Amplifier Noise Testing Through Multi-Impedance Model Fitting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for determining noise parameters of amplifiers, particularly in magnetic resonance imaging preamplifiers, are inaccurate due to high input reflection and sensitivity to source impedance variations, especially when using preamp decoupling techniques, which complicates noise measurement and characterization.
Innovation Solution
A noise test system that uses a computational system to receive calibration data and fit multiple noise power measurements to a circuit model of the amplifier, accounting for temperature-dependent source impedance variations and correlations between voltage and current noise sources, to determine a set of linear noise parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If preamplifier decoupling technique is used to avoid coupling between antenna elements, then coupling between antenna elements is reduced, but noise measurement accuracy deteriorates due to high input reflection and sensitivity to source impedance variations
Solution Approach 1:
The patent changes the measurement parameters by performing noise measurements at multiple different source impedance values rather than at a single impedance. This allows the system to capture the amplifier's noise characteristics across a range of impedances, enabling accurate determination of noise parameters even when operating at high reflection conditions with preamplifier decoupling.
Solution Approach 2:
The patent performs preliminary noise measurements at multiple source impedance values before determining the final noise parameters. By collecting measurement data across different impedance conditions in advance, the system can then use curve fitting to accurately extract the noise parameters, compensating for the high input reflection effects.
2Ease of operation
If traditional noise measurement methods are used, then measurement process is simple, but measurement accuracy deteriorates due to high input reflection and source impedance sensitivity
Solution Approach 1:
The patent creates a mathematical model (circuit model) that replicates the amplifier's noise behavior based on measurements taken at multiple source impedance values. This model serves as a copy of the actual noise characteristics, allowing accurate noise parameter determination without requiring direct measurement at the exact operating point, thus overcoming the limitations of traditional single-point measurement methods.
Solution Approach 2:
The patent uses curve fitting as a feedback mechanism where the measured noise data from multiple impedance points is continuously compared against the circuit model predictions. The model parameters are adjusted iteratively to minimize the difference between measured and predicted values, providing feedback that improves the accuracy of the determined noise parameters.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Disclosed herein is a system (100, 900, 1000) and a method of determining noise parameters (128) of an amplifier or receiver device under test (DUT). The system comprises a computational system (104) configured to perform a method comprising: receiving (200) calibration data (124) that comprises multiple noise power measurements descriptive of the output of the DUT corresponding to a predetermined set of complex noise input signals (126); and determining (202) a set of linear noise parameters of the DUT by fitting the multiple noise power measurements and the corresponding set of complex noise input signals to a circuit model (122, 700, 800) of the DUT.