Visible light communication device and driving method thereof

1. A visible light communication device, comprising:

a light-emitting unit;

a switch-mode light-emitting diode (LED) driver, providing a driving current for driving the light-emitting unit;

a synthesizing circuit, synthesizing a data signal and a dimming signal to form a synthesized signal; and

a path selection circuit, according to a data frequency and a dimming ratio obtained from one or more path selection information, selecting to turn on a bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit along one path, wherein the bypass current modulation unit controls the light-emitting unit for displaying the data signal according to the synthesized signal, or selecting to inject the synthesized signal to the switch-mode LED driver along another path, wherein the switch-mode LED driver controls the light-emitting unit according to the synthesized signal for displaying the data signal,

wherein the bypass current modulation unit includes a voltage-controlled current source (VCCS), generates a controlling voltage of the VCCS according to the synthesized signal, and controls a current passing through the VCCS by the controlling voltage for displaying the data signal.

2. The visible light communication device of claim 1 , wherein the one or more path selection information is the synthesized signal, and the data frequency and the dimming ratio are obtained from the synthesized signal.

3. The visible light communication device of claim 2 , wherein the path selection circuit comprises:

a decision circuit, receiving the synthesized signal, calculating the data frequency and the dimming ratio from the synthesized signal, and generating an output signal having a first state when the data frequency is greater than a critical frequency or the data frequency is lower than or equal to the critical frequency and the dimming ratio is not in an interval between two different percentages or generating the output signal having a second state when the data frequency is lower than or equal to the critical frequency and the dimming ratio is in the interval between the two different percentages; and

a driving circuit, receiving the output signal and the synthesized signal, and turning on the bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit according to the output signal having the first state, or injecting the synthesized signal to the switch-mode LED driver according to the output signal having the second state.

4. The visible light communication device of claim 2 , wherein the path selection circuit further comprises a decision circuit, the decision circuit is a counter, and the counter receives at least one synthesized signal in a time period, counts a number of the at least one synthesized signal being in a high state and a number of the at least one synthesized signal being in a low state, obtains the data frequency according to a predefined clock frequency and the number of the at least one synthesized signal being in the high state, and obtains the dimming ratio according to the predefined clock frequency, the number of the at least one synthesized signal being in the high state and the number of the at least one synthesized signal being in the low state.

5. The visible light communication device of claim 1 , wherein the one or more path selection information is the data frequency and the dimming ratio received by the path selection circuit, and the data frequency is obtained from the data signal and the dimming ratio is obtained from the dimming signal.

6. The visible light communication device of claim 5 , wherein the path selection circuit comprises:

a decision circuit, receiving the data frequency and the dimming ratio, and generating an output signal having a first state when the data frequency is greater than a critical frequency or the data frequency is lower than or equal to the critical frequency and the dimming ratio is not in an interval between two different percentages or generating the output signal having a second state when the data frequency is lower than or equal to the critical frequency and the dimming ratio is in the interval between the two different percentages; and

a driving circuit, receiving the output signal and the synthesized signal, and turning on the bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit according to the output signal having the first state or inject the synthesized signal to the switch-mode LED driver according to the output signal having the second state.

7. The visible light communication device of claim 1 , wherein the bypass current modulation unit is a multi-level current amplitude modulation circuit, and the multi-level current amplitude modulation circuit comprises:

at least a combination of a group consisting of a plurality of switches and a plurality of constant current sources, and the multi-level current amplitude modulation circuit controls the plurality of switches according to the synthesized signal for displaying the data signal.

8. The visible light communication device of claim 1 , wherein the switch-mode LED driver generates a pulse width modulation (PWM) signal having a modulated duty cycle according to the synthesized signal for displaying the data signal.

9. A driving method for driving a visible light communication device, comprising:

synthesizing a data signal and a dimming signal in the visible light communication device to form a synthesized signal; and

selecting to inject the synthesized signal along one path to a bypass current modulation unit or along another path to a switch-mode light-emitting diode (LED) driver of the visible light communication device according to a data frequency and a dimming ratio obtained from one or more path selection information, wherein the bypass current modulation unit or the switch-mode LED driver controls a light-emitting unit of the visible light communication device according to the synthesized signal for displaying the data signal,

wherein the driving method further comprises:

performing a data frequency determining step comprising determining whether the data frequency is lower than or equal to a critical frequency or not, if not, turning on a bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit and the bypass current modulation unit controls a light-emitting unit according to the synthesized signal for displaying the data signal, if yes, further performing a dimming ratio determining step; and

in the dimming ratio determining step, determining whether the dimming ratio is in an interval between two different percentages or not, if not, turning on the bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit along one path, wherein the bypass current modulation unit controls the light-emitting unit according to the synthesized signal for displaying the data signal, if yes, injecting the synthesized signal to a switch-mode LED driver along another path, wherein the switch-mode LED driver controls the light-emitting unit according to the synthesized signal for displaying the data signal.

10. The driving method for driving the visible light communication device of claim 9 , wherein the one or more path selection information is the synthesized signal, and the data frequency and the dimming ratio are obtained from the synthesized signal.

11. The driving method for driving the visible light communication device of claim 10 , further comprising:

calculating the data frequency and the dimming ratio from the synthesized signal, and generating an output signal having a first state when the data frequency is greater than a critical frequency or the data frequency is lower than or equal to the critical frequency and the dimming ratio is not in an interval between two different percentages or generating the output signal having a second state when the data frequency is lower than or equal to the critical frequency and the dimming ratio is in the interval between the two different percentages; and

turning on the bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit along one path according to the output signal having the first state or injecting the synthesized signal to the switch-mode LED driver along another path according to the output signal having the second state.

12. The driving method for driving the visible light communication device of claim 10 , further comprising:

counting a number of the synthesized signal being in a high state and a number of the synthesized signal being in a low state in a time period, obtaining the data frequency according to a predefined clock frequency and the number of the synthesized signal being in the high state, and obtaining the dimming ratio according to the predefined clock frequency, the number of the synthesized signal being in the high state and the number of the synthesized signal being in the low state.

13. The driving method for driving the visible light communication device of claim 10 , wherein the one or more path selection information is the data frequency and the dimming ratio received by the path selection circuit, and the data frequency is obtained from the data signal and the dimming ratio is obtained from the dimming signal.

14. The driving method for driving the visible light communication of claim 13 , further comprising:

generating an output signal having a first state when the data frequency is greater than a critical frequency or the data frequency is lower than or equal to the critical frequency and the dimming ratio is not in the interval between the two different percentages or generating the output signal having a second state when the data frequency is lower than or equal to the critical frequency and the dimming ratio is in the interval between the two different percentages; and

turning on the bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit alone one path according to the output signal having the first state, or inject the synthesized signal to the switch-mode LED driver along another path according to the output signal having the second state.

15. A visible light communication device, comprising:

a light-emitting unit;

a switch-mode light-emitting diode (LED) driver, providing a driving current for driving the light-emitting unit;

a synthesizing circuit, synthesizing a data signal and a dimming signal to form a synthesized signal; and

a path selection circuit, according to a data frequency and a dimming ratio obtained from one or more path selection information, selecting to turn on a bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit along one path, wherein the bypass current modulation unit controls the light-emitting unit for displaying the data signal according to the synthesized signal, or selecting to inject the synthesized signal to the switch-mode LED driver along another path, wherein the switch-mode LED driver controls the light-emitting unit according to the synthesized signal for displaying the data signal, wherein the one or more path selection information is the synthesized signal, and the data frequency and the dimming ratio are obtained from the synthesized signal;

wherein the path selection circuit comprises:

a decision circuit, receiving the synthesized signal, calculating the data frequency and the dimming ratio from the synthesized signal, and generating an output signal having a first state when the data frequency is greater than a critical frequency or the data frequency is lower than or equal to the critical frequency and the dimming ratio is not in an interval between two different percentages or generating the output signal having a second state when the data frequency is lower than or equal to the critical frequency and the dimming ratio is in the interval between the two different percentages; and

a driving circuit, receiving the output signal and the synthesized signal, and turning on the bypass current modulation unit to inject the synthesized signal to the bypass current modulation unit according to the output signal having the first state, or injecting the synthesized signal to the switch-mode LED driver according to the output signal having the second state.