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CC1125: swrr097 - Decoupling and matching networks capacitor selection

David Dominguez Moises
Intellectual 570 points
Part Number: CC1125
Other Parts Discussed in Thread: CC1200

Hi,

I'm following the swrr097 reference design for a new board for 915MHz transmission. I'm developing this with some limitations in components availability, thus the following questions:

1. Would 70nF or 33nF capacitors work for power supply decoupling instead of the 47nF used in the reference design?

2. Would 1.5nF or 2.2nF capacitors work as a replacement for the 1.8nF capacitor on pins 23 and 24?

3. In the matching network, before the antenna between the 18nH and 12nH, there is a 3pF cap. Would it be good to replace this with a 3.3pF or 2.7pF? or even try to replace it with 3 parallel 1pF caps?

Thanks,

David

  • 0
    TI__Guru**** 317180 points

    We have only tested with the values given in the reference design and we can therefore not state how the performance will be if other component values are used. 

    1) Decoupling: The most important decoupling is for the AVDD_XOSC pin. If you change values for the decoupling, the output spectrum should be checked for spurs.

    2) You can try 1.5 nF since CC1200 uses this and the synth is fairly similar. 

    3) This will impact the filtering of harmonics. If you change the value here you have to check the value of the harmonics to see if they are within the regulatory limits. 

    You can also consider moving to 0201 components since the production has been moved more to smaller sizes. Since the layout will be different and the components will behave slightly different you have to compare the S parameters between a 0402 and 0201 design and compare.

  • 0 in reply to TER
    Intellectual 570 points

    Thanks, just needed some guidance on possible effects of these changes.

    I'll try using 70nF for decoupling, 1.5nF for LPF and leave the 3.3pF in the matching network.

    I'm not intending this product to be certified, so this will help me validate some aspects and later on will try to adjust to RDK values.