Closed-Loop Class-D Amplifier With Fixed Switching Frequency
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Solution Overview
Problem
Class-D power amplifiers face issues with electromagnetic interference (EMI) due to varying switching frequencies, which can affect audio performance and sensitivity, particularly in applications like vehicle electronics and audio broadcasting.
Innovation Solution
A close-loop Class-D power amplifier with a fixed-frequency control method that uses a comparator with a small hysteresis loop, coupled with a high-frequency triangular or rectangular wave, and a feedback circuit to maintain a stable switching frequency, reducing EMI and improving system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog adaptive modulation (AAM) technology is used to simplify the control circuit structure, then device complexity is reduced, but switching frequency varies heavily causing electromagnetic interference (EMI)
Solution Approach 1:
The patent implements a feedback mechanism where the output signal is fed back to the input stage through a feedback circuit. This feedback loop enables automatic regulation of the switching frequency to maintain it at a fixed value, thereby resolving the EMI issue caused by frequency variation while keeping the control circuit relatively simple
Solution Approach 2:
The patent changes the switching frequency parameter from variable (in AAM) to fixed by introducing a frequency stabilization mechanism. The feedback circuit detects output variations and adjusts the switching frequency accordingly to maintain it constant, thus eliminating EMI problems associated with frequency modulation
2Measurement precision
If conventional close-loop feedback control methods (instantaneous voltage mode or voltage-current double feedback loops) are used, then control precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses a simplified feedback approach where only the output voltage is fed back to the input stage through a single feedback circuit, avoiding the complexity of dual feedback loops or instantaneous voltage mode control while still achieving effective closed-loop control and acceptable precision
Solution Approach 2:
The patent extracts only the essential feedback function needed for stable operation, removing unnecessary complex control circuits. By implementing a single feedback path rather than multiple interconnected feedback loops, the design achieves adequate control precision with significantly reduced complexity
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 effectively minimizes EMI by maintaining a fixed switching frequency, enhancing audio performance and reliability in various electronic applications while simplifying the control circuit structure and reducing costs.
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 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
Implementation Method 3
The SW signal at the output node C is restored to an amplified audio signal through a filter circuit composed of the inductor L and capacitor C1
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.