Light Source Modulation Circuit Jitter Reduction
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Solution Overview
Problem
Projector apparatuses using semiconductor light sources experience jitter issues due to interference between PWM-modulated and on/off modulation signals when adjusting light source brightness, leading to unstable information transfer.
Innovation Solution
A light source modulation circuit comprising a pulse width modulator, frequency divider circuit, communication modulator, AND operation circuit, and light source drive circuit, which generates a light source modulation signal by performing logical operations on PWM-modulated and communication modulation signals, preventing jitter by synchronizing the timing of PWM and communication carrier signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the brightness of the light source is adjusted by PWM and the resulting PWM waveform is on/off modulated according to the information to be transferred, then information transfer is enabled, but jitters occur due to interference between the PWM-modulated signal and the on/off modulation signal
Solution Approach 1:
The patent divides the modulation process into separate functional blocks: a PWM modulation unit that adjusts brightness, and a communication modulation unit that encodes information. By segmenting these functions and processing them independently before combining, the patent avoids direct interference between PWM and communication signals, thereby preventing jitters while maintaining information transfer stability.
Solution Approach 2:
The patent introduces an intermediary processing stage where PWM-modulated signals and communication modulation signals are separately generated and then combined through a logical AND operation. This intermediary approach allows each signal to be processed independently without direct interference, resolving the contradiction between enabling information transfer and maintaining signal stability.
2Illumination intensity
If PWM modulation is applied to adjust light source brightness, then brightness control is achieved, but pulse position shifts and jitters occur in the resulting modulation signal
Solution Approach 1:
The patent segments the brightness control function from the position control function. The PWM modulation unit handles brightness adjustment independently, while the communication modulation unit handles timing and position information. This segmentation allows brightness control without compromising pulse position accuracy, as each function operates independently.
Solution Approach 2:
The patent performs preliminary PWM modulation on the light source before applying communication modulation. By pre-adjusting the brightness through PWM and then superimposing communication signals, the patent ensures that pulse position information is established beforehand and not distorted by subsequent brightness adjustments, thereby maintaining pulse position accuracy.
Data Source
AI summary
A light source modulation circuit includes a pulse width modulator (PWM) PWM-modulating an input PWM carrier signal according to an input on-time ratio signal to output a PWM-modulated signal, a frequency divider circuit frequency-dividing the PWM carrier signal at a predetermined frequency division ratio to output a communication carrier signal, a communication modulator modulating the communication carrier signal according to an input communication modulation code to output a communication modulation signal, an operational circuit performing a logical AND operation of the PWM-modulated signal and the communication modulation signal to output a resulting signal of the operation as a light source modulation signal, and a light source drive circuit generating a light source drive signal based on the light source modulation signal.