High-performance clock buffers are sensitive to noise on the power supply, which can dramatically increase the additive jitter of the buffer. Reducing noise from the system power supply is essential, especially when jitter or phase noise is critical to applications.

Filter capacitors are used to eliminate the low-frequency noise from the power supply, where the bypass capacitors provide the low impedance path for high-frequency noise and guard the power-supply system against the induced fluctuations. These bypass capacitors also provide instantaneous current surges as required by the device and must have low equivalent series resistance (ESR). To properly use the bypass capacitors, the capacitors must be placed close to the power-supply pins and laid out with short loops to minimize inductance. TI recommends adding as many high-frequency (for example, 0.1µF) bypass capacitors as there are supply pins in the package. TI recommends, but does not require, inserting a ferrite bead between the board power supply and the chip power supply that isolates the high-frequency switching noises generated by the clock driver. These ferrite beads prevent the switching noise from leaking into the board supply. Choose an appropriate ferrite bead with low DC resistance because providing adequate isolation between the board supply and the chip supply is imperative, as well as to maintain a voltage at the supply pins that is greater than the minimum voltage required for proper operation.

Figure 9-5 shows this recommended power-supply decoupling method.

Figure 9-5 Power Supply Decoupling