Common Mode Sensing Amplifier Architecture for Noise Rejection
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Solution Overview
Problem
Instrumentation amplifiers face challenges in achieving high common mode rejection ratio due to mismatches in resistor ratios and common mode gains of input op-amps, leading to inefficiencies in noise rejection and signal accuracy, particularly in noisy environments like those encountered in sensor applications.
Innovation Solution
A common mode sensing amplifier architecture that includes a differential positive input, a differential negative input, and transistors configured to track input common mode, with cross-coupled current sources to match current differential and generate a common mode output, which is used to improve common mode rejection by compensating for mismatched impedance in shielded cables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a classical three-amplifier architecture with resistor feedback network is used, then differential gain can be achieved, but common mode rejection ratio deteriorates due to mismatch in resistor ratios and common mode gains
Solution Approach 1:
The patent extracts the common mode sensing function from the main signal path by adding a dedicated common mode sensing amplifier that separately tracks and processes common mode signals. This extraction allows independent optimization of common mode rejection without affecting the main differential signal path, directly resolving the contradiction between achieving high common mode rejection ratio and maintaining signal accuracy.
Solution Approach 2:
The patent introduces an intermediary common mode sensing amplifier that acts as a mediator between the differential inputs and the output stage. This intermediary component tracks the common mode voltage and provides compensation signals that improve common mode rejection ratio while maintaining overall signal accuracy, effectively resolving the technical contradiction.
2Measurement precision
If external common mode amplifiers or extra components are added to improve common mode rejection, then common mode rejection ratio improves, but device complexity increases
Solution Approach 1:
The patent merges the common mode sensing function with the existing differential amplifier structure by using the same input nodes and integrating the common mode amplifier within the existing circuit framework. This merging approach improves common mode rejection ratio while minimizing the addition of external components and maintaining relatively simple circuit complexity.
Solution Approach 2:
The common mode sensing amplifier serves multiple functions: it tracks common mode voltage, generates compensation signals, and improves overall common mode rejection. This multi-functionality allows a single added component to address common mode issues comprehensively without requiring multiple separate external components, thus improving common mode rejection ratio while limiting the increase in device complexity.
Data Source
AI summary
An amplifier includes a differential positive input, a differential negative input, and a transistor. The transistor is communicatively coupled to the differential positive input and differential negative input at a source of the transistor. The transistor is configured to track input common mode of the differential positive input and differential negative input.