Microwave Engineering Europe - January/February 2008 - (Page 32)

32 DSP AND OFDM Bridging the gap from the CMOS DSP to the antenna in OFDM Systems By Henrik Morkner, Gary Carr and Alan Rixon, Avago Technologies W ireless data devices are fast encroaching on territory historically covered by wired systems. New systems using WiFi or WiMAX OFDM modulation schemes can be tasked with handling large amounts of data for entertainment applications, like HDTV and gaming, making data access ubiquitous for everyday needs. OFDM system speciﬁcations present unique challenges for system designers. Avago Technologies is helping to drive this communications revolution by supplying captive-fabricated GaAs PHEMT products that effectively address performance, design and cost requirements for OFDM applications ranging from 2.4 GHz to 50 GHz. OFDM landscape Below 6 GHz, the trend for high volume applications has been to integrate the CMOS DSP to the antenna interface with a single FEM (Front End Module). This FEM must be very small to enable multiple-input, multiple-output (MIMO) placements in a laptop or other portable device. Additionally, the FEM should contain multiple functions including Tx and Rx signal ampliﬁcation, ﬁltering, and switching. For the 6 to 33 GHz range, the trend has been to integrate single functions such as LNA, power ampliﬁers, drivers, and mixers into surface mount packages. Above 33 GHz, the market is still dominated by chip-and-wire, but innovative package solutions are on the horizon. The challenge for designers is to identify and leverage full-featured compact solutions that overcome OFDM’s technical issues while meeting system cost objectives. CMOS limitations for OFDM DSP (Digital Signal Processing) within any OFDM (Orthogonal Frequency Division Multiplexing) scheme, such as WiFi (802.11), WiMAX (802.16) or licensed point-to-point radios, is dominated by CMOS processors. The strength of these processors is in its clever base band and RF band signal processing in standard CMOS. While CMOS makes an excellent signal processing medium, it falls short Figure 2: Realistic OFDM data frame at 6.6 dB PAR with a base level distortion of 2.4 percent. Figure 1: Typical OFDM Data frame and channel power as measured for WiFi. Figure 3: Modern WiFi power class AB ampliﬁer with distortion compensation. Microwave Engineering Europe ● January/February 2008 ● www.mwee.com 032-033-034-035-036_MWEE.indd 32 25/01/08 13:39:29 http://www.mwee.com

Table of Contents Feed for the Digital Edition of Microwave Engineering Europe - January/February 2008

Microwave Engineering Europe - January/February 2008 Contents News Comment Radio: Raising the Bar for the Radio: Making 802.11n Work Cover Feature: The RF-System-In-Package Trend - Efficient Design with Advanced Design System 2008 Wireless Sensor Networks: The Zigbee PRO Feature Set: More of a Good Thing Very Fast Measurements of Wireless Devices with Small Antennas in Reverberation Chambers WiMAX Update 2008 Bridging the Gap from the CMOS DSP to the Antenna in OFDM Systems Products Calendar

Microwave Engineering Europe - January/February 2008

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