• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 53 subscribers
  • Views 503 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

The value of some parts on CC1200 BPF circuit for ARIB T108

Nobuyoshi Arai44
Expert 2575 points
Other Parts Discussed in Thread: CC1200

Hello CC1200 team,

 

I have a question about the document, swra445.pdf(Using the CC1200 Under ARIB STD T108).

www.ti.com/.../swra445.pdf

 

Currently our customer is considering to design the circuit with BPF by referring to the schematic of page 42 on this document.

But they think they have to change the values of some parts due to the characteristics.

So, they have two questions.

1. Are there any parts that they should not change the value on this schematic?

2. Would you please tell us the role of C174, L172, C176 before BPF?

   We think this block is also a part of the filter. But we would like to know whether there is any side effect or problem, if they change the value of these parts.

 

 

It would be appreciated if you can give any comment.

 

Best Regards,

 

Nobuyoshi Arai

  • 0
    TI__Guru**** 317180 points
    - The network connected to LNA_P, LNA_N, PA and TRX_SW are finely tuned for this application and the values should not be changed without a good reason. C175/ C174 form a notch to attenuate the phase noise @~760 MHz and changing this will alter the functionality. Could you elaborate some on why the customer want to change the component values?
    - C174: Originally a DC block, copied from the CC1200 868 MHz ref design. Could be that in this design this is not needed.
    L172: Part of filtering
    C176: Added to give the same sensitivity for all frequency in the band. Without this the sensitivity have a variation equal to 2-3 dB over the band.
  • 0 in reply to TER
    Expert 2575 points
    TER,
    Thank you for the answer. I understand these parts basically should not be changed.
    We will try to ask whetehr our customer can tell us the reason why they need to change the value of these parts.
    Best Regards,Nobu Arai
  • 0 in reply to Nobuyoshi Arai44
    Expert 2575 points

    Hello TER,

     

    Thank you for your supporting.

     

    >> Could you elaborate some on why the customer want to change the component values?

     

    I have got an answer from the question above.

    The reason why they changed the values is the following two points;

    1. Output power is not so higher than they expected (about 8 – 9 dBm at a maximum)

    2. 710-900MHz of spurious is not good (out of spec).

     

    This may be caused by their board design. Or, they are changing the circuit so that they can add the SAW filter just after BPF optionally to solve the spurious problem and this may be one of the cause of the problems above.

     

    That is why they changed the component values. But as a result of these changes, they can keep the specification and characteristics.

    Regarding the spurious, if they do not add the SAW filter, it seems there is a problem in their board.

     

    So, please give any comment again whether or not they may change the value of C174, C176 and L172.

    If they still should not change these values, would you please give any advice to solve the spurious problem?

     

     

    Best Regards,

    Nobu Arai

  • 0 in reply to Nobuyoshi Arai44
    TI__Guru**** 317180 points
    If the maximum power on their board is 9 dBm:
    - They have mounted other components than they think they have (we see from time to time that assembly is wrong even when the BOM is correct)
    - They have not managed to follow the ref design.

    I can take a quick look at their schematic (pdf reqired) and layout (gerber files required) to see if I see something obvious. These files could also be sent through a friend request.