Oversampled Digital PWM Control With Dithering for High Resolution

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Solution Overview

Problem

Digital feedback control systems face challenges in achieving high resolution and high speed, particularly in PWM switched power supplies, which require complex designs and high-speed PWM frequencies, and often necessitate expensive multiplication and high PWM resolution, limiting their adoption in cost-sensitive fields like portable consumer appliances.

Innovation Solution

A digital controller that includes an oversampling ADC, a compensating filter, a low pass filter, and a subsampling component, along with a dither generating component and a digital pulse width modulator, allowing for high PWM resolution without expensive multiplication and enabling arbitrarily controlled coefficients, thereby simplifying logic complexity and reducing power dissipation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If high PWM resolution is implemented using conventional digital control methods, then control precision is improved, but device complexity and cost increase due to requirements for expensive multiplication and high-speed PWM circuits

Engineering Contradiction:

ImprovePWM resolutionVSAvoidlogic complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the high-resolution PWM generation into multiple lower-resolution steps. Instead of directly generating high-resolution PWM signals, the system first generates lower-resolution PWM signals and then applies dithering techniques to achieve the equivalent of high-resolution control through statistical averaging over multiple cycles

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces dithering signals as an intermediary mechanism. These low-level random signals are added to the control signal to enable fine-grained control resolution without requiring high-resolution digital circuits. The dithering acts as a mediator that translates coarse digital control into fine-grained effective control

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If high-speed PWM is used to achieve high control bandwidth, then response speed is improved, but power dissipation increases

Engineering Contradiction:

ImprovePWM frequencyVSAvoidpower dissipation

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The patent employs periodic dithering sequences that operate at frequencies much lower than the PWM frequency. By using periodic low-frequency dithering signals, the system achieves high effective control bandwidth without requiring the PWM itself to operate at extremely high frequencies, thereby reducing power dissipation

Inventive Principle:

Principle #19Periodic action

3Measurement precision

If multiplication operations are used in digital control algorithms, then control accuracy is improved, but cost and power dissipation increase

Engineering Contradiction:

Improvecontrol accuracyVSAvoidpower dissipation

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent replaces expensive multiplication operations with cheaper addition and subtraction operations. By using dithering-based approaches, the system achieves equivalent control accuracy without requiring complex multiplication circuits, thereby reducing both cost and power dissipation

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentUS8059018B2Systems and methods for digital control utilizing oversampling

Publication Date: 2011.11.15 L&L ENGINEERING LLC

AI summary

Methods and systems for digital control utilizing oversampling.