Amplifier Feedback Circuit for Stable Low-Capacitance Regulators
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Solution Overview
Problem
Conventional step-down regulators in semiconductor integrated circuits face issues with phase compensation, leading to oscillation when the capacitance value is reduced, and suffer from overcurrent during startup, which deteriorates circuit elements and slows the stabilization of output voltage.
Innovation Solution
Incorporating a negative feedback circuit between the input and output stage amplifying circuits, which differential-amplifies input voltages and feeds back a current to prevent oscillation and overcurrent, allowing for a smaller capacitance without increasing the circuit scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the capacitance value of the stabilization capacitor is reduced, then the circuit size is reduced, but the phase margin decreases causing oscillation
Solution Approach 1:
The patent introduces a negative feedback circuit that samples the output current and feeds it back to the input stage through a feedback current amplifier. This feedback mechanism provides additional phase compensation and stabilizes the system, allowing the use of smaller capacitance values without causing oscillation. The feedback loop continuously adjusts the input based on output conditions, maintaining stability even with reduced capacitor size.
2Device complexity
If the capacitance value is reduced, then the circuit scale is reduced, but oscillation occurs due to insufficient phase compensation
Solution Approach 1:
The negative feedback circuit provides continuous monitoring and adjustment of the output current, feeding back compensating signals to prevent oscillation. This feedback mechanism replaces the need for large phase compensation capacitors, reducing circuit scale while maintaining reliability and preventing oscillation through active control.
Solution Approach 2:
The patent changes the approach from passive phase compensation using large capacitors to active phase compensation by adjusting the feedback current parameters. By modifying the feedback current amplifier gain and characteristics, the system achieves stable operation with smaller capacitance values, effectively changing the compensation parameter from capacitance magnitude to feedback current characteristics.
3Device complexity
If conventional amplifying circuits are used, then the circuit structure is simple, but overcurrent occurs during startup deteriorating circuit elements
Solution Approach 1:
The negative feedback circuit continuously monitors the output current and compares it with the reference voltage. During startup, when output current exceeds safe levels, the feedback mechanism automatically reduces the amplifying circuit's gain or blocks the output, preventing overcurrent damage. This feedback control adds protection functionality without requiring a completely different circuit structure.
Data Source
AI summary
An amplifier has an input stage amplifying circuit, an output stage amplifying circuit, and a negative feedback circuit. The input stage amplifying circuit differential-amplifies a first input voltage inputted to a positive phase input node and a second input voltage inputted to an opposite phase input node, and outputs from a positive phase output node. The output stage amplifying circuit amplifies output voltage from a node and outputs it from an output terminal, and generates the second input voltage corresponding to output voltage and feedback-inputs it to the opposite phase input node. The negative feedback circuit has a first PMOS for a current source whose output current fluctuates due to output voltage of the positive phase output node, and a differential amplifying section to which the output current of the first PMOS is supplied and which is formed from a second and third PMOS which differential-amplify the first input voltage and the second input voltage. The negative feedback circuit feeds-back, to an opposite phase output node, a positive phase current corresponding to output current of the differential amplifying section.