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Wireless Communciations Introduction to Wireless Wireless Solutions Literature
Wireless Terms |
Analog BasebandDigital signal processors, the key enabling technology of the digital wireless industry, require mixed-signal and RF components that serve as a bridge to the real world of analog signals. Using a seamless architecture for wireless communications technology, TI matches its baseband interfaces, radio frequency ICs and power management ICs to digital signal processing engines to create complete DSP Solutions for digital wireless systems.Today, communications have gone mobile. In the car, at the game, at the store -- wherever active people go, they take wireless telephones and other communications systems along with them. Behind this new mobility in communications is high-speed digital technology, and in the forefront of this technology is Texas Instruments, the industry leader in Digital Signal Processors (DSPs) and DSP Solutions. Offering several times the transmission capacity of older analog technology, digital technology opens new possibilities for mobile communications. More subscribers can place calls simultaneously. With digital technology, wireless handsets consume less power, extending talk and standby times between battery charges. And digital encryption enhances security for users and service providers alike. Today, digital wireless telephones are the fastest-growing segment of the wireless telephone industry. Figure 1 shows that by the end of the decade more than 80 percent of the cellular and Personal Communications Systems telephones sold will be digital.
The Role of DSP SolutionsWhile DSPs are the key enabling technology of the digital wireless industry, they do not exist in a vacuum. DSPs require mixed-signal ICs that can bridge to the real world of analog signals. In wireless systems, ICs that handle radio frequency signals are also essential, as are components that manage power. DSP Solutions bring all these components together, plus memory and additional logic functions such as microcontrollers.TI has the digital, mixed-signal and RF products, system-level expertise, integration technologies and manufacturing processes needed to create solutions for the wireless systems of today and tommorow. To create DSP Solutions for wireless more effectively, TI has organized a unified Wireless Business Unit that helps TI design and manufacturing experts follow a seamless architectural approach to product development. The result has been the rapid development of a series of highly integrated products that support wireless base stations and handsets used with different standards around the world. Baseband Interface ICsIn wireless systems, the most important mixed-signal and RF components that work with the DSP are baseband interfaces, radio frequency (RF) ICs and power management ICs. Figure 2 shows how these components fit into the three major subsystems in a digital wireless telephone. Two subsystems handle system power and radio frequency (RF) transmission and reception, while the third processes the communicated signal at baseband frequencies -- hearing-range frequencies and higher, up to but not including RF modulation.At the heart of the baseband subsystem is the DSP, responsible for speech encoding and decoding, error correction, channel encoding and decoding, equalization, demodulation and encryption of the digital signal. Linking the DSP to the microphone and speaker is the voice coder/decoder (codec), and to the radio frequency subsystem is the RF codec. These two baseband interface devices provide a sophisticated front end to digital communications systems. Baseband interfaces not only link DSPs with users' voices and the RF subsystem, they also carry a great deal of processing workload -- maintaining signal quality, extending talk time and improving overall system performance. A voice codec performs the dual functions of sending a user's voice to the DSP and allowing the received signal to be heard through the earphone speaker. In transmitting, the codec receives analog input from the microphone, filters out non-voice frequencies, converts the signal from analog to digital, then passes it along to the DSP. In receiving, the device accepts the digital signal from the DSP, converts it to analog, passes the signal through filters that correct and smooth it, then sends the signal to an amplifier for output through the speaker. The overall performance of the filtering and amplification circuitry directly affects the voice quality. By contrast, an RF codec performs the functions involved in readying a signal for output from the RF subsystem and converting a received analog signal for further processing by the DSP. Before sending an outgoing signal, an RF codec converts the digital data stream from the DSP into the modulation format appropriate to the transmission standard. The codec also routes the I and Q modulation signals from the DSP to the RF transmit subsystem, where they are translated from baseband to radio frequency. When the RF receive subsystem has received an incoming signal and translated it to baseband frequencies, the codec extracts the I and Q signals, converts the signal to digital, filters the signal to shape it, then sends it to the DSP. Baseband Interface IntegrationBaseband interface ICs must achieve a remarkable balance among requirements, providing at the same time flexibility, feature-rich functionality, ease of design, very low power consumption and economy. The devices must easily accommodate a variety of system configurations, so they must provide a simple, straightforward connection with microphones, speakers and other components.Voice products from TI are either stand-alone or integrated with the RF codec. TI's voice-band audio processor (VBAPª) is popular with designers due to the design flexibility it offers, particularly in wireless telephone systems, but also in a variety of telecommunications, digital audio and multimedia products that require digital processing of voice signals. The Advanced RF Cellular Telephone Interface Circuit (ARCTICª) family provides an RF codec tailored for cellular applications supporting the North American IS-54B and IS-136 standards. Another device, the TCM4400, integrates both the voice and RF codecs on the same silicon for cellular handsets supporting the Global System for Mobile Communications (GSM) standard, used throughout Europe and widely in the rest of the world. The ARCTIC Family and TCM4400 also offer the flexibility to support upbanded versions of their respective standards. Other standards TI is positioned to support with baseband interface products include the Japanese Personal Digital Cellular (PDC) standard, the varied standards appearing in the newly-allocated PCS frequency range, and IS-95, a North American CDMA standard based on spread-spectrum technology. These baseband interface devices, used in conjunction with TMS320 DSPs and TI-supplied software, provide highly optimized DSP Solutions for digital baseband systems. The high level of integration in these baseband products reduces chip counts, saves board space and wiring, lowers costs and helps to simplify design for faster time to market. Minimizing power consumption is also an important design constraint in wireless systems. In the TI baseband products, functional blocks in every device are designed to be powered on and off independently to help conserve battery power. In the RF codecs, the receive-only functions are powered off when the system is transmitting, and the transmit-only functions when the system is receiving. Another design strategy takes advantage of the fact that when the system is in standby mode, most of the baseband subsystem can be powered down. With some standards, just a small part of the RF codec can be used along with the RF receiver to monitor the airwaves for a paging signal, indicating an incoming call. When the RF codec detects the paging signal, it signals the rest of the baseband section to power up. The resulting power savings are significant: while in analog idle mode, the IS-136 chip set can consume as little as 27 percent of the power it consumes while in digital active mode. Strategies such as these have made TI's baseband solutions among the most power-efficient in the industry, allowing manufacturers to use smaller batteries in their systems and helping to prolong standby and talk times for users. Radio Frequency (RF) and Power Management ICsThe RF subsystem of a wireless telephone has traditionally required scores, even hundreds, of ICs and passive components. TI's families of RF ICs reduce all of these to just a few ICs that perform each of the major RF small-signal and power amplification functions within wireless handsets. By combining several functions on each chip and by operating from lower supply voltages, the devices enable wireless systems to be smaller, lighter and less expensive, while providing longer talk and standby times from a single battery charge.Initial offerings support time-division multiple access (TDMA) cellular standards, particularly the IS-54B, IS-136 and GSM standards. These ICs include the TRF1015 receiver, TRF2050 synthesizer, TRF3020 modulator, TRF8010 driver/amplifier and TRF7000 power amplifier. Some of these products also support the AMPS standard traditionally used for analog cellular phones in North America, and some the newly allocated PCS transmission frequencies. Additional TI products will enlarge the RF family, providing even greater support for these and other major wireless standards worldwide. Figure 3 shows how the levels of integration in the RF subsystem will increase in future. In the power subsystem, TI has introduced a family of power management devices that are designed to reduce design cycle times for cellular telephones and other wireless communications systems by integrating a complete baseband power supply with or without an audio system amplification on one chip. Among these devices, the TPS9104 has three low dropout voltage regulators that provide all of the power supply needs for the baseband portion of a cellular phone. A low dropout of 200 millivolts maximum from the regulators, coupled with micropower operation, extends the life of batteries significantly by continuing to regulate the system voltage even as the battery voltage approaches the regulated system operating level. The regulators are capable of delivering 100 milliamps of output current. Advanced Processes and PackagingIn order to enhance its baseband interface ICs, TI continues to minimize power dissipation through improved process technologies. Analog CMOS technology, pioneered by TI and used today, is far more cost-effective and power-efficient than older bipolar technologies. TI's continual refinement of its analog CMOS process also lowers noise, so that components can achieve the same signal clarity while consuming less power.Integration in the RF subsystem requires the precision of advanced manufacturing, TI has developed or adapted IC manufacturing processes specifically to support wireless applications at frequencies in the cellular and PCS ranges. TI merged bipolar and CMOS processes as BiCMOS in order to marry the efficiencies of CMOS with the speed of bipolar. TI's RF circuits are manufactured in state-of-the-art facilities that produce hundreds of thousands of 6-inch wafers annually. These high-flow factories constantly improve yield and reduce variance to ensure lower costs and more predictable RF performance in the end equipment. TI also continues to refine the state of the art in gallium-arsenide (GaAS) with 0.25-micron transistor geometries and 4-inch production wafers. Every process plays an important role in creating cost-effective solutions for the varying power and frequency levels in wireless communications systems. To help wireless designers achieve the small system size the market demands, advanced IC packaging is a must. TI has dedicated itself to providing smaller, thinner, more cost-effective packages that support the frequency and current demands of wireless communications systems. Based on popular TSSOP packaging, TI's enhanced "TSSOP" packages provide metal-to-metal grounding and thermal paths to improve RF signal and power efficiencies. Improved lead connections cut signal loss and raise bandwidth dramatically. TI's expertise and advances in manufacturing processes, enable these innovative packages to flow on the same high-rate equipment that manufactures millions and millions of wireless mixed-signal products each year. Enabling Future Wireless CommunicationsTI has shown its technical and organizational commitment to the wireless industry through the development of DSP Solutions for base stations and handsets supporting major standards around the world. In addition to the DSPs themselves, these solutions encompass RF ICs, power management ICs, and the baseband interfaces that link the processors to the analog world of audio and RF signals. TI's highly integrated products provide complete system-level solutions for digital wireless communications. In the future, TI's products, process strengths design expertise and focused business organization will continue to lead the way to even more highly integrated solutions, helping to enable the ubiquitous wireless communications of the next century. |