Linearization And Optimization Of 802.11ac Tx Radio Chain

Abstract

In the design and performance evaluation of radio communication systems, it is necessary to have an accurate characterization of the Tx Chain of the Radio (radio here is referred as chip containing both TX and Rx path). Tx Chain of a radio is an important part of the design. It has DAC (digital to analog converter), filters, mixer, Power Amplifiers Tx-Rx switch and matching network. Filter non-idealities, nonlinearity of power amplifier, leakage or coupling of signals from different compo- nents which lead to spurs coming up in the regulatory band and clock impairments causing spurs. Consequently, desired performance of the whole design is degraded. To improve degraded performance, first where exactly the problem is occurring need to be identifued and corrected because Tx chain has a very important role to play in the WLAN chips. Linearization and optimization of RF Radio supports various tests. These tests can be di-vided 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 Noise Figure are required. Out of these, EVM test and OOB Test is carried out for optimization and linearization of Tx Chain as this test are considered to be very important tests. Nonlinearity, phase and gain imbalance, DC o sets, spurious tones, phase noise, etc. are degrading factors of EVM. So, a single EVM test result gives information about all these factors. That is why EVM is the most important test to evaluate trans- mitter characteristics. Also there has been some regulatory standards laid down by FCC for Out of Band Emission Tests.