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Only one inductor separates these power channels. According to “Connection Guidelines” it should be an inductor with ferrite core.
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Although the symbol on the schematic looks like an inductor, its not really. The word BEAD indicates that what they have used (correctly) on the board is a ferrite bead. Look at the MuRata web site for details on the different types of beads.
http://www.murata.com/products/emc/selection_guide/emc/index.html A ferrite bead has low resistance at DC, and an increasing resistance (impedance) with frequency. The ferrite bead is used as a filter to remove high frequency components from the power supply. The image you show is not a good filter; the ferrite bead should have capacitors on either side to create a pi-filter. The 10uF capacitor is bulk capacitance, so that does not count as part of the pi-filter. The filter should have a couple of 0.1uF or 0.01uF ceramic caps. The filter needs to have capacitors on both sides of the bead, as in one direction, the filter stops noise from the main supply coupling into you sensitive circuit (eg. PLL), and in the other direction the filter stops noise from the PLL getting back onto your main power supply.
For examples of correctly design decoupling filters, see this schematic:
http://www.ovro.caltech.edu/~dwh/carma_board/gda06rb004_carma_v0.87_dec03.pdf (
http://www.ovro.caltech.edu/%7edwh/carma_board/gda06rb004_carma_v0.87_dec03.pdf)
The PCB layout files are also on this page along with links to a free viewer. The design contains both switch-mode power supplies and linear supplies.
http://www.ovro.caltech.edu/~dwh/carma_board/ (
http://www.ovro.caltech.edu/%7edwh/carma_board/)
Here's some notes on the power supply designs:
http://www.ovro.caltech.edu/~dwh/carma_board/power_supply_design.pdf (
http://www.ovro.caltech.edu/%7edwh/carma_board/power_supply_design.pdf)
Cheers,
Dave
Honored Contributor
