Loop Filter Pole-Zero Design for Stable Class D Feedback
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Solution Overview
Problem
Class D audio amplifiers face stability issues due to fluctuations in loop gain, which affect signal-to-noise and distortion ratio (SNDR), necessitating a solution to enhance stability and noise suppression.
Innovation Solution
A negative feedback system architecture incorporating a three-stage series integrator loop filter with three in-bandwidth poles and at least two in-bandwidth zeros, coupled with a pulse width modulation circuit and driver, to stabilize loop gain and improve noise and distortion suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a higher loop order is used to increase loop gain and improve signal to noise and distortion ratio, then noise and distortion suppression is improved, but system stability deteriorates
Solution Approach 1:
The patent changes the parameters of the loop filter by introducing a three-stage series integrator with specific pole and zero configurations. The three in-bandwidth poles and at least two in-bandwidth zeros are strategically positioned to achieve both high loop gain for noise/distortion suppression and adequate phase margin for system stability. This parameter optimization resolves the contradiction between suppression performance and stability.
Solution Approach 2:
The patent employs a negative feedback architecture where the output signal is fed back through the loop filter to the input. The feedback path includes the three-stage series integrator which shapes the loop gain and phase characteristics. This feedback mechanism allows the system to achieve high suppression of noise and distortion while maintaining stability through proper compensation of phase shift.
2Measurement precision
If loop gain is increased to suppress noise and distortion, then signal to noise and distortion ratio is improved, but loop gain stability deteriorates
Solution Approach 1:
The patent optimizes the loop filter parameters by configuring three in-bandwidth poles and at least two in-bandwidth zeros in the three-stage series integrator. This specific parameter configuration achieves a balance between high loop gain for improved SNDR and sufficient phase margin for loop gain stability, resolving the contradiction between measurement precision and reliability.
Data Source
AI summary
A negative feedback system architecture and a loop filter thereof are provided. The negative feedback system architecture includes a loop filter, a pulse width modulation circuit, and a driver. The loop filter includes a three-stage series integrator for receiving a signal and outputting the filtered signal. The loop filter has three in-bandwidth poles and at least two in-bandwidth zeros. The pulse width modulation circuit is electrically connected to the loop filter for receiving the filtered signal and modulating it into a pulse width modulation signal to output. The driver is electrically connected to the pulse width modulation circuit and the loop filter for receiving the pulse width modulation signal to generate an output signal to drive a load device, and the output signal is fed back to the loop filter.