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ELECTRONICS

analogue and digital ground planes. For more complex References
designs, the star ground is commonly implemented with a • Walt Kester. The Data Conversion Handbook. Analog Devices, Inc., 2005.
jumper shunt to a ground header. No high current carrying • John Ardizzoni. “A Practical Guide to High-Speed Printed-Circuit-Board
a header and jumper shunt is required as there will be Layout.” Analog Dialogue, Vol. 39, No. 9, September 2005.
no flow of current in the star ground, but rather its main • Ralph Morrison. Grounding and Shielding Techniques. John Wiley & Sons,
purpose is to make sure that both grounds have the same Inc., 1998.
reference levels. • Thomas O’Shea. “AN-1349 Application Note: PCB Implementation
Designers must always check grounding recommendations Guidelines to Minimise Radiated Emissions on the ADM2582E/ADM2587E
found in each device’s data sheet to ensure grounding RS-485/RS-422 Transceivers.” Analog Devices, Inc., August 2018.
specifications will be met and avoid ground related issues. • “MT-101 Tutorial Decoupling Techniques.” Analog Devices, Inc., 2009.
• Linear Circuit Design Handbook. Analog Devices, Inc., 2008.
On another note, for mixed-signal devices that have AGND
• Paul Brokaw. “AN-342 Application Note, Analog Signal-Handling for High
and DGND pins, these can be tied to their respective ground
Speed and Accuracy.” Analog Devices, Inc.
planes since the star ground will also connect both grounds • Walt Kester, James Bryant, and Mike Byrne. “MT-031 Tutorial Grounding
at one point. In this way, all noisy digital currents will flow
Data Converters and Solving the Mystery of ‘AGND’ and ‘DGND’.” Analog
through the digital power supply down to the digital ground
Devices, Inc., 2009.
plane and back to the digital supply all the while being • Paul Brokaw and Jeff Barrow. “AN-345 Application Note: Grounding for
isolated from the sensitive analogue circuitry. Isolation of the Low- and High-Frequency Circuits, Know Your Ground and Signal Paths for
AGND and DGND planes must be implemented on all layers of Effective Designs, Current Flow Seeks Path of Least Impedance–Not Just
a multilayer PCB. Resistance.” Analog Devices, Inc.
• Doug Grant and Scott Wurce. “AN-348 Application Note: Avoiding Passive
Other common grounding practices Component Pitfalls, The Wrong Passive Component Can Derail Even the

Here is a procedure/checklist that one can follow to ensure Best Op Amp or Data Converter Here Are Some Basic Traps to Watch For.”
an appropriate grounding scheme has been implemented in a Analog Devices, Inc.
mixed-signal analogue/digital system:
• Wide copper traces should make up the connections at About the Authors
the star point. May Anne Porley is an applications
• Check the ground plane for narrow traces, as these engineer at Analog Devices,
connections are undesired. Philippines, within the Automated
• It is useful to provide pads and vias so that the analogue Test Equipment (ATE) Group. She
and digital ground planes can be connected, if necessary. joined ADI in 2012 and provides
applications support for switches,
Conclusion multiplexers, level translators, and

The PCB layout for mixed-signal applications can be unbuffered crosspoint switches
challenging. Creating a component floor plan is just the portfolios. May Anne graduated
starting point. Properly managing board layers and preparing from De La Salle University – Dasmariñas, Philippines, with a
an adequate grounding scheme are also part of the key points bachelor’s degree in electronics engineering.
a system designer must consider when trying to achieve
optimum performance in a mixed-signal system layout. Kevin Chesser was a product
Preparing a component floor plan will help set the overall application engineer with the
integrity of the system design. Proper board layer organisation SMX Group at ADI, Limerick. He is
will help manage the currents and signal throughout the very passionate about electronics
board. Finally, choosing the most beneficial grounding scheme and the real-world problems that
will improve the system’s performance and prevent any issues can be solved using technology.
with noisy signals and return current. n Kevin provided customer support
focusing on the ADG7xx family of
Acknowledgement switches and multiplexers.
The material presented in this article was compiled from
many contributors, including Eric Carty, Genesis Garcia, Analog Devices is represented in South African by
Giovanni Aguirri, Brendan Somers, Stuart Servis, Leandro Peje, Altron Arrow. For more information contact Conrad Coetzee
Mar Christian Lacida and Yoworex Tiu. at ccoetzee@arrow.altech.co.za

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