Wireless basestations continue to grow in size and complexity as they support new technologies and services in addition to the older air interfaces still in use. While analog cell phones will be officially phased out in a few years, most carriers will continue to support older air interfaces like North American TDMA (IS-136) and GSM while adding GPRS, EDGE, and eventually WCDMA. Others are dealing with CDMA upgrades from the older IS-95 to the newer versions of cdma2000.
Now, basestation designers can accommodate all of these technologies and even newer ones to come. TelASIC Communications' BaseFlex chip set supports all major cellular air-interface standards. Using its high-performance data-converter technology, a high IF sampling rate can reduce upconversion and downconversion to a single stage, simplifying the RF front end of a wideband wireless radio.
A transceiver architecture covers the entire licensed band up to 75 MHz wide, so one basestation can simultaneously support any combinations of bands. The chip set also can process multiple simultaneous 2G, 2.5G, and 3G standards within the same footprint as today's single-carrier, narrowband architectures.
TelASIC says these features translate into several important benefits for basestation designers. First, system costs are lowered when implementing multiple air interfaces. Further reductions result from evolving standards and more network capacity. Second, the elimination of multiple air interface-specific equipment simplifies product-line management.
Third, production and operation costs drop due to reduced product lines and increased economies of scale. Fourth, the development cycle decreases, speeding time-to-market. Finally, the BaseFlex architecture complements the industry organizations that support open radio interfaces, including the Common Public Radio Interface (CPRI) and the Open Base Station Architecture Interface (OBSAI).
BASEFLEX IN ACTION
The figure shows the architecture using the BaseFlex chip set. It consists of an analog-to-digital converter (ADC), a digital tuner, and a digital-to-analog converter (DAC). The TC1410, one of the fastest ADCs available, is a 14-bit multistage subranging ADC with a 240-Msamples/s conversion rate, giving the chip a 120-MHz Nyquist bandwidth. On-chip circuits include the sample/hold, precision voltage reference, all quantizing elements, and error-correction circuitry. The low-voltage differential signalling output interface has saturation and data-valid bits. Made with silicon-germanium (SiGe) biCMOS, the chip comes in a 256-pin BGA package. Its applications include other wireless systems, high-performance scopes, spectrum analyzers, and automatic test equipment.
The TC2400 is the companion DAC. This 14-bit device supports the 120-MHz IF produced by the ADC. It can accept parallel data at 480 MHz. The TC2400 uses a 5-bit Unary and 9-bit binary R2R DAC structure, and the 2.5-V bandgap voltage reference is on-chip. Also made with SiGe biCMOS, it comes in a 96-pin BGA package.
The device between the ADC and DAC is the TC4000 multichannel programmable tuner. This chip performs all of the transmit and receive processing, both analog and digital signal processing, for virtually any air interface. It has eight receive channels, four transmit channels, and a fully programmable numerically controlled oscillator (NCO) or direct digital synthesizer (DDS) for super-fast hopping between channels.
The TC4000 accepts two ADC inputs that go into a crossbar switch, which distributes the input to the eight channels. The crossbar also lets the tuner support multiple sector antennas. Each receive channel includes a 32-bit NCO/DDS on the downconverter, multistage filters, and digital automatic gain control. The output can be serial or parallel.
There are four channels on the transmit side. The signals to be transmitted are filtered and otherwise processed according to the desired air interface. Next, they're upconverted using a 32-bit NCO/DDS and sent to a transmit summing tree, where they can be sent to up to four of the DACs. Then, they go to the power amps.
A demo board is available now. The company will begin sampling by the end of the year.