Clock translator attenuates jitter, saves power

May 21, 2014 // By Graham Prophet
A clocking IC from Analog Devices reduces costs in optical transport network mapping and Ethernet line cards in optical and networking communications applications. The AD9554 multi-service adaptive quad-channel clock translator with clock multiplier provides jitter cleanup and synchronisation for many systems, including synchronous optical networks (SONET/SDH).

An embedded cross-point switch at its input provides greater flexibility and lower cost of ownership than maintaining different clocking configurations of multiple parts. The AD9554 dissipates only 940 mW while generating up to eight output clocks over an output range of 430 kHz to 941 MHz, synchronised to four 2-kHz to 1-GHz external input references, with a loop bandwidth as low as 0.1 Hz.

The four analogue-digital phase-locked loops (ADPLLs) enable the reduction of input jitter or phase noise associated with the external references. The digitally controlled loop and holdover circuitry of the AD9554 continuously generates a low jitter output clock even when all reference inputs have failed. The AD9554 has adaptive clocking capability that allows the user to dynamically change the DPLL divide ratios while they are locked.

The AD9554 clock's high level of integration, adaptive clocking capability, and optical transport network (OTN) mapping algorithm embedded in DPLL reduces system costs by simplifying clocking circuitry and eliminating software control routines. Output jitter is 250 fs over the 50-kHz to 80-MHz range and 350 fs over the 12-kHz to 20-MHz range.

Features include GR-1244 Stratum 3 stability in holdover mode and smooth reference switchover with virtually no disturbance on output phase. Adaptive clocking allows dynamic adjustment of feedback dividers in OTN mapping/demapping.

The Quad ADPLL architecture offers four reference inputs (single-ended or differential), eight outputs (single-ended or differential), and 4x4 crosspoint that allows any reference input to drive any output.

The AD9554 supports ITU-T G.823, ITU-T G.824, ITU-T G.825, and ITU-T G.8261, and ITU-T G.8262 Loop bandwidth is as low as 0.1 Hz to guarantee SyncE compliance.