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Communications

Signal integrity is critical to communications devices. SpectraLinear products offer a range of solutions to the complex system-level application and signal timing problems that can lead to degradation of signal integrity in network communications equipment.

Designers creating the devices that make up the Internet backbone and provide access to it use SpectraLiner’s EProClock^® technology to overcome system timing integrity problems. The SL15xxx and SL38xxx product families feature independently programmable clock output impedance matching to minimize reflection and signal integrity problems. These innovative products bring additional capabilities to the communications systems designer:

• Minimize undesirable EMI levels to meet Electromagnetic Compliance (EMC) regulatory requirements by adjusting clock edge rise and fall times
• Eliminate system setup and hold times using the programmable skew feature
• Minimize or eliminate critical Radio Frequency Interference (RFI) by shifting fundamental and harmonic spurs with fine adjustment of clock signal frequencies.

Better testing for reliability and manufacturability

SpectraLinear’s programmable clocks also enable system designers to conduct a wide range of system reliability and margin tests during the design and production stages, leading to more robust, production-worthy communications systems with a high level of reliable manufacturability. These margin tests include over/under clocking, verification of setup and hold time margins, verification of critical downstream PLL parameter tolerances (frequency, bandwidth, duty-cycle, tracking and spread spectrum clock frequency, etc.) and spread percent limits by using a larger spread percent than is used in the final version of the product in production.

SpectraLinear timing distribution ZDB and NZDB products offer excellent performance specifications in terms of delay time, skew and jitter. They are offered with 4 to 9 outputs and operate up to 220MHz, meeting most system requirements using LVCMOS/TTL I/O levels. The products are capable of operation in power supply ranges of 3.3V to 2.5V and 1.8V.

Minimizing Crystals in Communications Systems

Many systems 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 (SL38xxx) outputs are embedded in these products, offering customers complete solutions to both problems.

 

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