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AFE8000EVM: Differences Between Tx Chains (Caps / Inductors)

Avihay Froo
Prodigy 160 points
Part Number: AFE8000EVM
Other Parts Discussed in Thread: AFE8000,

Hi, 

I have two questions regarding the Tx chains of the AFE8000 EVM board:

(1)  I've noticed that there are values differences of caps & inductors on the AFE8000EVM board matching network:
For example -
* (TXE_OUT, J14) C498 = 3pF, C497 = 0.7nH (inductor), C352 = 1.2pF [Capacitor] ...
* (TXF_OUT, J12) C602 = 2.7pF, C501 = 2.2pF [Capacitor], C79 = 3nH (inductor) ...

What is the reason for these differences?
Is it due to the EVB layout, to compatible to the AFE8000's relevant output (5TXOUT vs 6TXOUT)?

(2) What is the reason for the 1.2v common-mode addition on the Tx signals?

Is it unique for the EVB, or a requirement of the AFE8000 component?

Please advise,

Avihay.

  • 0
    TI__Genius 17771 points

    Hi Avihay,

    1. The changes in the caps and inductors is because each of these channels have different routing, on EVM and substrate, and therefore require a slightly different matching network. 

    2. On the DACs it is required that a 1.2V bias be applied to all outputs. The reason is that the internally we do not bias the DAC outputs. This is an AFE8000 requirement. 

    Regards,

    David Chaparro