Low-frequency RFID tag positioning system based on resonance backscattering

Abstract

The invention discloses a low-frequency RFID (Radio Frequency Identification) tag positioning system based on resonance backscattering, which can be applied to the technical field of RFID tag data processing. When the microcontroller generates the driving signal, the on-off state of the analog switch is controlled through the three-state gate according to the periodic driving signal, so that the antenna array is controlled to generate alternating magnetic fields in different directions, and magnetic field energy is sent to the low-frequency tag through the alternating magnetic fields; an LC resonance circuit in the low-frequency tag captures magnetic field energy emitted by the card reader and stores the magnetic field energy through an energy storage capacitor; when the microcontroller stops generating the driving signal, the LC resonance circuit is driven by the energy stored by the energy storage capacitor to generate a backscatter signal, and the backscatter signal processing circuit processes the backscatter signal received by the analog switch to obtain the target signal intensity. And the microcontroller calculates the position information of the low-frequency tag according to the target signal intensity, so that the positioning precision of the low-frequency tag can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of RFID tag data processing, and particularly relates to a low-frequency RFID tag positioning system based on resonant backscattering. BACKGROUND

[0002] In the related art, radio frequency identification (RFID) is a technology of non-contact data interaction between an electromagnetic field and a tag, and is widely applied to fields such as logistics management, access control, intelligent transportation, etc. According to different working frequencies, RFID can be divided into the following three types: low frequency (LF, 125-134 kHz): based on magnetic induction coupling (inductive coupling), typical application scenarios include animal identification, automobile theft prevention; high frequency (HF, 13.56 MHz): based on magnetic induction coupling (inductive coupling), used for bus cards, electronic ticketing, industrial identification; ultra-high frequency (UHF, 860-960 MHz): based on electromagnetic wave reflection (backscattering), suitable for warehouse logistics. At present, low-frequency RFID positioning relies on the detection signal strength of the identified tag for triangulation calculation, which results in low positioning resolution and cannot meet the needs of high-precision application scenarios.

[0003] To sum up, the technical problems in the related art need to be improved. SUMMARY

[0004] The main purpose of the embodiments of the present application is to provide a low-frequency RFID tag positioning system based on resonant backscattering, which can effectively improve the positioning accuracy.

[0005] To achieve the above purpose, the embodiments of the present application provide a low-frequency RFID tag positioning system based on resonant backscattering, which comprises:

[0006] A low-frequency tag, an LC resonant circuit and an energy storage capacitor are arranged on the low-frequency tag; the LC resonant circuit is used to capture the magnetic field energy transmitted by a card reader, and the energy storage capacitor is used to store the magnetic field energy; when the card reader stops transmitting the magnetic field energy, the energy stored in the energy storage capacitor is used to drive the LC resonant circuit to generate a backscattering signal;

[0007] The card reader comprises an antenna array, an analog switch, a microcontroller, a tri-state gate and a backscatter signal processing circuit; the microcontroller is configured to output a periodic driving signal to the tri-state gate; the tri-state gate is configured to control the switching state of the analog switch according to the periodic driving signal, thereby controlling the antenna array to generate alternating magnetic fields in different directions, so as to send the magnetic field energy to the low-frequency tag through the alternating magnetic fields; the backscatter signal processing circuit is connected in series between the analog switch and the microcontroller, and is configured to process the backscatter signal received by the analog switch to obtain a target signal strength; and the microcontroller is configured to calculate the position information of the low-frequency tag according to the target signal strength.

[0008] In some embodiments, the antenna array adopts a nested double-axis cross layout.

[0009] In some embodiments, the antenna array comprises an X-axis coil group and a Y-axis coil group, and the X-axis coil group and the Y-axis coil group are orthogonally and laminatedly distributed in space; the X-axis coil group is configured to generate an X-axis alternating magnetic field, and the Y-axis coil group is configured to generate a Y-axis alternating magnetic field.

[0010] In some embodiments, the backscatter signal processing circuit comprises a filtering circuit, a detection circuit, a shielding circuit and an integration circuit; the filtering circuit is configured to perform filtering operation on the backscatter signal; the detection circuit is configured to perform envelope detection on the filtered backscatter signal to obtain a pulse signal; the shielding circuit is configured to eliminate the interference of the card reader on the backscatter signal; and the integration circuit is configured to perform smoothing processing on the pulse signal to obtain the target signal strength.

[0011] In some embodiments, the filtering circuit comprises a Butterworth filter.

[0012] In some embodiments, the processing of the backscatter signal received by the analog switch to obtain the target signal strength comprises:

[0013] performing filtering processing on the backscatter signal received by the analog switch to obtain a target resonant component;

[0014] performing envelope detection on the target resonant component to obtain a pulse signal;

[0015] removing interference signals of the pulse signal;

[0016] performing time-domain integration on the pulse signal from which the interference signals are removed to obtain the target signal strength.

[0017] In some embodiments, the tri-state gate comprises a single-pass tri-state buffer.

[0018] In some embodiments, the system further comprises an interface unit, and the microcontroller interacts with the host computer through the interface unit.

[0019] In some embodiments, the calculating the position information of the low-frequency tag according to the target signal strength comprises:

[0020] constructing a spatial signal feature matrix according to the target signal strength;

[0021] calculating the position information of the low-frequency tag according to the spatial signal feature matrix.

[0022] In some embodiments, the microcontroller comprises an analog-to-digital converter, which is used to convert an analog voltage corresponding to the target signal strength into a digital signal.

[0023] The embodiments of the present application have at least the following beneficial effects: the present application provides a low-frequency RFID tag positioning system based on resonant backscattering, which comprises the following steps: an LC resonant circuit and an energy storage capacitor are arranged in a low-frequency tag; an antenna array, an analog switch, a microcontroller, a tri-state gate and a backscattering signal processing circuit are arranged in a card reader; then when the microcontroller generates a driving signal, the tri-state gate controls the switching state of the analog switch according to the periodic driving signal, and then controls the antenna array to generate an alternating magnetic field in different directions, so as to send the magnetic field energy to the low-frequency tag through the alternating magnetic field; the LC resonant circuit in the low-frequency tag captures the magnetic field energy transmitted by the card reader, and stores the magnetic field energy through the energy storage capacitor; when the microcontroller stops generating the driving signal, the energy stored in the energy storage capacitor drives the LC resonant circuit to generate a backscattering signal; after the backscattering signal processing circuit processes the backscattering signal received by the analog switch to obtain a target signal strength, the microcontroller calculates the position information of the low-frequency tag according to the target signal strength, so as to effectively improve the positioning accuracy of the low-frequency tag. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of a low-frequency RFID tag positioning system based on resonant backscattering provided by the embodiments of the present application;

[0025] Figure 2 is a schematic diagram of an antenna array provided by the embodiments of the present application;

[0026] Figure 3 is a schematic diagram of a periodic signal waveform output by a microcontroller provided by the embodiments of the present application;

[0027] Figure 4 is a schematic diagram of a resonant waveform received by a card reader when a tag exists provided by the embodiments of the present application;

[0028] Figure 5is a resonant waveform diagram received by the card reader when a tag does not exist, provided by an embodiment of the present application;

[0029] Figure 6 is a schematic diagram of a microcontroller and its peripheral circuit, provided by an embodiment of the present application;

[0030] Figure 7 is a schematic diagram of an analog switch and antenna interface circuit, provided by an embodiment of the present application;

[0031] Figure 8 is a schematic diagram of a Butterworth filter and integration circuit, provided by an embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementation described in the following exemplary embodiments does not represent all the implementations consistent with the embodiments of the present application. They are only examples of devices and methods consistent with some aspects of the embodiments of the present application as detailed in the appended claims.

[0033] It can be understood that the terms "first", "second", and the like used in the present application can be used herein to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of the present application, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "when" or "in response to determining".

[0034] The terms "at least one", "multiple", "each", "any" and the like used in the present application include one, two or more than two, multiple includes two or more than two, each refers to each of the corresponding multiple, and any refers to any one of the multiple.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by those skilled in the art to which the present application belongs. The terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0036] Before the embodiments of the present application are described in detail, first, some of the terms and terminology involved in the embodiments of the present application are explained, and the terms and terminology involved in the embodiments of the present application are applicable to the following explanations:

[0037] An ADC (Analog-to-Digital Conversion) is an electronic device that converts analog signals into digital signals, widely used in sensor data acquisition, signal processing and other fields. ADC converts continuous analog signals (such as voltage, current) into discrete digital values through sampling, quantization and encoding steps for digital system processing.

[0038] RFID (Radio Frequency Identification) is a technology that interacts with tags through electromagnetic fields in a non-contact manner, widely used in logistics management, access control, intelligent transportation and other fields. According to the working frequency, RFID can be divided into the following three categories:

[0039] Low frequency (LF, 125-134 kHz): based on magnetic induction coupling (inductive coupling), typical application scenarios include animal identification, car theft prevention.

[0040] High frequency (HF, 13.56 MHz): based on magnetic induction coupling (inductive coupling), used for bus cards, electronic ticketing, industrial identification.

[0041] Ultra-high frequency (UHF, 860-960 MHz): based on electromagnetic wave reflection (backscatter), suitable for warehouse logistics.

[0042] PC (Personal Computer) is a general-purpose computing device designed for personal use, running an operating system (such as Windows, MacOS), supporting multitasking, software applications and Internet connections, suitable for office, entertainment, data processing and other scenarios.

[0043] PLC (Programmable Logic Controller) is a special control device in the field of industrial automation, controlling machinery or production processes through digital / analog input / output, with functions such as logic operation, timing / counting, arithmetic operation, suitable for complex industrial control tasks.

[0044] In the related art, in the application process of low-frequency RFID tags, energy transmission and data communication are achieved through mutual inductance between card readers and tag coils, and no battery is needed to be built-in in the tag, relying on the power supply of the card reader magnetic field. And, the penetration of low-frequency magnetic field to metal environment is due to high-frequency electromagnetic waves. However, the current low-frequency RFID positioning relies on the detection signal strength of the identified tag for triangulation calculation, resulting in low positioning resolution, which cannot meet the needs of high-precision application scenarios.

[0045] Therefore, the embodiment of the present application provides a low-frequency RFID tag positioning system based on resonant backscattering, which can effectively improve the positioning accuracy.

[0046] The embodiment of the present application will be described in detail below with reference to the accompanying drawings:

[0047] Figure 1 is an optional system schematic diagram of the low-frequency RFID tag positioning system based on resonant backscattering provided by the embodiment of the present application, Figure 1 The system in the figure can include but is not limited to including a low-frequency tag 100 and a card reader. Wherein, the low-frequency tag is provided with an LC resonant circuit and an energy storage capacitor, and the card reader includes an antenna array 210, an analog switch 220, a microcontroller 240, a tri-state gate 230 and a backscattering signal processing circuit. It can be understood that the tri-state gate 230 can adopt a single-pass tri-state buffer, and the microcontroller 240 and its peripheral circuit are as shown in Figure 6 The analog switch 220 is connected with an antenna interface circuit as shown in Figure 7 Specifically, the LC resonant circuit is used to capture the magnetic field energy transmitted by the card reader, and the energy storage capacitor is used to store the magnetic field energy; when the card reader stops transmitting the magnetic field energy, the energy stored by the energy storage capacitor drives the LC resonant circuit to generate a backscattering signal; the microcontroller is used to output a periodic driving signal to the tri-state gate; the tri-state gate is used to control the switching state of the analog switch according to the periodic driving signal, and further control the antenna array to generate alternating magnetic field in different directions to transmit the magnetic field energy to the low-frequency tag through the alternating magnetic field; the backscattering signal processing circuit is connected in series between the analog switch and the microcontroller, and is used to process the backscattering signal received by the analog switch to obtain a target signal strength; the microcontroller is used to calculate the position information of the low-frequency tag according to the target signal strength.

[0048] It can be understood that, as shown in Figure 2 The antenna array 210 adopts a nested double-axis cross layout. Specifically, the antenna array includes an X-axis coil group and a Y-axis coil group, and the X-axis coil group and the Y-axis coil group are orthogonally distributed in space. The X-axis coil group is arranged along the horizontal direction and is used to generate X-axis alternating magnetic field; the Y-axis coil group is arranged along the vertical direction and is used to generate Y-axis alternating magnetic field. In this embodiment, through the nested design, when the tag is located at any non-edge position in the antenna array coverage area, it is at least in the effective excitation range of the X-axis or Y-axis coil, and the signal blind area is eliminated through the orthogonal magnetic field coverage, which can effectively improve the positioning robustness.

[0049] It can be understood that, as shown in Figure 1As shown, the backscatter signal processing circuit of this embodiment includes a filter circuit 261, a detector circuit 262, a shielding circuit 263, and an integrator circuit 264. The filter circuit is used to filter the backscatter signal; the detector circuit is used to perform envelope detection on the filtered backscatter signal to obtain a pulse signal; the shielding circuit eliminates interference from the card reader on the backscatter signal; and the integrator circuit is used to smooth the pulse signal to obtain the target signal strength. The filter circuit can employ a Butterworth filter, and the Butterworth filter and integrator circuit are as follows: Figure 8 As shown.

[0050] In this embodiment, the microcontroller generates a 134.5kHz periodic drive signal to control the analog switch's selection logic for the antenna array and detects the strength of the backscattered signal returned by the tag, calculating the spatial position of the RFID tag based on the signal strength. A tri-state gate is used to isolate the receiving channel from the transmitting channel during drive signal transmission. The transmitting channel is the channel directly connected to the analog switch and the microcontroller, while the receiving channel is the channel connecting the analog switch, the backscattered signal processing circuit, and the microcontroller. The analog switch selects either the X-axis or Y-axis channel in the antenna array based on the drive signal sent by the microcontroller, thus switching the magnetic field direction. The low-frequency RFID tag in this embodiment operates at 134.5kHz and has a built-in LC resonant circuit capable of capturing and storing energy in an internal capacitor. When the microcontroller stops sending the drive signal, the LC resonant circuit induces mutual inductance fluctuations through impedance changes, which can then use magnetic induction coupling to transmit the signal back to the reader antenna.

[0051] After reading the signal strength returned by the tag, the card reader uses a six-stage active structure to filter the signal, suppressing high-frequency signals and retaining the amplified 134.5kHz resonant component as the target resonant component. The detection circuit performs envelope detection on the filtered target resonant component, outputting a pulse signal proportional to the tag signal strength. Simultaneously, a shielding circuit eliminates interference from the reader's own drive signal, retaining only the tag's resonant reflected signal. The integrator circuit performs time-domain integration (RC) smoothing on the detected pulse signal to generate a stable voltage signal as the target signal strength, which is then input to the microcontroller's analog-to-digital converter (ADC) for analog-to-digital conversion.

[0052] It is understood that the system in this embodiment also includes an interface unit, such as... Figure 1 As shown, the microcontroller interacts with the host computer 250 through an interface unit. The host computer includes, but is not limited to, host computer systems such as PCs and PLCs.

[0053] During operation, this embodiment uses a microcontroller to periodically generate a 134.5kHz square wave signal (drive signal) as the carrier frequency for communication between the card reader and the tag, matching the LC resonant frequency of the tag. For example, as shown... Figure 3 The waveform of the periodic signal output by the microcontroller is shown. Figure 3 In the diagram, the green waveform represents the timing signal when the tri-state gate switches to the high-impedance state, isolating the transmit channel and preparing to receive the tag's resonant return signal. The red waveform represents the timing signal when the microcontroller controls the analog switch to switch the transmit channel, corresponding to the drive signal waveform output by the tri-state gate.

[0054] When the microcontroller generates a drive signal, the tri-state gate enters the conduction state, allowing the drive signal to pass. The analog switch sequentially selects the X-axis or Y-axis coils (time-division multiplexed) in the antenna array according to the received drive signal, driving the magnetic field to radiate outwards. The tag's built-in LC resonant circuit captures the magnetic field energy through magnetic induction coupling, and stores it in an internal capacitor after rectification. When the drive signal transmission ends, the microcontroller controls the tri-state gate to enter a high-impedance state, isolating the transmit and receive channels, thereby preventing signal interference. The LC resonant circuit within the tag generates a strong backscattered signal at its resonant frequency. This backscattered signal is transmitted back to the reader antenna through magnetic induction coupling, manifesting as a decaying oscillation signal at the resonant frequency. For example, when a tag is present, such as... Figure 4 As shown, the reader's antenna receives the resonant signal returned by the LC resonant circuit inside the tag, which manifests as a decaying oscillation waveform, specifically as follows: Figure 4 The green waveform; when no label exists, such as... Figure 5 As shown, after the driving signal stopped, no significant resonant signal was detected by the antenna, specifically as follows: Figure 5 Medium green lines.

[0055] Specifically, after receiving the backscattered signal, the backscatter signal processing circuit performs a sixth-order active bandpass filter on the signal received by the antenna using a Butterworth filter, retaining and amplifying the 134.5kHz resonant component. The detection circuit performs envelope detection on the filtered signal, outputting a pulsed DC voltage proportional to the tag signal strength. Simultaneously, after suppressing interference from the reader's own drive signal through a shielding circuit, the pulse signal output from the detection circuit is integrated by an RC circuit to generate a stable voltage signal, which is then input into the microcontroller for processing.

[0056] It is understood that the microcontroller in this embodiment can construct a spatial signal feature matrix based on the target signal strength (RSSI), and then calculate the two-dimensional coordinates of the low-frequency tag as position information based on the spatial signal feature matrix. Specifically, this embodiment uses a sliding window for signal sampling. For example, a fixed window size (coil window size = 5, indicating that the sliding window covers 5 coil antennas) is selected with the current coil antenna index lastpos as the center for sampling, and the corresponding signal strength sequence (signal strength array [i]) is obtained as the signal for subsequent position calculation. Among them, the signal strength array [i] = (float) acquired signal strength (x_yn) - signal offset correction value. The acquired signal strength can be calculated by the signal strength acquisition function, which is used to read the signal strength of a specified coil. The signal offset correction value is used as a correction parameter to eliminate baseline noise. For example, assuming lastpos = 3, the window covers coil indices 1–5, and the analog switch is switched sequentially to read the signal strength of each coil.

[0057] After acquiring the signal strength of each coil, a quadratic polynomial model y = ax² + bx + c (where a, b, and c are fitting coefficients) is constructed for two-dimensional coordinate calculation. Specifically, in this embodiment, the coefficients a, b, and c are solved by fitting the signal strength data within the window using the least squares method, and the peak position of the signal strength curve is calculated as -2ab. Then, the final two-dimensional coordinates are calculated as peak position + current coil index - window half-width (the window half-width is half the size of the positioning window). For example, if the window signal strength is [120, 200, 300, 250, 150], and the interpolation yields a peak position of 2.3, then the final coordinates are 2.3 + 3 - 2 = 3.3 (the index precision is improved to level 0.1). Next, the coil index is converted into physical coordinates using the linear mapping formula x = round(linear mapping(source range minimum, source range maximum, target range minimum, target range maximum, current coordinates)) to obtain the tag position.

[0058] As can be seen from the above, this embodiment, based on the sub-coil level positioning algorithm of resonant backscattering and the nested dual-axis cross antenna array design, improves the positioning accuracy of low-frequency RFID tags from the integer level (cm) to the fractional level (mm), thereby achieving millimeter-level (mm) positioning resolution.

[0059] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0060] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0061] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0062] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0063] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0064] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A low-frequency RFID tag positioning system based on resonant backscattering, characterized in that, The system includes: A low-frequency tag is provided with an LC resonant circuit and an energy storage capacitor; the LC resonant circuit is used to capture the magnetic field energy emitted by the card reader, and the energy storage capacitor is used to store the magnetic field energy; when the card reader stops emitting the magnetic field energy, the energy stored in the energy storage capacitor drives the LC resonant circuit to generate a backscatter signal. A card reader includes an antenna array, an analog switch, a microcontroller, a tri-state gate, and a backscatter signal processing circuit. The microcontroller outputs a periodic drive signal to the tri-state gate. The tri-state gate controls the switching state of the analog switch according to the periodic drive signal, thereby controlling the antenna array to generate alternating magnetic fields in different directions to transmit magnetic field energy to the low-frequency tag. The backscatter signal processing circuit is connected in series between the analog switch and the microcontroller to process the backscatter signal received by the analog switch to obtain the target signal strength. The microcontroller calculates the location information of the low-frequency tag based on the target signal strength.

2. The system according to claim 1, characterized in that, The antenna array adopts a nested dual-axis cross layout.

3. The system according to claim 2, characterized in that, The antenna array includes an X-axis coil group and a Y-axis coil group, which are orthogonally stacked in space. The X-axis coil group is used to generate an alternating magnetic field along the X-axis, and the Y-axis coil group is used to generate an alternating magnetic field along the Y-axis.

4. The system according to claim 1, characterized in that, The backscatter signal processing circuit includes a filtering circuit, a detection circuit, a shielding circuit, and an integration circuit. The filtering circuit is used to filter the backscatter signal. The detection circuit is used to perform envelope detection on the filtered backscatter signal to obtain a pulse signal. The shielding circuit eliminates the interference of the card reader on the backscatter signal. The integration circuit is used to smooth the pulse signal to obtain the target signal strength.

5. The system according to claim 4, characterized in that, The filtering circuit includes a Butterworth filter.

6. The system according to claim 4, characterized in that, The process of processing the backscattered signal received by the analog switch to obtain the target signal strength includes: The backscattered signal received by the analog switch is filtered to obtain the target resonant component; Envelope detection is performed on the target resonant component to obtain a pulse signal; Remove interference signals from the pulse signal; The target signal strength is obtained by time-domain integration of the pulse signal after removing the interference signal.

7. The system according to claim 1, characterized in that, The tri-state gate includes a single-pass tri-state buffer.

8. The system according to claim 1, characterized in that, The system also includes an interface unit, through which the microcontroller interacts with the host computer.

9. The system according to claim 1, characterized in that, The step of calculating the location information of the low-frequency tag based on the target signal strength includes: Construct a spatial signal feature matrix based on the target signal strength; The location information of the low-frequency tag is calculated based on the spatial signal feature matrix.

10. The system according to claim 6, characterized in that, The microcontroller includes an analog-to-digital converter (ADC) for converting an analog voltage corresponding to a target signal strength into a digital signal.

Images