Adaptive Control Buffer Slew Rate Tuning for Source Driver EMI
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Solution Overview
Problem
As semiconductor integration increases, electromagnetic interference (EMI) phenomena also rise, affecting display image quality and receiver sensitivity, particularly in source drivers where high peak currents during switch signal transitions lead to significant EMI.
Innovation Solution
A control buffer in a source driver is designed with CMOS inverters and tri-state inverters that adjust the slew rate of switch signals based on the size of the control buffer, allowing for selective adjustment of the control buffer's size in response to load changes, thereby reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If each output switch is turned on simultaneously to supply driving voltages, then the switching speed is improved, but high peak current occurs causing electromagnetic interference
Solution Approach 1:
The patent applies dynamics by making the control buffer size adjustable rather than fixed. The control buffer's transistor sizes are dynamically changed based on operating conditions (full screen refresh vs. partial refresh), allowing the system to optimize between switching speed and EMI reduction for different display scenarios
Solution Approach 2:
The patent changes physical parameters of the control buffer, specifically the transistor size parameters. By adjusting the size of transistors in the control buffer, the slew rate of switch signals is modified, which directly controls the peak current magnitude and thus the EMI level while maintaining adequate switching performance
2Object-generated harmful factors
If a large-size driver is used during transitional period to reduce average slew rate, then EMI is reduced, but the device complexity increases
Solution Approach 1:
The patent uses dynamics to switch between different control buffer configurations based on the display refresh mode. A selection signal determines whether to use the first control buffer (for full screen refresh) or the second control buffer (for partial refresh), enabling adaptive EMI reduction without requiring a completely new driver design
Solution Approach 2:
The patent segments the control buffer functionality into two separate control buffers with different transistor sizes. The first control buffer has larger transistors for reducing EMI during partial refresh, while the second has smaller transistors for full screen refresh, allowing independent optimization for each operating mode
3Object-generated harmful factors
If the control buffer size is increased to reduce slew rate, then EMI is reduced, but propagation delay increases
Solution Approach 1:
The patent changes the transistor size parameter of the control buffer to optimize the balance between slew rate and propagation delay. By carefully selecting the transistor size, the design achieves sufficient EMI reduction while maintaining acceptable signal propagation timing for the display interface
Data Source
AI summary
A control buffer in a source driver includes a first CMOS inverter configured to output a switch signal to control turning on and off of a switch, and a first tri-state inverter that is connected to the first CMOS inverter and configured to selectively adjust a size of the control buffer, wherein a slew rate of the switch signal is adjusted depending on the size of the control buffer.