I'm getting ready to layout my PCB. Do you have a list of recommendations or best practices to follow?
The following are some general layout guidelines to follow for the DDS in your PCB layout.
Ground and Power Planes:
Separating analog and digital ground planes can work well, but not always necessary. It is often very difficult to implement properly, so one should proceed with caution. The customer DDS evaluation board uses a common analog and digital ground plane. However, in some layouts the common ground plane is partially etched away (a thin line) to better direct the ground return paths of the digital and analog circuitry.
The power plane on the DDS customer evaluation board is separated. Separating digital and analog power planes is not a requirement but should provide better isolation between analog and digital circuits. It will help digital switching transient currents from contaminating the analog circuitry. The gerber files for all the evaluation boards are available on the website.
It is important that all supply pins (GND, AVDD, DVDD) connect to their respective GND or POWER plane with the shortest amount of trace length. This will reduce the total series inductance. Equally important is to connect bypass chip-capacitors as close as possible to each and every power pin. Typically, we recommend 0.01uF for these capacitors. This will provide a good AC ground at the power pins for higher frequencies in order to minimize noise coupling from the part to the power supply rail, and vice versa.
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