RF Front End Characterization for Narrow and Wide Band Radios

Abstract

In the design and performance evaluation of radio communication systems, it is necessary to have an accurate characterization of RF front end. Front end is an important part of the design. It has Band Pass Filter, Power Amplifier, Low Noise Amplifier, Tx-Rx switch and matching network. Filter non-idealities, nonlinearity of power amplifier, high noise figure of Low Noise Amplifier and many other impairments affect the ideal behavior of the Front End design. Consequently, desired performance of the whole design is degraded. To improve degraded performance, it is necessary to know what exactly is causing the problem. This is the reason why characterization of RF Front End is essential.

RF Characterization of front end supports various tests. These tests can be divided in two parts: Transmitter tests and Receiver tests. Transmitter tests involve tests like Transmit Signal Strength Indicator, Error Vector Magnitude, Harmonic Distortion, Out of Band Transmission, etc. At receiver side, tests like Receiver Sensitivity and Noise Figure are required. Out of these, EVM test, TSSI test and Receiver Sensitivity (Rx BER & PER) test are carried out.

Nonlinearity, phase & gain imbalance, DC offsets, spurious tones, phase noise, etc. are degrading factors of EVM. So, a single EVM test result gives information about all these factors. That’s why EVM is the most important test to evaluate transmitter section of the front end. Noise added by the receiver system affects the receiver sensitivity. Therefore it is necessary to perform Sensitivity and Noise Figure tests for receiver system and evaluate their results.

To accomplish these tests, automated test set-up (station) plays an important role. Bringing up the station from not connected test instruments to station’s final working condition is an important part in testing phase. Station bring-up which requires loss calibration and sanity tests to validate test result data is carried out. Result data of the tests executed on automated test stations is stored in station controller/computer. Arranging this raw result data in a proper format and plotting it, is an important task to make result analysis easy. The automation tool named Report Generator has already been developed to accomplish the same task. Python automaton scripts written for this tool had bugs which are identified and removed. Moreover, existing code for report generator is modified to add a new functionality.