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AD9361 Fast AGC Periodic Unlock?

Question asked by c3commsystems on Nov 14, 2016
Latest reply on Dec 22, 2016 by andrew_senior



I am testing the AD9361 fast AGC mode using Ettus E310. I used one E310 as the transmitter to send a 250 kHz complex sinusoid in 2.xx GHz, and use another E310 as the receiver to record the sinusoid signal samples.


Snapshots of received real samples are shown in the attached two figures with the fast AGC enabled. Instead of a sinusoid with stable amplitude, what I got are periodic AGC adjustment. It seems that the fast AGC is able to reach State 5, but can only stay in State 5 for about 10 sinusoid periods (~40us). AGC will then unlock by itself and start from State 1 again. This process repeats itself continuously. I also saw this phenomenon in receiving burst packets. The gain changes in a similar periodic pattern within a single packet. 


I actually prevented all unlock conditions as described in the user guide, but this automatic unlocking still occurs. In fact, the attached figures are captured when all unlock conditions are prevented by registers.


We would really appreciate it if any community members can help and guide us on how to deal with this problem. Thanks! 


EN_AGC is kept low. The register settings are listed in the following.


================ Current Settings of AGC Related Registers ================

Register (0x014): 0x23 -- FDD mode; Auto Gain Locked; to Alert

Register (0x021): 0x0a -- 

Register (0x022): 0x0a

Register (0x03a): 0x27

Register (0x15c): 0x61

Register (0x0fa): 0xe5

Register (0x0fb): 0x48

Register (0x0fc): 0x23

Register (0x0fd): 0x4c

Register (0x0fe): 0x44

Register (0x0ff): 0x8e

Register (0x100): 0x6f

Register (0x101): 0x0f

Register (0x102): 0x29

Register (0x103): 0x08

Register (0x104): 0x2f

Register (0x105): 0x3a

Register (0x106): 0x5a

Register (0x107): 0x1f

Register (0x108): 0x27

Register (0x109): 0x4c

Register (0x10a): 0x58

Register (0x10b): 0x00

Register (0x10c): 0x4c

Register (0x10d): 0x00

Register (0x10e): 0x00

Register (0x10f): 0x00

Register (0x110): 0x0a

Register (0x111): 0x0a

Register (0x112): 0x42

Register (0x113): 0x44

Register (0x114): 0xff

Register (0x115): 0x80

Register (0x116): 0x65

Register (0x117): 0x08

Register (0x118): 0x3f

Register (0x119): 0x10

Register (0x11a): 0x1c

Register (0x11b): 0x0a


RX TIA Config Register (0x1db) is 0xe0


I'd really appreciate your help to solve this problem. Thanks!