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RF/Microwave??

HD chips do double duty for standard definition

Posted: 16 Dec 2003 ?? ?Print Version ?Bookmark and Share

Keywords:high definition chip? hd? video channel? multi-channel audio and video?

There are times when simple ideas can add the most value. As in when you realize that you are throwing away parts that would be perfect for an important segment of your market. The case in point is Magis Networks and the product is Magis' wireless-networking chipset for home entertainment networks.

The 2-chipset is used by STB, TV monitor, recorder and audio equipment makers to permit wireless connection of multichannel video and audio throughout a home. It has been gaining traction in the market, said director of marketing Tom Kovanic, as small players looking for differentiation up to industry heavyweights like Sanyo and JVC become interested in home media networks.

Magis could be well-positioned for this market's takeoff, having shown a working chipset as early as January 2002. That set, the MGS6200, was designed to carry multiple high-definition (HD) video channels. But as the market has expanded, Kovanic said, a split has developed between manufacturers embedding the networking capability into their equipment - which universally go for HD video--and makers of add-on boxes, which primarily focus on supporting older, standard-definition (SD) products.

Magis' 2-chipset is specified with sufficiently low-phase noise, and sufficiently good control over similar parameters, to handle HD data. But the process was yielding a quantity of chips not quite up to HD, yet sufficient for the data rate necessary for SD video. Hence, a new product line without a new design: the MGS5200 is function and pin-compatible with the 6200, but is made for SD connections only.

Don't fight it

Magis' Air5 technology, while superficially similar to IEEE 802.11a and using the same 5GHz frequency band, is in fact different in several specific ways. First, the technology uses a synchronous time division multiple access protocol with bit-stream prioritization to guarantee quality of service. This makes the MAC design significantly different from the collision-detecting controller for 802.11 systems.

Second, the Air5 system uses 5-way receive antenna diversity - which exploits, instead of fighting the high-multipath environment in the typical home. Each millisecond, the Air5 chipset examines the signal patterns coming in on five discrete antennas and selects two. Those two signals are then routed through the RF front-end and into the baseband section, where the two streams are digitized, processed and digitally recorrelated.

This antenna diversity algorithm not only allows the receiver to benefit from the two best signal paths - thereby getting better SNR than would be possible with a single antenna - but it can dynamically compensate for, and even exploit, a changing RF environment, such as the TV viewer heading for the kitchen for another beer, according to Kovanic.

The first member of the 2-chipset is a SiGe RF front-end fabricated at Jazz Semiconductor. This device includes low-noise amplifiers and a unique RF multiplexer for antenna selection, and a 2-stage superheterodyne using a 900MHz IF to exploit low-cost cellphone passives. It has a somewhat simpler transmit path with a variable-power output stage driving a single transmit antenna. The Air5 system uses only sufficient transmit power to achieve adequate receiver SNR.

The baseband signal is passed in analog form to the baseband chip, a TSMC CMOS device that includes the ADC, signal-combiner circuitry and MAC. The latter block is an augmented ARM9 core with hardware support for 3DES encryption. The baseband IC includes two MPEG-2 transport interfaces and a control port that can be configured either for PCI or as a generic MPU bus interface.

- Ron Wilson

EE Times





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