Norwood, Mass—Analog Devices, Inc. released its single-chip radio transceiver for the EDGE (Enhanced Data Rates for GSM Evolution) cellular standard. Based on Analog Devices’ award-winning direct conversion Othello radio architecture, the new Othello-E transceiver integrates virtually all the necessary components, including voltage-controlled oscillators (VCOs), PLL loop filters and power management, for a complete quad-band EDGE radio design. Additionally, because of its ultra-small packaging, the Othello-E transceiver is among the smallest EDGE transceivers available on the market today. The device can operate in the 850, 900, 1800, and 1900 MHz frequency bands, enabling worldwide coverage.

To achieve the increased linearity necessary for the signals that support EDGE data rates, Analog Devices Othello-E radio leverages a high–performance logarithmic RF power detector to enable a closed-loop polar modulation transmitter design, which also contributes to better manufacturability and reduced design complexity. Closed-loop polar modulation is an improvement over open-loop polar designs, which require close matching of the transceiver and power amplifier. The Othello-E radio complements Analog Devices’ Blackfin SoftFone for EDGE baseband chipset, one of the most successful open-market EDGE baseband processors, which is currently featured in EDGE mobile devices from leading wireless device manufacturers.

“We have experienced great success with our SoftFone EDGE baseband processors over the past two years and we are excited to now offer our EDGE customers the benefits of our innovative Othello radio architecture in a single-chip solution,” said Christian Kermarrec, vice president, RF and wireless systems, Analog Devices, Inc. “There is renewed interest for EDGE throughout the world as a low-cost upgrade to existing 2G networks, and as a reliable, high-speed fallback technology for cellular operators launching 3G networks.”

According to data from the GSA (Global mobile Suppliers Association), 116 GSM/EDGE networks have launched commercial services in 70 countries. The GSA also found that 169 operators in 91 countries have committed to EDGE deployments. Illustrating the role of EDGE as a complementary technology to 3G networks, the GSA found that there are 55 operators deploying both EDGE and WCDMA, with 23 combined networks now in commercial service.

Analog Devices Othello-E transceiver (part number AD6546) is a single-chip solution combining all the radio and power management functions for an ultra-compact, cost-effective EDGE radio. It includes separate low-noise amplifiers (LNA) for all four GSM bands (850, 900, 1800 and 1900 MHz) and a fractional-N PLL synthesizer with integrated VCO and loop filter for local oscillator (LO) generation. An on-chip high-accuracy logarithmic power detector enables the closed-loop polar modulation, and ensures compatibility with power amplifiers from multiple suppliers while maintaining loop stability. In addition, the closed-loop architecture maintains stable, reliable, spec-compliant performance regardless of variations in PA characteristics due to manufacturing process variations, component aging, temperature, or frequency. On-chip voltage regulators enable direct connection to the battery supply, eliminating the external regulators needed by other transceivers and reducing BOM component count and PC board area.

The new Othello-E radio also complements Analog Devices’ family of SoftFone baseband chipsets for EDGE wireless terminals. ADI’s SoftFone chipsets are entirely RAM-based, thereby providing handset manufacturers with the flexibility to support changes in cellular standards and/or customize features and options for a wide range of phones by simply changing software and without the need to add new hardware. Together, SoftFone and Othello enable substantial BOM savings while maintaining flexibility, providing benefits to handset manufacturers and operators.

"We have chosen to use closed-loop polar modulation architecture," explains Doug Grant, ADI's director of business development, "so that any errors in the PA stage get swallowed up inside the loop." The alternative is to use an open-loop architecture, which requires designers to compensate for the PA's inefficiency by predistorting the signal. The challenge with that approach is that from lot to lot and band to band, and through component aging and other factors, the design can go out of spec. In a closed-loop approach, any errors in the PA are contained within a feedback loop.

This all sounds good, but how did the implementation go? "We had to stabilize a closed-loop polar modulation architecture which has two loops operating simultaneously with different time constants in the feedback loop," notes Grant, "While this required careful design, the advantage is that we only needed to do it once." In fact, the team spent a fair amount of engineering time to ensure that the design was stable and repeatable over temperature and process variations. The Othello-E's power detector and power control loop is based on some of the company's precision log amplifier technology, which gave the team a head start.

Another important part of the design process was performing extensive interoperability testing to ensure that the transceiver worked with PAs from various third-party vendors. "People tend to think of PAs as having one input. In fact, there is a second input that is critical when doing a polar modulation, and it is imperative to know the characteristics of the PA power control input," reports Grant.

Sometimes, the key to a good design is knowing when to stop. The team at ADI was aware that their customers really wanted a small package and minimal external components. So they wanted to make sure they hit all of their customers' expectations, yet added nothing unnecessary. In the end, the result was a 2.1 cm² design laid out on a 4-layer PCB.

The design team reports that it was careful to optimize power consumption, even beyond the ability to use a higher efficiency PA in the signal chain. As a result, the device features individual on-chip voltage regulators that can all be individually controlled to power each section in a predetermined sequence in order to minimize power consumption.

Where does this product fit in to the big picture at ADI? "It gives us a very competitive transceiver that complements our complete EDGE chipset, which consists of a baseband processor, the Blackfin processor for DSP functionality, and a mixed-signal and power management chip with A/D D/A converters to generate the required supply voltage/battery management," says Grant. Looking forward, the company plans to use EDGE as its "fallback" mode for its 3G chipsets, as opposed to GPRS.

The Othello-E radio is priced at under $3.00 each in production quantities. It is sampling now. Click here for more information.