CC1125: CC1125 when used with clipped sine TCXO

Part Number: CC1125

HI,

I am using the CC1125 with a clipped Sine TCXO (Taitien part TYETBLSANF-40.000000).

This part has a low signal level output (approx 820mV pk-pk at ambient).  As the temperature is reduced, the amplitude falls.  At much below -10C the amplitude is less than the 800mV minimum specification for the CC1125. (It has also fallen out of the published spec of the Taitien part).  But, this is one of the few TCXOs that are currently available from distribution.

I am experiencing issues whereby the CC1125 is not receiving this clock as the tempertaure falls.  I do understand that I am going outside of the published spec.

Does anyone know of any means of increasing the sensitivity of the external clock input of the CC1125?  Do any of the register settings affect this? (I know there are several XOSC registers with the description as 'reserved!')

Any help in this matter would be greatly appreciated.

Regards,

Ian

  • Hi Ian,

    After looking into this, from the information on the CC1125 registers that I can find I don't think this is possible. The reserved register bits will not affect what you are interested in.

    Regards,

    Zack

  • HI,

    Another option I am considering is to feed the TSCO signal into the XOSC-Q1 pin instead of the EXT_XOSC pin.  Is this a feasible option with this TCXO?  Will the signal amplitude be compatible with the XOSC-Q1 pin?

    Regards,

    Ian

  • Hi Ian,

    I have asked for advice on this but our designer who is best able to answer is on leave (they will be back in 2 weeks) - I will have to follow up when they are back. Whether this would work or not depends on the internals of the XOSC-Q1 pin.


    Regards,

    Zack

  • The CC1125 is designed to be using a TCXO from a dedicated input. One potential issue with using the Q1 input is that TCXOs often have a "messy" startup meaning you get some pulses on the output, then it stops, start again etc. Not sure if the Q1 input is connected to a ripple counter that will suppress this (the TCXO input has a ripple counter) meaning that it could be that the digital part of the chip is clocked with a clock that doesn't follow the wanted spec and hence the chip may enter an invalid state. A fair amount of testing is required to ensure that that doesn't happen.

  • Thanks. Ideally I would use the Oscillator input pin, but the margin at low temperature is not compatible with the Taitien TCXO. Ideally I’d use a different TCXO but there is very poor availability from other manufacturers. 

  • Hi Ian,

    I've talked to a designer about the possibility of this - it's best to describe our conclusions in a private message. Please accept the friend request I sent and I can discuss this via the messenger.

    I will mark this thread as resolved in the meantime.

    Regards,

    Zack

  • Thanks Zack, I have accepted the request