Hearing Aid Amplifier Dynamic Bias Control for Power Reduction
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Solution Overview
Problem
Hearing aids face challenges in reducing power consumption, particularly in maintaining linearity and avoiding slew rate limiting and crossover distortion, especially at high frequencies and loud volumes, which is exacerbated by constant bias current consumption.
Innovation Solution
A method and device that dynamically adjust the bias current based on the frequency content of ambient sound by splitting the signal into narrowband frequencies, forming volume envelopes, weighting them by frequency, and applying a dynamic bias current to the output amplifier, reducing power consumption while maintaining linearity and minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant bias current is used to maintain linearity and avoid slew rate limiting, then the amplifier performance is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic bias current control that adjusts the bias level in real-time based on signal characteristics. The system transitions from a static constant bias current to a dynamic bias current that varies with signal amplitude and frequency, allowing the amplifier to maintain optimal performance only when needed rather than continuously consuming power at maximum levels
Solution Approach 2:
The system changes the bias current parameter dynamically based on signal conditions. By monitoring signal amplitude and frequency content, the controller adjusts the bias current parameter to match actual operational requirements, reducing it during low-demand conditions while maintaining it at higher levels when signal integrity demands it
2Use of energy by moving object
If the bias current is reduced to save power, then power consumption decreases, but slew rate limiting and crossover distortion occur
Solution Approach 1:
The system employs feedback mechanisms where signal amplitude and frequency information is continuously monitored and fed back to the bias control circuit. This feedback loop enables the system to detect when signal conditions require higher bias current to prevent distortion, and automatically adjusts the bias accordingly, creating a closed-loop control system that maintains signal integrity
Solution Approach 2:
The system takes preliminary action by adjusting the bias current before distortion can occur. By anticipating signal demands based on amplitude and frequency analysis, the bias current is proactively increased to prevent slew rate limiting and crossover distortion before they manifest in the output signal
3Reliability
If a constant high bias current is used to handle loud high-frequency signals, then linearity is maintained, but power is wasted during quiet or low-frequency periods
Solution Approach 1:
The system dynamically adapts the bias current to match actual signal demands rather than maintaining a constant high level. By making the bias current variable and responsive to real-time signal conditions, the system eliminates energy waste during quiet or low-frequency periods while preserving amplifier performance when needed
Solution Approach 2:
The bias current parameter is changed dynamically based on signal amplitude and frequency analysis. The system transitions from a fixed parameter to a variable parameter that adapts to operational conditions, reducing the parameter value during low-demand periods to eliminate unnecessary energy consumption
Data Source
AI summary
A hearing aid is disclosed, which can autonomously track the bias current requirements of its output amplifier and control the current bias accordingly, resulting in less power consumption than if the bias current were delivered at a constant, worst-case level. An input signal is split into different frequency bands. A volume envelope is formed for each frequency band, which may function like an instantaneous volume level for each frequency band. The volume envelopes are weighted by frequency, with high frequencies being weighted more heavily than low frequencies. The weighted volume envelopes are used to calculate a dynamic bias current level, and a current with that level is provided to the output amplifier of the hearing aid. In some cases, the narrowband input signals for the frequency bands are amplified with respective predetermined gains, and are then combined to form a broadband output signal, which is sent to the output amplifier.