LDO Regulator Feedback Circuit for High PSRR at Low Dropout
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Solution Overview
Problem
Designing a low dropout voltage regulator with high power supply rejection capability and improved efficiency is challenging due to smaller power supply voltage levels and degradation of performance when power transistors enter the triode region.
Innovation Solution
A voltage regulator apparatus comprising an operational amplifier, resistors, a driving transistor, and an amplifier circuit that forms a feedback loop to boost gain and enhance power supply rejection ratio, using a common gate and common source amplifier configuration to regulate output voltage and control the gate of a specific transistor in the output circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power supply voltage level is reduced to meet advanced technology requirements, then power consumption is reduced, but dropout voltage increases and power supply rejection capability deteriorates
Solution Approach 1:
The voltage regulator is divided into two independent control loops: a main control loop using an operational amplifier for general regulation, and a secondary control loop using a dedicated amplifier circuit for high-frequency noise rejection. This segmentation allows each loop to be optimized for its specific function, enabling the system to maintain low dropout voltage while achieving high power supply rejection ratio across different frequency ranges.
Solution Approach 2:
The amplifier circuit is configured to sense the output voltage and feed it back to regulate the output transistor, creating a closed-loop feedback system. This feedback mechanism enables the circuit to dynamically adjust and compensate for power supply variations and noise, significantly improving power supply rejection capability while maintaining low dropout performance.
2Reliability
If amplifier gain is increased to improve power supply rejection, then noise rejection is improved, but signal noise increases and bandwidth is reduced
Solution Approach 1:
The amplifier circuit is designed with specific local characteristics: high gain is applied only to the frequency range where power supply noise is dominant, while the bandwidth is carefully controlled to roll off at frequencies where signal content is important. This localized amplification approach improves power supply rejection without significantly degrading signal quality or increasing overall signal noise.
Solution Approach 2:
The amplifier circuit parameters (gain, bandwidth, pole locations) are specifically optimized to achieve high power supply rejection ratio. By carefully selecting and tuning these parameters, the circuit achieves high gain for noise rejection while maintaining acceptable bandwidth and minimizing signal noise, resolving the trade-off between these competing requirements.
Data Source
AI summary
A voltage regulator apparatus includes operational amplifier, first resistor, second resistor, driving transistor, amplifier circuit, and output circuit. The operational amplifier has first input terminal coupled to reference voltage, second input terminal, and output terminal. The first resistor has first terminal coupled to second input terminal. The second resistor is coupled between first resistor and ground level. The driving transistor has control terminal coupled to output terminal of operational amplifier and first terminal coupled to second terminal of first resistor. The amplifier circuit is coupled to output terminal of operational amplifier and configured to sense output voltage of voltage regulator apparatus to amplify the sensed voltage with specific gain to regulate a transistor of output circuit. The transistor has control terminal controlled by amplifier circuit. The output voltage is generated at first terminal of the transistor.