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Ultralow Jitter Clock Synthesizer Has Multichip Synchronization, JESD204B Clocking

30 March 2016

The LTC6951 from Linear Technology Corporation is a low-phase noise integer-N synthesizer with an integrated VCO and an ultralow jitter clock distribution section, ideal for clocking data converters. The LTC6951 features four high-performance current mode logic (CML) outputs, each equipped with an independent low-noise clock divider and digital delay block to cover a wide frequency range between 1.95 MHz and 2700 MHz. With a total of 115 fsRMS absolute jitter (SNR method), the LTC6951 delivers the low jitter clocks necessary to achieve optimal signal-to-noise ratio when clocking data converters with high input frequencies and fast output data rates.
Linear Technology’s?LTC6951 integer-N synthesizer. Source: Linear Technology   Linear Technology’s?LTC6951 integer-N synthesizer. Source: Linear Technology
The LTC6951 introduces three intelligent schemes to simplify output clock expansion and the creation of large clock trees employed in systems with multiple daughter cards or with a large number of data converters. Linear Technology’s EZSync output synchronization method ensures repeatable and deterministic phase relationships between all clock divider outputs on the LTC6951 and accompanying EZSync supporting devices. The ParallelSync multichip parallel synchronization feature allows the outputs of multiple LTC6951 ICs to be retimed to the common reference clock. This permits reference-aligned synchronization in the reference clock domain with easy-to-meet nanosecond range setup and hold time requirements.
The EZ204Sync™ JESD204B subclass 1 compliant synchronization method builds on the previous two approaches and enables the generation of the SYSREF and DEVCLK signals essential to this JEDEC standard across multiple parallel- connected LTC6951 ICs along with any other EZSync™ compatible clock devices.
The LTC6951Wizard™ simulation and design tool, available for free download at, provides appropriate PLL settings and loop filter component values with a click of a button, and accurately predicts the individual output’s phase noise and jitter. Besides performance simulation, the LTC6951Wizard GUI features a scope plot that simulates time- domain results of the LTC6951 outputs based on the clock divider, delay and synchronization settings, simplifying the design process and assisting in the circuit debugging phase.
The LTC6951 is specified over the full junction temperature range from -40° C to 105° C. It is available in a space-saving 5 mm x 7 mm, 40-lead plastic QFN package. List price is $8.75 each in 1,000-piece quantities and availability is from stock.

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