SkyBlue™ Technology Overview  


SkyBlue™ is a groundbreaking step in cellular power amplifier technology addressing the most pressing design challenges facing smartphone UE developers.

Skyworks developed SkyBlue™ as an enabling technology to meet the current and future needs of the market – namely, increasingly higher performance targets with complex carrier aggregation requirements and simplified design as consumers demand sleeker and thinner designs, faster data rates, and longer battery life.

SkyBlue™ delivers envelope tracking (ET)-like system efficiency, but with a far simpler implementation method when compared to ET systems. Utilizing the more conventional average power tracking (APT)-like approach, SkyBlue™ control is very intuitive and has a very rapid learning curve relative to ET calibration requirements. Skyworks has revolutionized the design methodology to develop high power out capability while delivering best-in-class system efficiency.

Key Highlights

Why SkyBlue™ from Skyworks?

From discussions about market drivers, it is clear that overall system efficiency is important and techniques to improve efficiency, such as envelope tracking, are critical. However, current ET designs have met with resistance given the complexity associated with implementation in a mass production environment.

Envelope tracking systems provide efficiency enhancement by rapidly modulating supply voltage to track the envelope of the transmitted modulation. This results in improved power added efficiency at high output powers, especially for high PAR signals such as LTE where four to five percent efficiency gains are achieved over traditional APT systems. However, in order to implement envelope tracking systems, there are several requirements and challenges. Engineers must use a costly envelope tracking modulator. Additionally, there is a complex procedure required to develop a Look Up Table (LUT) to ensure the system can be calibrated over process, voltage, and temperature extremes. Further, as LTE data rates continue to increase, ET modulators must operate at higher and higher bandwidths. Today’s ET trackers operate at 20 MHz; future LTE speeds will require 40 MHz bandwidth, which will be extremely challenging for OEMs to adopt.

Envelope tracking can be problematic and in many cases, the end customer has chosen to abandon envelope tracking due to these difficulties and added cost.

Figure 1 compares Skyworks SkyBlue™ versus conventional envelope tracking systems.

SkyBlue™ Advantages

Skyworks’ SkyBlue™ uses a much simpler approach to control the PA, while still offering benefits that meet or exceed envelope tracking performance. SkyBlue™ is based on the well-known, easy to implement, low cost APT PA control technique, which has been widely adopted in the cellular handset market. As the graph shows (Figure 1), there are significant benefits using SkyBlue™ when compared to ET operating near max power. That is where SkyBlue™ shines – a specific design objective from Skyworks.

Market Drivers Requiring New Methodologies

Key factors for this new approach include cell edge limitations and new LTE transmission schemes, which drive the need for higher power and more efficient PA technology.

Research indicates that approximately 75% of cellular traffic originating in cities is within buildings1. Devices transmitting from inside buildings are impacted by poor signal environments – signal attenuation by glass/brick/steel structures severely weakens radio frequency (RF) signal propagation. We refer to that as cell edge performance, reducing the effective cell radius, which leads to customer dissatisfaction with smartphone data transmission.

Another compounding factor is that new LTE networks are transmitting data burst at near full power, which means maximum efficiency matters more in LTE networks compared with 3G (WCDMA systems). Most networks have average antenna power transmission in the +20 to +25 dBm range, which if you include typical post PA losses meaning that typical PA output powers need to be in range of +28 to +30 dB in conventional systems today.

1 Ericsson Mobility Report

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