Audio Amplifier Offset Correction Using Digital-Analog Transition Comparison
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Solution Overview
Problem
Audio amplifiers face challenges in reducing offset between digital audio inputs and analog outputs, leading to power wastage, reduced dynamic range, and pops during gain changes, especially in battery-operated devices where small offsets can significantly impact energy consumption.
Innovation Solution
An audio output monitor compares transitions in the analog output with digital values to correct DC offset, using a servo control loop and filtering to minimize errors, and a chopped comparator to further reduce measurement errors, effectively eliminating offset and conserving battery energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If switched resistor networks are used to control gain in audio amplifiers, then gain selection resolution and accuracy are improved, but resistor area becomes too large due to necessary offset allowance
Solution Approach 1:
The patent extracts the offset component from the audio signal by comparing the digital input with the analog output and identifying the offset portion, then removes this extracted offset from the output signal, allowing smaller resistors to be used while maintaining precision
Solution Approach 2:
The patent implements a feedback mechanism where the analog output is monitored and compared with the digital input, and the detected offset is fed back to be subtracted from the output, enabling precise gain control with smaller resistors
2Reliability
If DC offset is present at analog audio output, then circuit operation is maintained, but power consumption increases and dynamic range is reduced
Solution Approach 1:
The patent converts the harmful DC offset into a measurable signal by comparing digital transitions with analog output transitions, then uses this information to actively remove the offset, transforming a power-wasting condition into a controllable parameter that can be eliminated
3Reliability
If DC offset is present at analog audio output, then amplifier operation is maintained, but dynamic range is reduced
Solution Approach 1:
The patent extracts the DC offset component from the audio signal through comparison of digital input transitions with analog output transitions, then removes this extracted offset, thereby restoring the full dynamic range while maintaining amplifier operation
4Ease of operation
If gain of audio amplifier is changed, then audio level control is improved, but pops are generated at output
Solution Approach 1:
The patent implements feedback monitoring of the analog output during gain changes, detects transitions that indicate pops, and uses this information to control the output or prevent the pops from occurring, enabling smooth gain adjustment without audible artifacts
Data Source
AI summary
An offset correction circuit removes DC offset from an analog audio output signal by comparing transitions of digital audio values to which the analog output signal is related to the output of a monitor that monitors the analog output signal. The monitor may be a zero-crossing detector and the transitions of the digital signal that are compared may be transitions of the most-significant bit (MSB) of the digital audio values. A filtering algorithm or filter circuit may be used to average a result of the comparison of the transitions, so that the offset is slowly and accurately removed. A chopped or autozero comparator may be used to further reduce error in the offset determination.