AFE7901: Impedance matching

Maor Bouhadana

Part Number: AFE7901

Tool/software:

Hi, I'm a little bit confused. The datasheet says that the impedance of the TX port is a differential 100 ohm, but in some application notes and the layout I can see the impedance is a differential of 50 ohm.
In the EVB scheme, we can see 2 types of Baluns - 1:1 and 1:2.
can you explain the cause?

10 months ago

0 Rob Reeder 10 months ago

TI__Mastermind 38690 points

HI Maor,

Typically differential traces for analog inputs are routed 50ohm single ended. Not 100ohm diff like on digital traces for LVDS, CML, etc.

For the balun, different baluns, with different impedance ratios, were selected based on a few different application BWs that the device can cover.

Regards,

Rob

0 Maor Bouhadana 10 months ago in reply to Rob Reeder

Prodigy 90 points

When the datasheet says

what does it mean? can you clear the input impedance requirements for RX and TX?

0 Camilo Garcia Trujillo 10 months ago in reply to Maor Bouhadana

TI__Expert 5035 points

Hi Maor,

Tx is 50ohm output differential termination impedance for the AFE795x family. And 100ohm output differential termination impedance for the AFE790x family.

For the Rx/FB channels, match using input differential impedance of 100 ohms.

Best,

Camilo

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AFE7901: Impedance matching