Amplitude-Selective Predistortion for Low-Power Audio Amplifiers
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Solution Overview
Problem
Audio and haptic power output systems with open-loop driver stages suffer from significant signal distortion due to non-linear behavior, leading to power consumption and die area penalties in existing pre-distortion solutions.
Innovation Solution
An amplifier system with a processing block that applies pre-distortion to input signals only when the signal level exceeds a threshold amplitude, using a pre-distortion circuit to generate the output signal, and disabling the pre-distortion when the signal level is below the threshold to conserve power, while calibrating coefficients to optimize distortion reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-distortion is applied to reduce output signal distortion in open-loop driver stages, then distortion is reduced, but power consumption increases
Solution Approach 1:
The pre-distortion circuit is implemented with dynamic control that enables or disables the pre-distortion function based on signal amplitude conditions. The circuit transitions between different operational states (enabled/disabled) depending on whether the input signal exceeds a threshold amplitude, allowing the system to adapt power consumption to actual distortion needs.
Solution Approach 2:
The system changes the operational parameter of the pre-distortion circuit based on signal amplitude. When the input signal amplitude exceeds a predetermined threshold, pre-distortion is enabled; when it falls below the threshold, pre-distortion is disabled. This parameter-based control optimizes the trade-off between distortion reduction and power consumption.
2Manufacturing precision
If pre-distortion is applied to reduce output signal distortion in open-loop driver stages, then distortion is reduced, but die area increases
Solution Approach 1:
The pre-distortion circuit utilizes dynamic enabling and disabling based on signal conditions, allowing the same hardware circuit to serve multiple operational requirements. By controlling the circuit's operational state rather than always activating it, the system achieves distortion reduction when needed while minimizing the effective use of die area resources.
Solution Approach 2:
The pre-distortion circuit is designed to serve multiple functions: it provides distortion correction when signal amplitude requires it, and can be disabled to conserve resources when distortion is not an issue. This multi-functionality allows a single circuit implementation to address both distortion reduction and resource optimization goals.
3Stability of the object's composition
If pre-distortion circuit is always enabled to maintain linearity, then linearity is maintained, but power consumption increases
Solution Approach 1:
The system dynamically adjusts the linearity maintenance strategy based on signal amplitude. For large signal swings where non-linear behavior occurs, pre-distortion is enabled to maintain linearity. For small signal swings where non-linear effects are negligible, pre-distortion is disabled to conserve power, accepting that linearity maintenance is not critical in this regime.
Solution Approach 2:
The operational state of the pre-distortion circuit is changed based on the parameter of signal amplitude. The system monitors signal amplitude and adjusts the pre-distortion enable/disable state accordingly, changing the linearity enforcement parameter to optimize the balance between linearity maintenance and power consumption.
Data Source
AI summary
An amplification system with an output driver stage for providing an output signal to acoustic output transducers such as speakers or haptic output devices removes signal distortion caused by output stage non-linearities by pre-distorting an input signal. The system includes the output driver stage, an input stage for receiving the input signal, and a processing block that receives the input signal and provides an output signal to the output driver stage. The processing block includes a pre-distortion circuit that applies a pre-distortion function to the input signal to generate the output signal if a signal level of the input signal is greater than a threshold amplitude, and if the signal level is less than or equal to the threshold amplitude, generates the output signal from the input signal by bypassing the pre-distortion circuit.