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AD9364 RSSI issue

Question asked by Olegis on Mar 4, 2015
Latest reply on Mar 10, 2015 by Olegis

Hello,

 

We are using AD9364 with an external LNA for receiver operation. The LNA has two modes - "LNA on" and "LNA Bypass". In "LNA Bypass" mode there is appx 2dB loss from the antenna to the AD9364 Rx input. In "LNA On" there is 18dB gain from the antenna to the AD9364.

 

The AD9364 is set to operate in TDD mode with Fast AGC and the external LNA to be controlled by GPO_0 automatically. To achieve this, a Full Gain table was extended to 90 entries and modified to accommodate the eLNA index bit (please see the attached file). The external LNA gain registers are set as follows -

Register 0x12C=28h (40d, corresponding to 20dB of gain difference between "LNA On" and "LNA Bypass" in 0.5dB/LSB resolution)

Register 0x12D=00h

 

The AGC works pretty good and the external LNA is controlled exactly as expected. The problem is that the RSSI reading jumps drastically when the external LNA is bypassed. I mean that when the AD9364 goes from Gain index 30h to 2Fh, the RSSI value from register 0x1A7 jumps from 68h to B4h (by ~38dB).

 

Any help with this issue would be greatly appreciated.

 

Best regards,

Oleg C.

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