Multi-Path Audio Driver Gain Calibration for Click-Free Switching
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Solution Overview
Problem
Existing audio amplifier systems, particularly those using single PWM amplifier circuits, experience perceptible audio artifacts such as 'pops' and 'clicks' when switching between open-loop and closed-loop operations, due to gain mismatches caused by changes in load transducer impedance and temperature effects.
Innovation Solution
A multi-path subsystem with a calibration engine that estimates and cancels DC offsets, phase differences, and gain variations between processing paths, ensuring equal gains for open-loop and closed-loop paths to minimize switching artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a single PWM amplifier circuit is used to drive loads in either open-loop or closed-loop mode, then power efficiency is improved, but perceptible audio artifacts occur when switching between modes
Solution Approach 1:
The system performs preliminary calibration of the open-loop path gain to match the closed-loop path gain before switching between modes. The calibration engine estimates the open-loop path gain using a test signal and adjusts the gain element to equalize the gains of both paths, preventing audio artifacts during mode transitions.
Solution Approach 2:
The system uses feedback through a mixed signal return path that captures the output signal and feeds it back to the calibration engine. This feedback mechanism enables the calibration engine to estimate the open-loop path gain and adjust the gain element accordingly, ensuring gain matching between open-loop and closed-loop paths.
2Object-generated harmful factors
If gain matching between open-loop and closed-loop paths is implemented, then audio artifact reduction is achieved, but system complexity increases
Solution Approach 1:
The calibration engine merges multiple calibration functions into a single integrated block. It simultaneously handles DC offset cancellation, phase difference compensation, return path gain estimation, and open-loop path gain calibration, reducing the need for separate calibration circuits and simplifying the overall system architecture.
Solution Approach 2:
The mixed signal return path serves multiple functions: it provides feedback for gain estimation, carries the output signal for calibration, and enables both open-loop and closed-loop operation modes. This multi-functional design reduces the need for separate dedicated circuits for each function.
Data Source
AI summary
A multi-path subsystem may include a first processing path, a second processing path, a mixed signal return path, and a calibration engine configured to: estimate and cancel a direct current (DC) offset of the mixed signal return path, estimate and cancel a DC offset between the first processing path and the second processing path, estimate and cancel a phase difference between the first processing path and a sum of the second processing path and the mixed signal return path, estimate and cancel a return path gain of the mixed signal return path, and track and correct for a gain difference between the first processing path and the second processing path.