Visible Light Communication Transmitter Multi-Level Driving
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Solution Overview
Problem
Existing visible light communication systems using blue-light-excitation-type white LEDs face limitations in high-speed data transmission due to low response speed of phosphor output, potential LED damage from overcurrent, and difficulty in adjusting driving conditions for high-speed transmission without using blue color filters.
Innovation Solution
A visible light communication transmitter employs a multi-level driving current signal with rising and falling pulses, where the pulse widths are half of the minimum pulse width of the transmission data, and the driving current values are controlled to prevent overcurrent and optimize transmission speed without a blue color filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If blue-light-excitation-type white LED is used for visible light communication, then energy efficiency and manufacturing cost are improved, but transmission speed is limited due to low response speed of phosphor output
Solution Approach 1:
The patent segments the white LED output into two distinct components: blue light component and phosphor light component. By using a color filter to separate these components, the system can selectively process the blue light component which has faster response characteristics, thereby improving transmission speed while maintaining the advantages of phosphor-based white LEDs
Solution Approach 2:
The patent introduces a color filter as an intermediary component between the white LED and the photodetector. This intermediary selectively transmits the blue light component while blocking the phosphor light component, enabling the system to exploit the faster response characteristics of the blue LED without requiring a complete system redesign
2Productivity
If driving current is increased to improve transmission speed, then productivity is improved, but LED may be damaged due to overcurrent
Solution Approach 1:
The patent changes the driving current parameters dynamically by adding rising and falling pulses to the driving current signal. This parameter modification enables faster LED response for high-speed data transmission while the current magnitude is carefully controlled to remain within safe operating limits, preventing LED damage
Solution Approach 2:
The patent employs periodic rising and falling pulses superimposed on the driving current. These periodic current variations create sharp transitions that improve the LED's response speed for high-speed communication, while the overall current envelope remains controlled to prevent thermal damage to the LED
3Productivity
If blue color filter is added to improve transmission speed, then productivity is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent designs the color filter to serve multiple functions: it acts as a wavelength selector for the blue light component, a protective element for the photodetector, and a structural component that can be integrated into the existing LED packaging. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high-speed data transmission up to 125Mbps while preventing LED damage and reducing component costs by eliminating the need for blue color filters, ensuring a cost-effective and controllable system configuration.
Implementation Method 1
a phosphor that emits mainly yellow light... the surrounding phosphor is excited by the blue light output from the blue LED arranged in the center, and the light (mainly yellow) that is mainly complementary to blue is output from the phosphor
Implementation Method 2
combining a blue LED with a phosphor that emits mainly yellow light
Implementation Method 3
the receiving side converts the intensity of the light into an electric signal through an optical-electrical converter (O/E converter), such as a photodiode (hereinafter referred to as a 'PD')
Data Source
AI summary
Visible light data communication with a sufficient transmission speed is performed using a general-purpose and cost-advantageous blue-light-excitation-type white LED without using a blue color filter while preventing the element from being damaged. When transmission data is inputted to a driving waveform generation unit (110) in a transmitter (100), the driving waveform generation unit (110) and a multi-gray scale driving unit (120) generate a multi-gray scale driving signal, which is supplied to the blue-light-excitation-type white LED (140) and allows the blue-light-excitation-type white LED (140) to emit light. A light signal outputted from the blue-light-excitation-type white LED (140) is collected by a lens or the like, is made incident into a PD (210) in a receiver (200), and is converted to a current signal. The current signal is converted into a voltage signal in a trans-impedance amplifier (212). Further, the light signal is subjected to equalization processing in an equalizer (214) and then is digitized by a limiting amplifier (216), thereby obtaining output data.