ADRF6720 EXT LO INPUT Impedance

Hi Chris,

The LO inputs are 50 ohm differential inputs.

On the AD9144/ADRF6720 eval board the LO input balun is 1:1 so it should translate a 50 ohm single ended impedance to a differential 50 ohm impedance.

Regards,

Liam

Thanks Liam,

Well, it is what I thought but by opening the layout of AD9144-M6720-EBZ, I can see the balun followed by 100Ohms differential pair (J18 connetor), is it a mistake then?

Thanks again,

Best

Chris

Hi Chris,

On the layout I only see spaces for the series capacitors and the balun before it goes to J18 SMA connector

This is the layout I am looking at:

ftp://ftp.analog.com/pub/HSSP_SW/HSCDAC/Documents/AD9144/AD9144-ADRF6720-EBZ%20RevC.brd

Hello Liam,

I am looking at the same layout. If I am correct, the differential impedance after the balun is 100Ohm.

Best,

Chris

Chris,

I'm afraid I don't understand. You said " I can see the balun followed by 100Ohms differential pair (J18 connetor)" but there are no resistors between the balun and the J18 SMA connector.

Hello Liam,

Sorry for the confusion. So there is the J18 connector, the balun and then the serie capacitors that are conneceted to the ADRF. The connection uses 100Ohm differential pair while the balun is 50Ohm and the external LO input impedance is 50 Ohm differential. Am I wrong?

Thanks for your help.

Best,

Chris

Hi Chris,

Yes I understand now.  Ideally these lines would be 50 ohm differential but since they are quite short there should not be much impact. When designing your own board you could use 50 ohm differential lines.