Closed-Loop Class-D Amplifier With Fixed-Frequency EMI Control
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Solution Overview
Problem
Class-D power amplifiers face challenges with electromagnetic interference (EMI) due to varying switching frequencies, which can disrupt audio signals and reduce sensitivity, particularly in vehicle electronics, where a fixed-frequency operation is desirable to mitigate these issues.
Innovation Solution
A close-loop Class-D power amplifier with a fixed-frequency control method using a comparator and a high-frequency triangular or rectangular wave generator, where the feedback signal is subtracted from the input signal to maintain a stable frequency, reducing EMI and simplifying the control circuit structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If adaptive modulation technology is used to simplify control circuit structure, then device complexity is reduced, but switching frequency varies heavily causing EMI problems
Solution Approach 1:
The patent applies periodic action by using a fixed-frequency triangular wave generator to generate a carrier signal with constant frequency. This periodic carrier wave is used in the PWM modulation process, ensuring that the switching frequency remains stable throughout operation. The fixed periodic nature of the carrier wave prevents the frequency variation that causes EMI in adaptive modulation schemes.
2Object-affected harmful factors
If fixed-frequency operation is implemented to reduce EMI, then electromagnetic interference is reduced, but control circuit complexity increases
Solution Approach 1:
The patent merges the frequency determination function into the PWM controller itself by integrating a fixed-frequency triangular wave generator within the controller. This consolidation eliminates the need for external frequency control circuits while maintaining stable switching frequency. The controller internally generates both the PWM signal and the fixed-frequency carrier, simplifying the overall control circuit structure.
3Reliability
If conventional close-loop feedback control methods are used to improve audio performance, then audio signal quality is improved, but circuit structure becomes complicated and cost increases
Solution Approach 1:
The patent implements feedback by feeding back a portion of the output signal to the inverting input terminal of the comparator. This negative feedback mechanism allows the circuit to automatically adjust and maintain accurate audio signal reproduction without requiring complex external feedback components. The feedback loop ensures high audio signal quality while keeping the circuit structure simple and integrated within the PWM controller.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves stable frequency operation, reducing EMI and improving audio performance by maintaining a fixed switching frequency, thus enhancing the reliability of audio signals in applications prone to interference.
Implementation Method 1
said comparator receives said input signal and the high-frequency triangular wave generated by said triangular wave generator or the high-frequency rectangular wave generated by said rectangular wave generator, and then outputs a first signal
Implementation Method 2
a filter coupled to the output node of said output stages for filtering said second signal to get an output signal
Implementation Method 3
a feedback circuit, coupled between the output node of said output stage and the input node of said input stage, shapes said second signal to get a feedback signal which is negatively feedback to said input stage, so as to subtract said feedback signal from said input signal
Implementation Method 4
said input stage comprises a comparator and a triangular wave generator or a rectangular wave generator, said comparator receives said input signal and the high-frequency triangular wave generated by said triangular wave generator
Data Source
AI summary
The present invention discloses a Class-D power amplifier and control method thereof. In one embodiment, the amplifier feeds back the signal at the output node to the inverting input of the comparator, and provides a high frequency triangular wave signal to the non-inverting input of the comparator. In addition, the non-inverting input of the comparator may be coupled to an offset voltage, while the inverting input of the comparator may be coupled to a fixed-frequency rectangular wave signal, a feedback signal which is derived from the output stage and an input signal. In use, the switching frequency may be at least substantially fixed, so as to reduce the influence on the system caused by electromagnetic interruption (EMI). Further, the control circuit is simple, and some devices can be integrated.