Audio Preamplifier Circuit With Distortion Compensation for Wide Dynamic Range
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Solution Overview
Problem
Audio amplification circuits for portable devices face challenges in handling audio signals with large dynamic ranges without excessive distortion or noise, particularly at low DC power supply voltages, which limits their ability to handle high sound pressure levels from sources like miniature microphones.
Innovation Solution
An audio amplification circuit with a dual-preamplifier structure and a distortion compensation network that uses an attenuator and non-linear elements to manage signal levels, providing separate amplification paths for low and high signal levels and compensating for distortion caused by non-linear elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single preamplifier is used to handle large dynamic range audio signals, then the circuit complexity is low, but distortion occurs at high signal levels and noise increases at low signal levels
Solution Approach 1:
The audio signal path is segmented into two separate preamplifier circuits: a first preamplifier for low-level signals and a second preamplifier for high-level signals. This segmentation allows each preamplifier to be optimized for its specific signal level range, preventing distortion at high levels while maintaining low noise at low levels, thereby resolving the contradiction between circuit simplicity and audio quality.
2Use of energy by moving object
If the DC power supply voltage is reduced to meet portable device constraints, then power consumption decreases, but the ability to handle high sound pressure levels without distortion deteriorates
Solution Approach 1:
By segmenting the signal path into two preamplifiers with different gain levels, the system can handle high sound pressure levels (110-130 dB SPL) without requiring high DC supply voltage. The second preamplifier with lower gain handles large signals directly from the microphone, preventing overload and distortion even when the DC supply voltage is reduced to 1.5V or 2V, thus maintaining audio quality while reducing power consumption.
Solution Approach 2:
The system changes the operating parameters of the preamplifiers by implementing different gain settings tailored to specific signal levels. The first preamplifier operates with high gain for low-level signals, while the second operates with low gain for high-level signals. This parameter differentiation enables the circuit to maintain linear operation and audio quality across the entire dynamic range despite reduced DC power supply voltage.
3Reliability
If a non-linear element is added to protect the preamplifier input, then distortion at large signal levels is reduced, but additional distortion is introduced at the preamplifier input
Solution Approach 1:
An attenuator is introduced as an intermediary component between the microphone input and the second preamplifier. This attenuator reduces the amplitude of large input signals before they reach the preamplifier, preventing overload and distortion without requiring aggressive non-linear protection elements that would introduce their own distortion. The attenuator acts as a gentle mediator that protects the circuit while maintaining signal fidelity.
Solution Approach 2:
A distortion compensation network is implemented that uses feedback to detect and correct distortion introduced by non-linear protection elements. The network monitors the output signal for distortion components and generates compensating signals that are fed back to cancel the distortion, thereby maintaining high audio quality even when protection elements are present in the signal path.
4Manufacturing precision
If the gain of the preamplifier is increased to amplify weak signals, then noise performance at low levels improves, but the maximum handleable signal level before distortion decreases
Solution Approach 1:
The solution segments the amplification function into two separate preamplifiers with different gain characteristics. The first preamplifier provides high gain for weak signals, achieving excellent noise performance for low-level inputs. The second preamplifier provides low gain for strong signals, maintaining the ability to handle high sound pressure levels without distortion. This segmentation resolves the contradiction by assigning different gain roles to different circuit blocks.
Data Source
AI summary
The present invention relates to an audio amplification circuit comprising a first preamplifier for receipt of an audio input signal and a second preamplifier comprising a first differential input for receipt of an attenuated audio input signal. The attenuated audio input signal is generated by an attenuator coupled to the audio input signal. A non-linear element is coupled to a first input of the first preamplifier thereby distorting the audio input signal at the first input at large signal levels. A distortion compensation network is adapted to supply a distortion compensation signal from the first input of the first preamplifier to a second differential input of the second preamplifier such that distortion in the output signal of the second preamplifier is cancelled or attenuated. The invention further relates to a corresponding method of compensating an audio amplification circuit for distortion induced by a non-linear element.