LDO Regulator Stability via Adaptive MOS Resistor
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Solution Overview
Problem
Low dropout (LDO) regulators face stability issues due to varying equivalent resistance, which depends on capacitor manufacturer, operating frequency, and temperature, and lack effective compensation for zero frequency variations with load changes, leading to unstable transient responses.
Innovation Solution
A low dropout voltage regulator with a regulation loop comprising PMOS or NMOS transistors and a stability compensation circuit using MOS resistors and capacitors, where the second MOS resistor's resistivity changes with load conditions, allowing adaptive zero frequency compensation and improved stability across varying loads and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is used for dominant pole frequency compensation, then the regulator achieves stability, but the equivalent resistance of the capacitor generates a zero in the loop transfer function that causes stability problems due to variations with operating frequency and temperature
Solution Approach 1:
The patent applies the Dynamics principle by making the equivalent resistance dynamic rather than fixed. The MOS transistor is configured to vary its resistance based on the instantaneous load current, automatically adjusting to compensate for the zero frequency shifts caused by capacitor variations under different operating conditions and temperatures.
Solution Approach 2:
The patent implements Parameter changes by modifying the equivalent resistance value of the compensation network based on operating conditions. The MOS transistor's resistance changes with load current and temperature, dynamically adjusting the zero frequency to maintain stability across varying operating parameters.
2Device complexity
If the equivalent resistance is fixed, then the circuit structure is simple, but the zero frequency cannot be compensated for variable load conditions
Solution Approach 1:
The patent applies the Self-service principle by enabling the MOS transistor to automatically adjust its own resistance based on the load current it senses. The transistor inherently responds to changing conditions without requiring external control circuits, achieving adaptive compensation through its natural electrical characteristics.
3Adaptability or versatility
If a variable MOS resistor is used to compensate zero frequency, then stability under variable load is improved, but the device complexity increases
Solution Approach 1:
The patent uses the MOS transistor as an intermediary element between the load and the compensation network. The transistor mediates the interaction by translating load current variations into corresponding resistance changes, providing a smooth adaptive compensation mechanism that integrates seamlessly into the existing regulator architecture.
Data Source
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AI summary
The voltage regulator comprises a regulation loop (2), which comprises at least a pass transistor (18), a source transistor (28), a sensing transistor (22) and a retention transistor (24), and a stability compensation circuit (10), which comprises a first MOS resistor (12) and a second MOS resistor (14) coupled with the first MOS resistor (12). The gate of the second MOS resistor (14) is coupled to the gate of the pass transistor (18).