PCB Layout
2-2
2.1
PCB Layout
The DAC8534EVM is designed to preserve the performance quality of the
DAC device under test, as specified in the datasheet. Carefully analyzing the
EVM’s physical restrictions and the given or known elements that contribute
to the EVM’s performance degradation is the key to a successful design
implementation. The obvious attributes, that diminish the performance of the
EVM, can be taken care of during the schematic design phase by properly
selecting the right components, and building the circuit correctly. The circuit
design phase should include adequate bypassing, identifying and managing
the analog and digital signals, and a knowedge or understanding of the
mechanical attributes of individual components.
An obscure part of the design phase is the layout process, where lack of
knowledge and inexperience can easily present a problem. The main concern
here is primarily with the placement of components and the proper routing of
signals. The bypass capacitors should be placed as close as possible to the
pins and the analog and digital signals should be properly separated from each
other. The power and ground plane is very important and should be carefully
considered in the layout process. A solid plane is ideally preferred but
sometimes impractical, so when solid planes are not possible, a split plane
does the job as well. When considering a split plane design, analyze the
component placement and carefully split the board into its analog and digital
sections starting from the device under test. The ground plane plays an
important role in controlling the noise and other effects that otherwise
contribute to the error of the DAC output. To ensure that the return currents are
handled properly, route the appropriate signals only in their respective
sections, meaning the analog traces should only lay directly above or below
the analog section and the digital traces in the digital section. Minimize the
length of the traces but using the largest possible trace width allowable in the
design. Good design practice is seen in the layout figures in this chapter.
The DAC8534EVM board is constructed on a four-layer printed circuit board
using a copper-clad FR-4 laminate material. The printed circuit board has a
dimension of 43,180 mm (1.7 inch)
×
82,550 mm (3.25 inch), and the board
thickness is 1,5748 mm (0.062 inch). Figures 2 through 6 show the individual
artwork layers.