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CC120XEM-868-930-RD: Add the LNA and the SAW filter into the CC1200 solution

Part Number: CC120XEM-868-930-RD
Other Parts Discussed in Thread: CC1200, CC1125

My customer who develops the wireless board using the CC1200 has tried to look into our reference design, would also like to add the LNA and the SAW filter into their own board.

 

1. Customer would like to add an LNA to the RX path and share its own filter (SAW filter) for both TX and RX as following instruction.

 

- Inserts the LNA to the TRX_SW side of L193

- Inserts the SAW filter to the antenna side of C174

- Inserts the branch point between TX and RX to between C174 and the SAW filter

 

- Deletes L193

- Deletes L173/C175/L174

 

Could you please let me know if you have any concern about this approach?

 

2. Customer also plans to supply from the same power supply source as the CC1200 to the external devices such as MCU. They afraid that the high frequency signal transmitted from the PA was superimposed on VDD_REG and input to other pins of the CC1200 since the L171 has a bit small value - 10nH.

 

Are there any comments on this concern?

 

Thanks.

  • 1) Think it's easier to explain with reference to the CC1125 CAT1 reference design (www.ti.com/.../swrr097).

    The LNA will be placed where there is a SAW filter in the RX path. Suggest to add placeholders for matching components at the LNA output and input.
    The LC filter can be replaced by a SAW filter. Again, suggest to add matching components. LNA and SAW filters are specified for 50 ohm in/out but it is good design practice to add placeholders for impedance matching components.

    2) CC1200 has been characterized with 10 nH PA load and this value shall be used. Use a star routing of power to minimize crosstalk between MCU and CC1200. Supply -> bead 1 -> shunt capacitor (e.g. 2.2 uF) -> CC1200. Supply -> bead 2 -> shunt capacitor (e.g. 2.2 uF) -> MCU