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ADRF6780 baseband common mode voltage

Question asked by user1283 on Apr 6, 2017
Latest reply on Apr 6, 2017 by Assaf

Hi, I have a problem with ADRF6780 while using baseband interface:

I have an IF signal on frequency 600 MHz, so I can't use the IF input of ADRF6780, since it works from 800MHz. This is the reason why I use the baseband interface. The picture below shows, how is my baseband circuit connected:

Now when I measure voltage on pin 2 of the transformer, there is 1V between this pin and ground.

 

In datasheet on page 21, there is a description of baseband inputs: "The input impedance of the basebands are high input impedance. These inputs are designed to operate with a 0.5 V common-mode voltage. These inputs are differentially terminated to a 100 Ω resistor using an off chip termination."

 

However on eval board schematic (page 32), there are the baseband inputs are tied to groung with 50 Ohm resistors. This looks quite strange to me if I consider, that there should be 0.5V common mode according to documentation...

 

MY QUESTION IS: Is my schematic correct? How should I connect the baseband inputs in order to have correct common mode voltage? Should I force the voltage to be 0.5V?

 

Thanks

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