Fast Precharge Circuit with Mismatch Cancellation for LED Drivers
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Solution Overview
Problem
As LED panel sizes and resolutions increase, the number of pixels driven by a single channel grows, leading to a heavier load on display data drivers, causing delayed light emission due to slow precharge voltage application and potential mismatches between precharge units, resulting in suboptimal brightness and visual artifacts.
Innovation Solution
A precharge method and circuit that employs a fast precharge circuit with a first precharge voltage for rapid voltage transition and a second precharge voltage for precise charging, along with an operational amplifier configuration and a mismatch cancellation circuit to ensure consistent precharge levels across output terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single precharge voltage is applied to output terminals, then the circuit structure remains simple, but the voltage transition speed is insufficient and precharge time is extended
Solution Approach 1:
The precharge process is divided into two distinct phases: a first precharge phase using a first precharge voltage for rapid voltage transition, and a second precharge phase using a second precharge voltage for precise charging closer to the output voltage. This segmentation allows each phase to be optimized independently, achieving fast transition without excessive complexity
Solution Approach 2:
The first precharge voltage is applied in advance before the second precharge voltage. This preliminary action rapidly brings the output terminal voltage close to the target level, reducing the workload and time required for the subsequent precise charging phase
2Manufacturing precision
If precharge voltage is applied earlier, then the precharge time is extended, but the brightness uniformity and visual quality deteriorate due to mismatches between precharge units
Solution Approach 1:
A mismatch cancellation circuit is introduced that receives precharge control signals and adjusts the precharge voltages applied to different output terminals. This feedback mechanism compensates for mismatches between precharge units, ensuring consistent precharge voltage levels across all terminals while maintaining precise timing control
3Quantity of substance
If the number of LED pixels per channel increases, then the panel resolution and size improve, but the load on the data driver increases causing slower precharge and delayed light emission
Solution Approach 1:
The precharge operation is segmented into two voltage phases with different characteristics. The first phase uses a voltage that provides faster transition to handle the increased capacitive load from more pixels, while the second phase completes the precise charging. This segmentation maintains precharge speed despite increased pixel quantity
Solution Approach 2:
The first precharge phase performs preliminary charging action that rapidly addresses the majority of the voltage requirement, reducing the subsequent charging burden. This preliminary action is particularly effective when driving larger numbers of pixels, as it quickly establishes the baseline voltage before precise adjustment
Data Source
AI summary
A precharge method for a data driver includes steps of: outputting a display data to a plurality of output terminals of the data driver; outputting a second precharge voltage to an output terminal among the plurality of output terminals prior to outputting the display data to the output terminal, to precharge the output terminal to a voltage level closer to an output voltage; and outputting a first precharge voltage to the output terminal prior to outputting the second precharge voltage. The first precharge voltage provides a faster voltage transition on the output terminal than the second precharge voltage.