# Marvell PHY to KS8999 PHY connection

I'm trying to design a custom board with Marvell 88E1111 PHY and I want to connect this board to another board with KS8999 PHY on it. I want to connect two phy sides with capacitive coupling.

The distance between two boards is less than 5 inches and I have no option for using another PHY chip or using a transformer. I have searched through web and found these links:

Transformerless design

So I think that capacitive coupling is an option.

Micrel KS8999 supports capacitive coupling [here], but there is no specific data in 88e1111 datasheet about capacitive coupling.

Now my question is:

1. Is it possible to connect two phy sides?

2. If yes, how to connect lanes in terms of using series capacitors, pull-up voltage at 88E1111 side and pull-up resistor values?

KS8999 Datasheet

Is it possible to connect two phy sides?

Yes, it is poosible. It is less unpredicatable in 100BASE-TX (100 Mbps) mode than in 1000BASE-T (1 Gbps) mode, therefore you have a good chance. But it always case dependent: there is no single, universal solution.

Thus, prepare your design to a trial-and-error process by adding four 0603 places on each line in each pair on both sides of the de-coupling capacitor, like this:

    vcc1          vcc2
|             |
[ ]0603       [ ]0603
|             |
<>----o----|cap|----o----<>
|             |
[ ]0603       [ ]0603
|             |
gnd           gnd