• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 51 subscribers
  • Views 915 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

CC2640: How to measure 24 MHz crystal tolerance

Eggsy Pang
Expert 4985 points
Other Parts Discussed in Thread: CC2640

Hi Fredrik,

   In this link processors.wiki.ti.com/.../CC26xx_Tips_and_Tricks, I saw  how not to measure the 24M crystal oscillator pin. Need to power down. 

If my customer need to measure the 24M crystal oscillator the PPM value, do you know how to do it? Using oscilloscope or network analyzer?

Thank you!

Best Regards,

Eggsy Pang

  

  • 0
    TI__Guru** 106705 points
    Hi Eggsy,

    I split your question into a separate thread since it is not related to the discussion where you posted.

    The easiest way to measure the crystal oscillator accuracy is to make the radio output an RF carrier and measure the frequency offset on a spectrum analyzer. The relative offset in ppm is the same for the crystal and the radio.

    Regards,
    Fredrik
  • 0 in reply to Fredrik K
    TI__Expert 4985 points
    Hi Fredrik,
    Sorry about that.
    Thank you for your good idea. Do you know how many ppm of 24M crystal oscillato using in Launchpad ? I guess it is 10 PPM.
    If our customer use 20 PPM (our chip range -40-+40PPM), what influence will be exist when CC2640R2 work ?
    Thanks.
    Best Regards,

    Eggsy Pang
  • 0 in reply to Eggsy Pang
    TI__Guru** 106705 points
    No worries!

    The LaunchPad is using a crystal with +/-10 ppm and +/-10 ppm over temperature (which means that worst case tolerance is ~+/-20 ppm).

    The crystal tolerance is dictated by the RF protocol specification. The BT spec says that the frequency deviation shall not exceed 150 kHz, out of which frequency drift through a packet can account for up to 50 kHz. This means that for BLE, maximum static frequency offset is +/- 100 kHz which is approximately 40 ppm.

    The CC2640 device itself can receive packets with much higher frequency offset (more than +/- 100 ppm) without problems.

    Anyway, using a crystal with +/- 20 ppm is perfectly fine.

    Best regards,
    Fredrik