Low Drop-Out Voltage Regulator Pull-Up Circuit Stability
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Solution Overview
Problem
Existing low drop-out voltage regulators face stability issues when operating under low load current and large load capacitor conditions, and vice versa, due to complex pole interactions and phase margin concerns, which affect their ability to maintain regulated voltage as the supply voltage drops close to the regulated voltage.
Innovation Solution
A low drop-out voltage regulator design incorporating a feedback-loop circuit with a pull-up circuit that generates a second feedback voltage with a different ratio than the first feedback voltage, preventing oscillations by carefully choosing resistor values and using n-type and p-type MOS transistors to manage voltage transitions smoothly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pull-up circuit is applied in a feedback loop of a voltage regulator to achieve low drop-out behavior, then the regulator can maintain regulated voltage when supply voltage drops close to regulated voltage, but stability issues occur due to sudden voltage changes at pulling-up and ending moments
Solution Approach 1:
The patent applies preliminary action by detecting the supply voltage level in advance and activating the pull-up circuit before the regulated voltage drops below the acceptable threshold. The detection circuit monitors the supply voltage and triggers the pull-up transistor to conduct when the supply voltage falls within a predetermined range above the regulated voltage, preventing the voltage drop before it occurs rather than reacting after the drop has happened.
Solution Approach 2:
The patent introduces an intermediary detection circuit that sits between the supply voltage source and the feedback loop, monitoring the supply voltage level and controlling the pull-up circuit activation. This intermediary circuit smooths the transition by providing early warning of supply voltage drops and coordinating the pull-up action, preventing sudden changes in the feedback loop while maintaining the low drop-out functionality.
2Stability of the object's composition
If a large output decoupling capacitor is used to smoothen fast load current spikes in a closed-loop system, then the regulated output voltage stability improves, but the device complexity and component requirements increase
Solution Approach 1:
The patent applies preliminary action by having the pull-up circuit ready and activated in advance to counteract load current spikes before they cause significant voltage drops. The detection circuit continuously monitors the supply voltage and pre-activates the pull-up transistor when a drop is anticipated, preventing the need for large decoupling capacitors to react after the voltage has already dropped.
Solution Approach 2:
The patent enhances the feedback mechanism by adding a secondary detection loop that specifically monitors supply voltage levels and triggers pull-up action. This additional feedback path works in conjunction with the main regulation feedback, providing earlier and more aggressive correction of voltage drops, thereby reducing the burden on output decoupling capacitors while maintaining stability.
Data Source
AI summary
A low drop-out voltage regulator, an integrated circuit, a sensor and a method of providing a regulated voltage are provided. The low drop-out voltage regulator comprises a regulated voltage driver for providing the regulated voltage in response to a control voltage, a feedback-loop circuit for generating the control signal such that the regulated voltage driving circuit provides the regulated voltage, and a pull-up circuit for pulling up the regulated voltage to a supply voltage when a difference between the supply voltage and the control voltage is smaller than a predetermined threshold value. In the feedback-loop circuit a first feedback voltage or a second feedback voltage is generated, respectively, on basis of a first ratio and a second ratio between the feedback voltage and the regulated voltage. The second feedback voltage is generated instead of the first feedback voltage when the regulated voltage is pulled-up to the supply voltage.