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  • Case ID: 345822
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LF/HF XTAL (ppm) tolerances vs performance

dav01

Hi, would like to understand what scenarios a clock stability better than +/-40ppm would be needed in a BLE setup.

i.e. channel sounding, and similar. I mean you can get a pretty reasonable price for a 10ppm or even down to 5ppm XTAL or TCXO nowdays.

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    Hello David,
    You're right, the clock accuracy of +/-40ppm is good enough for most applications and usually also come with a built in margin. A more accurate crystal might give you some benefits in noisy environment as out of band noise could become less. Although for BLE you often only have control of one side of the link, so you don't necessarily know what the other end have installed.
    There's drift and degradation across the lifetime of the crystal and related components and this is usually the deciding factor. Some products are designed to meet larger temperature variations and life. For these products it can be useful to have a tighter spec crystal that across time and temperature still is within the requirement.
    The channel sounding profile could benefit from a tighter crystal, but if that level of accuracy is desired, you often end up with an application with more HW as well (antenna and supporting circuitry) which makes the additional cost of a tighter crystal far smaller in the overall cost of the application.
    Best regards
    Asbjørn
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  • 0
    Hello David,
    You're right, the clock accuracy of +/-40ppm is good enough for most applications and usually also come with a built in margin. A more accurate crystal might give you some benefits in noisy environment as out of band noise could become less. Although for BLE you often only have control of one side of the link, so you don't necessarily know what the other end have installed.
    There's drift and degradation across the lifetime of the crystal and related components and this is usually the deciding factor. Some products are designed to meet larger temperature variations and life. For these products it can be useful to have a tighter spec crystal that across time and temperature still is within the requirement.
    The channel sounding profile could benefit from a tighter crystal, but if that level of accuracy is desired, you often end up with an application with more HW as well (antenna and supporting circuitry) which makes the additional cost of a tighter crystal far smaller in the overall cost of the application.
    Best regards
    Asbjørn
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