TI India develops SoC for broadband modems

Texas Instruments, India’s oldest MNC R&D set-up, has successfully developed the world’s first system-on-a-chip for the DSL segment. Prashant L Rao narrates the success tale of this mission impossible

The challenge was to implement analogue and digital components in a .13 sub-micron process, says Vivek Pawar

Sangam is the culmination of the dream that evolved in the Broadband Software Techno logy Centre at TI. This system-on-a-chip (SoC) is the outcome of questioning the possibility of integrating all the chips—the network processor, DSP, analogue front-end, line driver and power management—to create a single chip solution for a DSL modem. Explaining the reasoning, Vivek Pawar general manager of the centre says, "We wanted to go beyond the box and be a market leader by reducing our customer’s costs."

Sangam will be the brain of a DSL router providing a high-speed link to the Internet over the phone line. Also known as the AR7, it is aimed at the consumer side of DSL, a technology that’s heading for a global market of 200 million subscribers by end-2005 (Source: DSL Forum). TI’s chips account for 55 percent of DSL ports worldwide. That gives the company a dominant position in the DSL central office-equipment market. It now wants to achieve the same with regard to home DSL modems. And the Indian team was picked for this job.

While Sangam was built in India, the network processor came from MIPS and the DSP technology from the US arm of TI. While the development effort was global, the core SoC product is Indian.

Sangam—a union of digital and analogue

TI India’s latest chip, Sangam (AR7), is unique in many ways. It is the first chip manufactured by the company to have a significant analogue component integrated into its digital circuitry. It is also the first such project in the DSL space to be executed anywhere in the world.

The core chip team consisted of 70 engineers who worked on this project for one year. In addition to the core team, software developers at TI India also worked on the project. Moreover, 50 percent of the Broadband Silicon Technology Centre’s resources were invested in it.

From concept to manufacturing

• Architecture definition - This stage took around 3-4 months and 20 core team members from TI India went to Dallas in the US to gain from the experience of the systems team there. "We talked to customers even at that stage," says Suresh Kumar, manager DSL at TI India. This was the stage where TI’s customers gave the team feedback on the degree of functionality they were expecting from the chip.
• Design - This stage took 5-6 months. Division of work was also finalised during this period.
• Analysis and implementation - The layout took around 4-5 months. The mask information (information used to manufacture the actual chips) was released by TI India to TI Dallas at the end of this stage.
• Fabrication - The Dallas team in turn passed on the information to the fabrication department that made the chips. The actual fabrication took about a month.

Sangam (AR7) wafer

Harmonising analogue and digital

As the first chip to be designed at TI India that had an in-built analogue component and the first such effort anywhere in the DSL space—it was a gargantuan task to blend the two technologies. Mixing digital and analogue is tricky; digital tends to be clear-cut whereas analogue work requires detailed analysis to ensure that nothing fails. "The challenge was the implementation of analogue and digital in a .13 sub-micron process," says Pawar.

As this was a huge project involving 70 people, managing such a large team to ensure the smooth execution of the project was another challenge. Keeping a big team motivated for such a long time was not easy. However, the importance of the project and the impact of its success played a major role in boosting motivation, as all those working on it knew that success could translate into more DSL work at TI India.

Getting both teams—analogue and digital—to work together was a challenge. The digital side of things involved managing millions of gates. The noise generated by the gates had to kept to the minimum to avoid disturbance in the performance of the analogue components. Just putting analogue onto the same chip required that TI India use state-of-the-art 130 nanometre technology. "We worked with the processor lab, the fabrication teams and the analogue circuit team," adds Pawar.

The list of tools used on this project varied from Microsoft Project to customised tools, including the I/O sheet filled by each member of the project team. Tight co-ordination was the name of the game as each sub-team’s outputs formed another’s inputs.

Success by any other name...

Despite the scale of the project, "Within five hours of fabrication, the chip was working in a system," says Kumar. The team continues to interact with manufacturers through the product engineering team in Dallas. There were 10-12 engineers from TI India in Dallas earlier for this project, now there are six.

Very often something doesn’t work in the final product for a variety of reasons—problems with the board, the software is not compatible or in some instance loosely connected components have resulted in the project not taking off. Then again, sometimes there’s a problem in the chip that has to be fixed. However, with Sangam none of these hitches have materialised so far. "There are no major problems in Sangam’s silicon," declares Kumar.

TI India’s aim is to fix each and every problem before the chip goes into production, by using methods such as stress testing, where it conducts temperature testing using a machine called Thermostream, to force cold or hot air onto the chip.

Four patents have been filed as part of the Sangam project, and four more are in the pipeline. All these patents deal with enhancements to DSL technology, including one to deal with bridge tap loops—a common way of tapping phone lines—creating impedance problems. (See box: Advantage Sangam).

The successful completion of this project bodes well for TI India. As India’s oldest MNC R&D setup it has a long string of achievements to its name, of which Sangam is the latest.

We expect that TI’s R&D team in Bangalore will come out with more cutting-edge products in the future, building on this latest success.