Parallel Open-Loop and Closed-Loop Class-D Modulation for Audio Dynamic Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Personal audio devices face challenges in maintaining a high dynamic range of audio signals while minimizing signal noise, as increased dynamic range through high-gain amplifiers can be offset by noise that masks lower-intensity audio signals.
Innovation Solution
A system with an open-loop and closed-loop Class-D modulator, where a control subsystem selects either modulator based on signal characteristics, using an open-loop modulator for lower-magnitude signals to reduce noise and power consumption, and a closed-loop modulator for higher-magnitude signals to enhance linearity, with techniques to minimize audio artifacts during path transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a high-gain amplifier is used to increase dynamic range, then the dynamic range is improved, but signal noise increases and masks lower-intensity audio signals
Solution Approach 1:
The audio signal path is segmented into two separate modulator paths: an open-loop modulator for low-level signals and a closed-loop modulator for high-level signals. This segmentation allows each modulator to be optimized for its specific signal range, preventing noise from masking low-intensity signals while maintaining high dynamic range capability.
Solution Approach 2:
Different quality characteristics are applied to different signal levels: the open-loop modulator provides low noise performance for low-level signals, while the closed-loop modulator provides high linearity for high-level signals. This local quality differentiation resolves the contradiction between noise reduction and dynamic range enhancement.
2Object-affected harmful factors
If an open-loop modulator is used for lower-magnitude signals, then noise and power consumption are reduced, but linearity may be compromised
Solution Approach 1:
The signal processing is segmented by amplitude level, with open-loop modulation handling low-level signals where noise reduction is critical, and closed-loop modulation handling high-level signals where linearity is more important. This segmentation allows each path to be optimized for its primary function.
Solution Approach 2:
The system dynamically changes the operational parameters by switching between open-loop and closed-loop modulation modes based on signal magnitude. This parameter change allows the system to optimize noise performance for low-level signals while maintaining linearity for high-level signals.
3Manufacturing precision
If a closed-loop modulator is used for higher-magnitude signals, then linearity is enhanced, but power consumption increases
Solution Approach 1:
The power consumption is segmented by signal level: the high-power closed-loop modulator is activated only when necessary for high-level signals requiring superior linearity, while the low-power open-loop modulator handles low-level signals. This segmentation reduces overall power consumption while maintaining linearity where needed.
Solution Approach 2:
The system periodically switches between open-loop and closed-loop modulation based on the instantaneous signal magnitude, activating the power-intensive closed-loop path only during periods when high-level signals are present, thereby reducing average power consumption while maintaining linearity when required.
4Stability of the object's composition
If switching between open-loop and closed-loop modulators is implemented, then dynamic range enhancement is achieved, but audio artifacts may occur during path transitions
Solution Approach 1:
The system performs preliminary actions by pre-processing the input signal and predicting when switching between modulation paths will occur. This allows the system to prepare for transitions in advance, ensuring smooth handoff between open-loop and closed-loop modulators and preventing audible artifacts during path switching.
Solution Approach 2:
The system uses feedback mechanisms to monitor the output signals from both open-loop and closed-loop modulators during transitions. This feedback allows the system to detect and correct potential artifacts in real-time, ensuring smooth transitions between modulation paths while maintaining enhanced dynamic range performance.
Data Source
AI summary
An integrated circuit may have two signal paths: an open-loop modulator (which may comprise a digital-input Class-D amplifier) and a closed-loop modulator (which may comprise an analog-input Class-D amplifier). A control subsystem may be capable of selecting either of the open-loop modulator or the closed-loop modulator as a selected path based on one or more characteristics (e.g., signal magnitude) of an input audio signal. For example, for higher-magnitude signals, the closed-loop modulator may be selected while the open-loop modulator may be selected for lower-magnitude signals. In some instances, when the open-loop modulator is selected as the selected path, the closed-loop modulator may power off, which may reduce power consumption. In addition, one or more techniques may be applied to reduce or eliminate user-perceptible audio artifacts caused by switching between the open-loop modulator and the closed-loop modulator, and vice versa.