Frequently Asked Question
Should the digital and analog GND planes on my board be separated?
One of the fundamental requirements in implementing a successful high speed mixed-signal PCB design is to incorporate large, low impedance ground planes. Low impedance ground planes act as a return-path for high frequency analog and digital signals and reduce the overall level of EMI/RFI emissions. DDS devices typically provide ground connections separately labeled as “digital ground” and “analog ground." It is generally desirable to connect these analog and digital ground pins to a single massive ground plane within the PCB. All IC ground pins should be soldered directly to their corresponding ground planes to minimize series inductance. The IC’s power supply pins should be decoupled to the ground plane, as close as possible to the chip with low inductance ceramic surface-mount capacitors. If through-hole capacitors must be used, their leads should be less than 1 mm in length, and Ferrite beads may be employed to compensate for parasitic resonance. Multilayer PCBs are recommended for “motherboard” designs, with individual layers utilized as dedicated analog and digital ground planes. Please refer to the device data, Tutorial MT-031, and Tutorial MT-101 for grounding, PCB layout, and power supply decoupling recommendations.