Charge Injection Circuit for Fast Voltage Control in LDOs
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Solution Overview
Problem
Existing power management integrated circuits (PMICs) with low-dropout regulators (LDOs) face challenges in achieving fast and accurate voltage regulation while maintaining efficiency, as the bandwidth of the main loop limits the change rate of the output voltage, and adding a fixed load to increase bandwidth compromises stability and efficiency.
Innovation Solution
A circuit incorporating a switchable voltage divider, error amplifier, and charge injection circuit that allows for rapid control of the output voltage by generating a variable fraction of the output voltage, enabling fast and stable regulation without significant efficiency loss, using a capacitive element and switching circuit to modify the control voltage at an intermediate node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bandwidth of the main loop is increased to increase the change rate of the output voltage, then the speed of voltage adjustment is improved, but the stability of the voltage regulator deteriorates
Solution Approach 1:
The patent divides the voltage control function into two separate loops: a main loop with low bandwidth for stability and a fast loop with high bandwidth for rapid response. The main loop includes the error amplifier stage for stable regulation, while the fast loop uses a buffer stage with charge injection for quick voltage changes. This segmentation allows each loop to optimize for its specific function without compromising the other.
Solution Approach 2:
The patent introduces a buffer stage as an intermediary between the error amplifier stage and the output. This buffer stage has very high bandwidth and low output impedance, allowing it to rapidly respond to control voltage changes and drive the output voltage quickly while the main loop maintains stability through its dominant pole.
2Speed
If a fixed load is added to the output to increase the bandwidth of the main loop, then the change rate of output voltage is improved, but the current consumption increases and efficiency decreases
Solution Approach 1:
The patent replaces the static fixed load with a dynamic charge injection mechanism. Instead of continuously consuming current through a fixed load, the system uses a buffer stage that injects charge only when needed to achieve fast voltage transitions. This dynamic approach provides high bandwidth during transient events while maintaining low quiescent current consumption during steady-state operation.
Solution Approach 2:
The charge injection circuit operates periodically or event-driven rather than continuously. The buffer stage is activated only when rapid voltage changes are required, injecting charge to accelerate the response. During normal operation, the main loop handles regulation with minimal additional current consumption, effectively providing high speed only when needed.
3Speed
If the bandwidth of the main loop is increased to improve the response speed, then the change rate is improved, but the bias current of the error amplifier must be increased which compromises stability
Solution Approach 1:
The patent separates the bandwidth requirements from the stability-critical error amplifier stage by introducing a dedicated buffer stage. The error amplifier maintains its low bandwidth and stable bias current for reliable regulation, while the buffer stage provides the high bandwidth needed for fast response. This segmentation allows the bias current to remain low without sacrificing response speed.
Solution Approach 2:
The buffer stage acts as an intermediary that decouples the stability requirements of the error amplifier from the speed requirements of the output response. The buffer stage has very high bandwidth and can rapidly amplify control voltage changes without affecting the stability margins of the main loop, as it operates outside the critical feedback path that determines stability.
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 solution enables fast, accurate, and stable control of the output voltage, independent of the main loop bandwidth, ensuring quick response to target voltage changes without efficiency degradation.
Implementation Method 1
a charge injection circuit configured to inject charge at an intermediate node between the error amplifier stage and the buffer stage to thereby modify the control voltage generated by the error amplifier stage
Implementation Method 2
using a capacitive element and switching circuit to modify the control voltage at an intermediate node
Data Source
AI summary
This application relates to a circuit for generating an output voltage and regulating the output voltage to a target voltage. The circuit includes a switchable voltage divider circuit configured to generate a feedback voltage that is a variable fraction of the output voltage, an error amplifier stage configured to generate a control voltage on the basis of a reference voltage and the variable fraction of the output voltage, a buffer stage configured to generate the output voltage on the basis of the control voltage, and a charge injection circuit configured to inject charge at an intermediate node between the error amplifier stage and the buffer stage to thereby modify the control voltage generated by the error amplifier stage. The application further relates to a method of operating such circuit.