Low-cost NFC radio frequency antenna debugging method based on signal generator and oscilloscope

Abstract

The invention discloses a low-cost NFC (Near Field Communication) radio frequency antenna debugging method based on a signal generator and an oscilloscope, which belongs to the technical field of wireless radio frequency and is mainly used for testing performance parameters of a radio frequency antenna under different impedances and frequencies through a method of combining the signal generator and the oscilloscope. A signal generator and an oscilloscope are used for replacing a network analyzer to debug a radio frequency antenna, a typical probe of the oscilloscope is used as a wireless radio frequency wave measuring tool without other professional radio frequency tools, and a probe of the oscilloscope and the antenna are used for capturing radio frequency waveforms and amplitudes in a mutual inductance mode without direct connection. According to the invention, non-professionals are helped to design, debug and optimize the antenna so as to meet basic requirements of using the antenna, and dependence on professional radio frequency tools such as a network analyzer is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless radio frequency, and particularly relates to a low-cost NFC radio frequency antenna debugging method based on a signal generator and an oscilloscope. BACKGROUND

[0002] With the rapid development of RFID technology, the field of wireless radio frequency is rapidly developed, especially in the field of NFC. In order to meet the increasing needs of production and life, the requirements for NFC antennas are higher and higher. The existing NFC antenna debugging method mainly includes theoretical calculation and debugging using professional equipment network analyzer. The former is complicated and inefficient, and it is difficult to guarantee the actual product effect. The latter needs to additionally purchase professional equipment (such as network analyzer), which limits the ability of small enterprises and individuals to independently develop high-performance NFC antennas. The application aims to provide a low-cost radio frequency antenna debugging scheme, which replaces the network analyzer with two commonly used devices, signal generator and oscilloscope, to perform relatively accurate and rapid NFC antenna debugging, so as to meet the performance requirements of small enterprises and individuals for NFC antenna products. SUMMARY

[0003] In view of the above problems existing in the prior art, the application provides a low-cost NFC radio frequency antenna debugging method based on a signal generator and an oscilloscope. The actual resonance point of the antenna is found by using mutual inductive coupling and LC resonance principle through general instruments. The design is reasonable, and the deficiencies of the prior art are solved, and good effects are obtained.

[0004] In order to achieve the above purpose, the application adopts the following technical scheme: A low-cost NFC radio frequency antenna debugging method based on a signal generator and an oscilloscope, comprising the following steps: Step 1: preparing an NFC antenna to be debugged, and reserving a debugging pad for matching a capacitor; Step 2: matching an initial capacitor for the NFC antenna according to an empirical formula; Step 3: connecting the output end of the signal generator to two input lines of the NFC antenna, and setting the output impedance of the signal generator to a fixed resistance value; Step 4: short-circuiting the positive and negative poles of the oscilloscope probe to form a detection coil; Step 5: coupling the detection coil and the NFC antenna by mutual inductance, and observing the waveform amplitude on the oscilloscope; Step 6: adjusting the output frequency of the signal generator, and monitoring the change of the waveform amplitude on the oscilloscope, finding the frequency corresponding to the maximum amplitude, which is the actual resonance frequency of the NFC antenna; Step 7: According to the actual resonant frequency and the value of the initial capacitance, the equivalent inductance of the NFC antenna is calculated by the LC resonant frequency formula; Step 8: According to the equivalent inductance, the target matching capacitance is recalculated and welded to make the resonant frequency of the antenna accurately align with the target operating frequency. If the obtained NFC antenna still deviates from the target operating frequency by more than ±10%, the target matching capacitance value is taken as the initial capacitance value to repeat the above steps 6-8 to improve the accuracy.

[0005] Further, a plurality of debugging pads for matching capacitors are provided on the antenna to be modulated.

[0006] Further, in step 2, the antenna inductance L is calculated according to the empirical formula or the NFC impedance matching tool, the theoretical matching capacitance is calculated by the LC resonant frequency formula, and a nominal value closest to the theoretical matching capacitance is selected as the initial capacitance and welded to the antenna pad.

[0007] Further, the output impedance of the signal generator is set to 25Ω to simulate the output condition of a typical radio frequency power amplifier, and a sine wave is set as the output of the signal generator.

[0008] Further, the initial output frequency of the signal generator is set within the range of 1 / 2±10% of the target operating frequency.

[0009] Further, in step 4, an oscilloscope is taken, and its standard ×1 or ×10 passive voltage probe is used. The hook at the tip of the probe and the ground clip are shorted together to form a closed metal ring, thereby forming a magnetic field detection coil.

[0010] Further, the detection coil is placed close to but not in contact with the NFC antenna to be debugged. At this time, the radio frequency signal output by the signal generator is coupled to the detection coil through the space magnetic field, and a sine wave can be observed on the oscilloscope.

[0011] The beneficial technical effects brought by the present application are: 1. Significantly reduce the cost: using general and inexpensive devices such as signal generators and oscilloscopes, instead of professional network analyzers, greatly reduces the hardware threshold of NFC product development.

[0012] 2. Simple and efficient operation: avoids complex Smith chart analysis and impedance transformation calculation. The entire process is based on the intuitive principle of "sweeping frequency and finding peak", and technical workers can master it after simple training. The debugging process is fast and direct.

[0013] 3. The accuracy meets the requirements: by calculating the equivalent inductance and performing multiple matching, the deviation between the theoretical calculation and the actual value can be effectively corrected, and finally the antenna resonant frequency is accurately aligned with the target frequency point, and the accuracy fully meets the needs of commercial NFC products.

[0014] .4. Strong universality: the method is not only suitable for NFC antenna, but also can be popularized to the debugging of resonant antennas of other frequency bands (such as wireless charging antennas), and has wide applicability. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the debugging schematic of the NFC radio frequency antenna in the application; Figure 2 is the second test wiring schematic of the first test board in the embodiment of the application; Figure 3 is the second wiring schematic of the second test board in the embodiment of the application. DETAILED DESCRIPTION

[0016] The specific implementation of the application will be further described in combination with specific embodiments: A low-cost NFC radio frequency antenna debugging method based on a signal generator and an oscilloscope, which uses a signal generator and an oscilloscope to replace a network analyzer for radio frequency antenna debugging, uses a typical probe of the oscilloscope as a wireless radio frequency wave measurement tool without other professional radio frequency tools, and uses the probe of the oscilloscope to capture radio frequency waveforms and amplitudes through mutual inductance without direct connection, as shown in the figure, and specifically includes the following steps: Figure 1 Step 1: preparing an NFC antenna to be debugged, and reserving debugging pads for matching capacitors; In this embodiment, a 13.56MHz NFC antenna coil to be debugged is prepared, for example, the inductance theoretical value is about 1-2μH, and a plurality of debugging pads for welding and replacing capacitors are reserved at the matching circuit connected in parallel with the NFC antenna coil, and the number of the pads is set to be more than 4. Step 2: matching an initial capacitor for the NFC antenna according to an empirical formula, so that the theoretical resonant frequency of the antenna is close to the target working frequency;

[0017] In this embodiment, according to the empirical formula and the commonly used NFC impedance matching tool, the antenna inductance L is calculated to be about 1.5μH, and the target frequency f is 13.56MHz. The theoretical matching capacitor C can be calculated to be about 92pF through the LC resonant frequency formula (as shown in formula 1), and therefore a nominal value closest to 100pF is selected as the initial capacitor and welded to the antenna pad.

[0018] (1) Step 3: connecting the output end of the signal generator to two input lines of the NFC antenna, and setting the output impedance of the signal generator to a fixed resistance value; ​Specifically, the output end of the signal generator is connected to the two input ends of the NFC antenna through a coaxial cable and a soldering lead. The output impedance of the signal generator is set to the typical RF output power amplifier output impedance, which is set to 25Ω, to simulate the driving source impedance of a real NFC chip. The signal generator is set to output a sine wave, and the initial amplitude is 3Vpp.

[0019] Step 4: Short the positive and negative poles of the oscilloscope probe to form a detection coil. Specifically, take an oscilloscope, use its standard ×1 or ×10 passive voltage probe, and directly short the hook and ground clip at the tip of the probe to form a closed metal ring, which constitutes a simple magnetic field detection coil.

[0020] Step 5: Couple the detection coil with the NFC antenna through mutual inductance, and observe the waveform amplitude on the oscilloscope. Specifically, place the detection coil made in step 4 close to but not touching the NFC antenna to be debugged, usually at the center or edge of the antenna coil. At this time, the RF signal output by the signal generator will be coupled into the detection coil through the space magnetic field, and a sine waveform can be observed on the oscilloscope.

[0021] Step 6: Adjust the output frequency of the signal generator and monitor the change in waveform amplitude on the oscilloscope, and find the frequency corresponding to the maximum amplitude, which is the actual resonance frequency of the NFC antenna. Specifically, the initial output frequency of the signal generator is set to be within 1 / 2±10% of the target operating frequency. Keep the relative position of the detection coil and the antenna unchanged, and slowly adjust the output frequency of the signal generator from 7MHz to 20MHz in this embodiment. At the same time, closely observe the change in waveform amplitude on the oscilloscope. When the frequency is adjusted to a certain point, the waveform amplitude on the oscilloscope will reach a maximum value. Record the frequency value displayed on the signal generator at this time, which is 12.8MHz, which is the actual resonance frequency of the antenna under the 100pF matching capacitor.

[0022] Step 7: Calculate the equivalent inductance of the NFC antenna according to the actual resonance frequency and the value of the initial capacitor using the LC resonance frequency formula. Specifically, since there is a deviation between the actual resonance frequency (12.8MHz) and the theoretical frequency (13.56MHz), the actual inductance of the antenna is different from the theoretical value. According to the resonance formula, f=12.8MHz, C=100pF, the real equivalent inductance L of the antenna can be calculated as L ≈ 1.55μH.

[0023] Step 8: According to the equivalent inductance, recalculate and solder the target matching capacitor to make the resonant frequency of the antenna accurately align with the target operating frequency. If the obtained NFC antenna still deviates from the target operating frequency by > ± 10%, the matching capacitor value obtained this time can be used as the initial capacitor value to repeat the above steps 6-8 to improve the accuracy.

[0024] Specifically, according to the calculated real inductance L = 1.55 μH, the accurate matching capacitor value is calculated using the formula: C ≈ 87 pF. Then, the initial capacitor of 100 pF is replaced with a matching capacitor of 87 pF. Using the method of step 6 again, it can be found that the actual resonant frequency of the antenna is very close to the target frequency of 13.56 MHz at this time, and the debugging is completed.

[0025] The entire debugging process does not need to use a network analyzer and Smith chart for impedance matching analysis, and the positioning and matching of the antenna resonant point can be completed by observing the time domain waveform amplitude change on the oscilloscope; The core operation process of the debugging method is simplified to "apply excitation signal, mutual inductance detection, sweep frequency peak search, and matching calculation", and the operator does not need to have professional knowledge of radio frequency impedance matching theory; In the entire debugging process, there is no need for complex operations based on Smith chart, such as series-parallel conversion of impedance, admittance calculation, etc., but only relying on the basic LC resonant frequency formula for calculation.

[0026] As shown in Table 1, the two 13.56 MHz NFC antenna test data tables, both tests are completed by matching twice, the single test time is about 6 minutes, and the completion of a NFC antenna matching only takes 12 minutes, the error is less than 2%, Figure 2 、 Figure 3 respectively Figure 2 are

[0027] Table 1 Test data table ; Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A low-cost NFC radio antenna debugging method based on a signal generator and an oscilloscope, characterized in that, The method comprises the following steps: Step 1: preparing an NFC antenna to be debugged, and reserving debug pads for matching capacitors; Step 2: matching an initial capacitor for the NFC antenna according to an empirical formula; Step 3: connecting the output end of a signal generator to two input lines of the NFC antenna, and setting the output impedance of the signal generator to a fixed resistance value; Step 4: short-circuiting the positive and negative electrodes of an oscilloscope probe to form a detection coil; Step 5: coupling the detection coil and the NFC antenna through mutual inductance, and observing the waveform amplitude on the oscilloscope; Step 6: adjusting the output frequency of the signal generator, and monitoring the change of the waveform amplitude on the oscilloscope, finding the frequency corresponding to the maximum amplitude, which is the actual resonance frequency of the NFC antenna; Step 7: calculating the equivalent inductance of the NFC antenna according to the LC resonance frequency formula based on the actual resonance frequency and the value of the initial capacitor; Step 8: recalculating and welding the target matching capacitor according to the equivalent inductance, so that the resonance frequency of the antenna is accurately aligned with the target working frequency, if the obtained NFC antenna still deviates from the target working frequency by more than ±10%, the target matching capacitor value is taken as the initial capacitor value to repeat the above steps 6-8 to improve the accuracy.

2. The low-cost NFC antenna debugging method based on a signal generator and an oscilloscope according to claim 1, characterized in that, The antenna to be modulated is provided with a plurality of debug pads for matching capacitors.

3. The low-cost NFC antenna debugging method based on a signal generator and an oscilloscope according to claim 1, characterized in that, In step 2, the antenna inductance L is calculated according to the empirical formula or the NFC impedance matching tool, the theoretical matching capacitor is calculated through the LC resonance frequency formula, and a nominal value closest to the theoretical matching capacitor is selected as the initial capacitor and welded to the antenna pad.

4. The low-cost NFC antenna debugging method based on a signal generator and an oscilloscope according to claim 1, characterized in that, The output impedance of the signal generator is set to 25Ω to simulate the output condition of a typical RF power amplifier, and a sine wave is output by the signal generator.

5. The low-cost NFC antenna debugging method based on a signal generator and an oscilloscope according to claim 1, characterized in that, The initial output frequency of the signal generator is set within 1 / 2±10% of the target working frequency.

6. The low-cost NFC antenna debugging method based on a signal generator and an oscilloscope according to claim 1, characterized in that, In step 4, an oscilloscope is taken, and the hook and ground clip at the tip of the ×1 or ×10 passive voltage probe are short-circuited together to form a closed metal ring, thereby constituting a magnetic field detection coil.

7. The low-cost NFC antenna debugging method based on a signal generator and an oscilloscope according to claim 1, characterized in that, The detection coil is placed close to but not in contact with the NFC antenna to be debugged, at this time, the RF signal output by the signal generator is coupled into the detection coil through the space magnetic field, and a sine waveform can be observed on the oscilloscope.

Images