Amplifying Circuit With Common-Mode Hold to Reduce EMI
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Solution Overview
Problem
Class-AB amplifiers in battery-powered devices like wireless earphones and headphones are inefficient, producing more heat and consuming more power, while Class-D amplifiers introduce electromagnetic interference (EMI) due to common mode voltage fluctuations, affecting audio quality.
Innovation Solution
An amplifying circuit with a first and second power stage circuit, a current path switch, and a voltage supply circuit that maintains a uniform common mode voltage by supplying it when the power stage circuits are off, reducing EMI and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Class-D amplifiers are used to improve power efficiency, then power consumption is reduced, but electromagnetic interference occurs due to common mode voltage fluctuations
Solution Approach 1:
The voltage supply circuit proactively supplies common mode voltage to the output nodes before and during the switching transitions of the power stage circuits. This preliminary action ensures that the output nodes are already at the appropriate voltage level when switching occurs, preventing voltage fluctuations and EMI generation while maintaining the high efficiency of Class-D operation
Solution Approach 2:
The voltage supply circuit acts as an intermediary between the power stage circuits and the output nodes. It mediates the voltage transitions by supplying common mode voltage during switching events, isolating the output from the harmful voltage fluctuations caused by the switching action while preserving the efficiency benefits
2Object-affected harmful factors
If Class-AB amplifiers are used to improve audio quality, then sound quality is enhanced, but power consumption increases and heat generation occurs
Solution Approach 1:
The amplifier is segmented into two distinct operational modes: Class-D switching operation for normal signal amplification (providing high efficiency), and Class-AB linear operation during switching transitions (providing clean voltage transitions without EMI). This segmentation allows each mode to excel at its specific function while avoiding their respective weaknesses
Solution Approach 2:
The amplifier periodically switches between Class-D and Class-AB modes during operation. The Class-AB mode is activated periodically during switching transitions to suppress EMI, while Class-D mode operates during normal signal amplification. This periodic switching allows the system to achieve both high efficiency and high audio quality
Data Source
AI summary
An amplifying circuit, which includes a first power stage circuit that outputs a first output signal to a first node based on a pull-up or a pull-down, a second power stage circuit that outputs a second output signal to a second node based on the pull-up or the pull-down, a current path switch connected to the first node and the second node, and that is turned on when the first power stage circuit and the second power stage circuit are turned off, and a voltage supply circuit that supplies a common mode voltage for the first output signal and the second output signal to the first node and the second node when the first power stage circuit and the second power stage circuit are turned off.