Audio Load Detection Using Out-of-Band Amplifier Noise
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Solution Overview
Problem
Existing audio systems face challenges in detecting the presence or absence of a load, such as a tweeter, without generating a reference signal, which can be audible and consume power, and may not accurately determine impedance in high-frequency regions.
Innovation Solution
A load detector for audio systems with a closed-loop amplifier that includes a noise detector and a parameter calculation module to determine impedance from detected current and voltage in high-frequency regions, allowing for load detection without a reference signal, using a noise detector and parameter calculation module to assess impedance based on out-of-band noise.
Engineering Contradictions & Design Principles
Engineering 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 the reference signal may be audible
Solution Approach 1:
The system uses the amplifier's own out-of-band noise as the detection signal source, eliminating the need for external reference signals. The noise detector captures noise already present in the amplifier output, and the parameter calculation module processes this self-generated noise to determine load impedance, achieving power-efficient load detection without additional signal generation
Solution Approach 2:
The invention extracts useful detection information from the out-of-band noise region (above audible frequency range) that is normally considered unwanted. By filtering and analyzing only the high-frequency noise components, the system separates the detection function from the audio output function, enabling load detection without affecting the audible audio signal
2Measurement precision
If a reference signal is played to detect load presence, then load detection accuracy is improved, but audibility issues occur
Solution Approach 1:
The system transitions from using audible frequency signals (0-20 kHz) to using out-of-band noise signals (above 20 kHz) for detection. By moving the detection operation to a different frequency dimension that is inaudible to humans, the system achieves accurate load detection without the harmful side effect of audible detection signals
Solution Approach 2:
The invention converts the amplifier's out-of-band noise, which is normally considered an unwanted byproduct or harmful distortion, into a useful detection signal. The noise detector and parameter calculation module process this previously wasted energy to accurately determine load impedance, transforming a harmful factor into a beneficial resource for load detection
3Use of energy by moving object
If impedance is determined from detected noise signal, then power consumption is reduced, but measurement precision may be affected
Solution Approach 1:
The system changes the frequency parameter of the detection signal to out-of-band regions above the audible range. This parameter change allows the use of noise signals instead of reference signals, reducing power consumption while maintaining measurement precision through careful selection of frequency bands where the noise characteristics provide sufficient signal-to-noise ratio for accurate impedance calculation
Data Source
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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.