Broadband is calling the shots…

Broadband is calling the shots…Roy Rubenstein  
“The broadband revolution is upon us.” This is the claim of Henry Samueli, chief technical officer at US firm Broadcom, writes Roy Rubenstein.
Such a claim may ring a little hollow to some, especially when the closest they get to ‘broadband’ services is when a V.90 modem works close to its 56kbit/s maximum data rate. Yet Samueli is in no doubt, the drivers for high bandwidth communications in the home and in the office are here today.
For the home, programming content starting to accompany digital TV services is one example, the demand created for high bandwidth cable and xDSL modems to access multimedia content on the Internet is another. Samueli also highlighted office requirements where bandwidth demand is being addressed by Fast and Gigabit Ethernet local area networks.
Meeting these broadband requirements is what concerns Samueli since the challenges posed by designing mixed-mode ICs are considerable. “These devices incorporate a significant amount of algorithmic complexity encompassing entire receiver systems,” said Samueli.
To give some insight, Samueli started with the issue of simulation. Exhaustively simulating a receiver’s circuitry – its adaptive filters and numerous feedback control loops – is now almost impossible due to time-to-market pressures. Coupled to this are the endless trade-offs when mapping the high-level floating point simulation models into finite precision implementations.
The consequences are that simulation short cuts are used to control the overall time spent verifying the design. This can result in a circuit meeting the specified design yet failing to work properly when used in the final communications system.
This is where specialist know-how proves invaluable: “It takes many generations of products to develop an appropriate ‘bag of simulation tricks’ to validate a receiver design,” said Samueli.
One key challenge facing mixed-mode IC designers is combining a sophisticated analogue front-end to a substrate containing millions of transistors of digital circuitry. Analogue designers are being forced to create robust circuits insensitive to process and temperature variations. “One cannot afford to throw away a fully functional multi-million transistor digital section because the A/D Converter is degraded,” said Samueli.
Perhaps the most striking challenge facing analogue designers is developing high-performance circuits capable of operating at low-voltage. Dual oxide processes help offset this problem by allowing the analogue section to enjoy a higher voltage than the digital one. However, Samueli is in no doubt that while this will help, the overall trend is very definitely towards lower voltage analogue circuitry.
For Samueli, the good news is that these challenges will continue to make IC design the most exciting profession for the foreseeable future. The bad news is the sheer amount of work this will entail.

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