A new standards-compliant timing module is about 75% smaller than competing products. Offered by chip maker Zarlink Semiconductor (Ottawa, Canada), the Type ZL30461 timing module is claimed by the firm to be the industry's smallest timing product for central timing cards as used in SONET/SDH systems. These systems typically require clocking at precisely 155.52-MHz.
Zarlink says that designing high-rel timing devices for central timing cards for SONET/SDH is a key challenge for communications equipment makers.
As such, the company asserts that its ZL30461 module can minimize design risks by combining digital and analog PLLs (phase-locked loops), as well as a 20-MHz master oscillator---all into one pre-designed package.
The module is indeed flexible, with no less than 14 output clocks. Zarlink claims that's the industry's widest range of clocks for SONET/SDH timing.
The module produces two ultra-low-jitter clocks, a 77.76-MHz LVPECL (low-voltage pseudo ECL) clock, and a 19.44-MHz CMOS clock, as well as jitter-attenuated clocks operating at 1.544-MHz, 2.048-MHz, 4.096-MHz, 6.312-MHz, 8.192-MHz, 34.368/44.736-MHz, and 155.52-MHz.
The module also produces three STbus-compatible 8-kHz frame pulses.
The inputs of the timing module accept frequency references from two independent sources programmable for operation at 8-kHz, 1.544-MHz, 2.048-MHz, or 19.44-MHz.
On top of that, the company says its module will require no external components or complex programming.
Zarlink says that equipment vendors are presently evaluating its module for SONET/SDH central timing cards used in DSLAMs (digital subscriber line access multiplexers), media gateways, and add/drop MUXes, as well as Internet routers, and network access equipment. The module can also be used on line cards in network element equipment.
The ZL30461 device is billed as a so-called System-in-Package. It's also quite small, measuring 23 mm X 23 mm, or less than one square inch in size. Zarlink claims that's the smallest footprint device in its class, saying it's 75% smaller than competing products.
The module is also very standards compliant. It complies with Telcordia's GR-253-CORE standard for SONET Stratum 3, GR-1244-CORE standard for Stratum 3, and the ITU-T's (International Telecommunication Union-Telecommunications) G.812 and G.813 Option 1 and 2 standards for SDH equipment clocks (SEC).
The module also exceeds OC-12/STM-4 (Optical Carrier level 12/Synchronous Transfer Module level 4) jitter requirements, at rates typically less than 7-ps rms.
To ensure reliability for central timing cards, the ZL30461 module offers so-called hitless reference switching and holdover. In use, the device monitors input references, and if the primary input is interrupted, the module enters a holdover mode, generating its own reference clock based on data collated from past reference signals. It does this while verifying the integrity of the secondary reference.
If the secondary reference is corrupted, the module can maintain holdover for over 24 hours, a common system requirement that lets service providers maintain service while problems are resolved.
Packaging and Pricing
The ZL30461 timing module, in a 240-pin BGA, is in volume production now. In OEM quantities of 1000, it's priced at about $164 a pop. An eval reference board is also available.
For more information, contact Zarlink Semiconductor, 400 March Rd., Ottawa, Canada K2K 3H4. Phone: (613) 592-0200. Fax: (613) 591-2317. Email: firstname.lastname@example.org. Be sure to review Zarlink's Web site for more details.