Class-D PWM Clipping Detection Using Internal Clocked Signals
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Solution Overview
Problem
Class-D amplifiers suffer from signal clipping, which causes distortion and undue stress on speaker systems due to input signals exceeding their proper range, leading to inefficient operation and potential damage.
Innovation Solution
A clipping detection circuit using internal signals in the system, specifically utilizing edge-triggered flip-flops and EXCLUSIVE NOR circuits to generate a clipping indication signal based on PWM signals' states during oscillator clock cycles, effectively detecting signal clipping conditions without requiring additional circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a clipping detection circuit is added to detect signal clipping conditions, then signal clipping detection capability is improved, but device complexity increases
Solution Approach 1:
The clipping detection circuit uses existing internal signals (PWM signals and oscillator clock) already present in the class-D amplifier system. By utilizing these existing resources, the circuit achieves clipping detection functionality without requiring external or additional complex circuitry, thus improving detection capability while minimizing increase in device complexity
Solution Approach 2:
The detection circuit leverages the existing PWM signals that are already being generated for amplifier operation. These same PWM signals serve dual purposes: controlling the output transistors and providing the basis for clipping detection. This multi-functional use of existing signals improves detection capability without adding separate dedicated detection hardware
2Measurement precision
If additional circuitry is used for clipping detection, then clipping detection accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The circuit uses internally available signals (PWM outputs and oscillator clock) that are already part of the amplifier's normal operation. By making these existing signals serve the additional function of clipping detection, the invention avoids the need for external sensors or additional signal sources, thereby reducing manufacturing cost while maintaining detection accuracy
Solution Approach 2:
The clipping detection functionality is merged with the existing PWM signal generation and processing paths. The same comparators and signal paths used for amplifier control are also used for clipping detection, combining multiple functions into existing circuit blocks rather than adding separate dedicated circuits, thus reducing overall manufacturing cost
Data Source
AI summary
An integrated circuit (IC) chip has a class D PWM (pulse width modulation) amplifier configured for generating first and second PWM signals. The class-D PWM modulator includes a differential output driver configured for driving a first and a second output signals in response to the first and the second PWM signals. A clipping detection circuit is configured to turn on a clipping indication signal when one or both of the first PWM signal and the second PWM signal maintain the same state between two consecutive edges of the oscillator clock signal. The clipping detection circuit is also configured to turn off the clipping indication signal when both the first PWM signal and the second PWM signal change states between two consecutive edges of the oscillator clock signal.