LCD Lamp Driving Circuit Reducing Ripple Noise
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Solution Overview
Problem
LCD systems suffer from interference noise known as the 'ripple phenomenon' due to synchronization issues between lamp driving signals and horizontal/vertical synchronization signals, degrading display quality.
Innovation Solution
A method and circuit that determine a lamp driving frequency responsive to the horizontal synchronization signal, using specific formulae to generate a lamp driving signal that reduces interference noise, ensuring the frequency is not a harmonic of the synchronization signal, thereby suppressing ripple phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the burst signal frequency of the burst mode inverter is set to be equal or near the frequency of the vertical synchronization signal or its harmonics, then the lamp driving is simplified and synchronized, but interference noise is generated periodically causing ripple phenomenon on the display screen
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the inverter driving frequency based on the horizontal synchronization signal frequency. The control circuit calculates a counting number from the ratio of crystal oscillation frequency to horizontal sync frequency, and uses this to determine an optimal inverter driving frequency that is not a harmonic of the vertical sync frequency, thereby avoiding ripple phenomenon while maintaining synchronized lamp operation
2Object-affected harmful factors
If the burst signal frequency is set to be about 150 Hz or higher to avoid being close to the harmonics or flicker perceived by human eyes, then the ripple phenomenon is reduced, but the tolerance of the burst mode frequency is big due to temperature-dependent components making it unstable
Solution Approach 1:
The patent implements feedback by having the control circuit continuously monitor the horizontal synchronization signal frequency and dynamically adjust the inverter driving frequency accordingly. The control circuit calculates the counting number based on the actual horizontal sync frequency and adjusts the inverter driving frequency to maintain optimal operation, ensuring stability despite temperature variations and component tolerances
3Object-affected harmful factors
If the lamp driving frequency is not synchronized with the horizontal synchronization signal, then interference noise is reduced, but the lamp operation becomes less controlled and may affect display quality
Solution Approach 1:
The patent uses the horizontal synchronization signal as an intermediary to establish a controlled relationship between the lamp driving and display refresh operations. The control circuit uses the horizontal sync signal to determine the inverter driving frequency through frequency division and counting number calculation, ensuring that the lamp operation is controlled and synchronized with the display refresh without creating harmonic interference
Data Source
AI summary
A circuit and method of reducing noises for improving quality of display in a liquid crystal display (LCD) system. The LCD system includes an LCD panel and at least one lamp. In operation the LCD system is supplied with a vertical synchronization signal and a horizontal synchronization signal. In one embodiment, the method comprises the steps of determining a lamp driving frequency for the at least one lamp responsive to the horizontal synchronization signal, and generating a lamp driving signal with the lamp driving frequency to be received by the at least one lamp for producing light, wherein the following formulae (1) and (2) are satisfied:flamp=2n-1mHsync+δ(1)andHsync/m≥δ≥0(2)where Hsync is the frequency of the horizontal synchronization signal in unit of (Hz); flamp is the lamp driving frequency for the lamp driving signal in unit of (Hz); m, n=1, 2, 3, . . . , an integer; and δ indicates the permissible error of the lamp driving frequency.