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Computer Peripherals

EMI Reduction in Peripheral Devices

In computer peripheral devices, clock generators add value when they can reduce Electromagnetic Interference (EMI). Computer peripherals, such as printers and copiers, typically use extensive digital circuits, generating large amounts of undesired EMI radiation and creating critical time-to-market and competitive cost issues.

One way to reduce cost is to reduce the number of PCB layers since the cost of manufacturing PCBs is directly proportional to the number of layers used. However, any such decrease in the number of layers increases EMI due to the reduced number of ground and power layers that shield EMI radiation at the board level. Filtering or additional external shielding can be used to reduce EMI emitted due to the smaller number of layers, but it is difficult and expensive.

The most effective way to solve this problem is to use Spread Spectrum Clock Generators (SSCGs). These products can be programmed with up to a +/- 2.5% spread, drastically reducing EMI and enabling designers to reduce the number of PCB layers, achieving superior cost savings while improving time-to-market. This is how manufacturers of low-cost ink-jet printers can get by with only 2-layer PCBs and why the makers of relatively complex and expensive laser or multi-function printers require only four layers.

Minimizing Crystals in Peripheral Devices

Many designers use programmable EProClocks^® products to eliminate the large numbers of crystals, crystal load capacitors (two for each crystal) and crystal oscillators found in most communications systems.

For example, using a single external fundamental crystal from 8 to 48MHz and eliminating external crystal load capacitors by using on-chip programmable capacitors, SL38xxx products coupled with EProClock^® technology can provide five unique frequencies, including divide-by values from 2 to 32 at its maximum twelve outputs. This eliminates a large number of crystals and crystal oscillators from the system, drastically reducing the cost of components and assembly, minimizing PCB space and improving overall manufacturing reliability.

SL15xxx products offer the same features and advantages but include a single PLL with up to 5 programmable output clocks. Spread Spectrum Clocks for EMI reduction and programmable clocks with up to 5 (SL15xxx) and up to 12 (SL38xx) outputs are embedded in these products, offering customers complete solutions to both problems.

 

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