Flip Voltage Follower LDO for Touch Sensing

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Solution Overview

Problem

Conventional low dropout regulators (LDOs) for touch sensing controllers face challenges in achieving a wide tuning range without sacrificing low output impedance, particularly in driving large capacitive switching loads, which results in stability issues and high power loss due to the need for large devices.

Innovation Solution

The implementation of a wide tuning-range and low output impedance flip voltage follower (FVF) LDO, incorporating an operational amplifier and FVF with an adaptive level shifter between the source follower and gain devices, allowing for smaller device sizes while maintaining low output impedance through adaptive level shifting and compensation capacitors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conventional source follower topology is used to drive large capacitive switching loads, then low output impedance is achieved, but device size becomes very large leading to significant power loss

Engineering Contradiction:

Improvepower lossVSAvoiddevice size

Core Design Contradiction:

Loss of energyVSArea of moving object

Solution Approach 1:

The patent changes the topology from conventional source follower to flip voltage follower (FVF), fundamentally altering the electrical parameters. The FVF configuration achieves low output impedance through a different mechanism (feedback from drain to gate via capacitor) that does not require large device dimensions, thus reducing both device size and associated power loss while maintaining the ability to drive large capacitive loads

Inventive Principle:

Principle #35Parameter changes

2Area of moving object

If flip voltage follower topology is used to reduce device size, then power loss is reduced, but output impedance increases making it difficult to drive capacitive loads quickly

Engineering Contradiction:

Improvedevice sizeVSAvoidpower loss

Core Design Contradiction:

Area of moving objectVSLoss of energy

Solution Approach 1:

The patent implements feedback by connecting a capacitor from the drain to the gate of the FVF transistor. This feedback mechanism dynamically adjusts the gate voltage to maintain low output impedance across the tuning range, enabling the smaller FVF device to drive capacitive loads effectively without the power loss associated with larger conventional devices

Inventive Principle:

Principle #23Feedback

3Adaptability or versatility

If adaptive level shifter is added to FVF LDO, then wide tuning range is achieved, but device complexity increases

Engineering Contradiction:

Improvetuning rangeVSAvoidcircuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the level shifting function into discrete, modular components (first level shifter, second level shifter, third level shifter) that can be independently controlled. Each level shifter handles a specific aspect of the tuning range extension, allowing the complex function to be achieved through coordinated simple modules rather than a monolithic complex circuit

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS10429868B2Flip voltage follower low dropout regulator

Publication Date: 2019.10.01 QUALCOMM INC

AI summary

A wide-tuning range low output impedance flip voltage follower (FVF) low dropout regulator (LDO) for large capacitor switching loads is disclosed. In some implementations, a touch sensing controller driver includes the LDO, which has an operational amplifier and a FVF. The FVF can have a gain device, a source follower device, and an adaptive level shifter coupled between a drain of the source follower device and a gate of the gain device.