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Putting the squeeze on RF

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A visitor from Mars could be excused for thinking that RF design is a newly-hatched discipline, such is the hype surrounding the subject. In fact, RF (standing for Radio Frequency) is a historical label, harking back to the days of the 30’s and 40’s when the circuits could only transmit in the AM and FM bands. The introduction of UHF TV in the 60’s boosted the outputs into the 300 MHz region.

Since then, communication applications have increased in content, frequency, and bandwidth, increasing the challenges for analogue/mixed-signal-IC designers at an unprecedented rate. Engineers are integrating RF circuitry with analogue and digital nanometre circuitry. Gigabit data rates are making digital circuits behave like microwave circuits. And complex wireless-communication standards—such as Wi-Fi, 802.11a/b/g and Bluetooth—require circuit designers to evaluate the impact of their designs on overall system performance.

Form factor, power and cost drive the increasing integration of analogue, RF and digital design. Portable-device applications, for example, demand that products are small and light, are extremely power-efficient and inexpensive. The race to integrate all RF and support functions, such as controllers and application interfaces, into the same chip is understandable, because it lowers manufacturing cost of the device, and reduces power demand. It is also likely to reduce the size of the chip.

Paying the price

But there is a price to pay, if not in terms of final cost, then in complicating the design. Whereas analogue and RF circuitry has traditionally existed on its own chip, making it much easier to isolate noise, integration of RF and analogue functions on the same chip exacerbates the noise problem. Unfortunately, individual designers rarely have both RF and analogue expertise, and design teams use different development tools for the separate functions, leading to difficulties during final chip integration. For example, engineers almost always perform digital design in the time domain and RF design in the frequency domain (for simulation speed). Integrating these two design styles on the chip can mean that simulation time of the entire chip is unrealistically long. The same situation is true for the test and verification phases of the design flow. The tests for digital differ from those for analogue, and, again, the analogue portion of the design differs from the RF portion. In spite of the problems, designers have developed and continue to develop products that integrate all three disciplines.

Depending on the size of a design, RF effects can become noticeable at frequencies as low as a few megahertz. Even clocks operating as low as a few hundred megahertz have frequency components well into the gigahertz range. These high-frequency harmonics of fundamental clock rate can easily radiate off the board or the chip and cause noise and interference problems elsewhere in the design. Analogue and digital designers are now seeing the undesirable consequences of “high frequencies” in their designs in the form of signal contamination, crosstalk, substrate coupling and parasitic effects. The industry uses the term “signal integrity” to describe unwanted RF effects in digital design.

Although both semiconductor and EDA vendors are working to develop accurate models of RF devices that they will be able to efficiently simulate, most designers still rely on design guidelines and reference designs from RFIC vendors.(1)

Whats new in RF?

Fortunately, the chip vendors have tackled the challenges of integration, price, size and power consumption with notable success. This has resulted in integrated RF chips across the spectrum from ICs for wireless keyboards, single-chip Bluetooth solutions, through 802a/b/g devices and on to mobile phone modules. All these solutions are available from local component distributors. When selecting intergrated RF products, perhaps the key to making the right choice of supplier isn’t so much in what products it offers, more in the quality of its field application engineers. This is because good technical back-up can overcome the fear of the “black art” of wireless design, and allow designers with minimal experience of RF to introduce the benefits of wireless into their products.

Here we provide details of just a small selection of products we have seen in the past few months. (For more comprehensive coverage of new releases, and an archive of hundreds of RF products, please visit our website at www.electronicsnews.com.au and our sister directory site at www.ferret.com.au.)

Following the launch of its integrated 2.4-GHz wireless transceiver/transmitter with 8051 microcontroller core last May (pictured), (see EDN Australia June 04 page 4), the company has now released a 433/868/915 MHz version, the nRF9E5/nRF905. The single chip solution will be distributed by Insight Electronics and Eaton Electric Systems in Australia.

The nRF9E5 transceiver has an embedded 8051 compatible microcontroller, and 4-input, 10-bit ADC. The company is claiming that this is the first time the market has been supplied with a complete low cost wireless system-on-a-chip solution with a single 1.9 to 3.6-V supply. Voltage regulators are embedded on-chip.

Both components include “ShockBurst”, a feature that aids CRC computation in both Tx and Rx mode, and address decoding in Rx mode, reducing the load and cost of the microcontroller running the RF protocol.

Nordic says that a crystal and a resistor are the two components needed externally to make up a complete system around the nRF905. The nRF9E5 requires an external EEPROM for program storage. Both the components are delivered in a 32-pin, 5 by 5 mm QFN package.

Design and layout files are available for both the nRF905 and nRF9E5 from Nordic VLSI to facilitate low risk development and short time-to-market for customers.

Of note to exporters is the fact that the nRF9X5 family has the capability to operate with the same layout and identical external components in the unlicensed European 868-MHz ISM band as well as the North American 915-MHz SRD band, easing logistics and lowering cost for manufacturers who have customers in both territories.

Also hailing from Scandinavia is the newly-available Chipcon CC1021 device which is described as “a multichannel RF transceiver for low-cost and robust RF performance”. It is distributed in Australia by Clarke & Severn. The CC1021 is a cost-optimised version of the CC1020, and operates in the 402–470 MHz and 804–940 MHz frequency ranges. The device features a software configurable radio architecture. RF frequency, modulation output power, data rate and IF bandwidth can be programmed via an SPI-compatible interface to suit each individual application to create low cost RF communication. Chipcon says the chip suits applications such as automatic meter reading, home automation, alarm and security systems and remote keyless entry. It offers a programmable data rate of up to 153.6 kbit/s, a 2.3 to 3.6-V supply voltage and programmable output power up.

Bluetooth made easy

Xemics has considerably eased the challenge of Bluetooth implementation with its newly-qualified EasyBlue ACL Drop-In board, which the company claims “significantly reduces the customers’ time to market as it bridges directly from a 4 wire UART to the air interface”. The board is distributed in Australia by Electronics Development Sales .

The Drop-In board is a qualified, class 2 reference design, to be used as a drop-in solution to all kinds of power sensitive Bluetooth data links. Xemics says that it completely bridges the Host Controller Interface (HCI) to the air interface and provides the full Bluetooth data communication feature set; ranging from high speed communication over seven slaves to scatter net support. The maximum power consumption of typically 21 mA at 1.8 V makes it suitable for any portable application requiring high speed data communication, full networking capabilities and low power consumption at the same time. Because of the qualification of the complete radio, antenna and all embedded Bluetooth layers, the design can be used as supplied.

The Drop-In board is designed for low cost volume manufacturing using a standard four-layer PCB layout and materials. Samples are available through the distributor. Development tools and a starter kit exist for first time Bluetooth developers.

National Semiconductor, represented by Arrow , has released a Bluetooth product family that complies with the recently-ratified Version 1.2 of the Bluetooth Specification. The new features found in Version 1.2 include faster connection times, improved voice transmissions and adaptive frequency hopping (AFH) to help avoid conflict with other 2.4-GHz devices.

The LMX5252 is a Bluetooth radio transceiver that claims to offer a high level of RF integration. The LMX5452 combines the radio with an enhanced Bluetooth 1.2 baseband processor into a small micro-module package. Both products offer analogue and RF integration in a small footprint, saving space and cost.

The LMX5252, in a 36-pin LLP package measuring 6 by 6 by 0.8 mm, includes a Tx/Rx switch and baluns. It supports multiple system clock frequencies of 10 to 40 MHz, and has a typical Rx sensitivity of -84dBm. It suits applications where the Bluetooth baseband functionality is already integrated into the primary processor.

The second device in the family, the LMX5452, in a 64-pin micro-module BGA package measuring 9 by 6 by 1.2 mm, combines the Bluetooth transceiver with the baseband processor.

The baseband processor features full Bluetooth 1.2 functionality and firmware, and an enhanced HCI command structure.

Stepping up the scale sees a module released for the GSM/GPRS mobile market from STMicroelectronics. (Braemac and Arrow.)

The triple-band GSM/GPRS transceiver modules use Silicon Germanium (SiGe) RF BiCMOS and “Integrated Passive & Active Devices” (IPAD) technologies to simplify and reduce the size of the modules.

In a 1.4 by 7 by 7-mm low profile BGA package, the new modules integrate all of the key functions, requiring only a 26-MHz crystal and a power amplifier to build a complete triple-band solution from antenna to baseband interface. Two versions are offered: type STw3100 addresses the European bands while the STw3101 targets the US bands.

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