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matching nrf24 to 100ohms balanced

iot_newb

I want to use the nrf24l01+ with the se2436 apmlifier, but the input of the amplifier requires an input of 100ohms balanced, while the nrf24 has a balanced output of 15ohm+j88ohm according to the datasheet.

Can I build a matching circuit to directly connect these to devices or is it recommended to first transform the signal to 50ohms unbalanced and then back again to 100ohms balanced.

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  • 0

    Thanks for the input.

    You are correct the impedance of the nrf24 is 15-j88 and therefor the load impedance should be 15+j88. And if my calculations are correct I would need a 3.9nH in series and a 1.5pF in paralell to get the proper matching at 2.4Ghz.

    image description

    According to the datasheet of the nrf24. ANT1 and ANT2 needs a DC path to the VDD_PA, should I connect that through the balun DC connection of the SE2436 as shown in the figure above?

    I've edited the figure according to your recommandations.

    I'm controlling the switching between TX_Mode and RX_Mode with CE and VDD_PA. The amplifier is in RX_Mode as long as the nrf is active, CE = high. When the nrf switches to TX_mode the VDD_PA goes high, and switches the amplifier to TX_mode. At this point both CTX and CRX is high, which is a state not specified in the datasheet, but tests has shown that the amplifier really is in TX_mode.

    image description

    Here is a picture of the layout, the nrf on the left and the amplifier to the right. I've been using 0402 inductors and capacitors.

  • 0 in reply to iot_newb

    Yes that is the correct way to power it. You run VDD_PA to VB. Remember to hook up the logic solution from nRF to SE2436. You should make sure the SDK for the nRF24 supports PA/LNA control. This is the best way to drive an external amp as there isn't a lot of good feedback with the RF events to do it on your own. I only code for nRF52 so I can't advise on the software link between softdevice and the hardware for nRF24. Otherwise you can use VDD_PA to drive the SE24 but the downside is it will be in an lna on state all the time whenever the pa isn't on. Not the best thing for low power consumption.

    You should repost your updated schematic to make sure you got it right. Then I would recommend you also submit your layout for review.

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  • 0 in reply to iot_newb

    Yes that is the correct way to power it. You run VDD_PA to VB. Remember to hook up the logic solution from nRF to SE2436. You should make sure the SDK for the nRF24 supports PA/LNA control. This is the best way to drive an external amp as there isn't a lot of good feedback with the RF events to do it on your own. I only code for nRF52 so I can't advise on the software link between softdevice and the hardware for nRF24. Otherwise you can use VDD_PA to drive the SE24 but the downside is it will be in an lna on state all the time whenever the pa isn't on. Not the best thing for low power consumption.

    You should repost your updated schematic to make sure you got it right. Then I would recommend you also submit your layout for review.

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