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Gain control issues with AD9364

Dear Support Team,

I have the custom board with the AD9364 and a demodulation core integrated with the AD HDL reference design. 

I have generated a test signal from an Arbitrary Waveform Generator to test my demod algorithm. The generated signal looks like in the figures below. 

The problem I have is that if I use the Manual gain mode on AD9364 and fixed power from signal generator I can demodulate almost all messages. However, with Slow attack mode the error rate is increased. It is even worst with the Fast attack mode. I tried to understand how those modes work and I think i do, but it is still not clear to me why would at least the slow attack introduce more errors? I can maybe see that happening if the power of the signal is changing causing gain changes in the Rx chain which in result can introduce phase shifts but here things are pretty much constant (at least thats what i can conclude).

If on the other hand I have same signal as below but introduce amplitude changes (i.e. for instance one of those below has amplitude below 1) then things are even worst. The fast attack mode is introducing a lot of errors while slow attack is slightly better compared to fast attack.  

Any suggestions would be appreciated.

Thanks

Milos

Zoomed in one of the above

  • In Manual mode and with AGC , Is the gain index (gain) same?

    Is your signal continuous or kind of Burst ? From above it looks like burst, in this case the AGC will go to max gain when signal is not there. Please refer table 23 and 24 of UG-570, you can set 'gain index when reset' to 'optimize gain' so that next time when signal comes it starts from the optimum value and not from max gain.

  • Hi Vinod,

    Thanks. I missed that there was a way to adjust gain index approach on reset. I still have some issues with the gain mode (not getting the best performance even if gain index set to optimum on reset) but at least now I have more things to explore and hopefully find the optimum setting.

    Milos

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