Amplifier PWM Pulse Width Control for Low-THDN Peak Power
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Solution Overview
Problem
Conventional Class-D amplifiers experience total harmonic distortion plus noise (THDN) degradation due to narrow pulse widths, particularly at high and low audio input levels, leading to inefficiencies in power delivery.
Innovation Solution
Implementing high- and low-side detection circuits to adjust pulse widths based on gate-to-source voltage thresholds, ensuring each pulse width is sufficient to complete output transitions, thereby maintaining distortion-free peak power delivery across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If narrow pulse widths are used in the output stage, then power delivery efficiency is improved, but total harmonic distortion plus noise (THDN) degradation occurs
Solution Approach 1:
The patent implements dynamic pulse width adjustment based on real-time detection of transistor switching states. The system adapts pulse widths according to operating conditions (high audio input near supply saturation or idle channel low audio amplitude) rather than using fixed minimum pulse widths, allowing optimal balance between power efficiency and signal fidelity across different operating scenarios
Solution Approach 2:
The patent employs feedback circuits that monitor the actual switching behavior of high-side and low-side transistors. By detecting when transistors fail to switch properly (indicated by inadequate gate-to-source voltage), the system adjusts subsequent pulse widths to ensure complete switching transitions, thereby preventing THDN degradation while maintaining maximum power delivery capability
2Reliability
If minimum pulse width generator is added downstream of modulation block, then pulse width control is improved, but device complexity increases
Solution Approach 1:
The patent introduces detection circuits as intermediary components between the modulation block and output stage. These circuits monitor transistor gate voltages and provide feedback signals that trigger adaptive pulse width adjustment, serving as a mediator that enables intelligent control without requiring a complex dedicated minimum pulse width generator downstream
Solution Approach 2:
The system enables the output stage to self-regulate pulse widths by detecting its own switching conditions. The detection circuits monitor the actual transistor behavior and automatically adjust pulse widths when switching failures are detected, allowing the system to self-correct without external intervention or complex additional control circuitry
Data Source
AI summary
Examples of amplifiers and components thereof are configured to adjust the OFF-pulse widths of a high-duty cycle pulse width modulated (PWM) output signal and the ON-pulse widths of a low-duty cycle PWM output signal. Such control is carried out using high- and low-side (HS and LS) detectors. The HS detector coupled to the control terminal of an HS transistor detects when the gate-to-source voltage (Vgs) of the HS transistor drops below a threshold and outputs an HS detection signal to adjust the OFF-pulse widths of the high-duty cycle PWM output signal. An LS detector coupled to the control terminal of an LS transistor detects when the Vgs of the LS transistor drops below the threshold and outputs a LS detection signal to adjust the ON-pulse widths of the low-duty cycle PWM output signal.