Class-D Modulation Loop With Filtered Feedback for Low-Power Linearity
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Solution Overview
Problem
Modern audio amplifiers in devices like smartphones and laptops face challenges in reducing power consumption, latency, and improving linearity, particularly in class-D amplifiers where high power consumption is associated with high bandwidth to handle fast signals.
Innovation Solution
The solution involves selectively prefiltering the feedback signal at the first integrator in a class-D amplifier circuit, allowing for reduced loop response and power consumption while maintaining high linearity and low delay, without the need for high power analog operational amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high bandwidth is used to handle fast signals in class-D amplifiers, then loop response speed is improved, but power consumption increases
Solution Approach 1:
The feedback signal is segmented and applied differently to different integrator stages. The first integrator receives a filtered version of the feedback signal, while subsequent integrators receive the full-bandwidth feedback signal. This segmentation allows the first integrator to operate with reduced bandwidth requirements, lowering power consumption while maintaining overall loop response performance.
Solution Approach 2:
Different quality requirements are applied locally to different parts of the system. The first integrator, which has the highest overall gain and controls noise and distortion, is provided with a filtered feedback signal optimized for its specific function. Other integrators receive unfiltered signals appropriate for their roles, achieving local optimization of both power consumption and signal fidelity.
2Manufacturing precision
If the first integrator is designed for good linearity and low noise, then output signal quality is improved, but quiescent current increases
Solution Approach 1:
The feedback signal is pre-filtered before being applied to the first integrator, preparing the signal in advance to match the integrator's optimal operating conditions. This preliminary filtering allows the first integrator to achieve high linearity and low noise performance without requiring excessive quiescent current, as the signal is already conditioned for its specific function.
3Use of energy by stationary object
If selective prefiltering is applied at the first integrator, then loop response is reduced and power consumption decreases, but may affect stability
Solution Approach 1:
The filtered feedback signal is fed back to the first integrator in a controlled manner, creating a stable feedback loop. The filtering is designed to maintain the stability of the loop filter response while reducing the bandwidth requirements and power consumption of the first integrator. The feedback mechanism ensures that stability is preserved despite the selective filtering applied to different integrator stages.
Data Source
AI summary
Systems and methods include a circuit having a plurality of integrator circuits arranged in series and configured to receive an input signal at a first of the plurality of integrators and generate an output signal at a last of the plurality of integrators, a filter arranged to receive a feedback signal comprising the output signal and generate a filtered feedback signal, which is applied to the input signal before input to the first of the plurality of integrators, and a feedback signal path configured to receive the feedback signal and apply the feedback signal to an input of a second of the plurality of integrators. The circuit may include a class-D amplifier and/or a delta-sigma modulator. The input signal may include an analog audio signal that is amplifier to drive an audio speaker.