Feedback Circuit Phase Margin Compensation in Active Noise Reduction Headphones
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Solution Overview
Problem
Active noise reduction headphones face challenges in achieving effective noise cancellation beyond the audible frequency range due to limitations in feedback circuit design, particularly in the frequency interval above 10 kHz, where existing systems often experience instability and reduced phase margin, leading to limited bandwidth and reduced noise reduction efficacy.
Innovation Solution
A feedback circuit for active noise reduction headphones is designed with a compensator that provides a positive slope in the frequency range above 10 kHz, combining with the acoustic block's frequency response to enhance noise reduction, using a digital or analog filter to achieve a stable and extended frequency response, thereby increasing the phase margin and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional feedback circuit is used in active noise reduction headphones, then the system is simple and stable at lower frequencies, but the bandwidth is limited and noise reduction efficacy is reduced above 10 kHz
Solution Approach 1:
The patent applies parameter changes by modifying the frequency response characteristics of the feedback circuit through a compensator with a positive slope above 10 kHz. This changes the electrical parameters (frequency response, phase margin) to extend the effective bandwidth and maintain stability at higher frequencies, thereby improving noise reduction efficacy without requiring fundamental redesign of the feedback circuit architecture
2Productivity
If the frequency response is extended above 10 kHz, then the bandwidth is increased, but the phase margin is reduced and stability is compromised
Solution Approach 1:
The compensator introduces a positive slope in the frequency response above 10 kHz, which changes the phase characteristics to maintain or increase phase margin at extended frequencies. This parameter modification allows the system to achieve broader bandwidth while preserving stability by carefully controlling the phase response through the compensator's frequency-dependent characteristics
3Reliability
If the feedback magnitude is increased above 10 kHz, then the noise reduction performance is enhanced, but the system becomes unstable
Solution Approach 1:
The compensator modifies the feedback circuit's frequency response by introducing a positive slope above 10 kHz, which allows the feedback magnitude to be increased at these frequencies without causing instability. The compensator's specific frequency response characteristics ensure that the phase margin is maintained while enabling higher feedback magnitude, thus enhancing noise reduction performance at ultrasonic frequencies
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
A method and apparatus for increasing phase margin in a feedback circuit of an active noise reduction headphone. The method includes providing an acoustic block comprising an acoustic driver comprising a voice coil mechanically coupled along an attachment line to an acoustic energy radiating diaphragm, the acoustic block further comprising a microphone positioned along a line parallel to an intended direction of vibration of the acoustic diaphragm and intersecting the attachment line, the acoustic block characterized by a magnitude frequency response compensating the magnitude frequency response by a compensation pattern that has a positive slope over at least one spectral range above 10 kHz.