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CDCE925: Input and output clock ppm specifications

Part Number: CDCE925

CDCE925 data sheet mentions below points: 

a) On-Chip VCXO: Pull Range ±150 ppm : Is this means the input clock source can have a tolerance up to ±150 ppm? Question especially applies when using a 16Mhz oscillator as input source.

b) Enables 0-PPM Clock Generation : Request to elaborate this concept. Even if the input clock source has tolerance up to ±150 ppm will the output can be generated with 0ppm tolerance?

We are designing a clock architecture using CDCE925 with input clock source from a 16MHz oscillator and the oscillator has a 50ppm tolerance. But the devices connected to the output of CDCE925 requires a tolerance of less than 30ppm. Will this can be achieved by CDCE925 (higher input tolerance and lesser output tolerance) ? 

Regards,

Thomas CN

  • Hi Thomas,

    a. With the onchip VCXO feature you can create a VCXO with a tunable crystal attached to the device. If you don't want/need the feature of frequency tuning then you don't need to use that. If you just use a 16MHz XO as input the output follows  the accuracy of the XO.

    b. no. the output will have the same ppm offset as the input. Or in other words the output tracks the input with 0 ppm offset.

    You will need to change your 16MHz oscillator to <30ppm tolerance.

    regards,

    Julian