Adaptive clock translators

Telecoms, Datacoms, Wireless, IoT

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23 November 2011 Telecoms, Datacoms, Wireless, IoT

Analog Devices has introduced two fully programmable jitter attenuating clock translators ICs that perform frequency translations for a wide range of wired communications applications – including Synchronous Ethernet and SONET/SDH optical networks – that require low jitter.

The AD9557 dual-input multiservice line card device and the AD9558 quad-input multiservice line card device translate any standard input frequency to any standard output frequency from 2 kHz to 1,25 GHz with sub 400 fs RMS total jitter on 12 kHz to 20 MHz. The new clock translators provide a high-performance alternative to traditional PLL (phase locked loop) designs that require the addition of expensive VCXOs (voltage-controlled crystal oscillators).

The built-in programmability of the AD9557 and AD9558 allow network line card designers to use the same component in many different board designs. This includes synchronisation for a wide variety of high-performance applications, including data communications, next-generation wired networking applications, telecommunications, test and measurement, high-speed data acquisition and wireless base station controllers.

Both devices integrate an on-chip, low-phase-noise, frequency-agile VCO (voltage-controlled oscillator) and loop filter along with dynamic adaptive clock support. Adaptive clocking allows the DPLL (digital PLL) divider ratios to be changed while the DPLL is locked. This enables the frequency value at the output to be dynamically adjusted by up to ±100 ppm from the nominal output frequency without manually breaking the loop and reprogramming the part with a sub 0,1 ppb step in frequency resolution. This adaptive clock function is used for applications such as SDH to OTN mapping/demapping and asynchronous mapping/demapping.

The adaptive clock translators’ programmable DPLL supports loop bandwidth from 0,1 Hz to 5 kHz and features three separate programming modes for ease of use and flexibility. The two devices are pin- or soft-pin pre-configured to support popular SONET/SDH, Ethernet, Synchronous Ethernet and Fiber Channel frequencies, while SPI and I²C ports are available to program customised input-to-output frequency translation.

At 6 x 6 mm and 9 x 9 mm in size, respectively, the AD9557 and AD9558 provide compact, cost effective clocks for line card designers. The AD9557 features two reference inputs (single-ended or differential) and two pairs of clock outputs. Each output pair is configurable as a single differential LVDS/HSTL output or as two single-ended CMOS outputs. The AD9558 offers the same features but with four reference inputs and six pairs of clock outputs.

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Adaptive clock translators

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