Ferrite Bead

Board

Supply

VDD

Chip

Supply

C

1 µF

C

10 µF

6 xC

0.1 µF

CDCLVC1310

www.ti.com

SCAS917B

– JULY 2011 – REVISED FEBRUARY 2012

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/phase noise is very critical to applications.

Filter capacitors are used to eliminate the low-frequency noise from power supply, where the bypass capacitors

provide the 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, they must be placed very close to the power

supply pins and must be laid out with short loops to minimize inductance. It is recommended to add as many

high-frequency (for example, 0.1-

µF) bypass capacitors as there are supply pins in the package. It is

recommended, but not required, to 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, preventing them from leaking

into the board supply. Choosing an appropriate ferrite bead with very low dc resistance is important, because it is

imperative to provide adequate isolation between the board supply and the chip supply, and to maintain a

voltage at the supply pins that is greater than the minimum voltage required for proper operation.

Figure 24. Power-Supply Decoupling

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© 2011–2012, Texas Instruments Incorporated

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