Audio Amplifier Feedforward Compensation for Low-Distortion Loads
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Solution Overview
Problem
Conventional audio amplifiers face challenges in maintaining low distortion, especially when driving low impedance loads, which often requires increased power consumption and larger circuitry, making them inefficient for battery-powered devices.
Innovation Solution
An audio driving circuit with a forward signal path, an amplifier module, an error block, and processing modules that generate a compensation signal based on error signals to reduce distortion, using adaptive linear transfer functions and gain control to optimize performance without increasing power or size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the output stage quiescent current is increased to maintain low distortion into low impedance load, then distortion is reduced, but power consumption increases
Solution Approach 1:
The invention applies preliminary action by pre-processing the input signal with a distortion compensation circuit that anticipates and corrects for expected distortion before the signal reaches the power amplifier stage. This allows the amplifier to operate at lower quiescent current while still achieving low distortion output, because the compensation is applied in advance rather than requiring high current throughout the signal path.
Solution Approach 2:
The distortion compensation circuit acts as an intermediary between the input signal and the power amplifier. It processes the signal to pre-distort it in the opposite direction of the expected amplifier distortion, thereby canceling out the distortion effects at the output without requiring the power amplifier to operate at high current levels.
2Manufacturing precision
If larger output driving devices and higher current pre-driver stages are used to maintain low distortion, then distortion is reduced, but device complexity and size increase
Solution Approach 1:
The invention substitutes the mechanical/approach of using larger physical amplifier components with a signal processing approach. Instead of increasing the size of output driving devices and pre-driver stages, the system uses a distortion compensation circuit that processes signals electronically to achieve the same distortion reduction effect with smaller, less complex hardware.
3Manufacturing precision
If multiple amplifier stages with high open-loop gain are used to suppress output distortion, then distortion is reduced, but power consumption and circuit complexity increase
Solution Approach 1:
The invention extracts the distortion compensation function from the main amplifier signal path and places it in a separate parallel compensation path. This allows distortion correction to be achieved without requiring multiple high-gain amplifier stages in the main signal path, thereby reducing the complexity and power consumption of the amplifier while maintaining low distortion performance.
Data Source
AI summary
This application relates to audio driving circuits having good audio performance. The circuit (301) has a forward signal path between an input (103) for receiving an input audio signal (SIN) and an output (104) for outputting an output signal (SOUT) with an amplifier module (102) in the forward signal path. An error block (302) is arranged to receive a first signal (SFF) derived from the input signal and also a second signal (SFB) derived from the output signal and determine a first error signal (ε1) indicative of a difference between the first and second signals. A first processing module (204) is operable to generate a compensation signal (SC) to be applied to the input signal (SIN) upstream of the amplifier module (102) based on the first error signal. The error block (302) comprises a second processing module (303/303a) configured to apply a linear transfer function to one of the first signal or the second signals prior to determining the first error signal. In some embodiments the second processing module may apply a linear transfer function which is adaptive based on a second error signal (ε2) indicative of the error between the first and second signals after the linear transfer function has been applied.