Audio Signal Offset Processing for Low-Distortion Class C Amplifiers
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Solution Overview
Problem
Existing audio amplifiers, particularly class A and class C amplifiers, suffer from high distortion and inefficiency when amplifying audio signals, limiting their use in audio applications due to unacceptable audio quality and high power consumption.
Innovation Solution
An audio processor is introduced that processes audio signals by determining a time-varying offset, combining it with the audio signal, and clipping the resulting signal to remove negative values, allowing the signal to be amplified by a class C amplifier with reduced distortion and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a class C amplifier is used to reduce power consumption, then energy efficiency is improved, but audio distortion increases to unacceptable levels
Solution Approach 1:
The audio processor performs preliminary processing of the audio signal before it reaches the class C amplifier. It determines a time-varying offset from the audio signal, combines this offset with the original signal, and clips the result to ensure only positive values are passed to the amplifier. This preliminary preparation allows the class C amplifier to operate without introducing unacceptable distortion while maintaining its energy efficiency advantages.
Solution Approach 2:
The audio processor acts as an intermediary between the audio source and the class C amplifier. It processes the audio signal by adding a time-varying offset and clipping negative values, thereby preparing the signal in a form that the class C amplifier can handle effectively. This intermediary processing resolves the contradiction by enabling the amplifier to operate efficiently while maintaining audio quality.
2Reliability
If a class A amplifier is used to maintain low distortion, then audio quality is improved, but power consumption increases significantly
Solution Approach 1:
The audio processor performs preliminary clipping of the audio signal to remove negative values before amplification. By ensuring the signal contains only positive values, the system can use a class C amplifier instead of a class A amplifier, achieving low distortion without the continuous high power consumption inherent to class A operation.
Solution Approach 2:
The system changes the parameter of the audio signal by adding a time-varying offset and clipping negative values to zero. This parameter transformation allows the use of class C amplifier operation mode, which consumes significantly less power than class A while maintaining acceptable audio quality through the processed signal format.
3Device complexity
If a single transistor class D amplifier with PWM is used to simplify the amplifier structure, then device complexity is reduced, but distortion occurs when the PWM duty cycle is 50% corresponding to zero audio signal
Solution Approach 1:
The audio processor performs preliminary clipping to eliminate negative values from the audio signal before it reaches the class D amplifier. By ensuring the input signal contains only positive values, the PWM duty cycle will not be 50% during normal operation, thereby preventing the distortion that occurs at the 50% duty cycle point while maintaining the simplicity of the single-transistor amplifier structure.
Data Source
AI summary
An audio processor and method of audio processing for an amplifier system is described. The audio processor may receive an audio signal and adapt the audio signal generating a time varying offset. The time varying offset may be combined with the audio signal resulting in a shifted the audio signal level. The processed audio signal may also be clipped to remove the negative samples values. The processed signal may be used to drive an amplifier designed to only accept positive (or negative) signals such as a class C amplifier.