Amplifier Auto-Calibration Using Trim Codes to Reduce DC Offset
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for reducing amplifier offset in class-D amplifiers increase die area and silicon cost, and frequency modulation approaches create unwanted mixing products, while gain-dependent correction signals change with output voltage, necessitating improved on-chip auto-calibration methods.
Innovation Solution
Implement a current steering DAC to isolate and trim amplifier mismatch, followed by a differential amplifier topology to sense and correct feedback resistor mismatches, using a calibration circuit to minimize offset during and post-production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing approaches are used to reduce amplifier offset, then offset reduction is achieved, but die area and silicon cost increase
Solution Approach 1:
The patent applies preliminary action by performing auto-calibration of the amplifier during the manufacturing process itself. The calibration circuit measures and compensates for offset errors before the amplifier is shipped, eliminating the need for post-manufacturing trimming or larger physical components. This preliminary calibration action achieves offset reduction without requiring additional die area.
2Manufacturing precision
If frequency modulation is used to reduce offset, then offset reduction is achieved, but unwanted mixing products are created
Solution Approach 1:
The patent extracts the offset compensation function from the main signal path by using a separate calibration circuit that operates independently. The calibration circuit measures the offset error and generates a compensation signal that is applied separately, rather than modulating the main feedback signal. This extraction approach reduces offset without creating unwanted mixing products in the audio signal path.
3Manufacturing precision
If gain-dependent correction signals are used, then offset correction is achieved, but performance changes with output voltage
Solution Approach 1:
The patent performs preliminary measurement and storage of the offset error at a known operating point during calibration. The stored calibration value is then used to compensate for offset across different output voltage conditions. This preliminary characterization approach provides stable, consistent performance regardless of varying output voltage, unlike gain-dependent correction signals that change with operating conditions.
Data Source
AI summary
Systems and methods reduce unwanted effects caused by mismatch in amplifier circuits having components that are trimmable during and post-production to minimize DC offset. Various embodiments of the invention trim out amplifier mismatch by determining trim codes for two or more phases of operation of an amplifier circuit and use those trim codes to determine a final trim code for use in regular operation.