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# [SOLVED]purpose of using Separate Grounds

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#### SughiRam P.

##### Member level 2
In ATE Board Designs, We are using two Grounds, AGND and DGND. Finally we shorted those two using Zero ohm Resistor. What is the purpose of using Separate Grounds? Can we use single GND??:-?:-? Is there any intention in shorting these two Grounds???

Re: urpose of using Separate Grounds

Use one ground seperate the digital and analogue sections and have fun.
ttp://www.hottconsultants.com/techt...gnd-plane.html
An intuitive, practical approach to mixed-signal grounding
http://focus.ti.com/lit/ml/slyp167/slyp167.pdf
http://www.ieee.org.uk/docs/emc1206a.pdf

Grounding of Mixes Signal Systems

Re: urpose of using Separate Grounds

I personally think that dividing the ground on the ground layer into analog and digital portion does not impose any benefits to layout. What if we have lots of ADC in one single board, are we going to bridge them together under the ADC? Where is the meeting point for analog and digital ground? Sometimes this is a very tough job for us to decide at which point should we divide these analog and digital ground, especially nowadays ADC ICs available in the market do not really convenient us much on this matter. In fact, analog ground and digital ground have been connected internally inside the IC, so what we do on the board might not achieve what we expect on the board. Accidentally, we might ruin our board ending up with noise and wide return loop.

The general concensous these days is to have only one ground, not only as pointed out above, multiple ADC's or DAC's make it impossible to have 1 star point, but historicly when the grounds were split, logic was 5V and analogue was quite often 12-16V, so a 16 bit convertor had steps of 0.75-1V. Nowadays convertors work anywhere between 1.2V to 5V, so for 16Bits you have steps of 75mV to 0.3V, so if you have two grounds connected by a high impedance star point, it dosen't take a lot to have the grounds at different levels, wiping out the conversion accuracy. This is even worse when you gey to 24 bits.

nelsonys

### nelsonys

Points: 2
Separating grounds into ( non isolated ) geometric planes, allow reduction of foulcault ring effect generated current.

+++

Do you meen splitting the plane into seperate areas? or multiple seperate but contigous planes.

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