Multi-Level Signal Amplifier Modulation for Boundary-Free Audio Output
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Solution Overview
Problem
Multi-level Class D amplifiers face challenges in maintaining audio fidelity as the audio output crosses supply level boundaries, leading to audio artifacts due to full modulation requirements.
Innovation Solution
A signal amplifier design incorporating a modulator circuit that generates logic signals by comparing the input signal with triangular waveforms, a power converter providing multiple voltage levels, and an H-bridge circuit using primary and secondary modulation based on the logic states of the generated signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a switched-capacitor structure is used to multiply or divide supply voltage with discrete levels, then the amplifier can operate at multiple voltage levels to improve efficiency, but the fidelity deteriorates when the audio output continuously crosses supply level boundaries
Solution Approach 1:
The patent implements dynamic supply voltage selection where the amplifier continuously adjusts its supply voltage level based on the instantaneous amplitude of the audio signal. Instead of fixed discrete levels that cause fidelity issues during transitions, the system dynamically switches between supply levels (VDD, VDD/2, VDD/4, etc.) to match the signal envelope, maintaining both efficiency and fidelity throughout the audio range
Solution Approach 2:
The envelope detector circuit performs preliminary detection of the audio signal amplitude to predict when the signal will cross supply level boundaries. This allows the supply voltage switching to be anticipatory rather than reactive, ensuring smooth transitions without audio artifacts by preparing the next supply level before the crossover point is reached
2Use of energy by moving object
If full supply range is used with 100% modulation to achieve maximum output, then the power efficiency improves, but audio artifacts are generated
Solution Approach 1:
The patent changes the modulation parameter from fixed 100% duty cycle to variable duty cycle that adapts to the audio signal characteristics. The modulator adjusts the PWM duty cycle dynamically based on the instantaneous signal amplitude and the selected supply voltage level, achieving full power efficiency only when needed while maintaining audio quality by reducing modulation depth during low-amplitude passages
Solution Approach 2:
The system implements dynamic modulation depth control where the PWM modulation index varies with the audio signal envelope and supply voltage level. Instead of constant full modulation, the system optimizes modulation depth in real-time to achieve maximum efficiency at high output levels while minimizing artifacts at lower levels, maintaining both efficiency and audio quality across the full operating range
Data Source
AI summary
A signal amplifier includes a modulator circuit, a power converter and a H-bridge circuit. The modulator circuit generates a first logic signal by comparing an input signal with a first waveform and generates a second logic signal by comparing the input signal with a second waveform. The power converter provides a first voltage and a second voltage. The H-bridge circuit has a first input terminal to receive the first voltage, a second input terminal to receive the second voltage and a pair of output terminals for providing an output modulated voltage to a load. The H-bridge circuit generates the output modulated voltage using a primary modulation when the second logic signal is in a first logic state and using a secondary modulation when the second logic signal is in a second logic state.