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  • 8T49N028 Low RMS Phase Jitter Clock Synthesizer

  • Created: Jul 01, 2015

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Description

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Summary

The jitter is the measured difference between the expected value and the actual value of signal edges generated by a clock source. The jitters in clock signals are typically caused by noises, power supply transients, loading conditions, interference from nearby circuits or any other disturbances in the system. In digital, analog, and RF communications systems, jitter plays a large role in the degradation of signal integrity. That is why both analog and digital systems clock sources are designed to be very accurate and stable over time.


This circuit is designed to generate multiple frequency clock sources with minimal jitters. The multiple frequency clock generator with fanout buffer 8T49N028 from IDT offers a very low RMS phase jitter clock synthesizer with selectable internal crystal oscillator or external clock references and eight outputs, configurable as either LVDS, LVPECL or High Impedance. It has two frequency-select pins that determine one of up to four different sets of factory preprogrammed crystal or input frequency and output frequency configurations. From a single input reference, output banks can select as many as three different output frequencies. The two of these frequencies can be generated by: the internal crystal oscillator and/or external clock pre-divider, and/or A output divider, and/or B output divider. The third output frequency is from the B output divider.


The 8T49N028 has an I2C-compatible configuration interface to access any of the internal registers for frequency and PLL parameter programming. The 8T49N028 acts as a slave device on the I2C bus and has the address 0b110111x, where x is set by the value on the ADDR_SEL input. For reprogramming, it is recommended to use external pull-up resistors for SDATA and SCLK for full electrical I2C compliance. The internal pull-up resistors have a size of 50kΩ typical. The device Core (VCC), Analog (VCCA), and Output (VCCO_x) supplies can be powered by a 3.3V/2.5V power supply with a 5 percent tolerance from the required voltage.