LDO Regulator Tail Current Boosting via Intermediary Capacitor
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Solution Overview
Problem
Low dropout regulators (LDOs) are sensitive to load transients, leading to slow response times and increased area consumption due to the need for large capacitors to mitigate output spikes, which compromises control speed, power efficiency, and circuit size.
Innovation Solution
Incorporating a differential amplifier with a pair of input transistors and two capacitive elements, where one capacitor is connected between the output terminal and the common connection of the input transistors' tail current source, and the other between the common connection and a supply rail, to boost the tail current and enhance the regulator's response to load changes without increasing power consumption or circuit size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large capacitor is provided at the regulated output to temporarily supply charge to the load, then output spikes are reduced, but area consumption is increased
Solution Approach 1:
The patent introduces an intermediary capacitor connected to the common connection of the differential pair's tail current source, which acts as a mediator to supply transient current during load changes. This intermediary capacitor reduces output spikes by providing local charge storage without requiring a large capacitor at the output terminal, thereby reducing area consumption while still mitigating harmful output spikes.
2Use of energy by moving object
If the bias current is reduced to achieve low power consumption, then power efficiency is improved, but sensitivity to load transients increases leading to slow response
Solution Approach 1:
The patent implements a dynamic current boosting mechanism where the tail current of the differential pair is normally kept low for power efficiency, but can be dynamically increased during load transients. The capacitor connected to the common connection supplies additional current during load changes, enabling the differential pair to respond quickly to transients without requiring a continuously high bias current, thus maintaining both low power consumption and fast response speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for faster control of the output transistor in response to load changes, reducing output spikes and ripples, while maintaining a compact and efficient design, suitable for low power applications with improved control speed and reduced area requirements.
Implementation Method 1
The first capacitive element is coupled between the output terminal of the low dropout regulator and the common connection of the input transistors of one pair with the respective tail current source
Implementation Method 2
The second capacitive element is coupled between a second supply terminal and the common connection of the input transistors of one pair with the respective tail current source
Data Source
AI summary
A low dropout regulator comprises an output transistor with a controlled section between a first supply terminal and an output terminal, and a differential amplifier comprising a feedback input coupled to the output terminal, a reference input receiving a reference voltage, an output connected to a control terminal of the output transistor, and a pair of input transistors connected to a tail current source. A control terminal of a first transistor is connected to the reference input. A control terminal of a second transistor is connected to the feedback input. A first capacitive element is coupled between the output terminal and common connection of the input transistors of one pair with their tail current source. A second capacitive element is coupled between a second supply terminal and the common connection of the input transistors of one pair with their tail current source.