby solving the problem of unstable BLE modulation center frequency in the current backscattering scheme.

[0014] Furthermore, after the frequency is locked, the capacitive load of the modulated voltage-controlled oscillator is controlled by using a digital Gaussian filter signal to achieve GFSK modulation with the frequency locked by the phase-locked loop as the center frequency; at the same time, by controlling the weight ratio of the capacitive load of the voltage-controlled oscillator, the GFSK modulation index is controlled, and combined with the frequency locking function of the phase-locked loop, the problem of unstable BLE modulation index in the current backscattering scheme is solved.

[0015] Furthermore, a BLE modulation frequency automatic calibration method for backscatter communication specifically includes the following steps: S1. Send the signal to be sent to the digital Gaussian filter at a rate of 1 Mbps for processing to obtain a digital Gaussian filtered baseband signal; S2, the phase-locked loop uses the reference clock input by the crystal oscillator to lock the frequency to f IF The modulated voltage controlled oscillator has the same structure as the voltage controlled oscillator in the phase-locked loop. Its control voltage is connected to the control voltage of the voltage controlled oscillator in the phase-locked loop, so that the intermediate frequency of the output signal of the modulated voltage controlled oscillator is also f IF . This enables the calibration of the center frequency of the modulated voltage-controlled oscillator.

[0016] S3, the capacitive load of the modulated voltage controlled oscillator is controlled by the digital Gaussian filter signal, and the output signal frequency is f IF ±f offset The digital Gaussian filter signal controls the capacitive load of the modulated voltage controlled oscillator, and the output signal is completed at a frequency of f IF ±f offset GFSK intermediate frequency modulation. Since the modulation voltage controlled oscillator is not in the phase-locked loop, the change of its output frequency will not affect the locking frequency of the phase-locked loop and the center frequency f of the signal. IF By controlling the proportion of modulation capacitance in the total capacitance, f offsetThe modulation index is adjusted by controlling the GFSK intermediate frequency signal. The generated GFSK intermediate frequency signal is used to control the anti-phase scattering load switch. By controlling the proportion of the modulation capacitor in the total capacitance, the f offset The modulation index is adjusted by controlling f IF =4.25MHz, baseband frequency f B Taking 1MHz as an example, to achieve a modulation index of 0.5, that is, 2*f offset / f B =0.5, then the capacitance ratio should be: modulation capacitance / total capacitance = 2*f offset / f IF +f offset =1 / 9.

[0017] In summary, Figure 2 The spectrum diagram of the reflected signal shows that the modulation scheme achieves an 11.1dB peak-to-sidelobe ratio optimization. Figure 3 In order to test the function of wearable devices using backscatter technology, this invention was applied to the mobile phone, and the BLE data packet named "EEIS" reflected by this invention was successfully received, and long-term stable reception was achieved.

[0018] In this embodiment, the present invention can be used in ultra-low-power IoT communication networks. Any IoT device that uses BLE communication, such as smart furniture, smart cars, and wearable devices, can use the present invention to modulate and transmit signals. Compared to traditional BLE devices, the present invention has significantly lower power consumption and cost; compared to traditional backscatter technology, the present invention offers higher signal modulation quality and longer data packet lengths.

[0019] The specific implementation method is as follows: An IoT device equipped with the present invention sends the baseband signal to be transmitted into the present invention. After processing, the present invention generates a GFSK intermediate frequency signal as the switching signal of the reflective load. The incident signal is a carrier signal sent by a carrier generator or a de-whitened BLE signal sent by a BLE device. After reflection by the reflective load, this signal is modulated and reflected as a BLE data packet, which the receiving device can then receive and display.

[0020] Figure 4 Taking a wearable device equipped with the present invention as an example, the incident signal is emitted by a smart watch, and the signal is reflected by the present invention to become a BLE data packet and then received by a mobile phone.

[0021] The number of devices and processing scales described herein are intended to simplify the description of the present invention, and the application, modification, and variation of the present invention will be apparent to those skilled in the art. Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiment. They can be applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily implemented. Therefore, the present invention is not limited to the specific details and illustrations shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for automatic calibration of BLE modulation frequency for backscatter communication, characterized in that: include: A digital Gaussian filter, a modulated voltage-controlled oscillator signal-connected to the digital Gaussian filter, and a voltage-controlled oscillator signal-connected to the modulated voltage-controlled oscillator; The voltage controlled oscillator includes a phase locked loop, which locks the frequency to f through the reference clock input by the crystal oscillator. IF ; The voltage of the voltage-controlled oscillator is a first control voltage, the voltage of the modulated voltage-controlled oscillator is a second control voltage, and the first control voltage is connected to the second control voltage.

2. A BLE modulation frequency automatic calibration method for backscatter communication according to claim 1, characterized in that: The digital Gaussian filter is used to generate a digital Gaussian filtered baseband signal, and the digital Gaussian filtered baseband signal is used to control the capacitive load of the modulated voltage-controlled oscillator.

3. The BLE modulation frequency automatic calibration method for backscatter communication according to claim 2, characterized in that: The specific steps include: S1. Send the signal to be sent to the digital Gaussian filter for processing to obtain a digital Gaussian filtered baseband signal; S2, the voltage controlled oscillator locks the frequency to f through the phase locked loop IF , so that the intermediate frequency of the output signal of the modulated voltage controlled oscillator is also f IF ; S3, the capacitive load of the modulated voltage controlled oscillator is controlled by the digital Gaussian filter signal, and the output signal frequency is f IF ±f offset GFSK intermediate frequency modulation.

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