SAN FRANCISCOThe Virtual Socket Interface Alliance (VSIA) released the initial version of a signal integrity extension to the specifications defined by its Analog/Mixed-Signal working group on Monday (March 11). The extensions were developed to help suppliers of intellectual property (IP) communicate signal integrity data to IP integrators.
"The signal integrity concern is not just among analog IC designers, but also for digital ASIC designers working with high interconnect densities at 0.18 micron and below," said Raminderpal Singh of IBM Microelectronics, co-chairman of the AMS working group, and primary author of the signal integrity specification. High interconnect densities that follow from shrinking CMOS geometries can cause signal interference between neighboring wires and often lead to unstable system-on-chip behavior, he said. Moreover, smaller noise margins can produce interference between IP blocks and increase the difficu lty of predicting signal integrity between connected logic blocks.
The VSIA specification consequently defines three areas in which a digital signal transfer can be corrupted by stray signals or noise. These include interconnect crosstalk, substrate coupling and signal electromigration.
"We're viewing it from the point of view of the designer who says, 'Oh! I didn't realize that occurred'!" said Singh, who works as a senior engineer at IBM's ASIC group. While the signal integrity specification is by no means a contract between IP supplier and user, it can provide some useful points of discussion.
The specification was developed to meet the needs of modeling tool developers, Singh said. "You can buy complex modeling tools, but some may not work at this level," he said. "The problems are difficult to get your hands on. You want to be certain your design has low risk. Identifying some things to look for at least will bring you closer to a 'warm, fuzzy feeling' at sign off."
VSIA said its signal integrity extensions were developed by working group members Intel, IBM, Motorola Semiconductor Products Sector, and Simplex Solutions. VSIA also credited the ARM consortium, Cadence Design Systems, Mentor Graphics, Philips Semiconductors, and the Special Interest Group representing Japanese interests in the VSIA.
VSIA members can downloaded the Signal Integrity VSI Extension Specification version 1.0 (AMS2 1.0) document free of charge from the VSIA Web site. Non-members must pay a licensing fee.
The AMS signal integrity study group is already looking ahead to version 2.0 of the spec, Singh said. "Because of process scaling, SI is always a moving target," he said. The next document will include ongoing research into mutual inductance effects at 0.13-micron and 0.10-micron process geometries; will help map signal integrity data and data types; and will streamline the process by which new VSIA participa nts are incorporated into IP trades, Singh said. "In all cases, we need to hit the ground running," he said.