A design method of a visible light emission equalizer based on an LED equivalent circuit

Abstract

The application provides a design method of a visible light emission equalizer based on an LED equivalent circuit, comprising: establishing a second-order equivalent circuit model of an electro-optical conversion LED device; assigning the values of poles p1 and p2 of an LED transfer function H1(s) to two zero points in an equalization structure model to obtain an amplitude-frequency response curve of a transfer function H(s) of a visible light communication system after cascading an equalization structure. The application has the following advantages: 1) the application can effectively expand the bandwidth of an illumination LED, thereby improving the communication rate of a wireless optical communication system; 2) the application is applicable to a wireless optical transmission system using an LED and other light sources; 3) the application has fewer parameters to be concerned in the flow of the implementation method, and is easy to implement; 4) the application has a mathematical model, and is easy to implement by means of a software tool and to perform hardware simulation; and 5) the application is verified by experiments and can effectively expand the system bandwidth.

Description

Technical Field

[0001] The present invention belongs to the technical field of equalizer design, and in particular relates to a design method of a visible light emission equalizer based on an LED equivalent circuit. Background Art

[0002] Visible light communication (VLC) is an optical wireless communication technology that encodes information through variations in light intensity. Compared to traditional radio frequency and 5G technologies, VLC promises to enhance wireless communication capabilities in terms of speed, reliability, and security. The rapid development of VLC is closely related to the significant progress and widespread adoption of solid-state light-emitting diode (LED) devices. However, LEDs have a limited modulation bandwidth, typically in the range of several megahertz, which significantly limits communication rates. Their inherent modulation bandwidth is a significant limiting factor in channel capacity. Therefore, effectively expanding the bandwidth of VLC is a key issue that needs to be addressed.

[0003] As the optical transmitter of visible light communication, the equalizer first performs equalization on the signal before transmitting it through the LED. In the prior art, the bandwidth can be expanded by designing the equalizer. Figure 1 Figure 1 shows an equalizer structure that uses a capacitor-resistor network to balance the link bandwidth. This offsets the cutoff frequency of the LED model and the equalization network, thereby achieving bandwidth expansion. However, this approach ultimately only achieves a bandwidth expansion from 7.5MHz to 48MHz, which is not ideal.

[0004] Therefore, how to effectively expand the bandwidth of optical fiber transmission networks is a key issue that needs to be solved at present. Summary of the Invention

[0005] In view of the defects of the prior art, the present invention provides a design method of a visible light emission equalizer based on an LED equivalent circuit, which can effectively solve the above problems.

[0006] The technical solution adopted in the present invention is as follows:

[0007] The present invention provides a design method for a visible light emission equalizer based on an LED equivalent circuit, comprising the following steps:

[0008] Step S1, building a visible light communication system; the visible light communication system includes a transmitter and a receiver; the transmitter includes an electro-optical conversion LED device;

[0009] Step S2, establishing an LED second-order equivalent circuit model of the electro-optical conversion LED device, and determining model parameters of the LED second-order equivalent circuit model to obtain a designed LED second-order equivalent circuit model, so that the designed LED second-order equivalent circuit model and the electro-optical conversion LED device are equivalent;

[0010] Step S3, determining the LED transfer function H1(s) of the LED second-order equivalent circuit model obtained in step S2, analyzing the LED transfer function H1(s) to obtain poles p1 and p2;

[0011] Step S4, establishing a transfer function model H2(s) of the balanced structure; the transfer function model H2(s) of the balanced structure has m zero points of the balanced structure model, represented by z e，x , x = 1, 2, ..., m, and n poles of the equilibrium structure model, denoted as p e，y , y=1,2,...,n; where n≥2;

[0012] Step S5, assign the values ​​of the poles p1 and p2 of the LED transfer function H1(s) to the two zero points in the equilibrium structure model, that is, let z e，1 =p1,z e，2 =p2;

[0013] Step S6, setting each pole p in the transfer function model H2(s) of the balanced structure e，y The initial value of and the initial values ​​of other m-2 zero points;

[0014] Step S7: cascade the equalization structure to the input end of the LED second-order equivalent circuit model to obtain a visible light communication system after the cascade equalization structure, whose transfer function H(s) is expressed as: H(s) = H1(s)·H2(s);

[0015] Step S8, analyzing the transfer function H(s) to obtain an amplitude-frequency response curve of the transfer function H(s) of the visible light communication system after the cascaded equalization structure, that is, a curve showing how the amplitude of the transfer function H(s) varies with frequency;

[0016] Step S9: Analyze the amplitude-frequency response curve of the transfer function H(s) obtained in step S8 to obtain the system bandwidth; determine whether the system bandwidth meets the requirements; if so, determine the transfer function model H2(s) of the equalizing structure, and design a visible light emission equalizer based on the transfer function model H2(s) of the equalizing structure; if not, adjust each pole p in the transfer function model H2(s) of the equalizing structure. e，y and the values ​​of the other m-2 zero points, and return to step S6 to loop.

[0017] Preferably, step S2 is specifically as follows:

[0018] Step S2.1, establish a second-order equivalent circuit model of LED; the second-order equivalent circuit model of LED includes a series inductor, a series resistor, a parallel resistor and a parallel capacitor; wherein the model parameters of the second-order equivalent circuit model of LED include: the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j ;

[0019] Step S2.2, measuring the performance of the visible light communication system in step S1, and obtaining the S within the preset frequency f range. 11 Parameter measurement curve and S 21 Parameter measurement curve; among them, S 11 The parameter measurement curve is S 11 Parameter amplitude phase variation curve with frequency; S 21 The parameter measurement curve is S 21 Curve of parameter amplitude changing with frequency;

[0020] Step S2.3, set the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The initial value of

[0021] Step S2.4, using S 11 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 11 Parameter calculation curve;

[0022] Step S2.5, determine the S obtained in step S2.4 11 Parameter calculation curve, and S obtained in step S2.2 11 Check whether the parameter measurement curve reaches the matching accuracy; if not, adjust the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j If the value is, return to step S2.4 and loop through steps S2.4 to S2.5; if so, the inductance value L of the series inductor is obtained at this time. b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The value of is used to form the LED second-order equivalent circuit model obtained by preliminary design, and then step S2.6 is executed;

[0023] Step S2.6, using S 21 The parameters further verify the LED second-order equivalent circuit model obtained from the preliminary design:

[0024] Step S2.6.1, using S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 Parameter calculation curve;

[0025] Step S2.6.2, calculate S 21 Parameter calculation curve and S obtained in step S2.2 21 N-point mean square error of parameter measurement curve judge Is it less than a given threshold? If so, the verification is successful and the final LED second-order equivalent circuit model is obtained; if not, the inductance value L of the series inductor is adjusted. b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The value of , returns to step S2.4, and loops through steps S2.4 to S2.6.

[0026] Preferably, step S2.2, S 11 Parameter measurement curve and S 21 The parameter measurement curve is obtained by:

[0027] In the visible light communication system constructed in step S1, a vector network analyzer is used to measure the scattering parameters within the preset frequency f range, including S 11 Parameters and S 21 Parameters, thus obtaining S 11 Parameter measurement curve and S 21 Parameter measurement curves.

[0028] Preferably, based on S 11 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 11 Parameter calculation curve; and, based on S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 Parameter calculation curve, specifically:

[0029] (1) Calculate the ABCD parameter matrix of the visible light communication system:

[0030]

[0031] Where: s is the complex frequency, s = jω, j is the imaginary unit, ω is the angular frequency;

[0032] (2) According to the conversion relationship between the ABCD parameter matrix and the scattering parameters of the visible light communication system, S is obtained 11 Parameter calculation model and S 21 The parameter calculation model is as follows:

[0033]

[0034]

[0035] Where: R0 represents the source internal resistance of the AC power supply;

[0036] (3) In the preset frequency f range, multiple frequencies f are selected at equal intervals. At each selected frequency f, S 11 Parameter calculation model, the corresponding S 11 The value of the parameter, and thus through curve fitting, we get S 11 Parameter calculation curve;

[0037] In the preset frequency f range, multiple frequencies f are selected at equal intervals. At each selected frequency f, S 21 Parameter calculation model, the corresponding S 21 The value of the parameter, and thus through curve fitting, we get S 21 Parameter calculation curve.

[0038] Preferably, in step S3, the expression of the LED transfer function H1(s) is:

[0039]

[0040] in:

[0041] V o (s) is the output voltage of the LED second-order equivalent circuit;

[0042] V in (s) is the input voltage of the second-order equivalent circuit of the LED;

[0043] K1 is the DC attenuation of LED;

[0044] pole pole

[0045] Preferably, in step S4, the transfer function model H2(s) of the balanced structure is expressed as:

[0046]

[0047] in:

[0048] K2 is the gain or attenuation of the equalization structure;

[0049] z e，x , x=1, 2, ..., m is the zero point of the equilibrium structure model;

[0050] p e，y , y=1,2,...,n are the poles of the equilibrium structure model.

[0051] Preferably, in step S6, each pole p in the transfer function model H2(s) of the balanced structure is set e，y The initial value of and the initial values ​​of other m-2 zero points must meet the following conditions:

[0052] Pole p e，y The absolute value of is greater than the absolute value of the pole p1 and the absolute value of the pole p2; the absolute value of each of the other m-2 zeros is greater than the absolute value of the pole p1 and the absolute value of the pole p2; the formula is expressed as:

[0053] |p e,y |>|p l |,|z e,v |>|p l |, l = 1, 2; v = 3, ..., m;

[0054] Where: p l Represents the poles p1 and p2.

[0055] Preferably, in step S7, the transfer function H(s) is expressed as:

[0056]

[0057] Wherein: K=K1K2; K is the gain of the visible light communication system after the cascade equalization structure.

[0058] Preferably, in step S8, the transfer function H(s) is analyzed to obtain an amplitude-frequency response curve of the transfer function H(s) of the visible light communication system after the cascade equalization structure, specifically:

[0059] Within the preset frequency f range, multiple frequencies f are equally spaced and at each selected frequency f, the corresponding value of the transfer function H(s) is obtained by using the transfer function H(s) expression, thereby obtaining the amplitude-frequency response curve of the transfer function H(s) by curve fitting;

[0060] or

[0061] In the visible light communication system after the cascade equalization structure, the amplitude-frequency response curve of the transfer function H(s) is directly measured by a vector network analyzer.

[0062] Preferably, the amplitude-frequency response curve of the transfer function H(s) obtained in step S8 is analyzed to obtain the system bandwidth, specifically:

[0063] In the amplitude-frequency response curve of the transfer function H(s), the frequency corresponding to the position where the amplitude is attenuated by 3dB compared to the maximum value is the system bandwidth.

[0064] The design method of a visible light emission equalizer based on an LED equivalent circuit provided by the present invention has the following advantages:

[0065] 1) The present invention can effectively expand the bandwidth of lighting LEDs, thereby improving the communication rate of wireless optical communication systems. For example, a wireless optical transmission system built for a certain type of lighting COTS LED has an original bandwidth of approximately 10 MHz. After bandwidth expansion using the method proposed in the present invention, the bandwidth can be increased to over 500 MHz.

[0066] 2) The bandwidth expansion method of the present invention only relies on the system's S parameters and is therefore generally applicable to wireless optical transmission systems using light sources such as LEDs.

[0067] 3) The process of the method of the present invention involves fewer parameters of concern, so the implementation is simple;

[0068] 4) The method of the present invention has a mathematical model, which is easy to implement with the help of software tools and also easy to perform hardware simulation;

[0069] 5) The present invention has been verified through experiments to be able to effectively expand the system bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 A structural diagram of an equalizer provided by the prior art;

[0071] Figure 2 A structural diagram of the visible light communication system before the cascade equalization structure provided by the present invention;

[0072] Figure 3 A structural diagram of a visible light communication system after the cascade equalization structure provided by the present invention;

[0073] Figure 4 A flow chart of a design method for a visible light emission equalizer based on an LED equivalent circuit provided by the present invention;

[0074] Figure 5 A circuit diagram of the second-order equivalent circuit model of an LED provided by the present invention;

[0075] Figure 6 The transfer function model H2(s) of the equalizing structure provided by the present invention, and the amplitude-frequency response curves of the transfer function H(s) of the system before and after the cascaded equalizing structure;

[0076] Figure 7 A diagram showing a first implementation of the equalization structure provided by the present invention;

[0077] Figure 8 A diagram showing a second implementation of the equalization structure provided by the present invention;

[0078] Figure 9 A diagram showing a third implementation of the equalization structure provided by the present invention;

[0079] Figure 10 A comparison chart of the amplitude-frequency response curves of the blue LED before and after equalization provided by the present invention;

[0080] Figure 11 A comparison diagram of the amplitude-frequency response curves of the green LED before and after equalization provided by the present invention;

[0081] Figure 12 This is a comparison diagram of the amplitude-frequency response curves of the red LED before and after equalization provided by the present invention. DETAILED DESCRIPTION

[0082] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0083] The present invention provides a design method for a visible light emission equalizer based on an LED equivalent circuit, which is used for bandwidth expansion of a visible light transmission system. The bandwidth expansion flow chart implemented by the present invention is as follows: Figure 4 As shown in the figure, the scheme consists of two steps: establishing a second-order equivalent circuit model for LEDs and determining the equalization structure. The amplitude-frequency response curve of the transfer function H(s) of a visible light communication system can well reflect the system's 3dB bandwidth. The inflection point of the curve is determined by both the zero and the pole. The bandwidth of a visible light transmission system is generally small because the pole of its transfer function H(s) is close to the origin. Therefore, the main idea of ​​the present invention is to adjust the zero and pole of the transfer function H(s) of the visible light communication system by cascading other equalization structures before the electro-optical conversion LED device, thereby expanding the bandwidth.

[0084] The present invention provides a design method for a visible light emission equalizer based on an LED equivalent circuit, such as Figure 4 As shown, the following steps are included:

[0085] Step S1, building a visible light communication system; the visible light communication system includes a transmitter and a receiver; the transmitter includes an electro-optical conversion LED device;

[0086] As a specific structure, it can be built as Figure 2 The visible light communication system shown,Figure 2 The visible light communication system is shown in a non-cascaded equalization structure. The transmitting end includes a broadband power amplifier 2, a driving circuit 3 and an electro-optical conversion LED device 4 in series. The signal to be transmitted is amplified by the broadband power amplifier 2, and then the driving circuit 3 drives the electro-optical conversion LED device 4 to convert the amplified electrical signal into an optical signal, which is then transmitted to the optical transmission link. The receiving end includes an opto-electric conversion device 5, a current-voltage conversion structure 6 and a signal processing circuit 7 in series. The opto-electric conversion device 5 converts the optical signal transmitted through the optical transmission link into an electrical signal, which is then converted into a voltage signal by the current-voltage conversion structure 6, and finally processed by the signal processing circuit 7.

[0087] The driving circuit 3, the current-voltage conversion structure 6 and the signal processing circuit 7 can improve the bandwidth through hardware or software design. The optical link is different from the radio frequency link, and can be considered as a straight-line propagation in a large distance range, so the channel equalization is not significant. Therefore, the limitations of the visible light communication link design mainly lie in the electro-optical conversion LED device 4 and the opto-electric conversion device 5. The electro-optical conversion LED device 4 of the transmitting end generally uses a low-cost light-emitting diode (LED), but the 3dB bandwidth of the LED device is generally only a few MHz, which severely limits the system bandwidth and further limits the communication rate of the visible light transmission system. Therefore, how to design a general low-complexity VLC transmitter with a 3dB bandwidth of hundreds of MHz is the problem concerned by the present application.

[0088] Figure 2 The vector network analyzer 8 is used to measure the performance parameters of the visible light communication system.

[0089] In addition, in the visible light communication system provided by the present application, a large-bandwidth receiver is used at the receiving end, so that the visible light communication system can be regarded as a two-port network, and the large-bandwidth receiver is considered as a lossless transmission.

[0090] Step S2, establishing an LED second-order equivalent circuit model of the electro-optical conversion LED device, and determining model parameters of the LED second-order equivalent circuit model to obtain a designed LED second-order equivalent circuit model, so that the designed LED second-order equivalent circuit model is equivalent to the electro-optical conversion LED device;

[0091] This step is specifically:

[0092] Step S2.1, establishing an LED second-order equivalent circuit model as shown in Figure 5 The LED second-order equivalent circuit model includes a series inductance, a series resistance, a parallel resistance and a parallel capacitance. The model parameters of the LED second-order equivalent circuit model include an inductance value L b of the series inductance, a resistance value R s, the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j ;

[0093] Step S2.2, measuring the performance of the visible light communication system in step S1, and obtaining the S within the preset frequency f range. 11 Parameter measurement curve and S 21 Parameter measurement curve; among them, S 11 The parameter measurement curve is S 11 Parameter amplitude phase variation curve with frequency; S 21 The parameter measurement curve is S 21 Parameter amplitude changes with frequency curve; among them, S 11 Parameters and S 21 Parameters are specific parameters used to describe the electrical behavior of a two-port linear microwave network.

[0094] In this step, S 11 Parameter measurement curve and S 21 The parameter measurement curve is obtained by:

[0095] In the visible light communication system constructed in step S1, a vector network analyzer is used to measure the scattering parameters within the preset frequency f range, including S 11 Parameters and S 21 Parameters, thus obtaining S 11 Parameter measurement curve and S 21 Parameter measurement curves.

[0096] Step S2.3, set the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The initial value of

[0097] Step S2.4, using S 11 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 11 Parameter calculation curve;

[0098] The specific method is:

[0099] (1) Calculate the ABCD parameter matrix of the visible light communication system:

[0100]

[0101] Where: s is the complex frequency, s = jω, j is the imaginary unit, ω is the angular frequency; the conversion relationship between frequency f and angular frequency ω is ω = 2πf;

[0102] (2) According to the conversion relationship between the ABCD parameter matrix and the scattering parameters of the visible light communication system, S is obtained 11 Parameter calculation model and S 21 The parameter calculation model is as follows:

[0103]

[0104] Where: R0 represents the source internal resistance of the AC power supply;

[0105] (3) In the preset frequency f range, multiple frequencies f are selected at equal intervals. At each selected frequency f, S 11 Parameter calculation model, the corresponding S 11 The value of the parameter, and thus through curve fitting, we get S 11 Parameter calculation curve;

[0106] In the preset frequency f range, multiple frequencies f are selected at equal intervals. At each selected frequency f, S 21 Parameter calculation model, the corresponding S 21 The value of the parameter, and thus through curve fitting, we get S 21 Parameter calculation curve.

[0107] For the convenience of description, this step also describes S 21 Parameter calculation model, and, based on S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 Parameter calculation curve. S described here 21 Parameter calculation model, and, based on S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 The parameters of the calculated curve are used in the subsequent step S2.6.1.

[0108] Step S2.5, determine the S obtained in step S2.4 11 Parameter calculation curve, and S obtained in step S2.2 11 Check whether the parameter measurement curve reaches the matching accuracy; if not, adjust the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j If the value is, return to step S2.4 and loop through steps S2.4 to S2.5; if so, the inductance value L of the series inductor is obtained at this time. b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor Cj The value of is used to form the LED second-order equivalent circuit model obtained by preliminary design, and then step S2.6 is executed;

[0109] Step S2.6, using S 21 The parameters further verify the LED second-order equivalent circuit model obtained from the preliminary design:

[0110] Step S2.6.1, using S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 Parameter calculation curve;

[0111] Step S2.6.2, calculate S 21 Parameter calculation curve and S obtained in step S2.2 21 N-point mean square error of parameter measurement curve judge Is it less than a given threshold? If so, the verification is successful and the final LED second-order equivalent circuit model is obtained; if not, the inductance value L of the series inductor is adjusted. b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The value of , returns to step S2.4, and loops through steps S2.4 to S2.6.

[0112] Through step S2, an LED second-order equivalent circuit model equivalent to the actual physical device, that is, the electro-optical conversion LED device, can be established. The LED second-order equivalent circuit model determined here is used to determine the balancing structure in subsequent steps.

[0113] Step S3, determining the LED transfer function H1(s) of the LED second-order equivalent circuit model obtained in step S2, analyzing the LED transfer function H1(s) to obtain poles p1 and p2;

[0114] Specifically, the expression of the LED transfer function H1(s) is:

[0115]

[0116] in:

[0117] V o (s) is the output voltage of the LED second-order equivalent circuit;

[0118] V in (s) is the input voltage of the second-order equivalent circuit of the LED;

[0119] K1 is the DC attenuation of LED;

[0120] pole pole

[0121] Step S4, establishing a transfer function model H2(s) of the balanced structure; the transfer function model H2(s) of the balanced structure has m zero points of the balanced structure model, represented by z e，x , x = 1, 2, ..., m, and n poles of the equilibrium structure model, denoted as p e，y , y=1,2,...,n; where n≥2;

[0122] Specifically, the transfer function model H2(s) of the balanced structure is expressed as:

[0123]

[0124] in:

[0125] K2 is the gain or attenuation of the equalization structure;

[0126] z e，x , x=1, 2, ..., m is the zero point of the equilibrium structure model;

[0127] p e，y , y = 1, 2, ..., n are the poles of the equilibrium structure model.

[0128] Step S5, assign the values ​​of the poles p1 and p2 of the LED transfer function H1(s) to the two zero points in the equilibrium structure model, that is, let z e，1 =p1,z e，2 =p2;

[0129] Step S6, setting each pole p in the transfer function model H2(s) of the balanced structure e，y The initial value of and the initial values ​​of other m-2 zero points;

[0130] In this step, each pole p in the transfer function model H2(s) of the balanced structure is set e，y The initial value of and the initial values ​​of other m-2 zero points must meet the following conditions:

[0131] Pole p e，y The absolute value of is greater than the absolute value of the pole p1 and the absolute value of the pole p2; the absolute value of each of the other m-2 zeros is greater than the absolute value of the pole p1 and the absolute value of the pole p2; the formula is expressed as:

[0132] |p e，y |>|p l |,|z e，v |>|p l|, l=1, 2; v=3,...,m;

[0133] Where: p l Represents the poles p1 and p2.

[0134] Step S7: cascade the equalization structure to the input end of the LED second-order equivalent circuit model to obtain a visible light communication system after the cascade equalization structure. Figure 2 The equalization structure can be cascaded in front of the broadband power amplifier 2 to obtain the following Figure 3 The visible light communication system after the cascade equalization structure shown in Figure 3 In the figure, 1 represents the balanced structure. In practical applications, the balanced structure can also be cascaded between the driving circuit 3 and the broadband power amplifier 2 to form another visible light communication system with a cascaded balanced structure. Both methods are acceptable and are not limited in the present invention. The transfer function H(s) of the visible light communication system with the cascaded balanced structure is expressed as:

[0135]

[0136] Wherein: K=K1K2; K is the gain of the visible light communication system after the cascade equalization structure.

[0137] Step S8, analyzing the transfer function H(s) to obtain an amplitude-frequency response curve of the transfer function H(s) of the visible light communication system after the cascaded equalization structure, that is, a curve showing how the amplitude of the transfer function H(s) varies with frequency;

[0138] Specifically, the amplitude-frequency response curve of the transfer function H(s) is obtained by one of the following two methods:

[0139] Within the preset frequency f range, multiple frequencies f are equally spaced and at each selected frequency f, the corresponding value of the transfer function H(s) is obtained by using the transfer function H(s) expression, thereby obtaining the amplitude-frequency response curve of the transfer function H(s) by curve fitting;

[0140] or

[0141] In the visible light communication system after the cascade equalization structure, the amplitude-frequency response curve of the transfer function H(s) is directly measured by a vector network analyzer.

[0142] Step S9: Analyze the amplitude-frequency response curve of the transfer function H(s) obtained in step S8 to obtain the system bandwidth. The specific method is as follows: determine whether the system is low-pass based on the transfer function H(s) of the visible light communication system after the cascaded equalization structure. In the amplitude-frequency response curve of the transfer function H(s), the frequency corresponding to the position where the amplitude is attenuated by 3 dB compared to the maximum value is the system bandwidth.

[0143] determining whether the system bandwidth meets the requirement, if yes, determining a transfer function model H2(s) of the equalization structure, and designing a visible light emission equalizer according to the transfer function model H2(s) of the equalization structure; if not, adjusting values of each pole p e，y and the other m-2 zero points, and returning to step S6 for circulation.

[0144] An embodiment is introduced as follows:

[0145] This embodiment sets up a wireless optical transmission system with an architecture as shown in the figure Figure 3 The electro-optical conversion LED device 4 uses a three-color LED LER TB N7WM (OSRAM ) and the to-be-transmitted signal is amplified by a power amplifier and driven by a Bias-Tee circuit to emit an optical signal; the receiving end uses an APD module C5658 (Hamamatsu). The specific parameters of the electro-optical conversion LED device 4 and the APD are shown in the following table.

[0146]

[0147] The wireless optical transmission system general bandwidth expansion scheme proposed in the present application is used to expand the bandwidth of the system in this embodiment.

[0148] First, the second-order equivalent circuit of the LED and the LED transfer function H1(s) are determined:

[0149]

[0150] In this embodiment, the equalization structure is established as a two-zero-point and two-pole model, and its transfer function model H2(s) is:

[0151]

[0152] The values of the pole p1 and the pole p2 of the LED transfer function H1(s) are assigned to the two zero points in the equalization structure model, i.e., z e，1 =p1 and z e，2 =p2.

[0153] The initial values of the poles p e，1 and p e，2 in the transfer function model H2(s) of the equalization structure are set.

[0154] The transfer function H(s) of the visible light communication system after cascading the equalization structure is H1(s)·H2(s);

[0155] The transfer function H(s) is analyzed and the amplitude-frequency response curve of the transfer function H(s) of the visible light communication system after the cascade equalization structure is obtained. Figure 6 As shown, there are the transfer function model H2(s) of the equalizing structure, the amplitude-frequency response curves of the transfer function H(s) of the system before and after the cascaded equalizing structure, and the intuitive display of the zero-pole matching.

[0156] One way to achieve the balanced structure in this embodiment is to use a second-order RC circuit. Figure 7 、 Figure 8 and Figure 9 Three possible implementation methods of the equilibrium structure are given respectively.

[0157] In use Figure 8 In the case of , the frequency response curves of the three color LED links before and after equalization are as follows Figure 10 、 Figure 11 and Figure 12 As shown. Among them, Figure 10 This is a comparison of the amplitude-frequency response curves of the blue LED before and after equalization; Figure 11 This is a comparison of the amplitude-frequency response curves of the green LED before and after equalization; Figure 12 This is a comparison of the amplitude-frequency response curves before and after red LED equalization.

[0158] by Figure 10 For example, the three test curves are: blue (PA,ori), blue (w / o R IM )、blue(withR IM ), respectively representing the test curves under three test conditions: no balancing, balancing structure but no matching resistor, and balancing structure and matching resistor. Figure 10 It can be seen that the blue (PA,ori) curve, that is, without equalization, has a bandwidth of 13.9MHz; the blue (w / o R IM ) curve, that is, when the balancing structure is added but the matching resistor is not added, the amplitude-frequency response curve fluctuates severely and the bandwidth cannot be obtained intuitively; blue (withR IM ) curve, that is, when the equalization structure and matching resistor are added, the bandwidth is extended to 525MHz. This shows that the present invention can effectively extend the system bandwidth after adding the equalization structure.

[0159] The present invention provides a design method for a visible light emission equalizer based on an LED equivalent circuit, which has the following characteristics:

[0160] The present invention proposes an original S 11 Parameter calculation model and S 21 Parameter calculation model, through S 11 Parameter calculation model and S21 Parameter calculation model, which can quickly and accurately obtain different model parameters L b 、R s 、r d and C j The corresponding S 11 Parameters and S 21 Parameters, and then we can get S at different frequencies f 11 Parameter calculation curve and S 21 Parameter calculation curve, through the S 11 Parameter measurement curve and S 21 By comparing the parameter measurement curves, an LED second-order equivalent circuit model equivalent to the electro-optical conversion LED device is obtained. Therefore, the LED second-order equivalent circuit model has the advantages of simple establishment process and accurate establishment results.

[0161] Since the zeros and poles of the system transfer function determine the inflection point and slope of the amplitude-frequency response curve, and thus affect the system bandwidth, when the zeros and poles are close to the coordinate origin, the corresponding system bandwidth will be smaller, and vice versa. Therefore, an effective method to expand the system bandwidth is to move the system zeros and poles away from the coordinate origin. The zeros and poles can be changed by multiplying the transfer functions. That is, the present invention corresponds the two zeros in the transfer function model H2(s) of the equalizing structure to the two poles in the LED transfer function H1(s), so that after cascading the transfer function model H2(s) of the equalizing structure and the LED transfer function H1(s), the transfer function H(s) after the cascaded equalizing structure is obtained = H1(s)·H2(s), and the inflection point of the frequency response of the transfer function H(s) is changed, thereby achieving bandwidth expansion of the visible light communication system after the cascaded equalizing structure.

[0162] The present invention provides a design method for a visible light emission equalizer based on an LED equivalent circuit, which has the following advantages:

[0163] 1) The present invention can effectively expand the bandwidth of lighting LEDs, thereby improving the communication rate of wireless optical communication systems. For example, a wireless optical transmission system built for a certain type of lighting COTS LED has an original bandwidth of approximately 10 MHz. After bandwidth expansion using the method proposed in the present invention, the bandwidth can be increased to over 500 MHz.

[0164] 2) The bandwidth expansion method of the present invention only relies on the system's S parameters and is therefore generally applicable to wireless optical transmission systems using light sources such as LEDs.

[0165] 3) The process of the method of the present invention involves fewer parameters of concern, so the implementation is simple;

[0166] 4) The method of the present invention has a mathematical model, which is easy to implement with the help of software tools and also easy to perform hardware simulation;

[0167] 5) The present invention has been verified through experiments to be able to effectively expand the system bandwidth.

[0168] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A design method for a visible light emission equalizer based on an LED equivalent circuit, characterized in that: The following steps are involved: Step S1, building a visible light communication system; the visible light communication system includes a transmitter and a receiver; the transmitter includes an electro-optical conversion LED device; Step S2, establishing an LED second-order equivalent circuit model of the electro-optical conversion LED device, and determining model parameters of the LED second-order equivalent circuit model to obtain a designed LED second-order equivalent circuit model, so that the designed LED second-order equivalent circuit model and the electro-optical conversion LED device are equivalent; Step S3, determining the LED transfer function H1(s) of the LED second-order equivalent circuit model obtained in step S2, analyzing the LED transfer function H1(s) to obtain poles p1 and p2; Step S4, establishing a transfer function model H2(s) of the balanced structure; the transfer function model H2(s) of the balanced structure has m zero points of the balanced structure model, represented by z e，x , x = 1, 2, ..., m, and n poles of the equilibrium structure model, denoted as p e，y , y=1,2,...,n; where n≥2; Step S5, assign the values ​​of the poles p1 and p2 of the LED transfer function H1(s) to the two zero points in the equilibrium structure model, that is, let z e,1 =p1,Z e,2 =p2; Step S6, setting each pole p in the transfer function model H2(s) of the balanced structure e，y The initial value of and the initial values ​​of other m-2 zero points; Step S7: cascade the equalization structure to the input end of the LED second-order equivalent circuit model to obtain a visible light communication system after the cascade equalization structure, whose transfer function H(s) is expressed as: H(s) = H1(s)·H2(s); Step S8, analyzing the transfer function H(s) to obtain an amplitude-frequency response curve of the transfer function H(s) of the visible light communication system after the cascaded equalization structure, that is, a curve showing how the amplitude of the transfer function H(s) varies with frequency; Step S9: Analyze the amplitude-frequency response curve of the transfer function H(s) obtained in step S8 to obtain the system bandwidth; determine whether the system bandwidth meets the requirements; if so, determine the transfer function model H2(s) of the equalizing structure, and design a visible light emission equalizer based on the transfer function model H2(s) of the equalizing structure; if not, adjust each pole p in the transfer function model H2(s) of the equalizing structure. e,y and the values ​​of the other m-2 zero points, and return to step S6 to loop.

2. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 1, characterized in that: Step S2 is specifically as follows: Step S2.1, establish a second-order equivalent circuit model of LED; the second-order equivalent circuit model of LED includes a series inductor, a series resistor, a parallel resistor and a parallel capacitor; wherein the model parameters of the second-order equivalent circuit model of LED include: the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j ; Step S2.2, measuring the performance of the visible light communication system in step S1, and obtaining the S within the preset frequency f range. 11 Parameter measurement curve and S 21 Parameter measurement curve; among them, S 11 The parameter measurement curve is S 11 Parameter amplitude phase variation curve with frequency; S 21 The parameter measurement curve is S 21 Curve of parameter amplitude changing with frequency; Step S2.3, set the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The initial value of Step S2.4, using S 11 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 11 Parameter calculation curve; Step S2.5, determine the S obtained in step S2.4 11 Parameter calculation curve, and S obtained in step S2.2 11 Check whether the parameter measurement curve reaches the matching accuracy; if not, adjust the inductance value L of the series inductor b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j If the value is, return to step S2.4 and loop through steps S2.4 to S2.5; if so, the inductance value L of the series inductor is obtained at this time. b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The value of is used to form the LED second-order equivalent circuit model obtained by preliminary design, and then step S2.6 is executed; Step S2.6, using S 21 The parameters further verify the LED second-order equivalent circuit model obtained from the preliminary design: Step S2.6.1, using S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 Parameter calculation curve; Step S2.6.2, calculate S 21 Parameter calculation curve and S obtained in step S2.2 21 N-point mean square error of parameter measurement curve judge Is it less than a given threshold? If so, the verification is successful and the final LED second-order equivalent circuit model is obtained; if not, the inductance value L of the series inductor is adjusted. b , the resistance value of the series resistor R s , the resistance value of the parallel resistor r d And the capacitance value of the parallel capacitor C j The value of , returns to step S2.4, and loops through steps S2.4 to S2.

6.

3. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 2, characterized in that: Step S2.2, S 11 Parameter measurement curve and S 21 The parameter measurement curve is obtained by: In the visible light communication system constructed in step S1, a vector network analyzer is used to measure the scattering parameters within the preset frequency f range, including S 11 Parameters and S 21 Parameters, thus obtaining S 11 Parameter measurement curve and S 21 Parameter measurement curves.

4. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 2, characterized in that: Based on S 11 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 11 Parameter calculation curve; and, based on S 21 Parameter calculation model, obtain the S of the visible light communication system within the preset frequency f range 21 Parameter calculation curve, specifically: (1) Calculate the ABCD parameter matrix of the visible light communication system: Where: s is the complex frequency, s = jω, j is the imaginary unit, ω is the angular frequency; (2) According to the conversion relationship between the ABCD parameter matrix and the scattering parameters of the visible light communication system, S is obtained 11 Parameter calculation model and S 21 The parameter calculation model is as follows: Where: R0 represents the source internal resistance of the AC power supply; (3) In the preset frequency f range, multiple frequencies f are selected at equal intervals. At each selected frequency f, S 11 Parameter calculation model, the corresponding S 11 The value of the parameter, and thus through curve fitting, we get S 11 Parameter calculation curve; In the preset frequency f range, multiple frequencies f are selected at equal intervals. At each selected frequency f, S 21 Parameter calculation model, the corresponding S 21 The value of the parameter, and thus through curve fitting, we get S 21 Parameter calculation curve.

5. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 3, characterized in that: In step S3, the expression of the LED transfer function H1(s) is: in: V o (s) is the output voltage of the LED second-order equivalent circuit; V in (s) is the input voltage of the second-order equivalent circuit of the LED; K1 is the DC attenuation of LED; pole pole 6. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 5, characterized in that: In step S4, the transfer function model H2(s) of the balanced structure is expressed as: in: K2 is the gain or attenuation of the equalization structure; Z e,x ,x=1,2,...,m is the zero point of the equilibrium structure model; p e,y ,y=1,2,...,n are the poles of the equilibrium structure model.

7. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 5, characterized in that: In step S6, each pole p in the transfer function model H2(s) of the balanced structure is set e，y The initial value of and the initial values ​​of other m-2 zero points must meet the following conditions: Pole p e，y The absolute value of is greater than the absolute value of the pole p1 and the absolute value of the pole p2; the absolute value of each of the other m-2 zeros is greater than the absolute value of the pole p1 and the absolute value of the pole p2; the formula is expressed as: |p e，y |>|p l |,|Z e，v |>|p l |,l=1,2;v=3,...,m; Where: p l Represents the poles p1 and p2.

8. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 5, characterized in that: In step S7, the transfer function H(s) is expressed as: Wherein: K=K1K2; K is the gain of the visible light communication system after the cascade equalization structure.

9. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 8, characterized in that: Step S8: Analyze the transfer function H(s) to obtain the amplitude-frequency response curve of the transfer function H(s) of the visible light communication system after the cascade equalization structure, specifically: Within the preset frequency f range, multiple frequencies f are equally spaced and at each selected frequency f, the corresponding value of the transfer function H(s) is obtained by using the transfer function H(s) expression, thereby obtaining the amplitude-frequency response curve of the transfer function H(s) by curve fitting; or In the visible light communication system after the cascade equalization structure, the amplitude-frequency response curve of the transfer function H(s) is directly measured by a vector network analyzer.

10. The design method of a visible light emission equalizer based on an LED equivalent circuit according to claim 1, characterized in that: The amplitude-frequency response curve of the transfer function H(s) obtained in step S8 is analyzed to obtain the system bandwidth, specifically: In the amplitude-frequency response curve of the transfer function H(s), the frequency corresponding to the position where the amplitude is attenuated by 3dB compared to the maximum value is the system bandwidth.

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