LCD Driver Buffer Circuit With Dynamic Bias Current Mirroring
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Solution Overview
Problem
Current CMOS buffer circuits for liquid crystal display (LCD) drivers face challenges in handling abruptly varying capacitive loads, leading to increased power consumption and instability, especially with larger loads.
Innovation Solution
A single-stage operational transconductance amplifier (OTA) with differential pairs of transistors and bias current generation stages that mirror current to increase bias current in response to input voltage changes, ensuring stability and quick response to capacitive load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the buffers are dimensioned to satisfy the maximum currents for abruptly varying capacitive loads, then the current delivery capability is improved, but the overall power consumption increases
Solution Approach 1:
The patent implements dynamic bias current adjustment by detecting the output voltage swing of the buffer and accordingly adjusting the bias current supplied to the operational amplifier. When the capacitive load changes abruptly, the buffer detects the voltage swing and increases the bias current to provide sufficient drive capability. When the load is stable, the bias current is reduced to minimize power consumption. This dynamic adaptation resolves the contradiction between maintaining high current delivery capability and reducing power consumption.
2Use of energy by moving object
If adaptively biased operational amplifier is used to reduce power consumption, then the power efficiency is improved, but the speed of response to capacitive load changes deteriorates
Solution Approach 1:
The patent employs a voltage swing detector that continuously monitors the output voltage of the buffer and predicts upcoming load changes. When a voltage swing indicative of capacitive load change is detected, the system proactively increases the bias current before the actual load change occurs. This preliminary action ensures that the operational amplifier is already prepared with sufficient current when the capacitive load changes, thereby maintaining fast response speed while still allowing for power savings during stable operating conditions.
3Speed
If several gain stages are used to improve speed, then the response speed is improved, but the stability of the amplifier deteriorates
Solution Approach 1:
The patent segments the buffer functionality into distinct modules: a voltage swing detector, a bias current generator, and a single-stage operational amplifier. By separating the detection and control functions from the amplification function, the system achieves fast response to capacitive load changes through the detector and controller, while the single-stage amplifier maintains inherent stability. The segmentation allows each module to be optimized independently, resolving the contradiction between speed and stability that plagues multi-stage amplifier designs.
Data Source
AI summary
The present invention relates to a CMOS buffer circuit for liquid crystal display (LCD) drivers, which includes a single stage operational transconductance amplifier (OTA) with a differential of transistors for receiving a differential input voltage, a bias current source coupled to the differential pair and a single-ended output, the first bias current generating stage with a differential pair of transistors coupled to receive the differential input voltage to produce an output current in an output current path in response to a positive differential input voltage, a second bias current generating stage with a differential pair of transistors coupled to receive the inverted differential input voltage to produce an output current in an output current path in response to a negative input voltage, wherein the output current paths of both bias current generating stages are combined in a common current path and the current in the common current path is mirrored to the bias current source of the single stage OTA, so as to increase the bias current through the bias current source in response to an increasing magnitude of the differential input voltage.