One of the most common instruments used to measure jitter is the real-time digital oscilloscope (scope). Real-time oscilloscopes must be configured properly to make accurate jitter measurements. This application note provides general guidelines to setup an oscilloscope for best jitter measurement accuracy. The digital scope uses an internal time base to sample its inputs at regular intervals. The sampling rate can range from 1 Gsps (giga-samples-per-second) to 256 Gsps for the high-end units. Figure 1 illustrates how the scope samples and displays a signal presented to its inputs. The arrows at the bottom of the figure represent the sampling points, the solid line is the actual signal, and the dots are the sampled values. The signal displayed by the scope (represented by the dotted line) is the best-fit curve across the sampled points.