Amplifier Loop Gain Calibration for Stable Unity-Gain Frequency
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Solution Overview
Problem
Class-D audio amplifiers with closed-loop feedback paths face challenges due to component tolerance inconsistencies and increasing costs, leading to limited stability ranges caused by variations in inductor and capacitor values in load circuits.
Innovation Solution
Incorporating a small control signal, or pilot-tone, into the feedback loop to regulate the unity-gain frequency, with a calibration circuit that adjusts the effective gain of the derived signal based on comparisons before and after the pilot-tone inclusion, ensuring proper control and stability within a narrow target range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If component tolerances are tightened to improve stability, then stability range is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the parameter of unity-gain frequency dynamically through calibration. By measuring the actual unity-gain frequency and adjusting it via a calibration loop, the system compensates for component variations without requiring tight manufacturing tolerances. This allows standard components to be used while maintaining stability across a wide range of operating conditions.
2Ease of manufacture
If component tolerances are relaxed to reduce manufacturing cost, then ease of manufacture is improved, but stability range deteriorates
Solution Approach 1:
The patent implements a feedback-based calibration system that measures the actual unity-gain frequency of the amplifier and adjusts it accordingly. The calibration loop continuously monitors performance and makes real-time corrections, enabling the use of cost-effective components with relaxed tolerances while maintaining optimal stability and performance characteristics.
3Adaptability or versatility
If unity-gain frequency is allowed to vary widely, then adaptability is improved, but control precision deteriorates
Solution Approach 1:
The patent performs preliminary calibration action during the amplifier's operation to establish the correct unity-gain frequency. By measuring the actual frequency and applying a calibration signal before normal operation, the system pre-adjusts the feedback loop to compensate for component variations, ensuring both adaptability to different components and precise control of the unity-gain frequency.
Data Source
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AI summary
Aspects are directed to an amplifier circuit including a signal processing circuit and a calibration circuit. In certain specific embodiments, the signal processing circuit includes a signal combiner and a closed-loop feedback path, and the signal processing circuit is designed to provide a loop transfer function for a derived signal partly representing contributions from an audio input signal, a control or pilot signal having a target frequency range, and a calibration signal. The signal combiner is designed to combine aspects of the control or pilot signal and aspects of the audio input signal, and the calibration circuit is designed to adjust an effective gain of the derived signal in response to whether a unity-gain frequency of a signal in the closed-loop feedback path, as provided via the loop transfer function, is higher or lower than the target frequency range. Consistent therewith and in yet more specific embodiments, such an amplifier circuit can define the target frequency range relative to the transfer function and an associated unity-gain frequency.