Low RSSI using CYBLE-224110-00 (non-extended)

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Anonymous
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I am experiencing low signal strength when using  the CYBLE-224110-EVAL in short range (i.e. PA/LNA disabled). My setup has it connected to the Pioneer CY8CKIT-042-BLE.

   

I have a simple BLE component that's advertising at 0dB TX power. RSSI (as checked on multiple known-good Android handsets) when right next to it is around -77dB - it should be more like -40.

   

If I enable the PA/LNA, then the RSSI improves massively to better than -30dB. However, the current will exceed our budget.

   

Is there any reason  the signal strength is so poor with the PA/LNA disabled? 

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1 Solution
Anonymous
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Hi Ben,

   

How exactly do you have the PA/LNA configured in your application? The "Enabling Extended Range Feature" section on page 16 of the current CYBLE-224110-00 datasheet describes how you should set up register values and output pins to operate the integrated PA/LNA. Most likely, you should enable everything but set the mode to 2 (pin P0[3] = 1 and pin P0[2] = 0) to enable TX/RX bypass mode, as described in the "Power Saving Measures with PA/LNA Operation" section following. If you simply turn off the PA/LNA completely, the RF path will probably be abruptly cut off such that the antenna cannot radiate properly when the chipset radio is attempting to transmit.

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4 Replies
Anonymous
Not applicable

Hi Ben,

   

How exactly do you have the PA/LNA configured in your application? The "Enabling Extended Range Feature" section on page 16 of the current CYBLE-224110-00 datasheet describes how you should set up register values and output pins to operate the integrated PA/LNA. Most likely, you should enable everything but set the mode to 2 (pin P0[3] = 1 and pin P0[2] = 0) to enable TX/RX bypass mode, as described in the "Power Saving Measures with PA/LNA Operation" section following. If you simply turn off the PA/LNA completely, the RF path will probably be abruptly cut off such that the antenna cannot radiate properly when the chipset radio is attempting to transmit.

Anonymous
Not applicable

That worked, thank you. Could you consider updating the documentation? I don't normally have to follow the instructions for enabling components that I *don't* want to use! Nonetheless, I had already read that section, but the description of bypass hardly matched my use-case.

   

"Power Mode 2 (TX/RX Bypass) is not recommended for typical low power mode use. The Bypass mode should be considered if a transition from Extended Range functionality to short-range communication is desired on-the-fly. Transitions from Active mode to Bypass mode are only recommended after a BLE event has completed and no RF activity is in process. "

   

To paraphrase, in order to not use the component, you have to enable it in the non-recommended mode. 

Anonymous
Not applicable

Hi Ben,

   

I'm glad to hear that the problem is resolved. I'll follow up with the documentation team about clarifying this and other extended-range module datasheets for this use case.

   

Out of curiosity, is there a reason that you chose the '224110 module (an extended-range device) for your design even though you are not intending to use the extended-range features? While there is certainly no harm in doing so, you may be able to reduce cost and possibly PCB footprint space if you select a module without the integrated PA/LNA component.

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Anonymous
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Thanks for chasing the docs team. We're using the module for its 105C temperature rating.

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