See Figure 27 for one preferred method for clocking the AD6644. The clock source (low jitter) is converted from single-ended to differential using an RF transformer. The back-to-back Schott kdiodes across the secondary windings of the transformer limit clock excursions into the AD6644 to approximately 0.8 V p-p differential. This helps prevent the large voltage swings of the clock from feeding through to the other portions of the AD6644, and limits the noise presented to the ENCODE inputs. A crystal clock oscillator can also be used to drive the RF transformer if an appropriate limiting resistor (typically 100 Ω) is placed in series with the primary winding of the transformer.