Adaptive Gate Buffer for Power Stage LDO Regulation
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Solution Overview
Problem
Conventional low dropout (LDO) voltage regulators face limitations in output voltage swing, quiescent current, and accuracy due to the use of single-pass transistors and separate control loops, leading to inefficiencies and increased battery drain in battery-operated devices.
Innovation Solution
The implementation of an adaptive buffer that controls two power transistors with a single error amplifier, allowing seamless load current sharing and near rail-to-rail output voltage swing, reducing quiescent current and enhancing accuracy across a wide range of load currents and input voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single pass transistor is used in conventional LDO regulators, then the device complexity is reduced, but the output voltage swing is limited and quiescent current increases
Solution Approach 1:
The single pass transistor is segmented into two power transistors (first power transistor and second power transistor) with separate control. This segmentation allows each transistor to operate in optimized regions, reducing overall quiescent current while expanding output voltage swing capability without significantly increasing device complexity
Solution Approach 2:
The adaptive buffer dynamically adjusts the control signals to the two power transistors based on operating conditions. This dynamic control enables seamless load current sharing between the transistors, optimizing quiescent current across different load conditions while maintaining full output voltage swing range
2Device complexity
If a single pass transistor is used in conventional LDO regulators, then the circuit structure is simplified, but the accuracy deteriorates across wide range of load currents
Solution Approach 1:
The single pass transistor is segmented into two power transistors (first power transistor and second power transistor) with separate control. This segmentation allows each transistor to operate in optimized regions, reducing overall quiescent current while expanding output voltage swing capability without significantly increasing device complexity
Solution Approach 2:
Each power transistor is assigned different local control characteristics through the adaptive buffer. The first power transistor handles specific current ranges while the second handles others, with each optimized for its designated operating region. This local quality differentiation maintains high accuracy across the full load current range
3Measurement precision
If separate control loops are used for each power transistor, then the accuracy is improved, but the device complexity increases
Solution Approach 1:
Two separate control loops are merged into a single adaptive buffer that controls both power transistors. This unified buffer integrates the control functions, maintaining accurate regulation across wide load ranges while avoiding the complexity of completely separate control circuits. The adaptive buffer seamlessly shares load current between transistors under unified control
Solution Approach 2:
The adaptive buffer serves multiple functions simultaneously: it controls both power transistors, performs seamless load current sharing, and provides accurate regulation across wide load and input voltage ranges. This multi-functionality achieves high accuracy without proportionally increasing device complexity
Data Source
AI summary
A circuit includes a first power transistor including a first control input and first and second current terminals. The circuit includes a second power transistor including a second control input and third and fourth current terminals. Third current terminal couples to the first current terminal, and the fourth current terminal couples to the second current terminal at an output node. An error amplifier generates an error signal based on a difference between a reference voltage and an output voltage on the output node. An adaptive buffer couples to an output of the error amplifier and couples to the first and second control inputs. The adaptive buffer causes the first power transistor to be on through a range of output current and to cause the second power transistor to be on through some, but not all, of the range of output current.