Lesson 1

Read the text: Mobile Devices

As wireless technology advances, new communications standards with new capabilities and protocols are being continually added to older, existing standards. Because the geographic coverage offered by those technologies is never uniform, future radios will have to become universal, or multistandard, so that the radio can continuously reconfigure itself for the most appropriate wireless network. This requirement is becoming more evident due to the advances in performance offered by third- and, in the future, fourth-generation wireless technology.

Mobile network operators are making significant investments in both new licenses and next-generation systems that need to be far more flexible than they were previously. With support for global roaming as one condition in the IMT-2000 standard for third-generation licenses, innovative design techniques are now being implemented to produce radio systems that can be reconfigured through software to handle different air interface protocols. Some of the key considerations to support the processing of signals in universal radios include process technology, radio architecture and radio design.

At present, wireless ICs are generally partitioned between small analog chips and large digital signal processors (DSPs). The analog portion is required to accurately transduce signals of only a few microvolts. For that reason, the IC fabrication technology is optimized for rapid amplification and conditioning of very small signals and for the suppression of noise and unwanted interfering signals at both microwave and very low frequencies. Those ICs are fabricated on low-noise processes with isolating high-resistivity substrates and high-Q passive components such as inductors, varactors and metal insulator metal capacitors. RF packages are small and their leads have low, well-controlled parasitics for transferring microwave signals on or off the silicon die with minimal loss, reflection or corruption.

DSPs are fabricated in processes whose transistors are optimized to switch from on to off at the highest possible speeds and lowest power dissipation. Noise is irrelevant, as the signals are large. DSP packages tend to be large with many more leads than the packages of analog ICs, and are optimized for cost. Since analog yields are determined by the values of linear parameters such as noise, linearity, dc offsets, microwave gain, return loss, channel matching and output power, their yields are expected to be significantly lower than those of DSPs. As a result, integrating them on the same silicon die often entails discarding many properly performing and expensive DSPs because of failed analog metrics. Further, because analog and digital requirements are so different, they are often designed on different processes or by different manufacturers, and the designs are often independently migrated to new technologies as they become available.

In fourth-generation wireless technology, it is expected that antenna arrays will be implemented with an array of analog multistandard ICs controlled by a central DSP. Consequently, the partitioning between analog and digital wireless functions will likely remain until IC technologies solve some of the existing yield, cost and performance limitations associated with universal, fully integrated radios.