Fabless semiconductor firm RFaxis Inc of Irvine,CA,USA,which designs RF semiconductors and embedded antenna solutions for the wireless connectivity and cellular mobility markets,has published the white paper'CMOS Wi-Fi RF Front-Ends for Mobile Handset Applications-Part-I',the first in a three-part series that discusses RF-related technical challenges for dual-mode Wi-Fi/cellular handset designs.The paper also discusses some of the technical solutions that RFaxis has developed to mitigate these critical issues faced by the RF/wireless community today.
According to the Linley Group,smartphones are one of the most rapidly growing market segments in wireless,with 600 million units projected to ship in 2014.The mobile devices are capable of simultaneous 3G/LTE operation and Wi-Fi connectivity,so users can connect to a cellular network for voice calls,while searching the Internet or downloading data files through Wi-Fi networks simultaneously.The concurrent operation of different radios inside a tightly spaced handset poses unprecedented challenges to RF designs that need to meet uncompromised performances at an ever-decreasing bill of materials(BOM)cost.
The white paper provides comprehensive test data and comparison of noise contributions from different Wi-Fi power amplifiers(PAs)and front-end modules(FEMs)in the UMTS/WCDMA receiver band(Band-1,2.11-2.17GHz)from multiple tier-one vendors.The PAs/FEMs have been developed by the RF/wireless industry over many years on different materials/process technologies including gallium arsenide(GaAs)HBT and pHEMT,BiCMOS SiGe HBT and,most recently,bulk RF CMOS.Some of the key findings from the study include:
Total noise power in the WCDMA receive band increases with WLAN transmit power level for all technologies except for bulk CMOS,which shows either negligible change or even slightly reduced noise power at high WLAN output signal levels.The need for high levels of rejection(30-35dB)for GaAs or SiGe HBT-based solutions translates to more expensive co-existence filters,as well as extra degradation in Wi-Fi receiver sensitivity and increased current consumption by the transmit chain.CMOS based Wi-Fi RF front-end ICs(RFeIC)from RFaxis require 1.0-1.5dB less linear power at PA output,which reduces current consumption significantly,it is claimed,as well as helping to improve receiver sensitivity of the Wi-Fi system by the same amount.
"As more mobile devices require concurrent operation of 3G/4G cellular and Wi-Fi,there is an increased demand to improve the performance and cost structure of co-existence filters with paradoxical criteria such as low in-band insertion loss,high out-band rejection,minimal component size and lowest price,"says chief technology officer Dr Oleksandr Gorbachov."We have found an alternative solution to this problem by taking advantage of the unique device/process characteristics of RF CMOS;along with proprietary design methodology,we are able to significantly reduce the Wi-Fi PA noise leakage to the WCDMA receive band,thus allowing RF system designers to use co-existence filters with highly relaxed specifications.This not only helps them reduce BOM cost,but also results in improved Wi-Fi performance,"he adds.
"We are pleased to share our results with the wireless community,and provide a ready-to-go solution to our OEM/ODM customers,"says chairman&CEO Mike Neshat."This is another key breakthrough from the RFaxis team,to make RF CMOS the next mainstream solution that can meet the most demanding RF front-end requirements for today's highly sophisticated wireless products such as smartphones,tablets and ultrabooks."
