Three-Level Current-Mode Amplifier Calibration for Low-Distortion Audio
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Solution Overview
Problem
Current audio amplifiers face challenges in balancing fidelity and power efficiency, particularly in handheld devices where class AB amplifiers are inefficient and class D amplifiers suffer from thermal noise and distortion issues.
Innovation Solution
A current-mode three-level digital amplifier design featuring adjustable current sources and switches, with calibration mechanisms to match current sources and reduce mismatches, allowing for efficient amplification while minimizing noise and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If class AB amplifier is used, then fidelity is improved, but power efficiency deteriorates
Solution Approach 1:
The amplifier is segmented into multiple current sources (first fixed current source, second fixed current source, first adjustable current source) that can be independently controlled and switched. This segmentation allows the system to operate in different modes (class AB, class D, calibration) by selectively enabling or disabling specific current sources, thereby achieving both high fidelity when needed and power efficiency during normal operation.
Solution Approach 2:
The amplifier employs dynamic switching between different operating modes through control circuits that adjust the current sources in real-time. The first adjustable current source can be dynamically calibrated to match the fixed current sources, and the system can transition between class AB and class D operation based on signal requirements, optimizing both fidelity and power efficiency adaptively.
2Use of energy by moving object
If class D amplifier is used, then power efficiency is improved, but fidelity deteriorates due to thermal noise and distortion
Solution Approach 1:
The system performs preliminary calibration of the first adjustable current source to match the fixed current sources before normal operation. This preliminary action ensures that when class D operation is used, the current matching is optimized in advance, reducing distortion and thermal noise effects while maintaining power efficiency benefits.
Solution Approach 2:
The amplifier incorporates feedback mechanisms where the output is monitored and used to adjust the current sources. During class D operation, feedback helps compensate for thermal noise and distortion by dynamically adjusting the adjustable current source to maintain signal fidelity while preserving power efficiency advantages.
3Device complexity
If current sources are not matched, then device complexity is reduced, but fidelity deteriorates due to mismatches
Solution Approach 1:
The amplifier employs self-calibration capabilities where the first adjustable current source automatically adjusts its output to match the fixed current sources through built-in calibration circuits. This self-service mechanism eliminates the need for external complex matching networks or manual calibration procedures, maintaining low device complexity while achieving high fidelity through automatic current matching.
Data Source
AI summary
Apparatus having corresponding methods comprise: a first fixed current source to produce a first fixed current; a second fixed current source to produce a second fixed current; a first adjustable current source to produce a first adjustable current; a first switch to deliver the first fixed current and the first adjustable current to a first output node when the first switch is closed; a second switch to deliver the second fixed current to the first output node when the second switch is closed; and an adjustment circuit to adjust the first adjustable current according to the first fixed current, the second fixed current, and the adjustable current.