Closed-loop class-D amplifier with modulated reference signal and related method
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Solution Overview
Problem
Conventional class-D amplifiers, especially closed-loop configurations, face issues with supply rejection and performance degradation due to loop saturation and power driving capability limitations in mobile applications with fluctuating supply voltages, leading to poor THD+N ratios and noisy outputs.
Innovation Solution
A closed-loop class-D amplifier with modulated reference signals is introduced, where the reference signals are adjusted based on input amplitude rather than fixed period, preventing loop filter output from swinging and thus avoiding saturation, and incorporating a feed-forward path with a PWM processor and feedback path to generate pulse-width-modulated signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional closed-loop class-D amplifier configurations are used to improve supply rejection and reduce THD+N, then performance is improved, but loop saturation occurs easily when output signal amplitude is close to supply voltage rail, limiting power driving capability
Solution Approach 1:
The patent implements dynamic supply voltage tracking by modulating the reference signal amplitude according to the actual supply voltage level. The reference signal generator adjusts the reference voltage dynamically to match supply variations, preventing loop saturation while maintaining closed-loop performance benefits. This dynamic adaptation allows the amplifier to maintain power driving capability even when operating near supply rails.
Solution Approach 2:
The patent changes the reference signal parameter (amplitude) based on supply voltage conditions. By modulating the reference signal amplitude to track supply voltage variations, the system prevents the loop filter output from hitting the supply rail, thereby avoiding saturation while maintaining good supply rejection and THD+N performance.
2Reliability
If conventional closed-loop class-D amplifier configurations are used to improve supply rejection, then supply rejection is improved, but loop filter output swings with output signal amplitude causing saturation and performance degradation
Solution Approach 1:
The system dynamically adjusts the reference signal amplitude to track supply voltage variations in real-time. This dynamic modulation prevents the loop filter output from swinging into saturation regardless of output signal amplitude, ensuring consistent performance across different operating conditions and supply voltage levels.
Solution Approach 2:
The patent implements a feedback mechanism where the supply voltage is monitored and used to modulate the reference signal amplitude. This feedback loop ensures that the reference signal remains appropriately scaled relative to supply voltage, preventing saturation and maintaining performance consistency across varying operating conditions.
3Power
If conventional open-loop class-D amplifiers are used to maintain power driving capability, then power efficiency is maintained, but poor THD+N ratio and high supply sensitivity result
Solution Approach 1:
The patent segments the amplifier into distinct functional blocks: an open-loop power amplification stage that maintains efficiency, a separate reference signal modulation stage that improves linearity, and a feedback stage that corrects distortions. This segmentation allows each stage to be optimized independently, achieving both power efficiency and low THD+N.
Solution Approach 2:
The modulated reference signal acts as an intermediary that bridges the open-loop power stage and the feedback control. By preprocessing the reference signal to track supply voltage, it improves the linearity of the power stage without requiring the power stage itself to be complex, thus maintaining efficiency while improving THD+N performance.
Data Source
AI summary
Disclosed is a closed-loop class-D amplifier circuit including a modulated reference signal generator that provides a modulated reference signal in a feed-forward path, where the reference signal is modulated corresponding to an input signal. The closed-loop class-D amplifier circuit further includes a comparator to generate a control signal based on a comparison of the modulated reference signal and a correction signal, which in turn is produced by filtering a combination of the input signal and a feedback signal. The closed-loop class-D amplifier circuit also includes a pulse generator to generate a pulse-width-modulated signal to drive an output stage of the closed-loop class-D amplifier based on the control signal.