AC-couple LVDS clocks before the balun to avoid significant attenuation of the clock signal. If a balun is unavailable, the measurements can be taken single-ended. Note that for single-ended measurements, it is important to correctly terminate the unused end of the output as shown in Figure 4-3 to make sure proper loading on the output driver. When taking single-ended measurements without a balun, there can also be some degradation in phase noise performance due to a decrease in signal power and lack of common-mode noise rejection.

Figure 4-2 Recommended LVDS Termination Scheme for Phase Noise Measurements

Figure 4-3 Alternative LVDS Termination Scheme for Phase Noise Measurements (Single-Ended)