Differential input-ouput buffers are frequently utilized in high-speed communication systems. Often, a transmit buffer is connected to a 100-Ω differential receive buffer through a passive interconnect link with no means of verifying the true differential signal quality of the transmitter. Additionally, many electrical protocol specifications are defined assuming differential transmitter termination into 100 Ω with no common-mode reference. Commercially available, active probe test equipment can be cost prohibitive or have limited functionality due to unwanted parasitics inherent in the active devices. This paper describes a passive high-bandwidth 100-Ω differential termination device for characterizing high-speed differential buffers using standard test equipment.