Differential Amplifier Calibration for Offset and Drift Control
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Solution Overview
Problem
Differential amplifiers in audio signal processing, such as those used in MEMS microphones, suffer from time-invariant offset and time-variant drift errors, leading to undesired common mode output voltage deviations from the desired level, which reduces the dynamic range and can result in signal clipping or saturation.
Innovation Solution
A differential amplifier circuit arrangement with a first feedback path for calibrating time-invariant offset errors and a second feedback path for calibrating time-variant drift errors, utilizing a comparator, counters, digital-to-analog converters, and an average filter to adjust the common mode output voltage, along with a multiplexer to combine these paths, allowing for digital correction of the analog signal at the input side of the amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional trimming processes are used to calibrate the amplifier, then manufacturing precision is improved, but device complexity and production time increase
Solution Approach 1:
The amplifier circuit performs self-calibration using internal feedback paths. The first feedback path measures the common mode output voltage and generates a correction signal to compensate for offset errors, while the second feedback path compensates for drift errors. This eliminates the need for external trimming processes during manufacturing, reducing production complexity while maintaining calibration precision.
Solution Approach 2:
The patent implements two feedback paths: the first feedback path uses a comparator and counter to measure the common mode output voltage and generate a digital correction signal that is converted to analog and fed back to the amplifier input to compensate for offset. The second feedback path uses an average filter to compensate for time-variant drift errors. These feedback mechanisms enable automatic calibration without external intervention.
2Device complexity
If offset and drift errors are not compensated, then device complexity is reduced, but signal quality and dynamic range deteriorate
Solution Approach 1:
The calibration system is segmented into two independent feedback paths: the first feedback path handles time-invariant offset errors using a comparator and counter mechanism, while the second feedback path handles time-variant drift errors using an average filter. This segmentation allows each path to be optimized for its specific error type without increasing overall system complexity excessively, while effectively improving signal quality through targeted compensation.
Data Source
AI summary
An amplifier circuit arrangement and a method for calibrating the same. In an embodiment an amplifier circuit arrangement includes a desired signal path including a differential amplifier for an analog signal having an input side and an output side and an analog-to-digital converter having an output terminal, a first feedback path to calibrate an offset of the desired signal path coupled to differential signal lines at the output side of the differential amplifier and to differential signal lines at the input side of the differential amplifier, the first feedback path including a comparator and at least one counter controlled by an output of the comparator and a second feedback path to calibrate a drift of the desired signal path coupled to the output terminal of the analog-to-digital converter and to the differential signal lines at the input side of the differential amplifier, the second feedback path including an average filter.