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Startup tames EMI using spectral-diffusion scheme

Posted: 03 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:sitera? electromagnetic-interference? x-emi?

A startup with roots in the network processor company SiTera Inc. has demonstrated a unique solution to electromagnetic-interference problems. X-EMI Inc. is using a proprietary method of spectral diffusion to modify system clocks in order to reduce EMI from a variety of sources.

The original single-channel transceiver shown to OEM customers this month will be followed quickly by quad and octal versions, said Steve Sheafor, a SiTera founder who serves as chief technology adviser to X-EMI. General sampling will begin in the fourth quarter, at which time pricing will be announced.

Unlike spread-spectrum clock concepts emerging from the PC community, the X-EMI solution does not change clock frequencies and can be designed into legacy systems. Nevertheless, the company is focusing primarily on designs for next-generation buses like PCI Express. "As your bus frequency exceeds 100MHz, what is advantageous [at lower speeds] becomes a necessity," Sheafor said.

The new company is built on ideas generated at Rice University and the University of Houston starting in 2003. Early this year, former SiTera executive Larry Woodson was brought in as chief executive officer to get products to market.

X-EMI will focus on sales of chips rather than intellectual property. The first such product is the XM1001, a simple standalone oscillator and frequency synthesizer with differential and single-ended I/O. The device provides an interface between the X-EMI XClk signal and a normal clock signal. At a transmit end, it converts a system clock signal into a very low-EMI signal. When used as a receiver, the XClk signal is recovered and converted to the normal system clock. Current 28-pin devices will move to eight-pin designs in the future, according to the company.

The key, said Sheafor, "is autosensing to tell whether we are encoding or not. These devices can be used within existing systems, with almost negligible footprint."

In X-EMI's Optimized Spectral Diffusion scheme, the source signal is multiplied by the output of a digital noise source. The resulting clock is then sent to a destination and multiplied by an identical noise source. X-EMI uses its own analytical algorithms to create efficient spread spectrums, with very low peak EMIs. Unlike native spread-spectrum clocks, the X-EMI method does not dither the signal, and affects all higher-order harmonics of a signal the same way. Some demonstrations have shown 30-dB reductions in EMI, said chief technology officer Ken Egan. The algorithms can be implemented in a solution that is almost fully digital, with only small analog blocks. "We've implemented the first XM1001 in quarter-micron CMOS," Sheafor said."

- Loring Wirbel

EE Times

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