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Gain issue in AD9361

Question asked by Sandeep007 on Mar 1, 2018
Latest reply on Mar 1, 2018 by sripad

We are getting gain issue in one Rx chain in a specific AD9361 chip. This issue is specific to this particular chip only.

We are getting low gain in Rx1 chain of this particular chip.

To analyse the issue, I have tested the Rx1 chain and Rx2 chain with different gain index. (gain index 20, 35,40 and 60).

Selected gain index uses LNA index 0, 1, 2 and 3 respectively so as to check all the lna. Both the chain is tested with same setting. Chain Rx2 seems to be OK but Chain Rx2 is misbehaving.

Pls find the attached report.

Following are the observations

Board is tested in FDD mode with single tone of 1MHz(LO=1750 MHz & cw= 1751MHz) with different gain index setting and RSSI AD count is read.

1. With gain index 20( LNA index=0 & reg0x131=04), both the chain having same performance. We are getting same RSSI AD count.

 

2. With Gain Index 35 (LNA index=1 & reg0x131=24), both the chain has large differnece in RSSI AD count reading(around 23 dB)

 

3. With gain index 40( LNAindex=2 &reg 0x131=44) and gain index 60(LNA index=3 & reg0x131=64) both the chain has large difference.(around 24 dB).

 

It seems that LNA with index0 is working fine but LNA with index 1,2 &3 not working.

 

Could you pls throw some light on the issue ? What could be possible reasons for such behaviour in this particular chip?#@@@@#

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