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Slicing through the Radio: An Integrated, Configurable Components Approach

June 16, 2008
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Highly integrated RF transceivers and system-on-chip (SOC) solutions are widely adopted in high-volume consumer products such as cellular handsets, WLAN routers and Bluetooth® headsets. However, the economics of semiconductor development do not support this high level of integration for low volume and custom-built radio designs. As such, these radios are designed using standard, off-the-shelf, RF components. Furthermore, many of these components were designed prior to the emergence of the latest radio standards, environmental directives and semiconductor technologies. Finding a balance between stringent performance targets and expectations for small, cost-effective and reliable solutions while using a catalogue of outdated components is very demanding. Couple in the call for lower power consumption and the ability to operate products from a single battery (Li-ion or polymer) and you have tremendous challenge to RF engineers as they tackle today’s radio designs.


RFMD® recently introduced a line of integrated, configurable components to specifically address these very issues. In combining an RF synthesizer with wideband RF mixers, the RF205X line of components offers a solution by integrating common radio functions into a single device that can be operated from a single 3 V supply. Their uniquely configurable yet highly integrated design makes them the perfect choice for frequency band shifters, diversity receivers, satellite communications equipment, wireless repeaters, point-to-point radio links, instrumentation and test equipment, cognitive radios or simply as wideband low-noise signal sources. The block diagrams for the RF2051, RF2052 and RF2053 are shown in Figures 1a, 1b and 1c.

Key Features of RF2051, RF2052 and RF2053

The RF2051, RF2052 and RF2053 are designed for 2.7 to 3.6 V operation and are housed in a plastic 32-pin, 5 x 5 mm QFN package for optimum compatibility with portable, battery-powered devices. The RF synthesizer includes an integrated fractional-N phase-locked loop (PLL) with voltage-controlled oscillators (VCO) and dividers to produce a LO signal with a very fine frequency resolution down to 1.5 Hz. Additionally, the fractional-N synthesizer allows for a wide loop bandwidth to be used for digital/phase modulation to achieve fast PLL locking times and lower noise within the loop bandwidth. The LO generation blocks in the RF2051 and RF2052 have been designed to continuously cover the frequency range of 300 to 2400 MHz without component replacement. The RF2053 allows designers to take advantage of an external VCO source, while exploiting the internal fractional-N PLL synthesizer and high linearity RF mixer. The integrated, high-linearity RF mixers are very broadband and operate from 50 to 2500 MHz as measured at the RF ports of the device. An external crystal or an external reference source of between 10 and 104 MHz is flexible enough to accommodate a variety of reference oscillator options.

Highly configurable in nature, the RF2051, RF2052 and RF2053 utilize two separate hardware-selectable frequency registers to allow switching between two independent frequencies without re-programming (i.e. Rx/Tx, Rx1/Rx2 or Tx1/Tx2). The devices are also programmed using a true three-wire serial control interface and feature an automatic calibration algorithm to provide an accurate and stable LO signal. Last but not least, the bias currents can be programmed to optimize supply current/performance tradeoffs.

The Integrated Configurable Advantage

Many benefits of this solution can be identified when compared with a discrete implementation of the same functionality:

Power consumption: The family of components is fabricated using circuit IP developed for RFMD’s POLARIS® EGPRS transceivers. The stringent GSM handset performance and low power consumption requirements from 3 V supplies are well known. With RFMD’s new RF205X line of components, the same current savings seen in transceiver-based solutions can be realized due to the integration of the RF interfaces such as those between the synthesizer LO output and the mixer, thus allowing optimization of impedances and parasitics, leading to this reduced power consumption. Furthermore, not all radio designs will have the same noise, linearity or supply current performance requirements, so the RF2051, RF2052 and RF2053 have been designed to allow power consumption in key circuit blocks such as the VCO, LO buffers and mixers to be programmed via the serial interface, thus minimizing current draw for a given application.

Solution size: The RF2051, RF2052 and RF2053 replace at least three to four single-function components—the synthesizer, the VCO and one or two mixers. Additional integrated functions that may otherwise have been required as discrete components include LO buffers and LO distribution. Integration of all of these functions, in addition to interconnect wiring, power supply decoupling, etc., leads to a significant reduction in solution size compared to a discrete component design.

Reduced development time: By integrating key interfaces between the VCO, the PLL and the mixers, the RF complexity of a radio solution is greatly reduced. Issues of RF pick-up and isolation related to these interfaces on a discrete component design may require many PCB spins to identify and correct. Moreover, because RFMD’s components are configurable they can be used for most frequency bands and performance standards, and a high degree of design reuse or platform design can be employed, reducing time to market and maximizing lifetime revenue.

Final product yield: With RF2051, RF2052 and RF2053 the final electrical specifications for the complete functionality is guaranteed. A discrete radio design requires that all performance permutations of the individual components and their effect on the overall system performance needs to be estimated. At best, this leads to a product that is over-designed in order to yield properly in the unlikely event that each of the individual component variations are at their worst-case limits. In the worst case, dramatic yield loss of the final product could result from unanticipated performance degradations when separately specified components are combined.

Example of the “Slice” Application

The following example exhibits a potential application for these integrated, configurable components as a frequency up and down conversion stage in a wireless repeater. In this application, both mixers are enabled concurrently and share the same LO frequency, which has been internally buffered to ensure isolation between the two paths. A significant reduction in solution complexity is achievable compared to a discrete component solution (see Figure 2).

Typical Performance

Figure 3 shows the IIP3 performance over temperature for the RF205X family. Figure 4 shows NF and IIP3 versus mixer current setting. Figures 5 and 6 show the phase noise performance at 500 and 2000 MHz, respectively, with 60 kHz LBW.

Conclusion

RFMD has developed a new family of integrated, configurable components, utilizing advanced circuit design techniques on modern semiconductor processes that are broadly applicable to any number of radio designs and over a wide range of frequencies. A number of advantages over discrete component solutions can be identified, including lower power consumption, simpler supply voltage requirements, smaller board area, increased design confidence and a faster time to market. Because these components are broadly applicable, they are available “off-the-shelf” with short lead-times and can be ordered through the local sales channels and via the RFMD webstore. Furthermore, to assist in their implementation, an evaluation board is available with a USB programming interface and a software suite to allow control from a standard PC.

RFMD®
Greensboro, NC
(336) 664-1233
www.rfmd.com

RS No. 301

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