Separate grounds, digital chip & analogue chip

Thread Starter

Tony Elliott

Joined May 8, 2015
158
Hi Allaboutcircuits,
I am using MM74C74N / MM74C00 digital chips powered gnd to 12v and analogue chips powered -/+ 12v.
I have heard that I need to use separate grounds to avoid interference.
Attached is my -/+ 12v power supply to power analogue chips. Does anyone have an idea how to power gnd to 12v supply (with bypass capacitors) that has a separate ground to power the digital chips MM74C74N / MM74C00?
 

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crutschow

Joined Mar 14, 2008
27,760
Max's recommendation may be okay, depending upon how sensitive the analog signals are to noise.
What's the lowest level analog signal you have?

If the analog signals are small, you may want to add a ferrite bead in series with the analog and digital power before the decoupling capacitors. This adds some inductance to help filter the high frequency digital power line spikes.
Also there should be separate grounds for the analog and digital with them tied together at only one point.
A ferrite bead between the two ground connections can also help minimize digital noise getting into the analog ground.
 

Thread Starter

Tony Elliott

Joined May 8, 2015
158
Max's recommendation may be okay, depending upon how sensitive the analog signals are to noise.
What's the lowest level analog signal you have?

If the analog signals are small, you may want to add a ferrite bead in series with the analog and digital power before the decoupling capacitors. This adds some inductance to help filter the high frequency digital power line spikes.
Also there should be separate grounds for the analog and digital with them tied together at only one point.
A ferrite bead between the two ground connections can also help minimize digital noise getting into the analog ground.
Fantastic I have some ferrite beads so Ill try that out:)
 

Veracohr

Joined Jan 3, 2011
759
The term "separate grounds" is misleading because it can be interpreted as grounds that are isolated from each other. There should be a better term.
 
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