Capacitive-Feedback Class-D Amplifier With Voltage Boosting and Low EMI
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Solution Overview
Problem
Class-D amplifiers face challenges in achieving low total harmonic distortion (THD), high signal-to-noise ratio (SNR), high output power, and low electromagnetic interference (EMI) simultaneously, while also dealing with increased system cost and bulk due to the use of resistive feedback, boost converters, and LC filters.
Innovation Solution
A Class-D amplifier with capacitive feedback and voltage boosting power stage, utilizing input and feedback capacitors to set closed-loop gain, a preamplifier, loop filter, PWM generator, and a voltage boosting power stage with transistors, inductors, and capacitors to generate a boosted output signal, filtering high-frequency components and reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If resistive feedback is used to suppress power stage non-ideal effects, then total harmonic distortion (THD) is reduced, but thermal noise increases which limits signal-to-noise ratio (SNR)
Solution Approach 1:
The patent changes the feedback mechanism from resistive to capacitive coupling. The capacitive feedback network (using capacitors C1-C4) replaces the resistive feedback path, fundamentally altering the electrical parameters of the feedback loop. This eliminates thermal noise generation in the feedback path while maintaining the ability to suppress power stage non-ideal effects through appropriate capacitor value selection and ratio matching.
Solution Approach 2:
The patent substitutes the resistive feedback mechanism with a capacitive feedback mechanism. By replacing resistors with capacitors in the feedback path, the system eliminates the thermal noise inherent in resistive elements while preserving the feedback function for suppressing distortion. The capacitive coupling achieves the same distortion suppression goal without the harmful thermal noise byproduct.
2Power
If a boost converter is used to provide higher supply voltage for increased output power, then maximum output power increases, but overall power efficiency degrades due to two-step power conversion
Solution Approach 1:
The patent merges the voltage boosting function with the power stage operation itself. Instead of using a separate boost converter followed by a power stage (two-step conversion), the capacitive feedback Class-D amplifier architecture integrates voltage multiplication through the capacitive network (C1-C4) and switching transistors (Q1-Q4) directly within the power delivery path. This single-step approach eliminates the intermediate conversion stage and reduces energy loss.
Solution Approach 2:
The capacitive feedback network serves multiple functions simultaneously: it provides voltage boosting, enables distortion suppression, and delivers power to the load in a single integrated stage. The same capacitors and switching elements that create the voltage multiplication effect also form the feedback loop for distortion correction, eliminating the need for separate dedicated components for each function and improving overall efficiency.
3Object-affected harmful factors
If LC filter is used to reduce EMI from rapid switching, then electromagnetic interference (EMI) is suppressed, but system cost and size increase
Solution Approach 1:
The patent extracts the EMI filtering function from the traditional separate LC filter component and integrates it into the capacitive feedback network itself. The feedback capacitors (C1-C4) and the inherent capacitance in the circuit serve as the filtering elements, eliminating the need for additional dedicated LC filter components. This integration reduces system size and cost while maintaining EMI suppression capability.
Solution Approach 2:
The capacitive feedback network performs multiple functions simultaneously: distortion suppression, voltage boosting, and EMI filtering. The same capacitors that provide the feedback path for distortion correction also serve as low-pass filtering elements that attenuate high-frequency switching noise and EMI. This multi-functionality eliminates the need for separate dedicated components for each function, reducing overall system complexity and cost.
4Power
If additional boost converter and LC components are added to achieve voltage boosting and EMI filtering, then output power and EMI performance improve, but system cost and bulk increase
Solution Approach 1:
The patent combines voltage boosting, EMI filtering, and distortion suppression functions into a single integrated capacitive feedback network. The capacitors C1-C4 and switching transistors Q1-Q4 work together to simultaneously achieve voltage multiplication, noise filtering, and distortion correction without requiring separate dedicated components for each function. This integration dramatically reduces system cost and bulk compared to using separate boost converter and LC filter modules.
Solution Approach 2:
The capacitive feedback architecture creates a multi-functional circuit block where the same components perform multiple roles: voltage boosting through capacitive multiplication, EMI filtering through low-pass characteristics, and distortion suppression through feedback. This universality eliminates the need for additional dedicated components and reduces overall system complexity and cost while achieving all desired performance improvements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves low THD, high SNR, and high output power with reduced EMI and system cost by using capacitive feedback and voltage boosting, eliminating the need for additional LC components and filters.
Implementation Method 1
a voltage boosting power stage with transistors, inductors, and capacitors to generate a boosted output signal
Implementation Method 2
utilizing input and feedback capacitors to set closed-loop gain
Implementation Method 3
filters the high-frequency components in the boosted output signal, wherein the voltage boosting power stage comprises a first transistor... an inductor... and a second capacitor
Data Source
AI summary
The present invention is a Class-D amplifier including: a capacitively-coupled amplifier, configured to receive an input signal and a feedback signal and generate an error signal; and a loop filter, coupled to input capacitor and the feedback capacitor, configured to generate a processed signal according to the error signal; and a pulse-width modulation (PWM) generator, coupled to the loop filter, configured to generate a plurality of PWM signals according to the processed signal and a control signal; and a voltage boosting power stage, coupled to the PWM generator, configured to generate a boosted output signal according to the plurality of PWM signals, the control signal and a power supply, and to feedback the boosted output signal to the loop filter, wherein the maximum voltage of the boosted output signal is greater than the voltage of the power supply.