Signal Analyzer Noise Compensation for Accurate DUT EVM
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Solution Overview
Problem
Conventional techniques for determining noise contributed by signal analyzers during RF signal measurements are time-consuming and require disconnecting the device under test, leading to inaccuracies in error vector magnitude (EVM) measurements due to the noise floor introduced by the signal analyzer.
Innovation Solution
A system and method that estimates the noise power of the signal analyzer without changing connections, using a noise figure extension (NFE) model based on instrument settings and coherent averaging to separate and remove the instrument noise from the DUT noise, allowing for accurate EVM measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional load-terminated noise correction is used, then noise power of signal analyzer can be measured in isolation, but measurement process becomes time-consuming and requires disconnecting DUT
Solution Approach 1:
The system performs preliminary characterization of the signal analyzer's noise floor by measuring noise power at multiple attenuation settings during calibration. These pre-characterized noise floor values are stored and later retrieved during actual DUT measurements, eliminating the need for real-time noise measurement and connection disconnection.
Solution Approach 2:
Instead of physically measuring noise power at each measurement instance, the system creates a digital copy of the noise floor characteristics through attenuation-based measurement. The noise floor is characterized at different attenuation levels and stored as reference data, which is then applied to correct measurements without requiring physical reconfiguration.
2Measurement precision
If signal analyzer noise floor is high, then measurement sensitivity is reduced, but increasing bandwidth requirements make noise floor impact more significant
Solution Approach 1:
The system extracts and removes the signal analyzer's noise floor contribution from the total measured noise power. By characterizing the noise floor at multiple attenuation settings and using these values to calculate corrected noise power, the harmful noise floor impact is mathematically removed from EVM measurements.
Solution Approach 2:
The system changes the measurement parameter approach by measuring noise power at multiple different attenuation settings rather than a single fixed setting. This allows the noise floor to be characterized across different power levels, enabling accurate correction regardless of the actual signal power level being measured.
Data Source
AI summary
A system for compensating for noise from by a test instrument measuring a signal from a DUT includes a processing unit and a memory storing instructions that cause the processing unit to receive a digital baseband signal from the test instrument including an ideal signal and a total noise signal including DUT noise from the DUT and instrument noise from the test instrument; perform coherent averaging of the digital baseband signal to determine estimated ideal signal I/Q components; determine estimated total noise I/Q components; estimate noise power of the instrument noise introduced by the test instrument using a noise figure extension (NFE) model; and determine corrected noise I/Q components of the digital baseband signals based on a ratio of estimated noise power of the DUT and the total noise power of the digital baseband signals; and combine the estimated ideal signal I/Q components and the corrected noise I/Q components.