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PLL clock lowers EMI

Posted: 13 Jul 2005 ?? ?Print Version ?Bookmark and Share

Keywords:alliance semiconductor? clock synthesizer? asm3p2853a?

Alliance Semiconductor Corp. has announced a dual phase-locked loop clock synthesizer for PC peripheral devices, consumer electronics, and embedded controller systems that is said to lower electromagnetic interference.

The ASM3P2853A is a versatile spread spectrum frequency clock generator that reduces EMI at the clock source, according to Nelson Arata, product marketing manager for Alliance's Analog and Mixed Signal business unit. This allows for significant system cost savings by reducing the number of circuit board layers and shielding that is required to pass EMI regulations, he said. Spread spectrum clocking technology can virtually eliminate EMI filter networks and ferrite beads, with an added benefit that circuit board traces can be routed more effectively, enhancing design flexibility and layout.

The ASM3P2853A modulates the output of the PLL in order to spread the bandwidth of the synthesized clock, thereby decreasing the peak amplitudes of its harmonics. This results in significantly lower system EMI compared to the typical narrow band signal produced by oscillators and most clock generators, Arata said.

"Spread Spectrum capability will help the system designer sleep better knowing that his system has up to 6dB of additional EMI clearance," Arata said.

Packaged in an 8-pin SOIC, the ASM3P2853A provides a 50MHz spread spectrum clock and a low jitter 48MHz USB clock from a 25MHz crystal source.

Samples are already available, with initial pricing set at $1.50 in 1,000-unit quantities.

- Bettyann Liotta


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