Visible Light Receiver AGC-Free Demodulation
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Solution Overview
Problem
Conventional visible light receiving devices have complex circuit structures and slow response times, making it difficult to handle significant changes in signal levels without using Automatic Gain Control (AGC), which can cause signal distortion and increased waiting times during state transitions.
Innovation Solution
A visible light receiving device with a first conversion unit to generate a voltage signal based on varying light intensity, an amplification unit to cut DC components and amplify AC components, and a processing unit that performs AD conversion, calculates differences, detects rising and falling points, and calculates sample periods to demodulate signals without AGC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Automatic Gain Control (AGC) is used to adjust signal levels, then signal stability is improved, but circuit complexity increases and response delay occurs
Solution Approach 1:
The patent extracts and removes the AGC circuit from the visible light receiving device, replacing it with a simplified processing approach that directly processes voltage signals from the photodetector through AD conversion and demodulation, eliminating the complex gain control machinery while maintaining signal stability through alternative processing methods
Solution Approach 2:
The patent replaces the mechanical/electrical AGC control system with a digital signal processing approach, where voltage signals are converted to digital values through AD conversion and processed algorithmically to achieve signal stabilization without physical gain control mechanisms
2Reliability
If Automatic Gain Control (AGC) is used to adjust signal levels, then signal stability is improved, but response time increases
Solution Approach 1:
By removing the AGC circuit entirely, the patent eliminates the transient response delay inherent in gain control systems, allowing the device to respond immediately to visible light signals without the several-second delay characteristic of AGC state transitions
Solution Approach 2:
The patent performs AD conversion and signal processing in advance without waiting for gain stabilization, enabling immediate demodulation of incoming signals while maintaining accuracy through direct voltage-to-digital conversion rather than delayed gain-adjusted sampling
3Reliability
If high-frequency carrier waves are used for modulation, then data communication stability is improved, but circuit complexity increases
Solution Approach 1:
The patent uses simple voltage signal representations instead of complex high-frequency carrier wave modulations, accepting that each voltage level change must be individually processed through AD conversion rather than relying on reusable carrier wave templates, thereby simplifying the transmitting and receiving circuits
Solution Approach 2:
The patent replaces electromagnetic carrier wave modulation with direct voltage level encoding, substituting complex RF modulation/demodulation circuits with straightforward photodetector-to-AD-converter signal paths that process visible light intensity changes as direct voltage signals
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
Enables rapid and accurate demodulation of visible light signals with significant changes in signal levels, reducing circuit complexity and response delays, allowing for stable operation even with varying communication distances and pulsed disturbance light.
Implementation Method 1
a light-receiving element that converts received visible light into a voltage signal
Data Source
Figure 1
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Figure 2B
AI summary
A receiving device (10) includes a first conversion unit (11), an amplification unit (12), and a microcomputer (13). The microcomputer (13) includes: a second conversion unit (14) that performs, for each sampling time duration, AD conversion on a voltage signal into an AD-converted value; a first calculation unit (15) that calculates a difference digital value by difference calculation; a second calculation unit (16) that calculates a positive reference value and a negative reference value; a detection unit (17) that detects a rising point starting difference digital values greater than the positive reference value, and a falling point starting difference digital values smaller than the negative reference value; a third calculation unit (18) that calculates a first sample period and a second sample period; and a fourth calculation unit (19) that calculates a modulated signal for each symbol time period based on the first sample period and the second sample period.