LCD Source Driver Output Buffer With Dynamic Current Switching
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Solution Overview
Problem
Conventional liquid crystal display (LCD) source driver circuits consume significant power due to high driving currents during both charge recycling and driving periods, leading to increased power consumption.
Innovation Solution
The proposed solution involves an output buffer with a differential amplification unit and a gain unit that adjust bias currents and quiescent currents based on the operational phase, increasing bias currents during charge recycling and decreasing them during driving periods to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high driving currents are used during both charge recycling and driving periods, then the source driver can reliably drive the source lines, but power consumption increases significantly
Solution Approach 1:
The output buffer dynamically adjusts its driving current based on the operational phase. During charge recycling period, the buffer operates with higher driving current to reliably charge the source line capacitance. During driving period, the buffer reduces its driving current while maintaining sufficient signal swing capability. This dynamic current adjustment resolves the contradiction by matching the driving current to the actual operational requirements of each phase, ensuring reliability when needed while minimizing power consumption during normal operation.
Solution Approach 2:
The output buffer operates in periodic cycles alternating between charge recycling period and driving period. During the charge recycling period, the buffer performs rapid charging of the source line with high current. During the subsequent driving period, the buffer transitions to lower current operation for sustained signal output. This periodic operation pattern allows the system to achieve reliable source line charging periodically while maintaining lower average power consumption through the alternating low-current driving phase.
2Speed
If high quiescent current is maintained in the output unit, then the output buffer can respond quickly to signal changes, but power consumption increases during idle periods
Solution Approach 1:
The output unit dynamically adjusts its quiescent current based on the operational phase. During the charge recycling period, the output unit operates with higher quiescent current to enable rapid voltage transitions and quick response to input signal changes. During the driving period, the output unit reduces its quiescent current to minimize power consumption while maintaining the ability to respond to signal changes when needed. This dynamic adjustment resolves the contradiction between fast response and low power consumption by adapting the quiescent current to the immediate operational requirements.
Data Source
AI summary
Provided is an output buffer, which may be included in a source driver of a liquid crystal display (LCD) device. The output buffer may include a differential amplification unit and an output unit. The differential amplification unit may generate control currents by amplifying the difference between the voltages of an analog image signal and a signal output from the output buffer. The output unit outputs the amplified analog image signal in response to the control currents. The amount of bias current used to drive the differential amplification unit increases during a charge recycling period, and the amount of quiescent current flowing through the output unit decreases during the charge recycling period. The amount of the bias current used to drive the differential amplification unit decreases during a driving period, and the amount of the quiescent current flowing through the output unit increases during the driving period.