Capacitor-Based LDO Regulator for Low Power Silicon Area
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Solution Overview
Problem
Traditional low-drop out (LDO) voltage regulators using resistor dividers in integrated circuits require large silicon area, introduce noise, and reduce feedback factor due to the large resistor needed to limit current, which is undesirable for low-power applications.
Innovation Solution
A low-drop out voltage regulator utilizing a feedback capacitor and a switched capacitor divider network, where capacitors are used instead of resistors to provide voltage division and regulation, with controllable switches managing charge transfer to maintain output voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a large value resistor is used in the feedback path to limit current, then current draw is reduced, but silicon area increases and noise increases
Solution Approach 1:
The patent changes the fundamental parameter from resistance to capacitance in the feedback path. Instead of using a large resistor to limit current, the invention uses a capacitor whose impedance varies with frequency, providing current limiting at high frequencies while maintaining low DC current draw. This parameter change from resistive to capacitive feedback eliminates the direct trade-off between current limitation and silicon area.
Solution Approach 2:
The patent substitutes the resistive feedback mechanism with a capacitive feedback mechanism. The resistor-based voltage division is replaced by a capacitor-based impedance network, fundamentally changing how current limiting is achieved. This substitution eliminates the noise and area problems associated with large resistors while maintaining current limiting functionality through the frequency-dependent impedance of the capacitor.
2Use of energy by moving object
If a large value resistor is used in the feedback path, then current draw is reduced, but feedback factor is reduced
Solution Approach 1:
The patent changes the feedback mechanism from resistive voltage division to capacitive impedance feedback. The feedback factor is no longer determined by a resistive divider ratio but by the capacitive impedance network, which maintains full feedback factor while limiting current through its frequency-dependent characteristics.
Solution Approach 2:
The resistive feedback system is replaced with a capacitive feedback system. This substitution preserves the feedback factor because the capacitor provides a different mechanism for current limiting that does not attenuate the feedback signal in the same way a large resistor would.
3Use of energy by moving object
If a large value resistor is used in the feedback path, then current draw is reduced, but noise increases
Solution Approach 1:
The patent changes from resistive to capacitive feedback, fundamentally altering the noise characteristics. Capacitors inherently generate less noise than large resistors, especially thermal noise, while still providing the necessary current limiting function through their impedance properties.
Solution Approach 2:
The noisy resistive feedback path is replaced with a quiet capacitive feedback path. This substitution eliminates the primary noise source (large value resistor) while maintaining the current limiting function through the capacitor's frequency-dependent impedance.
4Use of energy by moving object
If a large value resistor is used in the feedback path, then current draw is reduced, but an extra pole is introduced in the feedback path
Solution Approach 1:
The patent changes the feedback element from resistor to capacitor, which alters the pole structure of the feedback path. The capacitive feedback introduces different pole locations that can be more favorably positioned for stability, and the switched capacitor divider network provides additional degrees of freedom for pole-zero cancellation and compensation.
Solution Approach 2:
The resistive feedback path is replaced with a capacitive feedback path, fundamentally changing the transfer function and pole structure. This substitution allows for better control of the feedback path characteristics and can eliminate unwanted poles through proper capacitor selection and switching timing.
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 reduces silicon area requirements, minimizes noise, and maintains full bandwidth and feedback factor, achieving better load regulation and efficiency compared to traditional resistor-based designs.
Implementation Method 1
a capacitor connected between the output node of the transistor and the first input of the differential amplifier, wherein a voltage at the output of the transistor is dependant on a charge across the capacitor
Implementation Method 2
The switched capacitor divider network may be periodically operational to apply charge to the feedback capacitor
Data Source
AI summary
A low drop out voltage regulator comprising: a transistor having an input node, an output node, and a control node; a differential amplifier having an output connected to the control node of the transistor and having a first input node; and a feedback capacitor connected between the output node of the transistor and the first input of the differential amplifier, wherein a voltage at the output of the transistor is dependent on a charge across the feedback capacitor.