Broadcom RFIC shrinks microwave backhaul nets

Rick Merritt, EE Times -- EDN, February 6, 2012

SAN JOSE, Calif -- Cellular carriers are seeking ways to lower the cost and size while increasing the bandwidth of the parts of their networks on the receiving end of the rising tide of mobile data. To date, much of their focus has been at the beginning and end of those so-called mobile backhaul networks.

Carriers and their OEMs are developing smaller more powerful base stations to take in more traffic for less cost and energy in their access networks. At the same time, they are shifting to use of Ethernet and fibre optics to link in faster, more cost-effective ways those access networks with their core nets.

Now a new group in Broadcom is taking some of the same techniques to the middle part of the backhaul network -- the microwave aggregation link. The BCM 85810 is a silicon germanium component that combines as many as 10 usually discrete devices into a single RF IC. It is geared to lower the size and cost of the electronics that drive microwave transmissions used to aggregate base station traffic on the way to the carrier's core net.

"No one else is doing SOCs for these kinds of products," said Aviv Ronai, a senior business development manager for Broadcom's networking group.

"Typically our competitors are the telecom OEMs themselves, developing their own chips," said Ronai. "We are trying to convince them our solutions are better and more cost effective."

The effort apparently is gaining some traction. About two months ago the Israel-based team released a baseband and networking SOCs for another part of the microwave nets that is getting design wins among top and second-tier telecom OEMs, he said.

With a staff of about 150 people, "we have the largest R&D team working on microwave technology SOCs," said Ronai. "Typically R&D engineers in the OEMs do systems design, and only a handful work on the chips, so their design time can be more lengthy and they can have more limited research and innovation," he added.

The Israeli team, formerly working as startup Provigent, was acquired by Broadcom last March.

"We started developing this chip before the acquisition," Ronai said. "Once we joined Broadcom we got connected to a lot of the company's RF know-how and that has made our life much easier," he said.

Provigent's strategy was similar to that of Broadcom in that both companies aimed to create solutions out of multiple integrated parts. However rather than CMOS integration, the startup's focus was on SiGe and gallium arsenide processes for devices such as 6-60 GHz microwave nets.

"The strategy of moving from the baseband and expanding to the RF domain follows Broadcom's strategy in other lines of business such as Wi-Fi and cable modems," said Ronai.

The group claims its new RF IC uses some of the same unique algorithms in its recently released baseband/networking chip. Such optimizations promise bandwidth increases of up to 25%, creating a benefit for the carrier if OEMs use both parts together, he claimed.

In addition, Broadcom is rolling out just two versions of the new chip to span the entire range of licensed microwave aggregation frequencies from 6 to 40 GHz. Currently, most competing chip sets are tuned to a narrower frequency range so that different systems require different designs, adding cost.

"This is a really significant simplification of inventory management" for carriers and OEMs, he said.

Microwave is used as the aggregation technology for about 60% of cellular networks worldwide, Ronai estimates. In countries such as India the percentage using microwave can be as high as 95%. In the US where bundles of copper T1 lines are still widely used, microwave is only used on about 15% of all links, but it expected to grow to more than 20%, he said.

The BCM 85810 supports both RF and intermediate frequency links. It includes low noise amps, automatic gain converters and IR mixers.

This story was originally posted by EE Times.