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WLAN gets a boost with a dual PA

Posted: 22 Dec 2005 ?? ?Print Version ?Bookmark and Share

Keywords:MIMO? SST Communications? power amplifier? PA? multiple-in-multiple-out?

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There is much talk about MIMO these days, and many vendors are looking for ways to simplify the multiple channel approach and circumvent the design challenges that are quickly emerging. SST Communications is no exception, and it recently reported that it was the first to market with a dual power amplifier (PA) for multiple-in-multiple-out (MIMO) WLAN systems. The SST12LP30 provides two amplification channels in the 2.4GHz band for 802.11b/g devices that feature an architecture with two transmitters and two receivers (2x2).

According to the design team, its customers' main concerns for MIMO systems are the high cost of multiple PAs and low board yield due to output power mismatch between multiple transmitters. SST took on the cost challenge by reducing package area and integrating on-chip power detectors, and it took on yield by providing factory pre-matched output power between the two channels.

Reducing the BOM were key design drivers in the development of the SST12LP30. For instance, in a typical 802.11 b/g system, the PA typically requires 12 to 15 external components. For a 2x2 MIMO, this component count jumps to 24 to 30 external capacitors, inductors, and components. "Our dual-PA SST12LP30 with on-chip power detectors requires only 16 external capacitors. Its two on-chip power detectors can be driven by 2mA quasi-digital signals without the need of external power regulation, which is a significant saving as compared to the competition," said Frank Chang, vice chairman and chief technical advisor, SST.

In terms of manufacturability for MIMO systems, "The biggest issue is its potential low board yield due to mismatched channel performance," noted Chang. "The 12LP30 provides factory pre-matched PAs within 0.3dB in both gain and output power. This would guarantee the board production yield and minimize customers' risk in fighting with two separate PAs that have different production histories and imperfect board layout differences between the two channels. This product enables the mass production of MIMO systems."

Manufactured using InGaP/GaAs HBT technology, the SST12LP30 is a natural extension of SST's discrete and single 802.11 b/g amplifiers, and its PAs are based on the company's existing SST12LP14A part. The design process was not without its challenges, though, and the design team spent some time developing the methods to produce well-matched dual channels with very tight specifications and still maintain sufficient isolation (20dB).

The SST12LP30 is now available in production quantities.

Pricing for the SST12LP30 devices start at 65 cents in 10,000-unit quantities. The devices are offered in a 3-by-3mm, 16-pin VQFN and Pb-free packages.

- Janine Love

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