Dual-Loop LDO Feedback Control for Low Output Ripple
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Solution Overview
Problem
Existing low drop-out voltage regulators (LDOs) suffer from significant ripple in output voltage due to fluctuations in load conditions, which can impair device performance, and increasing capacitance to reduce ripple significantly increases circuit area.
Innovation Solution
A low drop-out voltage regulator (LDO) circuit structure employing a pair of feedback control loops, comprising a comparator and a push capacitor in the first loop, and an operational amplifier in the second loop, to quickly adjust the conductivity of a drive transistor in response to load variations, reducing ripple without increasing circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If capacitance load (CL) is increased to reduce Vout ripple, then output voltage ripple is reduced, but circuit area significantly increases
Solution Approach 1:
The single feedback control loop is segmented into two separate feedback control loops with different functions. The first loop (comparator + capacitor) handles fast transient responses to reduce ripple, while the second loop (operational amplifier) maintains steady-state accuracy. This segmentation allows ripple reduction without requiring large capacitance, thus avoiding circuit area increase.
Solution Approach 2:
The patent introduces dynamic control by using a capacitor in the first feedback loop that can rapidly charge and discharge in response to load transients. This dynamic element provides fast transient response to counteract voltage ripple caused by load changes, replacing the need for large static capacitance that would increase circuit area.
2Object-affected harmful factors
If single feedback control loop is used, then circuit complexity is low, but output voltage ripple is significant
Solution Approach 1:
The feedback control function is divided into two specialized loops: a fast transient response loop (comparator + capacitor) and a steady-state regulation loop (operational amplifier). Each loop is optimized for its specific function, allowing effective ripple reduction while keeping each individual loop relatively simple in structure.
Solution Approach 2:
The capacitor in the first feedback loop acts as an intermediary element that rapidly responds to transient changes and directly counteracts voltage ripple. This intermediary component enables the comparator-based loop to effectively suppress ripple without requiring complex circuitry.
3Reliability
If conventional single-loop LDO is used, then settling time is acceptable, but output voltage ripple impairs device performance
Solution Approach 1:
The capacitor in the first feedback loop provides dynamic transient response that rapidly counteracts load-induced voltage variations. This dynamic control mechanism reduces output voltage ripple that would otherwise impair connected device performance, while maintaining the settling time characteristics of conventional LDO designs.
Solution Approach 2:
The patent employs dual feedback control loops that continuously monitor and adjust the drive transistor conductivity in response to output voltage changes. This enhanced feedback mechanism more effectively suppresses output voltage ripple, improving the reliability of connected devices without altering settling time or output voltage level.
Data Source
AI summary
A low drop-out voltage regulator (LDO) circuit structure includes a drive transistor with first connected to an input voltage node, a second terminal connected to an output voltage node and a voltage divider, and a third terminal (i.e., a control terminal). The structure employs a pair of concurrently operating feedback control loops between a feedback voltage node of the voltage divider and the control terminal to continuously adjust a control voltage applied to the control terminal and thereby reduce ripple of an output voltage (Vout) at the output voltage node. A first feedback control loop includes comparator and a push capacitor connected between the feedback voltage node and the control terminal. The second feedback control loop includes an operational amplifier connected between the feedback voltage node and the control terminal. The first feedback control loop operates a faster speed than the second to quickly initiate the necessary control voltage adjustments.