Tri-Level PWM Audio Amplifier Without Low-Pass Filtering
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Solution Overview
Problem
Conventional audio amplifiers face challenges in balancing fidelity and power efficiency, particularly in handheld devices where low efficiency leads to limited battery life and cooling issues.
Innovation Solution
A filterless, DC-free amplifier design that generates tri-level output signals using pulse-width modulated (PWM) signals, integrating feedback and comparator signals to control a driver with transistors switching between positive, negative, and ground voltages, optimizing power usage without the need for low-pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a class AB amplifier is used to amplify audio signals, then fidelity is maintained, but power efficiency deteriorates leading to limited battery life and cooling issues
Solution Approach 1:
The patent employs pulse-width modulation (PWM) to convert the audio signal into periodic pulse trains where the duty cycle varies according to the audio signal amplitude. This periodic switching action allows the amplifier to operate in a highly efficient class-D mode while preserving the audio fidelity through proper pulse width control and reconstruction filtering.
Solution Approach 2:
The invention changes the operating parameters of the amplifier by transitioning from continuous analog amplification (class AB) to switched-mode PWM amplification (class D). This parameter change involves modulating the pulse width according to the audio signal and using high-frequency switching to achieve both high efficiency and high fidelity simultaneously.
2Use of energy by moving object
If conventional class D audio amplifier components are used, then power efficiency is improved, but device complexity increases due to required low-pass filtering and additional components
Solution Approach 1:
The patent extracts and eliminates the low-pass filter component from the traditional class-D amplifier architecture. By using a different modulation and reconstruction approach, the invention removes the need for complex filtering components while maintaining power efficiency and audio quality.
Solution Approach 2:
The invention integrates multiple functions into fewer components. The PWM modulator and output stage are designed to simultaneously achieve power efficiency, signal reconstruction, and filtering functions without requiring separate dedicated components for each function, thereby reducing overall device complexity.
3Measurement precision
If handheld portable devices use low efficiency amplifiers, then fidelity can be maintained, but battery life is limited and cooling capacity is insufficient
Solution Approach 1:
The PWM-based periodic switching allows the amplifier to spend most of its time in a high-efficiency off state, with brief on-states that deliver the required audio power. This dramatically reduces average power consumption and extends battery life while maintaining audio fidelity through proper pulse width control.
Solution Approach 2:
By changing from continuous analog operation to high-frequency pulsed operation, the amplifier achieves superior power efficiency. The parameter change in operating mode allows the device to maintain high fidelity output while consuming significantly less average power, thereby extending battery life in portable applications.
Data Source
AI summary
An amplifier generates a tri-level output signal in response to an input signal that is pulse-width modulated. The amplifier is filterless and DC free. A control block supplies a multitude of pulse-width modulated (PWM) signals in response to the received digital input signal. A pair of the PWM signals are applied to the signal generator which in response supplies a third signal to the integrator. The integrator integrates the third signal in accordance with a feedback signal.