Linear Voltage Regulator Feedforward PSRR in Dropout
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Solution Overview
Problem
Conventional linear voltage regulators face challenges in efficiently rejecting supply noise at the output voltage while maintaining power efficiency, often requiring a trade-off between noise rejection and power efficiency.
Innovation Solution
The proposed linear voltage regulator employs a feedforward technique that selectively injects a fraction of the supply voltage into a buffer to cancel supply noise during intervals where the input voltage and output voltage difference is small, and disables this technique when the difference is greater than or equal to a threshold, allowing the power transistor to operate in the saturation region for noise filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional linear voltage regulator uses a simple feedforward design or negative feedback, then the circuit structure remains simple, but the power supply rejection ratio is insufficient and supply noise cannot be effectively rejected
Solution Approach 1:
The voltage regulator is divided into multiple functional modules: a buffer module for signal processing, a dropout detection module for condition monitoring, and a feedforward module for noise cancellation. This segmentation allows each module to perform its specific function optimally while maintaining overall system manageability and effectiveness.
Solution Approach 2:
The feedforward module proactively injects a noise cancellation signal into the buffer before the supply noise affects the output. By detecting dropout conditions in advance and preparing the cancellation signal beforehand, the system can effectively reject supply noise without waiting for it to manifest as output distortion.
2Reliability
If the linear voltage regulator operates with a small voltage difference between input and output, then the dropout voltage is reduced, but supply noise rejection becomes difficult and power efficiency decreases
Solution Approach 1:
The dropout detection module continuously monitors the voltage difference between input and output, dynamically adjusting the operation mode. When the voltage difference is small (dropout condition), the feedforward noise cancellation is activated. When the voltage difference is large, the system operates in standard mode. This dynamic adaptation allows the regulator to maintain low dropout voltage when needed while preserving power efficiency during normal operation.
Solution Approach 2:
The system changes its operational parameters based on the voltage difference condition. In dropout mode, it enables the feedforward noise cancellation path with specific gain settings. In normal mode, it disables this path to avoid unnecessary power consumption. This parameter switching allows optimal performance across different operating conditions.
3Reliability
If noise rejection techniques are continuously applied, then the power supply rejection ratio improves, but power efficiency is reduced due to continuous operation of noise cancellation circuits
Solution Approach 1:
Instead of continuous noise rejection, the system applies noise cancellation periodically based on detected dropout conditions. The dropout detection module triggers the feedforward noise cancellation only when supply noise is likely to affect output quality (during dropout events). This periodic, condition-based operation maintains high power supply rejection ratio when needed while minimizing energy loss during normal operation.
Data Source
AI summary
A linear voltage regulator includes a voltage input and a voltage output. The linear voltage regulator includes a buffer having a voltage node, an input node, an output node and a control node and a power transistor having a control node coupled to the output node of the buffer, an input node coupled to the voltage input and an output node coupled to the voltage output. The linear voltage regulator includes a dropout detection module having a control node coupled to the control node of the power transistor, a voltage input node coupled to the voltage input, a voltage output node coupled to the voltage output and an output node. The linear voltage regulator includes a feedforward module having an input node coupled to the output node of the dropout detection module and an output node coupled to the control node of the buffer.