Amplifier Load Detection Using Out-of-Band Noise Signals

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Solution Overview

Problem

Existing audio systems face challenges in detecting the presence or absence of a load, particularly a tweeter, without generating a reference signal, which can be audible and increase power consumption.

Innovation Solution

A load detector for a closed-loop amplifier is introduced, comprising a noise detector and a parameter calculation module that determines impedance from noise signals outside the audible frequency range, allowing for load detection without a reference signal, and includes a comparator to generate a load detection signal based on predetermined threshold values.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a reference signal is played to detect load presence, then load detection accuracy is improved, but power consumption increases and audible noise is generated

Engineering Contradiction:

Improveload detection accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The system uses the noise already generated by the amplifier's noise shaper to perform load detection, rather than introducing a separate reference signal. The noise detector captures this self-generated noise, and the parameter calculation module extracts impedance information from it, allowing the system to serve its own detection needs without external excitation signals.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent converts the harmful effect of noise (which is filtered out in audio applications) into a useful resource for load detection. The noise shaper's output, normally considered unwanted noise in the audible range, contains valuable impedance information when analyzed in higher frequency bands, turning a detrimental element into a beneficial detection signal.

Inventive Principle:

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

2Measurement precision

If a reference signal is played to detect load presence, then load detection accuracy is improved, but audible noise is generated

Engineering Contradiction:

Improveload detection accuracyVSAvoidaudible noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

Inventive Principle:

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

3Use of energy by moving object

If noise signals outside audible frequency range are used for detection, then power consumption is reduced and audible noise is avoided, but detection complexity increases

Engineering Contradiction:

Improvepower consumptionVSAvoiddetection system complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The noise detector acts as an intermediary component that captures the noise shaper's output signal. It bridges the gap between the amplifier's internal noise generation and the parameter calculation module, which then processes this signal to extract impedance information. This intermediary structure manages the complexity by creating dedicated functional blocks for signal capture and analysis.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the frequency parameter of the detection signal from the audible range to higher frequency bands. By analyzing the noise shaper's output in frequency ranges above the audible spectrum, the system accesses impedance information that is more pronounced and easier to measure, simplifying the overall detection approach despite the higher frequency operation.

Inventive Principle:

Principle #35Parameter changes

4Reliability

If continuous detection is implemented, then reliability is improved, but power consumption increases

Engineering Contradiction:

Improvedetection reliabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

Inventive Principle:

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

Data Source

PatentUS10436828B2Load detector

Publication Date: 2019.10.08 NXP BV

AI summary

A load detector for an audio system comprising a closed-loop amplifier is described. The load detector includes a noise detector configured to be coupled to the output of the closed-loop amplifier. The noise detector detects a noise signal at least partially generated by the amplifier. The generated noise signal comprises frequencies outside the audible frequency range due to the noise shaping of the amplifier. The load detector further includes a parameter calculation module having an input coupled to the output of the noise detector and an output. The parameter calculation module is configured to determine a parameter value relating to an impedance of the amplifier output load from the detected noise signal and to output a load detection signal dependent on the determined parameter value. The load detector may detect the presence of a load such as a tweeter without generating a reference signal.