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Problem with AGC on ADF7021-N

Question asked by dvar on Jan 9, 2013
Latest reply on Jan 10, 2013 by dvar

Hello,

 

I am facing a strange issue with AGC on the ADF7021-N chip.

 

I am using an external oscillator at 14,7456 MHz, listening to a transmitter sending analog audio at 324,0875 MHz and my register settings looks like this:

 

reg0: 0x095f8c80

reg1: 0x037ad021

reg2: 0x009610a2

reg3: 0x3e4c0493

reg4: 0x80a73694

reg5: 0x000024f5

reg6: 0x0a07ebb6

reg9: 0x000231e9

reg10: 0x0896355a

reg14: 0x0000001e

reg15: 0x0000000f

 

I observe the following:

  1. If I program the chip after turning the transmitter on, audio is fine and I can read an RSSI value from register 7 that makes sense.
  2. If I program the chip and THEN turn the transmitter on, audio quality is really bad and the RSSI value is low even though the filter gain and LNA Gain are set at maximum (2 and 2).
  3. When I have proper audio quality and degrade the signal such that AGC sets the Filter and LNA Gain to maximum, then it doesn't reduce the gain again when I restore a good signal quality, and the RSSI value read back is still extremely low.
  4. When I end up in situation 2. or 3., reprogramming the chip (All the above mentioned registers, in the way it is advised to in the datasheet), good audio quality is restored and RSSI reading makes sense again.

 

So, my question is simple: what can be the reason for that? I haven't found any article describing any similar problem in this forum so I guess there's nothing wrong with the chip in the first place.

 

Thanks for your help!

 

Best regards,

 

Damien.

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