Hi,
The unused LVDS data input lane should be terminated by connecting a 100 ohm resistor between positive data lane and negative data lane pair, and having a 100mV drop across that 100 ohm resistor. The positive data pin should also be tied to DVDD through a pull up resistor and the negative data pin to the ground through a pull down resistor. The negative data lane should have a voltage 1.15V and positive data lane should have 1.25V giving us common mode voltage of 1.2V. The setup is shown in Fig 1 below.
Fig 1.
If you have more than one unused LVDS data lanes you could use the following example.
In the example I am assuming, there are 4 unused LVDS data lanes. To make the connections easier, all the four unused LVDS data lane pairs can be connected together as shown in Fig 2 below. To make the circuit even simple we could use a parallel combination of 100 ohm resistor, and use just one 25 ohm resistor instead of four 100 ohm resistors.
Fig 2.
Calculating the value of pull up and pull down resistor.
First calculate the current, since we know that we want 100mV drop across the termination resistor 25 ohm (parallel combination of four 100 ohm resistors). Using V = IR
I=.1V/25ohms
I= 0.004A
Pull up resistor.
The voltage drop across pull up resistor is 1.8v (DVDD)-1.25=0.55V and current is 0.004A
Rpull_up = 0.55V/0.004
Rpull_up = 137.5 ohm
Pull down resistor
we know V=1.15V and I = .004A and value of R can be calculated.
Rpull_down =1.15V/.004A
Rpull_down = 287.5 ohm
Regards,
Neeraj
