Variable Common Mode Voltage Buffer for Switched Mode Audio Amplifiers
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Solution Overview
Problem
Existing approaches to driving audio output signals to audio transducers in personal devices, such as wireless telephones and media players, face challenges in efficiently managing load voltages and minimizing non-linearities, particularly at low signal magnitudes where the switched mode amplifier's saturation limit restricts the output.
Innovation Solution
A switched mode amplifier system that combines a power converter with a power inductor and multiple switches, controlled by a controller, and a linear amplifier to generate load voltages, ensuring energy is predominantly supplied by the power converter. This system includes a loop filter to manage input and feedback signals, and an output stage with a linear amplifier to maintain linearity and allow the audio output signal to cross zero, using various converter types like boost, buck, and buck-boost configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a switched mode amplifier is used to drive audio transducers, then energy efficiency is improved, but non-linearities increase particularly at low signal magnitudes
Solution Approach 1:
The output stage is segmented into multiple independent push-pull amplifier channels, each capable of independently driving different portions of the load. This segmentation allows each channel to operate within its linear range while collectively providing efficient switched mode operation across the full output range.
Solution Approach 2:
The system dynamically switches between different operating modes and configurations based on signal conditions. The variable common mode voltage buffer dynamically adjusts voltage levels to maintain linearity across varying signal magnitudes, and the push-pull channels are dynamically activated based on signal polarity and amplitude.
2Device complexity
If the common mode voltage is fixed, then circuit simplicity is improved, but the ability to maintain linearity across varying signal magnitudes deteriorates
Solution Approach 1:
The common mode voltage buffer transitions from a fixed voltage source to a dynamic voltage source that adjusts its output based on signal conditions. This dynamic adjustment maintains the differential operation of the push-pull channels while accommodating varying signal magnitudes, preserving linearity without requiring overly complex circuitry.
Solution Approach 2:
The variable common mode voltage buffer acts as an intermediary between the power converter and the push-pull output channels. It mediates the voltage levels to ensure that the differential amplifiers operate correctly across the full range of signal magnitudes, maintaining linearity while simplifying the overall control architecture.
3Use of energy by moving object
If the saturation limit of the amplifier is low, then power consumption is reduced, but the output signal range is restricted
Solution Approach 1:
The system dynamically adjusts the operating point and voltage levels based on signal demands. When high output range is needed, the variable common mode voltage buffer raises the operating point to allow larger signal excursions. When signal levels are low, the system operates at lower power consumption levels, effectively managing the trade-off between power and output range.
Solution Approach 2:
The system changes key operating parameters including common mode voltage level and channel activation states based on signal conditions. This allows the amplifier to adapt its power consumption and output range dynamically, providing high output range when needed while maintaining low power consumption during normal operation.
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 reduces non-linearities and allows the audio output signal to approach zero, enhancing the efficiency and linearity of audio output by controlling the power converter and linear amplifier to manage voltages within the saturation limits, thereby improving the driving of audio transducers.
Implementation Method 1
a power converter including a power inductor and a first plurality of switches
Data Source
AI summary
A switching power stage for producing a load voltage at a load output of the switching power stage, wherein the load output comprises a first load terminal having a first load voltage and a second load terminal having a second load voltage such that the load voltage comprises a difference between the first and the second load voltages, that may include: a power converter comprising a power inductor and a plurality of switches, wherein the power converter is configured to drive a power converter output terminal; a linear amplifier configured to drive a linear amplifier output terminal; and a controller for controlling the plurality of switches and the linear amplifier in order to generate the load voltage as a function of an input signal to the controller such that energy delivered to the load output is supplied predominantly by the power converter.