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Out Of Band Rejection

Question asked by Golan_X on Jul 23, 2018
Latest reply on Aug 6, 2018 by PVALAVAN

Hello,

After reading the Application note (AN-1354) i would like to ask some question that wasn't clear:

 

1) In order to determine what is the rejection between TX to RX i would like to know what is the attenuation that should be define to the TX signals in order to avoid degradation in the AD9375 performance. Take under consideration that the LNA on the RX can receive up to 2dBm input power . 

 

Example:

TX output power 30dBm LTE 10 MHZ (LTE PAR 8.5dB)

Duplexer Front-End Rejection: 60dB

Guard between TX To RX Bands 38MHz

LNA maximum input power 2dBm

RX Gain : 38dB

 

In that case the receive power to the LNA will be -30dBm AVG ( -21.5dBm Peak) so i am not compressing the LNA.

Now after 20dB analog gain and 18dB of the AD9375 Gain the Out of band signal will reach up to 8dBm AVG.

 

I would like to understand if i need to add more filtering (like Duplexer with higher rejection or SAW near the AD9375 RX path) in order to avoid problems. 

Please let me know what is the rejection that i need and how did you got in to the number (so i can calculate similar cases by my self).

 

Also , please let me know if there is any limitation to the AD9375 filters by the Guard between the In-Band to the Out of band.

 

Let's say that the TX to RX signals is 8 MHz Gourd. It will change your answer regarding to the rejection betwen TX signals to RX ?

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