CN107592163B - Method for determining optimal serial number of LEDs in optical communication system - Google Patents
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Abstract
The invention provides an LED connection mode with optimal LED series connection in an optical communication system, and provides a method for determining the optimal LED series connection number in the optical communication system, which comprises the following steps: determining LED array alternating current small signal models with different series quantities by using a vector network analyzer; obtaining alternating currents flowing through different series-connected quantity of LED arrays by using Multisim simulation; determining the equivalent total current of a receiving end by using Matlab in combination with a Lambert body radiation equation; and finally, the number of the conducted LEDs with the maximum total current is used as the optimal number of the LEDs connected in series. The present invention verifies that LED array series is beneficial for improving transmitter efficiency in optical communication systems and provides a method for determining the optimal number of LEDs in series.
Description
Technical Field
The invention relates to the field of optical communication, in particular to a method for determining the optimal serial number of LEDs in an optical communication system.
Background
Optical communication technology has become a focus of research in the field of communications in recent years. The broadband spectrum resource has the advantages of being independent of a radio frequency spectrum, free of electromagnetic interference and radiation, green, safe, easy to cut off signals, good in confidentiality and the like. In the design of optical communication systems, Light Emitting Diodes (LEDs) are the first choice for electro-optical conversion devices in optical communication systems due to their advantages in technical conditions.
In the LED-based optical communication scheme, an electric signal is converted into an optical signal through an LED at a transmitting end, the signal amplitude is represented by light intensity, and the signal is received by detecting the light intensity at a receiving end. The number of the LED tubes is increased at the transmitting end, the transmitting light intensity can be increased, the signal-to-noise ratio of the whole system is improved, the system performance is improved, and the LED series connection is the simplest and most effective optimization method.
Disclosure of Invention
The technical problem is as follows: the invention aims to provide an optimal LED (light emitting diode) connecting means in an optical communication system by serial connection, and provides a method for determining the optimal serial number of LEDs in the optical communication system, wherein the optimal serial number of LEDs is found under the condition that other parameters of an optical transmitter are not changed, so that the transmitted alternating current power is maximized.
The technical scheme is as follows: in order to achieve the above object, the present invention provides a method for determining the optimal number of serial LEDs in an optical communication system, which comprises the following steps:
the method comprises the following steps that N LED tubes are connected in series to form an LED array, the conduction number of the LED tubes in series is changed on the assumption that each LED tube in the LED array can be independently controlled to be switched on or switched off, a vector network analyzer is used for determining alternating current small-signal circuit models of the LED arrays in series under different conduction numbers, and circuit simulation is used for determining alternating current small current flowing through the LED arrays under different conduction numbers; and fixing the receiving position, fixing the serial layout of N LED tubes of the LED array, and changing the conduction number of the LED tubes, so that the serial number with the maximum receiving equivalent current is the optimal serial number of the LEDs.
Wherein:
the method for determining the alternating current small signal circuit model of the series LED array under different conduction numbers by using the vector network analyzer comprises the following specific steps:
1) setting the test frequency range of the vector network analyzer to be 300kHz-100MHz, setting the signal output power of a port 1 to be-30 dBm, calibrating the port 1 of the vector network analyzer by using an open-circuit load, a short-circuit load and a 50 omega matching load, and storing calibration parameters;
2) a circuit is connected according to an experimental system diagram, and only one lamp in the LED array can be conducted;
3) adjusting the output current of the direct current source from 1mA to 10mA, stepping by 1mA, and respectively storing impedance parameters under different frequency points measured by a vector network analyzer from small to large;
4) changing the number of the conducted LEDs in the LED array, and repeating the step 3);
5) with reference to a single LED AC small-signal circuit model, the input impedance is
Wherein R issIs an equivalent circuit series resistance, RdAnd CdResistance and capacitance being equivalent parallel circuits, LsAn equivalent circuit is connected with an inductor in series; r in single LED alternating small signal circuit model can be determineds、Rd、Ls、CdA parameter;
6) according to the result obtained in the step 4), the alternating current small signal model with the plurality of LED tubes connected in series can be approximately equivalent to the series connection between the small signal models of the single LED tubes.
The method for determining the alternating current small current flowing through the LED array under different conduction quantities by using circuit simulation is specifically characterized in that: the method comprises the steps of changing the conduction number of LEDs in an LED array by using a power amplifier which is provided by Windows platform software Multisim and is connected with an alternating current signal, wherein the power amplifier is used for carrying out circuit simulation in a circuit diagram building mode, connecting LED array equivalent circuits with different conduction numbers in series at the rear stage of the power amplifier, and measuring alternating current flowing through the equivalent circuits to obtain LED array equivalent alternating currents with different conduction numbers.
The fixed receiving position fixes the serial layout of the N LED tubes of the LED array, and changes the conducting quantity of the LED tubes, so that the serial quantity with the maximum receiving equivalent current is the optimal serial quantity of the LEDs, and the method specifically comprises the following steps:
1) assuming that path losses from different LED tubes to a receiving end are approximately the same, alternating currents flowing through the LED array under different series quantities are utilized, the current of each LED tube at the receiving end has a weighting coefficient, the weighted sum of the currents under different conditions is equivalent received power, and the weight of each lamp is determined by a lambertian body radiation equation, which is as follows:
E＝cosmθ
where E is the normalized radiant power, θ is the radiant angle, and m is the power attenuation order, depending on the relative positions of the LED light emitting area and the center of curvature of the spherical encapsulant.
Has the advantages that: the method for determining the optimal serial number of the LEDs in the optical communication system has the advantages that:
1. the LED tubes are connected in series in a connection mode which improves the optical communication emission power and is better than other various LED tubes;
2. under the condition of maximizing the emission power, the optimal serial number of the LED tubes is found, the system cost is reduced, and the cost performance maximization is realized.
Drawings
FIG. 1 is a diagram of an experimental system of the present invention.
Fig. 2 is a circuit model of an LED ac small signal.
FIG. 3 shows the real part and imaginary part of the LED impedance measured by the vector network analyzer in the frequency range of 300kHz to 100MHz when a single LED tube is in the on state, using TSFF6410LED tube as an example.
FIG. 4 is a graph of the mode of impedance and the inverse of bias current at 300kHz for an example of a TSFF6410LED tube.
Fig. 5 shows the arrangement of the LED arrays and the corresponding LED lamp numbers given by way of example.
Fig. 6 shows the equivalent total current of different LED lamp series numbers using TSFF6410LED tube as an example.
Detailed Description
N LED tubes are connected in series to form an LED array. And assuming that each LED in the LED array can be independently controlled to be switched on or switched off, the switching-on quantity of the series LED tubes is changed, and the vector network analyzer is used for determining the alternating current small signal circuit model of the series LED array under different switching-on quantities. And connecting the LED array equivalent circuits with different conduction quantities in series at the rear stage of the power amplifier by using a power amplifier connected with an alternating current signal, and measuring alternating current flowing through the equivalent circuits to obtain the LED array currents with different conduction quantities. And fixing the receiving position, and determining the weight of the current which can be received by each conducting LED tube according to the Lambert body radiation equation of the LED. The LED tube with the heavy current weight is the LED tube which is preferentially conducted. And obtaining the weighted total current according to different weights, wherein the number of the LEDs which are conducted with the maximum total current is the optimal number of the LEDs connected in series. The invention can find the best LED connection mode and the best serial number under the condition of improving the signal-to-noise ratio of the system by using a plurality of LEDs.
Specifically, the measurement and simulation in the above scheme includes the following steps:
1) setting the test frequency range of the vector network analyzer to be 300kHz-100MHz, setting the signal output power of a port 1 to be-30 dBm, calibrating the port 1 of the vector network analyzer by using an open-circuit load, a short-circuit load and a 50 omega matching load, and storing calibration parameters;
2) referring to the connection of fig. 1, only one lamp in the LED array is guaranteed to be turned on;
3) adjusting the output current of the current source from 1mA to 10mA, stepping by 1mA, and respectively storing impedance parameters under different frequency points measured by a vector network analyzer from small to large;
4) changing the number of the conducted LEDs in the LED array, and repeating the step (3);
5) referring to the single LED AC small signal circuit model, see FIG. 2, the input impedance is
According to the formula
Wherein R issCan be obtained from the intercept of this first order curve, then Rd＝|Zin|-Rs.
The 3dB bandwidth of an LED can be determined by the real part of the LED impedance and is recorded as
Further obtain CdFinally, from the imaginary part of the impedance, L is obtaineds.
6) According to the result obtained by the measurement in the step 4), the alternating current small signal model with the plurality of LED tubes connected in series can be approximately equivalent to the series connection between the small signal models of the single LED tube, and then the LED array equivalent circuit can be further obtained.
7) Circuit simulation is performed in Multisim with reference to fig. 1, the value of an alternating current ammeter is read, the number of series networks in the LED array equivalent circuit is changed, and therefore equivalent alternating currents of LEDs in different series numbers are obtained.
8) Fixing a receiving position, fixing the serial layout of N LED tubes of the LED array, assuming that path losses from different LED tubes to a receiving end are approximately the same, changing the conduction number of the LED tubes, utilizing alternating currents flowing through an equivalent circuit of the LED array under different serial numbers, wherein each LED tube has a weighting coefficient at the equivalent power of the receiving end, and the weighted sum of the currents under different conditions is the equivalent receiving power and is recorded as:
wherein, I is the alternating current of the LED array equivalent circuit under different conduction quantities.
Weight E of each lampjDetermined by the lambertian radiation equation, which is as follows:
E＝cosmθ
where E is the normalized radiant power, θ is the radiant angle, and m is dependent on the relative position of the LED light emitting area and the center of curvature of the spherical encapsulant.
In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings. Examples illustrate that:
LED tube type selection: TSFF6410
Array size: n-16
Array arrangement, square arrangement, with adjacent LED tubes spaced 0.2m apart, see FIG. 5
Receiving point position: the connecting line of the receiving point and the center of the LED array is vertical to the plane of the LED array, and the distance between the receiving point and the plane of the LED array is 1m
The lambertian radiation equation is:
E＝cos9θ
FIG. 2 shows a circuit model of LED AC small signal with corresponding impedance of
Fig. 3 shows the real and imaginary parts of the LED impedance measured by the vector network analyzer in the frequency range of 300kHz to 100MHz in the on state of a single LED tube.
FIG. 4 shows a broken line of the mode of the impedance and the inverse of the bias current at a frequency of 300kHz, according to the formula
Fitting a broken line intercept to obtain Rs＝2.65Ω,Rd＝14.125Ω.
31.207MHz according to the 3dB bandwidth of the LED tube, therefore tauc＝RdCdTo 32.044ns. end, we obtained CdA further fit gives L according to fig. 3 as the imaginary part of the LED impedance, 0.36nF.s＝22nH.
Table 1 shows the ac current flowing through the LED array equivalent circuit driven by an ac signal of 10MHz at different LED series numbers.
| Number of LED tube on | Alternating current of LED array |
| 1 | 21.576 |
| 2 | 17.467 |
| 3 | 14.667 |
| 4 | 12.683 |
| 5 | 11.099 |
| 6 | 9.894 |
| 7 | 8.924 |
| 8 | 8.127 |
| 9 | 7.461 |
| 10 | 6.895 |
| 11 | 6.409 |
| 12 | 5.987 |
| 13 | 5.617 |
| 14 | 5.290 |
| 15 | 5.000 |
| 16 | 4.739 |
TABLE 1
Table 2 shows the equivalent power of the corresponding LED tube at the receiving end according to the LED array layout and the LED numbers provided in fig. 4.
TABLE 2
Fig. 5 shows the equivalent power of the receiving terminal at different numbers of LEDs in series. The maximum equivalent power obtained in comparison is obtained by connecting 12 LEDs in series, namely 12 is the optimal number of LEDs in series. Further considering the improvement of cost and the trend of increasing the equivalent total current of a receiving end on the premise of increasing the number of the LED tubes, 4-5 LED tubes are selected as the optimal cost performance.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (3)
1. A method for determining the optimal number of LEDs connected in series in an optical communication system is characterized in that: n LED tubes are connected in series to form an LED array, if each LED tube in the LED array can be independently controlled to be switched on or switched off, the switching-on quantity of the LED tubes in series is changed, a vector network analyzer is used for determining alternating current small-signal circuit models of the LED arrays in series under different switching-on quantities, and circuit simulation is used for determining alternating current small current flowing through the LED arrays under different switching-on quantities; fixing a receiving position, fixing the serial layout of N LED tubes of the LED array, and changing the conduction number of the LED tubes so that the serial number with the maximum receiving equivalent current is the optimal serial number of the LEDs;
the method for determining the alternating current small signal circuit model of the series LED array under different conduction numbers by using the vector network analyzer comprises the following specific steps:
1) setting the test frequency range of the vector network analyzer to be 300kHz-100MHz, setting the signal output power of a port 1 to be-30 dBm, calibrating the port 1 of the vector network analyzer by using an open-circuit load, a short-circuit load and a 50 omega matching load, and storing calibration parameters;
2) an LED array circuit is connected according to an experimental system diagram, and only one lamp in the LED array can be conducted;
3) adjusting the output current of the direct current source from 1mA to 10mA, stepping by 1mA, and respectively storing impedance parameters under different frequency points measured by a vector network analyzer from small to large;
4) changing the number of the conducted LEDs in the LED array, and repeating the step 3);
5) with reference to a single LED AC small-signal circuit model, the input impedance is
Wherein R issIs an equivalent circuit series resistance, RdAnd CdResistance and capacitance being equivalent parallel circuits, LsAn equivalent circuit is connected with an inductor in series; r in single LED alternating small signal circuit model can be determineds、Rd、Ls、CdA parameter;
6) according to the result obtained in the step 4), the alternating current small signal model with the plurality of LED tubes connected in series can be approximately equivalent to the series connection between the small signal models of the single LED tubes.
2. The method for determining the optimal serial number of LEDs in an optical communication system according to claim 1, wherein the circuit simulation is used to determine the ac small current flowing through the LED array at different turn-on numbers, specifically: the method comprises the steps of changing the conduction number of LEDs in an LED array by using a power amplifier which is provided by Windows platform software Multisim and is connected with an alternating current signal, wherein the power amplifier is used for carrying out circuit simulation in a circuit diagram building mode, connecting LED array equivalent circuits with different conduction numbers in series at the rear stage of the power amplifier, and measuring alternating current flowing through the equivalent circuits to obtain LED array equivalent alternating currents with different conduction numbers.
3. The method for determining the optimal serial number of LEDs in an optical communication system according to claim 1, wherein the receiving position is fixed, the serial layout of N LED tubes in the LED array is fixed, and the conducting number of the LED tubes is changed, so that the serial number with the maximum receiving equivalent current is the optimal serial number of LEDs, specifically:
if the path losses from different LED tubes to the receiving end are approximately the same, the alternating currents flowing through the LED array under different series quantities are utilized, the current of each LED tube at the receiving end has a weighting coefficient, the weighted sum of the currents under different conditions is the equivalent receiving power, the weight of each lamp is determined by a Lambert radiation equation, and the equation is as follows:
E＝cosmθ
where E is the normalized radiant power, θ is the radiant angle, m is the power attenuation order, and m is dependent on the relative position of the LED light emitting area and the center of curvature of the spherical encapsulant.
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| CN1324153A (en) * | 2000-05-16 | 2001-11-28 | 株式会社东芝 | Light-emitting diode and transmitting/receiving modular |
| CN105282068A (en) * | 2015-09-18 | 2016-01-27 | 北京邮电大学 | Pre-emphasis and equalization method based on least square method in wireless light communication |
| CN106788760A (en) * | 2016-11-11 | 2017-05-31 | 华南师范大学 | Lift the visible light communication ballistic device of response frequency |
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| CN1324153A (en) * | 2000-05-16 | 2001-11-28 | 株式会社东芝 | Light-emitting diode and transmitting/receiving modular |
| CN105282068A (en) * | 2015-09-18 | 2016-01-27 | 北京邮电大学 | Pre-emphasis and equalization method based on least square method in wireless light communication |
| CN106788760A (en) * | 2016-11-11 | 2017-05-31 | 华南师范大学 | Lift the visible light communication ballistic device of response frequency |
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