879 - LatticeXP2: How can I drive mini-LVDS output on LatticeXP2 if mini-LVDS IO standard is not available? <br>
If user's design is using 50 ohm PCB trace and cable impedances, user can set the LatticeXP2 IO output type to LVDS and this will produce 400mv peak signal swing at the receiver's 100 ohm termination with proper common mode output voltage. The mini-LVDS specification lists 0.3v to 0.6v peak differential, so 400mv peak is within the acceptable range for mini-LVDS.
If user have PCB trace impedances near the extremes of the mini-LVDS spec, user can turn on the RSDS output type and add a series resistor at each of the differential output pins located physically close to the LatticeXP2 device with resistance value of:
Rseries = (3.167 * PCB_Z0) - 33
This will produce 600mv peak differential signal swing into the mini-LVDS receiver. User can also lower the peak differential signal swing by raising the Rseries resistor value. IOs set to the RSDS output type will switch over the full power supply range into the external resistor network, so you can see higher SSO and edge skew than when using the LVDS output type in a 50 ohm environment.