PWM Bit Sequence Reordering for LED Display Power Reduction
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Solution Overview
Problem
Electronic displays face high dynamic power consumption due to frequent charging and discharging of storage capacitors in control circuits, particularly in sub-pixels, which increases energy usage without corresponding improvements in brightness levels.
Innovation Solution
A modified digital word and PWM signal are generated with fewer transitions from a lower to a higher voltage level, optimizing the sequence of pulses to reduce capacitor charging and maintain specified brightness levels, thereby minimizing dynamic power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the storage capacitor is frequently charged and discharged during operation, then the brightness control precision is improved, but the dynamic power consumption increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal bit sequences that minimize voltage transitions before they are needed during display operation. The lookup table is populated in advance with pre-optimized grayscale values that achieve the desired brightness precision while minimizing capacitor charging cycles, thus reducing dynamic power consumption without sacrificing brightness control precision
Solution Approach 2:
The patent changes the parameter of bit sequence ordering to optimize power consumption. By rearranging the order of bits in the grayscale value representation and selecting sequences with fewer transitions from low to high voltage levels, the patent reduces the number of capacitor charging events while maintaining the same brightness output, directly addressing the contradiction between precision and power consumption
2Use of energy by moving object
If the bit sequence is optimized to reduce voltage transitions, then the dynamic power consumption is reduced, but the complexity of the control circuit increases
Solution Approach 1:
The patent uses preliminary action to pre-compute and store optimized bit sequences in a lookup table before the display operates. This shifts the computational complexity from the real-time control circuit to an offline preprocessing stage, allowing the actual control circuit to simply retrieve pre-optimized values without performing complex calculations, thus reducing power consumption without significantly increasing control circuit complexity
Solution Approach 2:
The patent creates a copy of the grayscale value in an optimized form from the lookup table. Instead of performing complex real-time optimization, the system copies pre-optimized bit sequences that have already been calculated to minimize voltage transitions, thereby reducing dynamic power consumption while keeping the control circuit relatively simple
Data Source
AI summary
An electronic display uses pulse-width modulation (PWM) to drive light emitting devices (LEDs) with reduced power consumption. A modified digital word including a modified sequence of bits is generated by modifying a bit sequence of a greyscale value for a sub-pixel. The modified bit sequence includes fewer transitions from a first voltage level to a second voltage level higher than the first voltage level than the bit sequence of the grayscale value. A modified sequence of pulses is generated based on ordering pulses of the PWM signal according to the modified bit sequence. The modified digital word and the modified sequence of pulses are used to control a light emitting device of the electronic display. The reduction in voltage level transitions results in reduced charging of a storage capacitor in the control circuit for the LED, while maintaining brightness level as specified by grayscale value.