PCB Layout
2-2
2.1
PCB Layout
The DAC8574 EVM is designed to preserve the performance quality of the
DAC, device under test, as specified in the data sheet. Carefully analyzing the
EVM’s physical restrictions and the given or known elements that contributes
to the EVM’s performance degradation is the key to a successful design
implementation. These 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
must include adequate bypassing, identifying and managing the analog, and
digital signals and knowing or understanding the components mechanical
attributes.
The obscure part of the design 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 must 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 can
do 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
contributes 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 use the biggest possible trace width allowable in the
design. These design practices discussed can be seen in the following figures
presented on the following pages.
The DAC8574 EVM 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 43,1800 mm (1.7000 inch) X 82,5500 mm (3.2500 inch), and the
board thickness is 1,5748 mm (0.0620 inch). Figures 2 - 1 through 2 - 6 show
the individual artwork layers.