Class-D Amplifier Gain Calibration for Stable Loop Gain
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Solution Overview
Problem
Class D amplifiers face challenges in maintaining stable gain settings due to variations in reconstruction filter components, leading to noise peaking and instability in audio performance, especially when using cheaper filter components with wider tolerance ranges.
Innovation Solution
A gain calibration controller is introduced that determines the stable gain range and preferred gain setting by measuring noise levels across specific frequency ranges, allowing for adjustment of the gain to optimal values within this range, thereby ensuring stable loop gain and improved audio performance even with components having higher tolerance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If cheaper filter components with wider tolerance ranges are used, then cost is reduced, but gain stability deteriorates leading to noise peaking and instability
Solution Approach 1:
The patent adjusts the gain parameter of the class-D amplifier based on the actual characteristics of the reconstruction filter components. By measuring the noise level and determining the stable gain range, the system dynamically changes the gain parameter to compensate for component variations, allowing cheaper components with wider tolerances to be used while maintaining stability.
Solution Approach 2:
The patent implements a feedback mechanism where the noise level is measured and used to determine the stable gain range. The measured noise level feeds back to the gain calibration controller, which adjusts the gain setting accordingly. This closed-loop feedback ensures that even with cheaper components having wider tolerance ranges, the amplifier maintains stable operation.
2Device complexity
If fixed gain settings are used, then device complexity is reduced, but adaptability to component variations deteriorates causing instability
Solution Approach 1:
The patent performs preliminary calibration of the gain setting based on the actual reconstruction filter components before normal operation. The gain calibration controller determines the stable gain range in advance by measuring noise levels, and stores this information for use during operation. This preliminary action allows the system to adapt to component variations without adding complex real-time adjustment mechanisms.
Solution Approach 2:
The system performs self-calibration by automatically measuring its own noise level and determining the appropriate gain setting. The gain calibration controller uses the measured noise level to self-adjust the gain parameter, eliminating the need for external calibration equipment or complex manual adjustment mechanisms, thus maintaining simplicity while achieving adaptability.
3Power
If gain is increased to improve signal level, then signal strength is improved, but noise peaking worsens causing instability
Solution Approach 1:
The patent optimizes the gain parameter by determining the stable gain range based on measured noise levels. Instead of using a fixed high gain setting, the system adjusts the gain parameter to the optimal value within the stable range, maximizing signal strength while avoiding the noise peaking that occurs at excessively high gain settings.
Data Source
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AI summary
A gain calibration controller (230) and gain calibration method is described for calibrating the gain of a class D audio amplifier (240) comprising an adjustable gain stage (208) and a feedback path coupled to an output of a reconstruction filter (216). The gain calibration controller detects a first output noise level in a first frequency range and a second output noise level in a second higher frequency range, varies the gain of the adjustable gain stage, determines a minimum stable gain value of a stable gain range from a change in at least one of the first and second output noise level in response to varying the gain of the adjustable gain stage, and determines a maximum stable gain value of the stable gain range from a change in at least one of the first and second output noise level in response to varying the gain of the adjustable gain stage.