Current-Feedback Instrumentation Amplifier Gain Matching Without Trimming
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Solution Overview
Problem
Current feedback instrumentation amplifiers face significant gain mismatch issues due to temperature variations, leading to inaccuracy, which is not adequately addressed by existing technologies.
Innovation Solution
The implementation of Dynamic Element Matching (DEM) and a Gain-Error Reduction Loop (GERL) in chopper current feedback instrumentation amplifiers, where input stages are swapped periodically and a feedback loop corrects gain mismatch, reducing ripple and achieving high gain accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If non-degenerated input stages are used to achieve low noise and low supply power, then power efficiency is improved, but gain mismatch increases leading to high inaccuracy
Solution Approach 1:
A feedback loop is implemented that senses the differential output voltage, demodulates it using a chopper synchronized with the DEM switching, integrates the signal to extract gain mismatch information, and feeds back a correction current to adjust the tail currents of the input stages. This continuous feedback mechanism dynamically compensates for gain mismatch while maintaining the power-efficient non-degenerated input stage configuration.
Solution Approach 2:
The tail currents of the input stages are dynamically adjusted based on the sensed gain mismatch. By changing the current parameters of the input stages in real-time according to the feedback signal, the system compensates for temperature-induced gain variations and achieves high accuracy without sacrificing power efficiency.
2Measurement precision
If Dynamic Element Matching with periodic swapping is implemented to reduce gain mismatch, then gain accuracy is improved, but ripple is generated at the output
Solution Approach 1:
The feedback loop detects the ripple-causing gain mismatch through demodulation and integration, then generates a correction signal that counteracts the mismatch. This feedback mechanism suppresses the ripple generation at its source while maintaining the benefits of DEM for gain accuracy.
Solution Approach 2:
The chopper and integrator circuitry serve as intermediaries that process the differential output signal to extract gain mismatch information. These intermediary components enable the system to sense and correct ripple-causing errors without directly interrupting the signal path, thus reducing ripple while preserving gain accuracy.
3Measurement precision
If trimming is applied to reduce gain mismatch, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The system performs self-correction of gain mismatch through the automatic feedback loop. The amplifier continuously monitors its own performance and adjusts its tail currents accordingly, eliminating the need for external trimming operations. This self-service mechanism maintains high accuracy while simplifying the overall system and reducing manufacturing complexity.
Solution Approach 2:
The feedback loop provides continuous automatic compensation for gain mismatch, replacing the need for manual or automated trimming processes. This feedback-based approach achieves comparable or superior accuracy to trimming while eliminating the associated complexity and cost.
Data Source
AI summary
Current-feedback instrumentation amplifiers that include dynamic element matching for the input transconductance amplifiers by periodically swapping the transconductance amplifiers between the instrumentation amplifier input and the feedback input. The instrumentation amplifiers may include a gain error reduction loop, which loop corrects differences in the gains of the input transconductance amplifiers and eliminates the ripple in the instrumentation amplifier output caused by the dynamic element matching. If chopper stabilization is used, the amplifiers may also include an offset reduction loop. Various embodiments are disclosed.