Impedance-Tracking Feedback Circuit for Faster LDO Transients
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Solution Overview
Problem
The transient response speed of low-dropout voltage regulators is hindered by the inability of feedback voltage to reflect the output voltage in real time due to the addition of a feedforward capacitor, leading to incorrect control by the error amplifier.
Innovation Solution
An impedance-tracking circuit comprising a voltage divider, dynamic resistors, and amplifiers that adjust resistance values in real time to maintain a preset impedance ratio, using a transconductance amplifier to generate control signals for the dynamic resistors based on voltage comparisons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedforward capacitor is added to increase loop frequency and improve phase margin, then frequency response characteristics are improved, but the feedback voltage cannot reflect the output voltage in real time, causing transient response degradation
Solution Approach 1:
The patent applies dynamics by making the feedback resistor ratio adjustable rather than fixed. The impedance tracking circuit dynamically adjusts the feedback resistor values based on the operating conditions to maintain optimal transient response while preserving the benefits of the feedforward capacitor for frequency response.
Solution Approach 2:
The patent changes the parameter of feedback resistor ratio from a fixed value to a dynamically adjustable parameter. By varying the resistance values of the first and second feedback resistors according to different operating states, the circuit achieves both improved frequency response and fast transient response.
2Device complexity
If fixed feedback resistors are used to maintain stable impedance ratio, then circuit simplicity is maintained, but the feedback voltage cannot track the output voltage during transient conditions
Solution Approach 1:
The patent introduces an impedance tracking feedback mechanism where the feedback resistor ratio is automatically adjusted based on the output voltage level. This feedback loop ensures that the feedback voltage accurately reflects the output voltage during both steady-state and transient conditions without requiring overly complex circuitry.
Solution Approach 2:
The patent uses an impedance tracking circuit as an intermediary between the output voltage and the feedback voltage. This intermediary component adjusts the feedback resistor ratio to ensure accurate voltage reflection during transient conditions while keeping the overall circuit structure relatively simple.
3Speed
If the feedback resistor ratio is adjusted in real time to improve transient response, then transient response speed is improved, but additional circuit components and control mechanisms are required
Solution Approach 1:
The patent merges the impedance tracking function with the existing feedback network by integrating the adjustable feedback resistors and control circuitry into the standard LDO architecture. This consolidation achieves improved transient response while minimizing additional circuit complexity through shared components and integrated design.
Data Source
AI summary
An impedance-tracking circuit includes a voltage divider, a first dynamic resistor, and a first amplifier. The voltage divider divides a voltage difference between a first voltage and a second voltage to generate a divided voltage. The first dynamic resistor has a first resistance value and is coupled between the first voltage and a third voltage. The first dynamic resistor adjusts the first resistance value according to a first control signal. The first amplifier compares the divided voltage with the third voltage to generate the first control signal.