Loudspeaker Current Limiting With Predictive Audio Sample Replacement
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Solution Overview
Problem
Existing audio power amplifiers face issues with current limiting solutions that either disrupt audio output or require complex control loops, leading to unacceptable pauses in audio playback during current limiting.
Innovation Solution
A current limiting device using a state-space model to predict and limit the current drawn by loudspeakers, employing a prediction algorithm to generate a replacement audio sample that maintains current within a specified threshold, ensuring continuous audio playback without hardware protection circuit triggers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional control loops with fast current measurements are used to perform pulse-by-pulse current limiting, then the output current can be limited to a maximum value, but the device complexity increases
Solution Approach 1:
The patent uses a state-space model to predict future current values before they actually occur. The prediction device generates a predicted current value for the next time step based on the current state vector, allowing the system to take preliminary action to prevent current exceeding before it happens, rather than reacting after the fact.
Solution Approach 2:
The patent implements a feedback mechanism where the measured current is fed back to update the state vector in the state-space model. The state feedback controller uses the comparison between measured and model-based estimated current to generate a feedback signal that corrects the model's state, improving prediction accuracy and enabling reliable current limiting.
2Reliability
If the driver IC turns off the output stage completely when the output current threshold is reached, then the current is limited to a maximum value, but the audio output is interrupted
Solution Approach 1:
Instead of completely turning off the output stage when current threshold is reached, the patent applies partial action by using the state-space model to predict future current and generating a replacement audio sample that limits the current to the maximum value while maintaining continuous audio output. This excessive prediction approach allows preventing overcurrent before it occurs without interrupting playback.
Solution Approach 2:
The patent introduces a replacement audio sample as an intermediary between the original audio signal and the output stage. When predicted current exceeds the threshold, this intermediary signal is used instead of the original audio sample, allowing current limiting while maintaining continuous audio output through the intermediary replacement signal.
3Productivity
If a state-space model with prediction is used to limit current, then uninterrupted audio output is maintained, but the computational complexity increases
Solution Approach 1:
The state-space model serves itself by using its own internal state variables to predict future current values. The model uses its current state vector to generate predictions without requiring external complex computation, making the system self-sufficient and reducing overall computational complexity despite the predictive capability.
Data Source
AI summary
A method for use with a sound system (called plant in control theory) including a loudspeaker set, the method comprising: obtaining input audio samples and a measured current drawn by the loudspeaker set; generating, for a current time step, using a state-space model of the loudspeaker set, a state vector and a model-based estimated current; generating, based on the state vector, a predicted current for a next time step; generating, for the current time step, a replacement audio sample based on the state vector; generating a feedback signal that contributes to the generation of the state vector for the next time step based on the measured current and a time-aligned model-based estimated current; generating an output audio sample for the current time step, wherein the output audio sample is either the input audio sample for the current time step or the replacement audio sample when the predicted current is higher in magnitude than a threshold.