Self-Oscillating Audio Amplifier with Parallel Forward Filters
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Solution Overview
Problem
Existing switching class D audio amplifiers face challenges with limited system bandwidth and complex design due to PWM limitations, making it difficult to achieve stable and robust control systems, particularly in high-definition applications.
Innovation Solution
A self-oscillating amplifier system with a forward path comprising a pulse modulator, switching power amplification stage, and demodulation filter, along with a feedback path including a phase lead network, and separate parallel branches for differentiating and integrating filters to control switching frequency and prevent sub-harmonic oscillations, enhancing open loop gain and frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PWM modulation is used in switching class D amplifiers, then power amplification efficiency is improved, but system bandwidth is limited and design complexity increases
Solution Approach 1:
The patent implements a feedback path from the output of the demodulation filter back to the input of the pulse modulator. This feedback loop enables the system to automatically regulate its operation, improving stability and reducing design complexity while maintaining the efficiency benefits of PWM modulation
Solution Approach 2:
The patent introduces a phase lead network that dynamically adjusts phase parameters to compensate for phase lag in the demodulation filter. This parameter adjustment resolves the bandwidth limitation issue while preserving the energy efficiency of the switching amplifier architecture
2Manufacturing precision
If a demodulation filter is added to the amplifier system, then output signal quality is improved, but phase lag increases reducing system bandwidth
Solution Approach 1:
The phase lead network is positioned in the feedback path to preemptively compensate for the phase lag introduced by the demodulation filter. By introducing leading phase shift before the lag occurs, the system maintains wider bandwidth while preserving output signal quality
3Device complexity
If self-oscillation is used to simplify control, then device complexity is reduced, but sub-harmonic oscillations may occur degrading performance
Solution Approach 1:
The feedback path monitors the output signal and regulates the pulse modulator to maintain stable self-oscillation at the desired frequency. This feedback mechanism suppresses sub-harmonic oscillations while preserving the simplicity of self-oscillating control architecture
Solution Approach 2:
The differentiating forward filter and integrating forward filter work together to shape the frequency response and damping characteristics, preventing sub-harmonic oscillations while maintaining the simplified self-oscillating control structure
Data Source
AI summary
A new and improved self-oscillating amplifier system is presented, suitable for use in high fidelity audio applications. The self-oscillating amplifier system comprises a feedback path and a forward path including a pulse modulator, a switching power amplification stage and a demodulation filter. The forward path further includes a pair of parallel forward filters preceding the pulse modulators, a differentiating forward filter and an integrating forward filter. The differentiating forward filter is utilized for controlling a switching frequency of the system while the integrating forward filter is utilized for controlling the behavior of the amplifier system within an operating frequency band (e.g. audio band). The self-oscillating amplifier system exhibits improved performance in terms of open loop gain, reduced phase turn and improved robustness as compared to other previously known self-oscillating amplifier systems.