CN110460377B - Device for LED optical communication by using drive circuit switch ripple - Google Patents

Abstract

The invention discloses a device for LED optical communication by using a drive circuit switch ripple, wherein the topology of the device adopts a DC-DC converter, the control mode adopts constant output current control, and the transmission of signals is realized by the switch ripple under the condition of not adding any device. The device realizes the transmission of data under the conditions of not influencing normal illumination and not increasing special wired and wireless communication equipment, so that the monitoring of the running state of the LED device becomes convenient and low in cost; meanwhile, the device of the invention uses the switch ripple as the carrier signal, and can meet the requirement of the low-speed communication field for data transmission.

Description

A device for LED optical communication using driving circuit switching ripple

technical field

The invention belongs to the technical field of optical communication, and in particular relates to a device for LED optical communication using switching ripple of a driving circuit.

Background technique

Visible light communication is developing rapidly as an emerging technology, because the frequency of visible light is much higher than that of the existing wireless communication technology, and its theoretical communication rate is more than 100 times faster than the existing technology. Visible light communication is achieved by controlling the on and off of LEDs. Because the frequency of LED on and off is very high, which exceeds the frequency that can be recognized by the naked eye, visible light communication can ensure that the normal lighting effect is maintained while communicating. At the same time, LED has a very broad market and is widely used in TVs, monitors, mobile phones, home lighting, etc., and has become an indispensable part of daily life, which means that visible light communication can cover a very large range.

In addition, the cost of visible light communication is also lower, and data interaction can be realized by relying on daily lighting. Visible light cannot penetrate opaque obstacles, so all communication information is limited to a room or a specific area, and with the increase of distance, the intensity of light decreases rapidly, and the signal-to-noise ratio also decreases. Wireless communication technology reduces the possibility of other people being exposed to these communication data, which can be understood as a security issue during communication from a certain perspective. More importantly, the spectrum of wireless communication is strictly controlled. Each communication company needs to complete the transmission of signals in the wired spectrum, but there is no such problem with light waves, and because light waves cannot penetrate opaque obstacles, the spectrum of light waves It can be reused in different areas.

However, there is no widely accepted mode for driving LEDs. There are three main considerations for driving LEDs: cost, efficiency and communication speed. One of the existing topologies is shown in Figure 1. The MOS tube is driven by a switching signal, because the characteristic of the volt-ampere characteristic curve of the MOS tube is that it exhibits a resistance property at a small current, that is, a linear resistance region; it basically remains at a large current. The current is constant and does not change with the source-drain voltage, that is, the saturation region, where the value of this maintained current is determined according to the voltage difference between the gate and the source. Therefore, the constant current control of the LED can be achieved by setting a certain gate voltage as the working voltage. The entire working process is switched back and forth between the set working voltage and 0 through the gate voltage. As shown in Figure 1, in the process of signal transmission, if the turn-on signal in a symbol is in front, it means 0, and the turn-off signal is in front, it means 1; this method is low cost, but the loss is high, because the MOS works in the saturation region , equivalent to a linear power supply, the efficiency calculation is equal to the voltage across the LED divided by the input DC power supply voltage. Generally, in order to ensure normal operation, the input DC power supply voltage and the voltage across the LED will retain a certain margin, which leads to low efficiency. Again the efficiency is calculated without considering the auxiliary power supply.

It can be seen that the LED driver circuits on the existing market are basically a trade-off between cost, efficiency and communication rate, and no solution that can take into account the three aspects has been proposed.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a device for LED optical communication using the switching ripple of a driving circuit. The topology of the device adopts a DC-DC converter, and the control method adopts constant output current control. The signal transmission is realized by switching ripple.

A device for LED optical communication using switching ripple of a driving circuit, which adopts a DC-DC converter with output constant current control, and adjusts the frequency, amplitude and phase of the switching ripple by controlling the PWM switching signal of the DC-DC converter , the switching ripple is superimposed on the LED radiation intensity to realize communication; the device uses the triangular wave of the switching frequency required to generate the PWM switching signal as the carrier signal, and the modulation mode is phase shift keying.

Further, the working state of the device is divided into two stages: an idle stage and a communication stage; data transmission is only performed in the communication stage, and the communication stage is alternately composed of a transition stage and a transmission symbol stage, and one communication stage corresponds to one frame. The transmission time of data, a frame of data contains N symbols, a group of alternating transition stages and transmission symbol stages together constitute the transmission time of a symbol, that is, the transmission time of a frame of data includes N groups of alternating transition stages And the transmission symbol stage, N is a natural number greater than 1.

Further, the switching frequency of the DC-DC converter in the idle stage is a fixed value f ₁ , the switching frequency of the DC-DC converter in the transmission symbol stage is a fixed value f ₂ , and the switching frequency of the DC-DC converter in the transition stage is Dynamic value; for the switching frequency f _ad (n) of the grid-connected inverter in the nth transition stage in a communication stage, its calculation expression is as follows:

If a _n-1 +data _n ≥K, then

If a _n-1 +data _n <K, then

且规定a₀＝0，％为取模运算符，data_i表示通信阶段对应传输的一帧数据中第i个码元，n为自然数且1≤n≤N。Among them: K represents the system of the transmitted data, data _n represents the n-th symbol in a frame of data transmitted corresponding to the communication stage, M is the number of switching cycles included in a transition stage,

And it is specified that a ₀ =0, % is a modulo operator, data _i represents the i-th symbol in a frame of data correspondingly transmitted in the communication stage, n is a natural number and 1≤n≤N.

Further, the duration T of each transmission symbol stage in a communication stage is fixed, and T=A/f ₂ , A is the number of switching cycles included in a transmission symbol stage; the duration of each transition stage in a communication stage Not fixed, and where the duration of the nth transition phase T(n)=M/f _ad (n).

Further, the value of the switching frequency f ₁ -f ₂ is greater than the crossover frequency of the closed-loop transfer function of the DC-DC converter, and the closed-loop transfer function of the inverter circuit indicates that the flow through The relationship between the output current of the LED and the duty cycle signal in the frequency domain is expressed. When the amplitudes of the two are equal at a certain frequency, the frequency is the crossover frequency.

Further, the device includes a DC source, an input capacitor C _in , switch tubes T ₁ and T ₂ , an inductance L, an output capacitor C _out , a load LED, a sampling resistor and a sampling control circuit; wherein one end of the input capacitor C _in is connected to a The anode of the DC source and the drain _of the switch tube T1 are connected, and the other end of the input capacitor _Cin is connected to the cathode of the DC source, the source of the switch tube T2, one end of the output _{capacitor Cout and} one end of the sampling resistor and is connected to ground, _The source of the switch tube T1 is connected to the drain of the switch tube T2 and _one end of the inductor L, the other end of the inductor L is connected to the other end of the output capacitor C _out and the anode of the load LED, and the cathode of the load LED is connected to the sampling resistor. The other end is connected, and the sampling control circuit obtains the current flowing through the load LED through the sampling resistor, and uses the output constant current control method to generate the corresponding PWM switching signal and provide it to the gates _of the switching tubes T1 and _T2 .

Some LED devices need to monitor their various states during operation, and the communication function of the LED device needs to be used at this time. The device of the present invention realizes the completion of data transmission without affecting normal lighting and without adding special wired and wireless communication equipment, which makes the monitoring of the operating state of the LED device convenient and low-cost; at the same time, the device of the present invention utilizes As a carrier signal, the switching ripple can meet the requirements for data transmission in the field of low-speed communication.

Description of drawings

FIG. 1 is a schematic diagram of a conventional LED driving circuit.

FIG. 2 is a block diagram of the system control flow of the DC-DC converter.

FIG. 3 is a schematic diagram of an LED driving circuit based on a Buck circuit.

FIG. 4 is a schematic diagram of the waveform of the modulation signal.

FIG. 5 is a schematic diagram of a communication frame format.

FIG. 6 is a schematic diagram of LED current and demodulation waveform.

Detailed ways

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below from specific embodiments with reference to the accompanying drawings.

The device of the present invention uses switching ripple for LED optical communication, adopts a DC-DC converter with output constant current control, adjusts the current ripple of the LED by controlling the PWM switching signal of the DC-DC converter, and superimposes the LED radiation intensity. The ripple signal is used to realize communication; the device of the present invention uses the triangular wave of the switching frequency as the carrier signal, and the modulation mode is phase shift keying.

The working state of the device of the present invention is divided into two stages: an idle stage and a communication stage. The communication stage also includes a transmission symbol stage and a transition stage, and the information transmission is only completed in the communication stage. The whole working process is composed of the idle phase and the communication phase alternately, and the communication phase is alternately composed of the transition phase and the transmission symbol phase. A transmission symbol phase and a transition phase together form a symbol. One communication stage contains one frame of data, and one frame of data contains N symbols, that is, one frame of data is alternately composed of N transmission symbol stages and transition stages; the switching frequency in the idle stage is a fixed value f ₁ , and the transmission symbol stage switches The frequency is a fixed value f ₂ , and the switching frequency in the transition phase is a dynamic value f _ad (n).

As shown in Figure 2, first determine whether the device needs to send data, if not, it is currently in the idle stage, and the switching frequency f _s is a fixed value f ₁ ; if necessary, it is currently in the communication stage, and then determine what kind of communication is currently in If it is a transmission symbol stage, the switching frequency f _s is a fixed value f ₂ ; if it is a transition stage, then f _s =f _ad (n), and its calculation expression is as follows:

If a _n-1 +data _n ≥K, then

If a _n-1 +data _n <K, then

且规定a₀＝0，％为取模运算符，data_i表示通信阶段对应传输的一帧数据中第i个码元，n为自然数且1≤n≤N。Among them: K represents the system of the transmitted data, data _n represents the n-th symbol in a frame of data transmitted corresponding to the communication stage, M is the number of switching cycles included in a transition stage,

And it is specified that a ₀ =0, % is a modulo operator, data _i represents the i-th symbol in a frame of data correspondingly transmitted in the communication stage, n is a natural number and 1≤n≤N.

The above f _s is the frequency of the triangular wave as the carrier. As shown in Figure 2, the reference current I _ref subtracts the output current i _o (s) from the signal of the current feedback network H(s) to obtain the error signal e(s), Then, the duty cycle signal d(s) is obtained through proportional and integral adjustment, and the duty cycle signal is compared with the triangular carrier wave through a comparator to generate a switch signal. The switch signal is amplified by the switch tube and then flows through the RLC filter circuit, which is composed of an output inductor, an output capacitor and a load, and then the signal is reflected on the output current i _o (s), and because the output current i _o (s) ) flows through the LED load, so the signal can finally be reflected in the radiated light intensity light(s).

A为固定值，每个过渡阶段时长不固定，

同时，为了保证通信的准确率，避免通信阶段和非通信阶段信号的相互干扰，需要设置f₁-f₂大于电路闭环传递函数的穿越频率，这样就避免了电路在动态相应的时候对通信产生频谱迁移的影响，影响到通信的可靠性。The duration of each transmission symbol stage is fixed,

A is a fixed value, and the duration of each transition stage is not fixed.

At the same time, in order to ensure the accuracy of communication and avoid the mutual interference of signals in the communication phase and the non-communication phase, it is necessary to set f ₁ -f ₂ to be greater than the pass-through frequency of the closed-loop transfer function of the circuit, so as to avoid the dynamic response of the circuit to communication. The impact of spectrum migration affects the reliability of communication.

In terms of hardware connection, the device of the present invention adopts a synchronous Buck circuit. The circuit structure is shown in FIG. 3 , including input capacitor C _in , switch tubes S ₁ and S ₂ , inductor L, output capacitor C _out , load LED and sampling control Circuit; wherein, the positive pole of the input capacitor C _in is connected to the drain _of the switch S1 and the input positive power supply line, the source of the switch _S1 is connected to the drain of the switch S2 and _one end of the inductor L, and the The other end is connected to the positive pole of the output capacitor C _out and the anode of the load LED, the cathode of the load LED, the negative pole of the output capacitor C _out , the source of the switch tube _S2 , the negative pole of the input capacitor C _in and the input negative power line are connected, the switch _The gates _of tubes S1 and S2 are connected to the control signal of the driver after being output by the controller. Among them, U _in is the 12V power supply, C _in is the 40uF input capacitor, T ₁ is the upper tube, T ₂ is the lower tube, L is the 30uH inductor, C _out is the 30uF output capacitor, the LED is the load, and R _sample is the sampling resistor for To measure the output current, T1 and T2 are _both MOS tubes with _a withstand voltage of 30V and an on-resistance of 4.4mΩ.

和

得到这段过渡阶段的时间为39us；第三个数据为3，根据

和

得到这段过渡阶段的时间为33us；第四个数据为3，根据

和

得到这段过渡阶段的时间为45us。The switching frequency of the idle phase and the communication phase should be greater than 3 kHz. The present invention relates to the switching frequency of the idle phase of 100 kHz and the switching frequency of the communication phase of 83.3 kHz. The signal is modulated by phase shift keying. To achieve phase modulation, it is necessary to change the time interval between symbols according to the data of the symbols; as shown in Figure 6, the length of each transmission symbol phase is 264us, that is, 22 switching cycles, The transition stage occupies 3 switching cycles, and the coding adopts 4 system. In Figure 4, the first data is 0, the second data is 1, according to

and

The time to get this transition stage is 39us; the third data is 3, according to

and

The time to get this transition stage is 33us; the fourth data is 3, according to

and

The time to get this transition phase is 45us.

Figure 5 is the frame format during communication, one frame is composed of 60 symbols, and the communication adopts 4 system. Data No. 0 to 3 represent the frame header; data No. 4 and 5 represent the device number; data No. 6 and 7 represent the working status; data No. 8 to 23 represent the total running time of the equipment since it was put into use (unit: second); 24 to 27 Data No. 28 to 35 represent temperature (unit: Celsius), temporarily reserved; data No. 36 to 43 are temporarily reserved; data No. 44 to 51 represent sum verification; data No. 52 to 59 represent end of frame.

As shown in Figure 6, the upper waveform is the current of the LED in one frame, and the lower one is the result of demodulating the optical signal. After demodulation, the waveform is analyzed. After demodulation, the data is output through the ADC. There are five levels in total, which represent the data "0", "1", "2", "3" and the idle level, the voltage of the idle level. The value is half the level of data "0" and "1", so the data obtained after demodulation is "003301020000000000000012022000000000000000000001033333333330", which corresponds to "0x0F12000000062800000000004FFFFC" in hexadecimal. After translating this information, the following information is obtained: equipment number: 01, working state: 02, total working time: 6 seconds, output power: 40 (in the experiment, the data divided by 40 is the actual output power, so the actual output power is 1.0 W), temperature: 0 (this data is now reserved data), sum check: 79=18+6+40+15 (the process of sum check is performed with hexadecimal data, and the last 15 is the frame header 0x0F ).

The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications to the above-described embodiments can be readily made, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention should all fall within the protection scope of the present invention.

Claims (5)

1. An apparatus for LED optical communication using a drive circuit switching ripple, comprising: the device adopts a DC-DC converter controlled by an output constant current, the frequency, the amplitude and the phase of a switching ripple wave are adjusted by controlling a PWM switching signal of the DC-DC converter, and the switching ripple wave is superposed in the LED radiation light intensity to realize communication; the device takes triangular waves of switching frequency required by generating PWM switching signals as carrier signals, and the modulation mode is phase shift keying;

the working state of the device is divided into two stages: an idle phase and a communication phase; the data transmission is only carried out in a communication stage, the communication stage is composed of transition stages and transmission code element stages in an alternating mode, one communication stage corresponds to the transmission time of one frame of data, one frame of data comprises N code elements, one group of alternating transition stages and transmission code element stages jointly form the transmission time of one code element, namely the transmission time of one frame of data comprises N groups of alternating transition stages and transmission code element stages, and N is a natural number larger than 1.

2. The apparatus of claim 1, wherein: the switching frequency of the idle-phase DC-DC converter is a fixed value f₁The switching frequency of the DC-DC converter at the phase of the transmission symbol is a fixed value f₂The switching frequency of the DC-DC converter in the transition stage is a dynamic value; switching frequency f for an nth transition phase grid-connected inverter in a communication phase_ad(n) the computational expression is as follows:

if a_n-1+data_nGreater than or equal to K, then

If a_n-1+data_nIf < K, then

Wherein: k denotes the system of the transmission data, data_nIndicating the nth symbol in a frame of data transmitted in correspondence with the communication phase, M being the number of switching cycles included in a transition phase,

and define a₀0,% is modulus operator, data_iThe symbol represents the ith symbol in a frame of data correspondingly transmitted in the communication stage, N is a natural number and is more than or equal to 1 and less than or equal to N.

3. The apparatus of claim 2, wherein: the duration T of each transmission code element stage in a communication stage is fixed, and T is A/f₂A is the number of switching cycles included in one transmission symbol phase; the duration of each transition phase in a communication phase is not fixed, and the duration of the nth transition phase t (n) M/f_ad(n)。

4. The apparatus of claim 2, wherein: switching frequency f₁-f₂The value of (2) is greater than the crossing frequency of a DC-DC converter closed-loop transfer function, the DC-DC converter closed-loop transfer function represents a relational expression of output current flowing through an LED and a duty ratio signal on a frequency domain after power electronic modeling is carried out on the DC-DC converter, and when the amplitude of the output current and the amplitude of the duty ratio signal on a certain frequency are equal, the frequency is the crossing frequency.

5. The apparatus of claim 1, wherein: the device comprises a DC source and an input capacitor C_inSwitch tube T₁And T₂Inductor L and output capacitor C_outThe load LED, the sampling resistor and the sampling control circuit; wherein the input capacitor C_inOne end of the switch tube T is connected with the anode of the direct current source and the switch tube T₁Is connected to the drain of the input capacitor C_inThe other end of the switch tube is connected with the negative electrode of the direct current source and the switching tube T₂Source electrode and output capacitor C_outOne end of the sampling resistor and one end of the sampling resistor are connected with the ground, and the switching tube T₁Source electrode and switch tube T₂Is connected with one end of an inductor L, and the other end of the inductor L is connected with an output capacitor C_outThe other end of the sampling control circuit is connected with the anode of the load LED, the cathode of the load LED is connected with the other end of the sampling resistor, the sampling control circuit obtains the current flowing through the load LED through the sampling resistor and generates a corresponding PWM switching signal by adopting an output constant current control method to provide the PWM switching signal for the switching tube T₁And T₂A gate electrode of (1).

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