Closed-Loop Amplifier Offset Calibration for Preceding Circuit Errors
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Solution Overview
Problem
Existing approaches to offset calibration in amplifiers, such as those in personal audio devices, are inadequate in accurately compensating for signal offsets caused by preceding circuitry and input impedances, leading to suboptimal performance.
Innovation Solution
A closed-loop amplifier system with a calibration subsystem that decouples stages, determines offset signals, and adjusts parameters to compensate for offsets in both the first stage and signal processing block, ensuring zero output when a specific signal is applied, thereby correcting for signal offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional offset calibration methods are used in amplifiers, then the calibration process is simple, but the offset compensation accuracy is insufficient due to inadequate consideration of preceding circuitry and input impedance effects
Solution Approach 1:
The calibration system is segmented into distinct functional blocks: a calibration signal generator that produces test signals, a calibration subsystem that measures offset voltages at different stages, and a control subsystem that processes measurements and applies corrections. This segmentation allows each component to be optimized independently while achieving high overall accuracy.
Solution Approach 2:
The calibration process performs preliminary measurements of offset voltages before normal operation, using a calibration signal generator to inject test signals and measure baseline offsets. These preliminary measurements enable the system to pre-calculate correction values that are applied during subsequent operation, ensuring accurate offset compensation without affecting real-time performance.
2Reliability
If offset calibration compensates for amplifier input stage only, then the calibration process is simple, but the compensation is inadequate due to unaccounted preceding circuitry offsets
Solution Approach 1:
A calibration signal generator acts as an intermediary device that injects known test signals into the signal path before the amplifier. This intermediary allows the calibration subsystem to measure offset voltages at multiple points including preceding circuitry and input impedance effects, providing comprehensive data for accurate compensation without directly measuring difficult-to-access internal nodes.
Solution Approach 2:
The calibration subsystem measures offset voltages and feeds this information back to the control subsystem, which calculates correction values and applies them through the signal processing block. This feedback loop ensures that offset compensation is continuously optimized based on actual measured conditions, accounting for both amplifier and preceding circuitry offsets.
Data Source
AI summary
A method may include, in an apparatus comprising a closed loop amplifier and a signal processing block configured to generate an amplifier input signal as a function of an upstream signal received at an input of the signal processing block, in a calibration mode of the apparatus: decoupling a second stage input of the amplifier from a first stage output of the amplifier; determining an offset signal that when applied to the input of a signal processing block as the upstream signal generates approximately zero as an intermediate signal generated by the first stage of the amplifier; and controlling one or more parameters of the apparatus based on the offset signal to compensate for an offset of at least one of the first stage and the signal processing block.