Class D Amplifier Pulse Blanking for Low-Power Switching Losses
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Solution Overview
Problem
Class D amplifiers experience significant switching losses at low power levels due to inherent capacitances of power transistors, especially during idle channels in audio applications, leading to inefficiency and degradation of out-of-band and in-band noise performance.
Innovation Solution
A circuit that includes a comparator to generate a pulse width modulated output signal and a pulse blanking circuit to prevent pulses narrower than a threshold from being passed to the driver, effectively turning off the amplifier at low error signal levels and mitigating inefficiency by only allowing pulses wider than the threshold to drive the power transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If Class D amplifier operates at low power levels, then audio signal amplification is provided, but switching losses increase due to inherent capacitances of power transistors
Solution Approach 1:
The pulse blanking circuit extracts and removes narrow pulses from the PWM signal that correspond to low power levels. By filtering out these narrow pulses through comparison with a threshold signal, the circuit prevents the amplifier from operating in the inefficient low-power region where switching losses dominate, thereby extracting the harmful operating condition and eliminating it.
Solution Approach 2:
The invention changes the operational parameter of the amplifier by introducing a minimum pulse width threshold. Pulses narrower than this threshold are blanked out, effectively changing the amplifier's operating characteristics to avoid the inefficient low-power region. This parameter-based filtering transforms the continuous PWM signal into a pulsed signal with minimum width constraints, reducing switching losses.
2Productivity
If Class D amplifier operates during idle channels, then no audio signal is amplified, but switching losses remain significant due to continuous switching
Solution Approach 1:
The pulse blanking circuit introduces periodic gating action to the PWM signal. During idle channels, the circuit periodically blocks narrow pulses that would otherwise cause continuous switching of power transistors. This periodic blanking action eliminates unnecessary switching during idle periods while maintaining amplification functionality when needed, thereby improving overall productivity and reducing energy losses.
3Ease of operation
If narrow pulses are passed to driver, then amplifier responds to low input signals, but switching losses increase and noise performance degrades
Solution Approach 1:
The pulse blanking circuit acts as an intermediary between the PWM signal generator and the driver stage. It mediates the signal transmission by selectively blocking narrow pulses that would cause noise degradation and switching losses, while allowing wider pulses to pass through. This intermediary function filters out harmful signal components without affecting the overall responsiveness of the amplifier to valid audio signals.
Data Source
AI summary
A circuit includes a comparator to compare an analog signal to a ramp signal to generate a pulse width modulated output signal and a driver to generate control signals for a plurality of power transistors. A pulse blanking circuit receives the pulse width modulated output signal. For each pulse of the pulse width modulated output signal, the pulse blanking circuit, responsive to a width of the pulse being greater than a threshold, passes the pulse to the driver. Responsive to the width of the pulse being less than the threshold, the pulse blanking circuit prevents the pulse from being passed to the driver.