July - 2007 issue > Cover Story

By Priya Pradeep

Who says we live in a digital world?” questions Ravi Subramanian, President and CEO of Berkeley Design Automation, a company that thinks and breathes analog.

He explains, “As the world gets digital the paradox is that there is more of analog.” For instance, be it the audio or the display or the memory peripherals of an iPod—analog is an essential component; digital music and movies means so much more analog stuff.
While the design engineers today are able to get the digital substance right, analog is where the big challenge is. Quite often managers scram, “Where’s the analog stuff. It is not working yet.” Subramanian questions the thesis: Why analog teams couldn’t get across the hurdle?

Ten to 15 years ago, analog designers were creating circuits using about a few dozen transistors. Analog designs did not need to use the most advanced silicon technology; there was no dearth of existing device models and design rules, and they benefited from the experience gained with previous designs implemented on the same. Basic circuit simulators were adequate to help the designer produce acceptable designs.

Today, analog design involves implementing 2.4-GHz RF transceivers using thousands of transistors in a 65-nm silicon technology, and the architecture is prone to wide performance variations across the process, voltage, and temperature ranges. This transceiver shares silicon with millions of gates of digital logic that produce substrate and power-supply noise that the transceiver must tolerate. And the cost of a silicon re-spin has escalated to more than a million dollars.

The old method of relying solely on experience from previous designs and using silicon for verification doesn’t work in this case. It is difficult or impossible for the designer to intuitively determine which of the thousands of devices in the transceiver is most vulnerable to the power-supply noise generated by the switching of the digital logic.

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