[Technology Report]
More Embedded Features Provide Easier Analog Designs
While suppliers at all levels focus on applications, analog IP enters its teens.
By building in more value-added features, companies hope to remove some of the hocus-pocus from the analog-design portions of new products. Obviously, these features can't instantly move OEM customers to the cutting edge of performance. But they're preventing the more predictable design errors that tend to scuttle schedules when a ones-and-zeros engineer tries to implement something with voltages that insist on wriggling around.
These value-added features are embedded in the products, in part as Web-based enhancements to paper data sheets and product-selector tables, and in part as new design tools.
TEST SYSTEMS, TOO, NOT JUST CHIPS Tektronix's latest oscilloscopes, which can test the most advanced serial data standards, come with the specs for those standards embedded in firmware. During the design cycle, engineers can trace problems that occur in levels 2 and 3 of the OCI model, right down to analog discrepancies that occur in the physical layer. In the production phase, these same scopes more or less painlessly test all of the characteristics called out in the standards to document conformance.
Tektronix pioneered that involvement in standards, down to the level of designating test methodologies, back in the analog-TV era. But these latest products represent the first time that standards were embedded in a general-purpose instrument. Speaking of firsts, 2005 may mark the true coming of age of analog intellectual property (IP). Purveyors are genuinely profitable members of the analog design community. As recently as the 2003 Design Automation Conference, panels were nearly unanimous in declaring that the day of analog IP was a still a long way off.
Today, there's a respectable if not huge number of companies whose analog IP runs on a large number of digital ICs fabbed by the world's established foundries. In addition to its digital IP, Artisan Components offers a range of specialty I/Os for HSTL, low-voltage differential signaling, PCIX, PECL, SSTL, and USB, plus a number of phase-locked loops (PLLs) and dynamic link libraries (DLLs). LTrim offers voltage references, LDO regulators, charge pumps, buck and boost converters, battery chargers, temperature sensors, and CPU reset for out-of-spec power excursions. QualCore Logic, which acquired LEDA Systems in 2004, has a large selection of data converters, multiplexers, switches, oscillators, DLLs, PLLs, amplifiers, filters, and voltage regulators.
Except for LC oscillators, analog cells are less sensitive to parasitics in the interconnect layers than digital, particularly with copper metal layers. Interconnect inductance generally isn't as significant as driver inductance. The most worrisome thing on the horizon, as process technology generations continue to shrink, is dealing with gate leakage and ever-shrinking threshold voltages, especially in the generations below 90 nm. Channel-length modulation affects transistors' abilities to work as current sources, and the threshold voltage problem will be particularly critical at low temperatures.
Peak-to-peak output jitter in embedded PLL specs should be expressed in terms of a percentage, rather than as an absolute value in terms of fractions of a second. The jitter spec is important because ASIC designers must use it to adjust their timing budgets. At the end of the day, except on test chips, jitter is hidden inside the IC and only manifests itself in bit error rate. That's why ASIC designers should seek long-term relationships with their analog IP suppliers. In fact, that's where today's realities contradict the gloomy predictions of a couple of years ago. Analog IP is yet another case where there aren't enough analog designers to go around. Using IP vendors for the analog cells of an ASIC isn't about more outsourcing. Instead, it's about making the best use of a scarce resource.
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