Regarding gain compensation implementation in FPGA

[Maitry07]

Hello support team,

I have one fixed gain LNA at the input of the RF direct sampling receiver. This LNA is to increase the dynamic range of the RF-ADC inside the Direct sampling receiver. As the output of direct sampling receiver is in the form of I and Q samples which use DDCalgorithm.
At the DDC output, I need to implement Digital gain compensation technique for the fixed gain LNA to have actual amplitude. can you please suggest a suitable technique for the implementation of digital gain compensation technique in FPGA for the external fixed gain LNA?

 

[kaz1]

Hello support team,

I have one fixed gain LNA at the input of the RF direct sampling receiver. This LNA is to increase the dynamic range of the RF-ADC inside the Direct sampling receiver. As the output of direct sampling receiver is in the form of I and Q samples which use DDCalgorithm.
At the DDC output, I need to implement Digital gain compensation technique for the fixed gain LNA to have actual amplitude. can you please suggest a suitable technique for the implementation of digital gain compensation technique in FPGA for the external fixed gain LNA?

One way to design AGC is insert running average filter on power value (I^2+Q^2) then apply square root of this average on I and Q amplitude values. This is commonly done as feedback on amplitude of I/Q. You can use look-up-table to get square root for a suitable range of power values or square root function if available.

 

[Maitry07]

Hi,

Thanks for your response. I am using this amplitude measurement only. But as I want to measure the actual input (which is at the input of LNA, which is unknown to me) . Due to LNA, fix gain is being added to the actual input. So, Before measuring the amplitude using I and Q, I need to add digital gain compensation , right?
This digital gain compensation will add Loss equivalent to gain of LNA. and then when I measure the amplitude, I will get the actual amplitude using I,Q.

So, my question is to add fixed loss( equivalent to LNA gain) to I,Q to compensate for the External LNA gain, what are the suitable implementation technique?