Self-Oscillating Amplifier with Parallel Filters for Phase Control
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Solution Overview
Problem
Existing switching class D amplifiers face challenges with limited system bandwidth and complex design due to PWM limitations, as well as difficulties in implementing a stable and robust control system, particularly in minimizing phase shift across the audio band.
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, featuring an amplitude limiting circuitry to maintain signal amplitude within predefined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM modulation is used in switching class D amplifiers, then power amplification efficiency is improved, but system bandwidth is limited and design becomes complex
Solution Approach 1:
The feedback path is segmented into multiple parallel branches with different filter characteristics (differentiating filter in first branch, integrating filter in second branch). This segmentation allows each branch to handle specific frequency ranges and control aspects independently, simplifying the overall design while maintaining wide bandwidth and high efficiency
2Speed
If global loop controlled oscillation modulator is used, then wide closed loop gain bandwidth is achieved, but phase shift across audio band increases
Solution Approach 1:
The feedback path is divided into parallel branches where the first branch contains a differentiating filter for high-frequency switching control and the second branch contains an integrating filter for low-frequency audio band compensation. This segmentation allows independent optimization of each branch's phase characteristics
Solution Approach 2:
By changing the filter type parameter (differentiating vs integrating) in different feedback branches, the system optimizes phase response across different frequency ranges. The differentiating filter minimizes phase shift at switching frequencies while the integrating filter compensates phase lag in the audio band
3Power
If integrating forward filter is used to control amplifier behavior, then open loop gain increases, but sub-harmonic oscillations occur
Solution Approach 1:
The feedback path is segmented into parallel branches with different filter characteristics. The first branch with differentiating filter handles switching frequency control without causing sub-harmonic oscillations, while the second branch with integrating filter provides gain enhancement in the audio band with proper phase compensation
Solution Approach 2:
The differentiating filter acts as an intermediary that prevents the integrating filter from causing sub-harmonic oscillations. By placing the differentiating filter in parallel in the feedback path, it mediates the control signal to eliminate harmful oscillations while allowing the integrating filter to provide beneficial gain enhancement
Data Source
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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.