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RF transmit processor optimises PA performance

Posted: 08 Feb 2008     Print Version  Bookmark and Share

Keywords:single-chip wireless transmit processor  digital upconverter  crest factor reduction  digital pre-distortion linearisation  multi-carrier power amplifiers 

A single-chip wireless transmit processor that combines digital upconverter, crest factor reduction and digital pre-distortion linearisation functions, has been launched by Texas Instruments Inc.

The GC5322 device increases the efficiency of multi-carrier power amplifiers (PAs) in the RF transmit signal chain and eliminates the need for more costly high-performance RF power amplifier components. This enables base station OEMs to achieve power efficiencies of 25 per cent or more for Class AB Pas, and reach 40 per cent or more for Doherty PAs.

Handling demand
Dealing Increased subscriber demand for wireless service, within limited licensed RF spectrum, has forced base station OEMs to adopt wideband, complex, spectrally efficient modulation schemes to increase voice and data capacity over cellular networks. These signals are more sensitive to distortion. As a result, multi-carrier PAs operate well below saturation, where they are much less efficient. RF systems engineers must compensate for this reduced efficiency by utilising more expensive components in the RF power amplifier subsystem design.

The advanced DPD linearisation technology of TI's GC5322 wireless transmit processor significantly reduces the requirements that would otherwise be placed on the base station power amplifier. The GC5322 processes composite input bandwidths of up to 40MHz and significantly reduces the Peak-to-Average ratio of the input signals while also improving adjacent channel leakage ratio. The flexible DSP-based pre-distortion linearisation algorithm supports multiple power amplifier architectures and emerging standards, such as CDMA2000, W-CDMA, TD-SCDMA, OFDMA (WiMAX, LTE), HSPA, and HSPA+. By optimising the PA performance, engineers will be able to meet the cost, linearity and efficiency goals of current and future radio card architectures.

Future proof
"As power demands, spectral masks, and EVM requirements become increasingly difficult to meet, base station OEMs are finding it challenging to design new transmitter systems and still meet BOM cost targets, power dissipation, and performance goals," said Jagdish Rebello, director and principal analyst with iSuppli. "The level of integration offered by TI's GC5322 transmit processor should not only reduce design complexity and power consumption, but will also deliver high power efficiencies and ACLR performance from a single highly integrated monolithic semiconductor device. This will allow OEMs to 'future proof' their design in the event that new standards or performance requirements become design criteria."

The GC5322, coupled with TI's TMS320C6727 low-cost, floating-point DSP, offers base station OEMs real-time processing power and the flexibility to modify the DPD algorithm to adapt to emerging wireless standards. The GC5322 is supported by a complete evaluation system, including high speed data converters, power solutions, clock synthesis, and high performance RF. TI's unique total signal chain solution allows engineers to obtain measurable performance results, shorten time-to-market and remove risk from critical development programs.




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