Sliding Bias Control for Class D Amplifier Efficiency
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Solution Overview
Problem
Class D and Class A power amplifiers in hearing aids face inefficiencies, particularly in idling current management, leading to rapid battery drain and distortion issues when using pulse duration modulation with LED loads, where idling current remains high even at low signal levels.
Innovation Solution
A sliding bias method is introduced, where a sliding bias voltage is superimposed onto the audio input signal to regulate the ON time of pulse trains, reducing idling current at low signal levels while maintaining undistorted output by dynamically adjusting the bias voltage based on audio input levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Class D pulse duration modulation is used to improve amplifier efficiency, then energy efficiency is improved, but idling current remains high at low signal levels causing distortion
Solution Approach 1:
The patent applies dynamics by making the bias voltage adjustable rather than fixed. The bias voltage dynamically adapts to the input signal level, being higher at low signal levels to maintain linearity and lower at high signal levels to maximize efficiency. This dynamic adjustment resolves the contradiction between maintaining low distortion and achieving high efficiency across different operating conditions.
Solution Approach 2:
The patent changes the bias voltage parameter based on signal level. At low signal levels, a higher bias voltage is applied to maintain proper operating point and reduce distortion. At high signal levels, the bias voltage is reduced to minimize idling current and maximize efficiency. This parameter change strategy allows the system to optimize both distortion performance and efficiency depending on operating conditions.
2Reliability
If high bias voltage is maintained to prevent distortion, then linearity is improved, but battery life decreases due to increased power consumption
Solution Approach 1:
The bias voltage is made dynamic rather than static, adjusting according to signal level. During low signal conditions where linearity is critical, higher bias maintains reliability. During high signal or idle conditions, lower bias extends battery life. This dynamic approach allows the system to prioritize linearity when needed while conserving energy when possible.
Solution Approach 2:
The bias voltage parameter is changed based on operating conditions. The system monitors signal level and adjusts bias accordingly - higher bias for low signals to maintain linearity, lower bias for high signals or idle states to extend battery life. This parameter adaptation resolves the contradiction between reliability and duration.
3Device complexity
If fixed bias is used to simplify circuit design, then device complexity is reduced, but efficiency varies poorly across different signal levels
Solution Approach 1:
The patent implements feedback by monitoring the input signal level and using this information to adjust the bias voltage. The system measures the signal level and automatically adjusts bias to optimize efficiency for each operating condition. This feedback mechanism improves efficiency across varying signal levels without requiring complex manual adjustment circuits.
Solution Approach 2:
The bias adjustment system serves itself by automatically adapting to signal levels without external intervention. The circuit monitors its own operating conditions and self-adjusts the bias voltage to maintain optimal efficiency. This self-service approach improves efficiency while keeping the control mechanism relatively simple.
Data Source
AI summary
Various embodiments include a system and method that control idling current of a pulse modulated driver. The system may include an audio input device configured to receive an audio input signal. The system can include sliding bias control circuitry configured to generate a sliding bias control signal based on a level of the audio input signal. The system may include sliding bias generation circuitry configured to generate a sliding bias voltage superimposed onto the audio input signal to generate a pulse modulated driver input signal that is input into an amplifier. The sliding bias voltage may be based on the sliding bias control signal.