3G/4G Multimode Cellular Front End: Impact on PA Design
3G technologies are growing at a rapid pace in today’s cellular industry. The outlook for multimode devices is growing more positive year over year as 2G cellular products mature in their life cycle. Handset users today demand higher data rates than ever before, which is increasing the complexity of the 3G system. To complicate the front end even more, the number of bands in which the modulations must operate has increased significantly. In order to meet these demands new standards are being developed, which will enable higher data rates through different modulation schemes across multiple frequency bands. WCDMA (Wideband Code Division Multiple Access) release 99 was released for voice capabilities followed by HSDPA (High Speed Downlink Packet Access), which increased the throughput capability of WCDMA. Now to satisfy user demand, even greater requirements are being placed on the system with HSUPA (High Speed Uplink Packet Access) and the follow-on standard of LTE.
As these modulation schemes become available, problems arise for the handset designer when it comes to current consumption of the front end. Each modulation scheme requires a different amount of linearity requirements, as well as inconsistent post-PA loss for different bands, which leads to increased current consumption when operating in any of the other modes and/or bands. In this paper, Part 3 of our three-part series on 3G/4G multimode handsets, the authors will examine the fundamental challenges engineers face when designing front ends to be multi-band and multi-standard across different modulations.