Wireless standards abound, causing near endless design cycles for semiconductor suppliers and foundries. Each new cellular or wireless-local-area-network (WLAN) standard invites the development of yet another wireless chip set and its associated components, such as power amplifiers (PAs) and surface-acoustic-wave (SAW) filters. But what if a single transceiver chip could serve all standards? Too many variables—frequency ranges, channel bandwidths, power levels, etc.—to ever entertain a practical single-chip solution? Not if that one chip is the Softransceiver RF integrated circuit (RF IC) from BitWave Semiconductor (Lowell, MA). The transceiver covers a total bandwidth of 700 to 4200 MHz and almost all critical performance parameters, including channel bandwidths and linearity—can be adjusted under software control. The initial product is aimed at handset and portable terminal applications, although follow-up versions are expected for base-transceiver-station (BTS) and microcell transceiver applications.
BitWave's Softransceiver (Fig. 1) represents the next stage in semiconductor evolution: a software-programmable RF chip. Traditionally, different wireless standards dictate different radio chip sets. But with BitWave's patent-pending RF IC architecture and their proprietary control software, this one chip can serve nearly all wireless airinterface standards, or at least all that fall within its operating bandwidth.
The transceiver IC fully supports third-generation (3G) cellular standards for the Universal Mobile Telecommunications System (UMTS), including GSM, GPRS, EDGE, WCDMA, and HSDPA protocols, as well as IS-95B, 1xRTT, EV-DO and even IEEE 802.11b/g WLANs. It provides partial support for older cellular standards such as AMPS, PHS, iDEN, IS-136; short-range wireless standards such as Bluetooth, WiBro, and WiMAX; position services such as the Global Positioning System (GPS); and digital audio and video broadcast standards including digital audio broadcast (DAB) and digital video broadcast ( DVBH, DVB-T, DTV, and ISDB-T). The RF IC even includes a modem interface for the 3G DigRF standard plus extensions, and FEM interfaces for multiport, single-band and single-port, multiband applications.
The transceiver is integrated with a combination of analog and digital components, including a high-performance voltagecontrolled oscillator (VCO), mixer, programmable-gain amplifier, baseband filter, sigma-delta analog-to-digital converter (ADC), and digital-to-analog converter (DAC). What sets the chip apart from conventional ICs is the inclusion of impedance tuning elements—essentially varactor diodes—at strategic component junctions throughout the RF IC layout. A close-up of one transceiver component, a low-noise amplifier (LNA), shows several of the impedance tuning junctions and voltage feed points (Fig. 2) . By changing the voltages to these tuning elements, the impedance match at different points along the chip can be altered to adjust key parameters, including input and output matching, center frequency, channel bandwidth, noise figure, gain, sampling frequency, second-order intercept point, and third-order intercept point. The overall performance of the chip can be orchestrated by a simple, low-power 8-b microcontroller core, which is fabricated as part of the IC.
Amazingly, the IC is fabricated with standard 0.13-µm digital CMOS rather than specialized RF CMOS. The use of digital CMOS allows the fabrication of RF/IF, mixed-signal, and digital componentson the same chip, including the data converters, generous digital signal processing (DSP), and the software transceiver controller. In terms of raw performance, the RF IC operates over a total bandwidth of 700 to 4200 MHz and can adjust channel bandwidths from 200 kHz to 20 MHz.
It is the software, of course, that makes the Softransceiver work. The software provides programmable control of the chip's key performance parameters in real time, allowing designers to optimize the transceiver's performance for their own handset designs or program the chip to switch among multiple standards in a single handset. Since the chip is fabricated with a low-power digital CMOS process, it is already designed to save power. By using the single chip to handle multiple wireless standards, the power savings (not to mention size) for a handset or portable terminal becomes significant.
As an example of the Softransceiver's capabilities, it can be tuned under software control to operate over a GSM network on channel 25. The software-defined controller would be commanded to tune to a center frequency of 940 MHz with 200-kHz channel bandwidth. The transceiver would achieve a 65-dB gain at that frequency with a noise figure of only 2.5 dB. The second-order intercept would be +41 dBm and the third-intercept point ?15.5 dBm. The sampling frequency of the ADC would be set to 26 MHz with 12-b resolution.
In a traditionally RF IC transceiver design, these would be considered relatively fixed performance parameters, at least as a function of the bias setting and external matching to the chip. With the Softransceiver, however, all of these parameters are variable, including the number of taps (32) on the digitally defined filter. This concept—of a transceiver with RF and digital parameters that can be changed in real time, even dynamically, under software control—will change the way that radio designers think of hardware. It need no longer be fixed in function or performance, but can be optimized to a standard, to environmental conditions, even to changing conditions at the base station.
The three founders of BitWave Semiconductor did not come upon the idea of the Softransceiver by accident. All have extensive backgrounds in RF and semiconductor engineering and all have wrestled with the cencept of the true digital receiver for some time. BitWave's CEO, Doug Shute, for example, ran Steinbrecher Corp. as president and CEO. Geoff Dawe, CTO of BitWave, was formerly president and CEO of Global Communication Devices. Russell Cyr, CMO of BitWave, was formerly with Global Communication Devices, Adaptive Broadband, and Steinbrecher Corp.
The reconfigurable transceiver technology and associated intellectual property (IP) were developed by BitWave Semiconductor in collaboration with Massachusetts Institute of Technology (Cambridge, MA, www.mit.edu), the University of Florida (Gainesville, FL, www.ufl.edu), and Worcester Polytechnic Institute (Worcester, MA, www.wpi.edu). In the Softransceiver, they have developed the world's smallest scalable radio core, operating analog components under digital control for a wide range of performance parameters.
BitWave Semiconductor, Inc.,
900 Chelmsford St., Tower 3, Floor 7,
Lowell, MA 01851; (978) 888-0200,