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Analog and Digital GND

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magnetra

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I'm working with A/D converters and I came across Analog and Digital Grounds. Two separate grounds for same ckt. I'm confused. What are they? Can any one give me some idea what two separate gnd are need?

Regards
M
 

Hi.

The 2 gnd is used to make a separation between the digital and the analog part of the circuit. If you use optocouplers in the digital part for comunication with PC(for example), then these are not requied.
 

They are supposed to be there to provide noise immunity. However, you can simply short them and connect them to the ckt. ground.

The actual use comes when the analog input that you are providing to the ADC comes from a separate circuit (which has a separate GND), and the digital ckt. in which the output of ADC goes in a separate circuit (separate GND).....

That is, when the analog circuit has a different power supply and the digital circuit in which the ADC is connected has another one.
 

Hi,
Actually the digital part of any circuit is very much noisy due to switching.Hence it is separated from analog part by using separate gnd and also by shielding.
 

Below you can find a couple of articles on analog/digital ground issue ..

Ask The Applications Engineer -12 GROUNDING (AGAIN)

Q. I’ve read your data sheets and application notes and also attended your seminars, but I’m still confused about how to deal with analog (AGND) and digital (DGND) ground pins on an ADC. Your data sheets usually say to tie the analog and digital grounds together at the device, but I don’t want the ADC to become my system’s star ground point. What do I do?
Click to expand...

https://www.analog.com/library/analogDialogue/Anniversary/12.html

The general solution to successfully mixing analog and digital probably doesn't exist, but everyone has a dozen or so partial solutions, and there are "very
long" threads about this on piclist - if you can find them. This whole area is probably more art than science.
Click to expand...

**broken link removed**


Regards,
IanP
 

magnetra said:
Can any one give me some idea what two separate gnd are need?
Click to expand...
The analog ground returns power supply current from analog circuits, while the digital ground returns supply current from digital circuitry.

The reason for having two grounds is so that digital current will not flow in the analog supply. If digital current was allowed to flow in the analog supply, it would couple digital noise onto sensitive analog signals. This would happen because the analog ground plane (or trace, if there is no plane) has finite electrical resistance. Digital currents flowing through this resistance result in small digital voltages on the ground that is used as a 0V reference by analog circuitry.
 
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Here is another useful article: h**p://www.sigcon.com/Pubs/edn/adcgrounding.htm
 

magnetra,
With regard to IC A/D converters, the analog and digital grounds refer to the internal usage of the separate grounds. In an application, they should be connected together at the IC package with as short a connection as possible.
Regards,
Kral
 

Analog Gnd is related to Analog section of the Circuit
Digital Gnd Digital Section of the circuit.
They run seperately and inter connected at power supply end to prevent noise contamination
 

purpose of having seperate gnd for analog and digital section is to avoid noise from digital to analog portion.
 

Hello

analog pads must be separated away from digital ones ,,for digital circuits ,,they perform strong switching,,if you talk about CMOS ,,it switches rail to rail supply,,this drives currents from supply and to groung making huge variationsin both of them,,while on the other hand , analog circuits most common is so sensitive,,it performs operations mainly on small signals,,which will be disturbed much if it shares a common supply and ground with digital circuits ,i.e. noise may cause the analog circuit to be malfunction....so separate supplies required for each of them ,,i hope that help you,,,,

regards
 

Separate grounds improve noise immunity betwee the two domains of a circuit but you can join these two if no fast switching is involved in the digital portion of the circuit.
 

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