Adaptive ANC Controller With Fixed-Response Filter
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Solution Overview
Problem
Existing adaptive noise cancellation (ANC) systems face stability challenges due to variations in the secondary path response, particularly in devices like wireless telephones where the acoustic environment changes, affecting the feedback loop stability and noise cancellation performance.
Innovation Solution
An ANC controller is designed with a combination of a fixed transfer function filter and a variable-response filter, where the fixed filter maintains stability and the variable filter compensates for secondary path variations, making the ANC gain independent of the secondary path transfer function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-response feedback filter is used in ANC systems, then the system is simpler to implement, but the system becomes unstable when the acoustic environment varies
Solution Approach 1:
The feedback filter is segmented into two independent parts: a fixed-response filter with predetermined coefficients and an adaptive filter with variable coefficients. The fixed filter provides a stable baseline response, while the adaptive filter compensates for environmental variations. This segmentation allows each component to have optimized characteristics without compromising overall system stability.
Solution Approach 2:
The system transitions from a purely static fixed-response filter to a dynamic hybrid structure where the adaptive filter continuously adjusts its coefficients based on environmental conditions. This dynamic adaptation maintains feedback loop stability despite variations in acoustic coupling between the transducer and sensor.
2Reliability
If an adaptive feedback filter is used to compensate for secondary path variations, then the system becomes more complex, but the noise cancellation performance improves
Solution Approach 1:
The adaptive noise cancellation function is segmented between the fixed filter and adaptive filter. The fixed filter handles the stable, predictable portion of the feedback response, while the adaptive filter specifically targets the variable secondary path characteristics. This division of labor improves noise cancellation performance without requiring the entire system to be highly complex.
Solution Approach 2:
The adaptive filter modifies its transfer function parameters (coefficients) in response to detected secondary path variations. By dynamically changing these parameters, the system maintains optimal noise cancellation performance across different acoustic environments without requiring complete reconfiguration of the entire filter structure.
3Stability of the object's composition
If the feedback filter response is made independent of the secondary path transfer function, then the ANC gain becomes stable, but the system requires more complex filtering
Solution Approach 1:
The feedback filter is segmented into a fixed component that provides stable ANC gain and an adaptive component that compensates for secondary path variations. This segmentation enables the ANC gain to remain stable while accounting for environmental changes through the adaptive portion.
Solution Approach 2:
The adaptive filter acts as an intermediary between the fixed filter and the variable secondary path. It mediates the interaction by adjusting its response to cancel out the effects of secondary path variations, thereby protecting the overall ANC gain stability without requiring direct coupling between the fixed filter and the variable acoustic environment.
Data Source
AI summary
A controller for an adaptive noise canceling (ANC) system simplifies the design of a stable control response by making the ANC gain of the system independent of a secondary path extending from a transducer of the ANC system to a sensor of the ANC system that measures the ambient noise. The controller includes a fixed filter having a predetermined fixed response, and a variable filter coupled together. The variable response filter compensates for variations of a transfer function of a secondary path that includes at least a path from a transducer of the ANC system to a sensor of the ANC system, so that the ANC gain is independent of the variations in the transfer function of the secondary path.