Reference crystal frequency, can we use 26MHz instead 32?

francis law

Other Parts Discussed in Thread: CC1120

Hi,

My channel frequency is 928MHz, the 32MHz X 29 = 928MHz, should we change the crystal frequency? let say 26MHz.

Thank you.

0 Igor Sherer over 13 years ago

Guru 31280 points

Hi,

What is the device (SoC?) involved in your question?

In any case, you should be using what is stated in datasheet of the device.

0 francis law over 13 years ago in reply to Igor Sherer

thank you for your reply. The device is CC1120.

0 Igor Sherer over 13 years ago in reply to francis law

Guru 31280 points

Hi,

I strongly recommend you to use crystal with values stated in the datasheet, that is 32MHz (min freq) to 33.6MHz (max freq).

Please refer to cc1120 datasheet, section 1.2 for confirmation.

0 francis law over 13 years ago in reply to Igor Sherer

I did read the data sheet, but my application require narrow bandwidth,such as 12.5KHz, I am unable to find a stable TCXO for 32~33.6MHz in low cost.

most of low cost TCXO is +/- 2.5ppm, if tx off +2.5ppm and RX off -.25ppm, total frequency error will be 5ppm, that mean is more 4KHz off for 900MHz,

it is too much for 12.5 KHz band width. If I can use another frequency, that will be more flexible.

thank you

0 yasuhiro matsumoto over 13 years ago in reply to francis law

I think CC1120 clock should be 32MHz or 33.6MHz.

If you run Smart RF studio 7 (It's OK to run offline mode) you can find that

clock selection is only 32MHz or 33.6MHz.

0 francis law over 13 years ago in reply to yasuhiro matsumoto

You could be right, I try that too. just try to verify by TI's people.

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