Windowed Supply Voltage Conditioning for Audio Noise Filtering

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Solution Overview

Problem

Noise in the supply voltage of Class-H boosted amplifiers and audio compressors and limiters causes random boost switching and variations in limiter gain, leading to spurious tones and degraded total harmonic distortion (THD) ratings due to incomplete noise removal by existing low pass filters.

Innovation Solution

A supply voltage conditioning circuit comprising a differential amplifier, comparator, sample and hold circuit, and delay circuit that filters the supply voltage by determining a noise margin and sampling the input voltage only when the difference exceeds this margin, ensuring the output supply voltage is substantially noise-free and tracks underlying changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a low pass filter is implemented to reduce noise amplitude in the supply voltage, then the noise amplitude is reduced, but the noise is not removed completely and reduced noise amplitude can still cause random boost switching and variation in limiter gain

Engineering Contradiction:

Improvenoise amplitude in supply voltageVSAvoidrandom boost switching and limiter gain variation

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent extracts only the significant changes in supply voltage that exceed the noise margin threshold, separating them from the noise component. The sample and hold circuit captures voltage samples only when the differential voltage exceeds the noise margin, effectively extracting useful signal changes while discarding noise fluctuations.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a noise margin value as an intermediary threshold parameter that mediates between the raw supply voltage and the processed output. This noise margin acts as a filter criterion, determining which voltage changes are significant enough to be captured and which are merely noise.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If hysteresis is implemented between boost on and boost off thresholds to prevent overly frequent boost switching, then switching frequency is reduced, but noise in supply voltage still causes random boost switching near the threshold

Engineering Contradiction:

Improveboost switching frequencyVSAvoidrandom boost switching near threshold

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent performs preliminary processing of the supply voltage signal before it reaches the threshold comparison stage. By pre-filtering the supply voltage through the differential amplifier, comparator, and sample and hold circuit, the system prepares a cleaned signal that prevents noise-induced threshold crossings before they can cause random switching.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the harmful effect of noise by using its statistical properties. By setting a noise margin threshold based on noise characteristics, the system allows small noise fluctuations to pass through while blocking larger, more frequent threshold crossings that would cause unwanted switching.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Stability of the object's composition

If hysteresis is implemented with upper and lower limiter thresholds to limit audio signals based on supply voltage, then limiter stability is improved, but noise in supply voltage causes variations in limiter gain

Engineering Contradiction:

Improvelimiter threshold stabilityVSAvoidlimiter gain variation

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent extracts only the significant supply voltage changes that exceed the noise margin, preventing noise from being transferred to the limiter thresholds. By sampling only when voltage changes are meaningful, the system eliminates noise-induced threshold variations while maintaining proper limiter operation.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS11183975B2Window based supply voltage conditioning circuit for noise filtering

Publication Date: 2021.11.23 TEXAS INSTRUMENTS INC

AI summary

A supply voltage conditioning circuit comprises a differential amplifier, a comparator, a sample and hold (S/H) circuit, and a delay circuit. The differential amplifier receives an input supply voltage and a reference voltage, and outputs a difference signal. The comparator receives the difference signal and a value representative of a noise margin, and outputs a control signal indicative of whether the difference signal is greater than the value representative of the noise margin. The S/H circuit samples the input supply voltage in response to the control signal indicating the difference signal is greater than the noise margin, and outputs a substantially noise free supply voltage. This allows the output supply voltage to track underlying changes in the input supply voltage but filter out noise in the input supply voltage. The delay circuit receives and delays the output supply voltage to generate the reference voltage.