10.1.1 Power-Supply Filtering

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

The use of bypass capacitors eliminates the low-frequency noise from power supply, because they can provide a very low-impedance path for high-frequency noise and guard the power-supply system against induced fluctuations. The bypass capacitors also provide instantaneous current surges as required by the device, and should have low ESR. To use the bypass capacitors properly, place them close to the power supply terminals and lay out traces with short loops to minimize inductance. TI recommends that the engineer add as many high-frequency (for example, 0.1-µF) bypass capacitors as there are supply terminals in the package. TI recommends that the engineer insert a ferrite bead between the board power supply and the chip power supply to isolate the high-frequency switching noises generated by the clock driver. This would prevent leakage into the board supply. It is important to choose an appropriate ferrite bead with low DC resistance, because the bead must provide adequate isolation between the board supply and the chip supply. It is also important to maintain a voltage at the supply terminals that is greater than the minimum voltage required for proper operation.