AN 447: Interfacing Intel® FPGA Devices with 3.3/3.0/2.5 V LVTTL/LVCMOS I/O Systems

ID 683295
Date 3/28/2022

Selecting Appropriate Series Termination Resistor Value

The series termination scheme works by introducing a resistor placed in series between the driver and receiver. The driver impedance and series resistance become the total effective driver impedance. The transmission line impedance has to match the driver impedance to minimize reflection and manage overshoot.
Figure 4. Series Termination Scheme

You must perform a simulation to determine the suitable series resistor value for your interface within the allowable tolerance condition. Choosing the appropriate resistor value for series termination is important:

  • If the resistance is too small, the termination may not effectively reduce or eliminate the overshoot.
  • If the resistance is too large, the driver may not sufficiently drive the transmission line and it can result in a stair-step response.

Did you find the information on this page useful?

Characters remaining:

Feedback Message