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Integrating an RF transceiver into a Cellular-Enabled Product Has Never Been Easier

Mon, 11/19/2007 - 6:06am
Enhancing RF transceivers with embedded intelligence can significantly reduce the burden on the phone manufacturer when integrating EDGE or UMTS transceivers and when testing phones on the production floor.

By Keith Tilley, Freescale Semiconductor

Over the years, design-engineering teams tasked with creating cellular phones have warily regarded the transceiver portion as unfamiliar territory. While of necessity, the RF and digital designers at phone manufacturers have grown a bit closer, the less time digital designers spend dealing with the vagaries of "fields and waves" the better.

Complicating matters, when transceiver manufacturers make changes to their designs, regardless of how minor, designers at the phone manufacturer have typically been

click to enlarge

Figure 1. Freescale’s RFX 300-30 is an example of a UMTS-EDGE radio system.
required to adjust a large number of variables to accommodate the changes, even though the basic functions—transmit and receive—remain the same. What’s more, calibration of phones in production requires a considerable amount of time, since many variables must be addressed.

The time to develop new phones is increasingly gated by software development, not hardware development. Simplifying phone software development tasks as much as possible and building in standards compliance can help improve time-to-market, ease the overall burden of integrating a new transceiver and increase the chances that a new customer could easily integrate an RF transceiver into a cellular-enabled product. Integrating digital functionality into a traditionally analog subsystem can reduce design cycle time and the time spent in production test. This "embedded intelligence" allows a single command to facilitate multiple actions, instead of performing those actions manually.

Enhancing RF transceivers with embedded intelligence can significantly reduce the burden on the phone manufacturer when integrating EDGE or UMTS transceivers and when testing phones on the production floor. This approach can shorten the design process and reduce time spent per phone in production test by an order of magnitude. Freescale has shown that with its EDGE and UMTS transceivers, embedded intelligence can reduce time to first call by more than 60%.

For the benefit of phone manufacturers, RF transceivers should be as integrated as possible with the digital circuits of the phone. Their achievements can best be shown by illustrating two examples that
Figure 2. Freescale’s MMM7210 UMTS/EDGE transceiver, which combines quad-band GSM/EDGE functionality with up to four of nine UMTS bands.
in the past have required significant effort by phone manufacturers. In a frequency synthesizer, the synthesizer’s integer divide ratio, the numerator and denominator of the fractional divide and other parameters are set by software. The specific details of this programming depend on the circuit and architecture. Embedded intelligence solves this problem by removing as many of the details from the software interface as possible. In the synthesizer case, the software simply commands the RF IC to (for example) "go to channel 1.

Since the device has been programmed with all the details of that channel (as specified in the 3GPP standard), no more programming is necessary. This allows the designer to freely incorporate circuit and architectural improvements to the synthesizer (or other components) without placing the burden on the software team to learn how to implement them. This is in direct contrast to the usual process in which designers have to program every component of every channel, a tedious process that this approach simply eliminates. Automatic gain control (AGC), a basic function of every phone, is another good example. Setting the gain on each of the amplifiers in a transceiver takes programming time. With this approach, when an AGC state is defined, not just one but all amplifiers are automatically set to the proper gain setting. While this may seem a minor improvement, it has already proven to significantly reduce development time, and allows designers to migrate from one device generation to another with far less difficulty.

Figure 3. Freescale’s MMM6038 EDGE power amplifier.
Embedded intelligence also helps eliminate many calibration steps during production test, eliminating adjustments that have historically been calibrated in the phone factory and performing them automatically on the chip.

There is also an advantage to programming the physical layer (Layer 1) as a whole, rather than in its many discrete elements. RF architectures historically have required that an RF designer be involved with Layer 1 software of the phone to understand precisely what is occurring at every point in the RF path, and orchestrate the required functions from the RF device level straight through to the antenna. If Layer 1 is programmed as a whole, the RF section is seen as just another hardware peripheral that must interface with the microcontroller or DSP at the baseband level.

Building more standards compliance and interoperability into RF software increases a phone manufacturer’s chances of getting a phone right the first time. Combined with time and cost-saving advantages of reducing calibration time and easing RF integration into a largely digital product, embedded intelligence is an optimal choice for designers of cellular-enabled products. About the Author

Keith Tilley is director , product management Freescale Radio Products Division, 2100 East Elliott Road, Tempe, AZ; (480) 413-4590; Keith.Tilley@freescale.com.

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