Microwave Engineering Europe - April 2008 - (Page 26)

26 INTERVIEW — Mitsubishi Electric Europe distortion technology based on ADPD (Adaptive Digital Pre-Distortion), high efﬁciency devices using a Doherty Ampliﬁer conﬁguration and high-power, high-efﬁciency GaN PAs. Further, bias control implemented using Envelop Tracking is also available. Though GaN offers high power and high-efﬁciency, it is seen as very important in the mid- to long-term as price issues still need to be resolved. On the handset side we are developing new transistors to provide an optimized PA solution in cooperation with hand set manufacturers and transceiver IC vendors. In the hand set, efﬁciency is not only important for battery life, but also for implementing multi-functionality. Mitsubishi has a wide range of GaAs PAs with world class efﬁciency and high linearity. MWEE: WiMAX seems poised for implementation in a variety of markets. What technological advantages can MELCO offer this emerging market? Dr Abdin: We can drive miniaturization and cost-effectiveness of the hand terminal through the use of mobile phone PA technology. MWEE: What is your view on WiMAX. Will it dominate? Is it disruptive? Is it restricted to underdeveloped markets? Dr Abdin: There is almost no doubt that WiMAX has promise as a core technology for next generation communications systems. It is predicted to become used as one of the high-speed mobile technology platforms in non-advanced countries as well as being used to implement new infrastructures in developing countries. Advantages are high data rates, interoperability and wide coverage. However, we are prepared for either WiMAX or LTE or both and have the technology to address both these potential markets. From the cellular point of view we see UMTS morphing into LTE through a variety of stages as HSDPA and HSUPA. MWEE: Recently, some companies are working on CMOS PAs with the aim of turning the whole RF world from baseband to antenna into CMOS. The claims are that costs can be reduced by around 50 percent versus GaAs. As a GaAs player, how do you see the threat of CMOS, especially at the lower frequencies such as WiMAX and UMTS? Switchable power ampliﬁer module from Mitsubishi Electric for WCDMA applications. Dr Abdin: Single chip solutions using SiCMOS are a threat to GaAs in particular for low-power and high integration applications. However, in higher power applications, GaAs is superior. With this in mind it should be noted that in the mobile phone market there is a clear trend towards higher power PAs in HSPDA, HSUPA, LTE, 4G WiMAX and so on. LDMOS is the mainstream base-station PA at present, but if systems go on to higher frequencies, GaAs will gain an advantage over Si-CMOS even in base station applications. There are many reasons to use GaAsbased technologies over Si-CMOS. One of the most important reasons CMOS PAs are not used in 3G handsets and 801.11a/g WLAN products is linearity. PAs in GSM handsets operate in saturated mode to achieve high efﬁciency and long talk times. Typically, a CMOS PA needs to back off from saturation much further than InGaP PAs for the same linearity and its efﬁciency becomes unacceptably low. In the trade-off between linearity and efﬁciency, InGaP PAs offer much better results. The power added efﬁciency (PAE) of a PA is directly related to battery life and talk time. Typically, the PAE of an InGaP PA is signiﬁcantly better than that of a comparable CMOS device. In spite of lower costs, CMOS is unattractive. Even in lowcost handsets, manufacturers are unlikely to trade-off talk-time to marginally reduce manufacturing cost. Though SiGe has been slated as an evolutionary step for CMOS and a viable alternative to GaAs, it has not been able to achieve the right combination of low-cost, high-yield production and performance to meet speciﬁc application requirements. In terms of integration, if the requirement is to combine the transceiver, base-band and PA, then it is necessary to use a silicon process. However, the industry is progressing along an integration path where the PA remains separate from the transceiver and in separate packaging. GaAs is ideally suited to this scenario. MWEE: How do you see GaAs technology going forward in terms of becoming more cost effective through better design and integration techniques? Dr Abdin: Chip shrink technology is important here, in which we basically shrink the chip geometry to get smaller sizes and higher yields at less cost. This is analogous to the gains achieved in Silicon digital circuits. In the case of GaAs, BiFET technology which monolithically integrates HBT and PHEMT epilayers in a vertically stacked structure is an important technology for cost reduction. BiFET enables us to integrate the PA and control function on a single chip. In WCDMA, for example, there are potentially 11 bands to choose from depending on the region in which the handset will operate. It would be reasonable to assume that low end phones will cater to one region and high end phones will target as many regions as possible, as is the case today. In a multi-region phone it would be ideal if one PA could be used to cope with all these bands. However, in reality such a PA cannot be made with acceptable Microwave Engineering Europe ● April 2008 ● www.mwee.com 024-025-026-027_MWEE.indd 26 28/03/08 14:07:14 http://www.mwee.com

Table of Contents Feed for the Digital Edition of Microwave Engineering Europe - April 2008

Microwave Engineering Europe - April 2008 News Contents Comment Test and Measurement: Comprehensive WiMAX and Wi-Fi Product Design Demands Effective Channel Emulation Military/Aerospace Focus: Hardware Needs Limit Software Radio Interview — Mitsubishi Electric Europe: GaAs Technologies Spanning High-End Space and Radar Through to Cost-Sensitive Handset and LNB Applications How Do You Test ZigBee Transmitters? Advanced Receiver Design Boosts Performance CMOS PAs Pave the Way for One-Chip Phones Products Calendar

Microwave Engineering Europe - April 2008

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