Zarlink Semiconductor touts the low jitter of its ZL30410 full-featured digital timing chip for access line cards operating at OC-3 rates. The digital phase-locked-loop jitter performance is given as 325 picoseconds on a 155.52-MHz clock rate, which, according to Zarlink, allows a direct interface to STM-1/OC-3 framers and mappers.
Jitter, a cyclical variation in signal frequency, causes data errors in optical networks. The performance of Zarlink's chip means it can generate-without external components-the 155.52-MHz clocks that drive OC-3/STM-1 access uplinks, and the 16.384-MHz clocks that drive jitter-sensitive time-division multiplex digital switches.
Automatic out-of-range detection continuously monitors timing references and sets off an alarm if the frequency error exceeds 12 parts per million. Holdover accuracy of 0.07 ppb ensures precise timing when the network reference is down, according to the company.
In addition to clocks for OC-3/STM-1 links, the ZL30410 is said to generate all other clocks typically used in high-speed access line cards, including a 19.44-MHz clock and clocks for ser-vices delivered over ST-BUS, DS1/E1, DS2 and DS3/E3.
On its inputs, the timing chip accepts two reference clocks. The chip detects the frequency of both and synchronizes to any combination of 8 kHz, 1.544 MHz, 2.048 MHz and 19.44 MHz.
The chip offers "hitless" reference switching, a feature that enhances reliability and eases maintenance procedures. It continuously monitors both input references.
If the active reference is interrupted, the chip switches instantly to holdover mode, generating its own reference clock based on data collected from past reference signals. This gives the system time to react to the problem and, if required, switch the ZL30410 to its other input reference signal without disturbing its output clocks.
The ZL30410 complies with Telcordia's GR-253-Core for OC-3 jitter generation and the International Telecommunication Union's G.813 Option 1 for STM-1 jitter generation. It is also compatible with GR-253-Core Sonet Stratum 3 clocks and G.813 slave equipment clocks.
The ZL30410, now in production, is offered in an 80-pin low-profile quad flat pack measuring 14 x 14 mm. In quantities of 1,000, the chip is priced at $22.50 each.
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