Class D Amplifier Feedback Loop With Second-Order Filter Gain
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Solution Overview
Problem
Legacy Class D amplifiers with first-order filters in the control loop face limitations in achieving sufficient loop gain at low frequencies and maintaining desired frequency responses, particularly in integrating amplifier configurations.
Innovation Solution
Incorporating a second-order filter in the feedback setup between the primary amplifier output and input, along with a compensator that can be disabled during certain operating modes, to enhance loop gain and frequency response characteristics, and using a low-pass filter to manage high-frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a first-order filter is used in the control loop of a Class D amplifier, then the device complexity is reduced, but the loop gain at low frequencies is insufficient and the frequency response cannot be optimized
Solution Approach 1:
The patent changes the filter order parameter from first-order to second-order in the feedback path. This parameter change increases the loop gain at low frequencies by an additional 20 dB/decade roll-off, thereby resolving the contradiction between device complexity and low-frequency loop gain performance.
2Reliability
If a second-order filter is added to the feedback path, then the loop gain at low frequencies is increased, but the device complexity increases
Solution Approach 1:
The patent implements a second-order filter by adding one additional pole to the feedback path compared to a first-order filter. This parameter change achieves the desired low-frequency loop gain improvement while maintaining a relatively simple circuit structure, thus resolving the contradiction between reliability and device complexity.
3Reliability
If the compensator is always active, then the frequency response is improved, but high-frequency noise is amplified
Solution Approach 1:
The patent makes the compensator dynamically controllable, allowing it to be enabled or disabled based on operating conditions. This dynamic adjustment enables the system to optimize frequency response when needed while suppressing high-frequency noise amplification during other operating modes, thereby resolving the contradiction between reliability and harmful factors.
Data Source
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AI summary
A Class D amplifier having an integrating primary amplifier with an internal feedback, the amplifier further comprising a feedback loop with a filter of at least second order.