III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words:

In; one; licenses; through; systems.

With support for global roaming as ________ condition ________ the IMT-2000 standard for third – generation ________, innovative design ________ are now being implemented to produce radio that can be reconfigured ________ software to handle different air interface protocols.

Exercise 2. Fill in the table with words and expressions from the text:

	parts	systems	processes
Example: mobile network, operator are making			significant investment in both new licenses and next generation systems that need to be far more flexible than they were previously.
wireless ICS are generally partitioned between
the IC fabrication technology is optimized for
DSPs are fabricated in processes

Exercise 3. Compose a story on one of the topics (up to 100 words):

“Universal Radios”

“Third – Generation Wireless Technology”

“Fourth – Generation Wireless Technology”

Lesson 2

Read the text: Universal Promises

But new process technologies show promise. For example, silicon germanium (SiGe) BiCMOS offers performance that can enable universal or multistandard analog radios. That technology supports active and passive devices with cutoff frequencies of 50 to 100 GHz. SiGe achieves its device speeds mainly by controlling the composition and thickness of the layers that comprise the transistor. Because of that, SiGe BiCMOS can achieve these levels with inexpensive lithography. In CMOS, device speeds are strongly determined by gate lengths, which are now moving to less than 0.2 micron in order to offer speed comparable to that of SiGe. Because these gate lengths are significantly smaller than the wavelength of visible light, much more expensive deep-ultraviolet lithography is required.

Radios that comply with many wireless standards may be required to support the complexities inherent in third- and fourth- generation wireless systems. Each wireless standard is allotted a narrow band of frequencies in a very broad spectrum. Because the cutoff frequencies of those new process technologies are much greater than the 1 to 2 GHz typical for wireless communication, they allow the switching and conditioning of microwave signals without significant degradation. Adaptable radios will use the high-speed transistors to switch the microwave signals associated with differing wireless standards through circuit blocks configured for these standards. By changing the division constant, N, and by switching passive components into and out of an on-chip local oscillator core, these processes will allow the generation of widely dispersed frequencies. Finally, it is likely that multistandard radios will dynamically select on-chip circuits for matching to off-chip narrowband RF circuits.

Independent of the radio standard being utilized, radios must be capable of receiving signals as small as a few microvolts in the presence of unwanted signals in adjacent bands that may be more than 80-dB stronger. A principal requirement of a true universal radio will be to remove many of the fixed, standard-specific, off-chip filters now used to define the desired radio passband. In heterodyne radios, which typically mix the desired signal band to an intermediate frequency of several hundred megahertz, eliminating off-chip filters would require analog-to- digital converters or subsampling mixers, which are very fast and of very high dynamic range. Realizing such circuits is difficult, especially in low-power radio applications. An alternative approach is to mix the desired signal down to a frequency low enough to allow efficient on-chip analog filtering. Because bipolar transistors are formed from silicon-on-silicon junctions, they have very low intrinsic dc offsets and thousands of times less 1/f noise than CMOS transistors in which carriers travel along an Si-SiO2 boundary. Therefore, an optimal solution is to utilize a SiGe BiCMOS process in a direct-conversion receiver that mixes the RF signal directly to dc with an on-chip local oscillator.

In the past, direct-conversion or zero-IF radios have been plagued by local-oscillator leakage. Perhaps the principal difficulty arising from that leakage is high levels of leakage onto the RF inputs of the IC. The leakage, in the range of -50 to -60 dBm, passes out of the receive antenna, scatters off nearby moving objects and then passes back into the antenna and receiver. Because the local-oscillator leakage can be 60-dB larger than the receiver signals, the time-varying reflected LO can overwhelm the integrated receiver.