Where how do i separate digital ground and analog ground on a breadboard?

MaxHeadRoom

Joined Jul 18, 2013
19,192
Generally breadboard have two or more power rails, the one I use has three separate ones that can be used independently, if need be.
Max.
 

SamR

Joined Mar 19, 2019
1,297
The typical breadboard has red and blue power rails on each side so it can support 2 different voltages if need be. Unless they are relative floating voltages ground is ground.
 

rsjsouza

Joined Apr 21, 2014
211
I'm following the pt2399 schematic sheet and I see that there are two grounds which are AGND and DGND. I'm a bit confused about it and dont know what to do.. So how do I separate them on a breadboard?
As others have said, modern breadboards come with dual rails for power, just like the one shown in the attached photo.

The separation between AGND (analog ground) and DGND (digital ground) is useful to improve the separation between the noisy part of the device (the digital) and the sensitive (the analog). The digital part has very steep voltage transitions that can induce ground currents that are amplified by the sensitive circuits of the analog sections of the IC.
 

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crutschow

Joined Mar 14, 2008
23,527
Ideally you separate the grounds and connect them together at only one point (close to any crossover signals between the analog and digital circuits, if there are any).
 

MisterBill2

Joined Jan 23, 2018
4,055
In this particular circuit there appear to be only two connections to the digital ground. The main digital ground connection is to pin #4, the other is from the resistors connected to pin #6 ALL of the other connections are identified as ANALOG ground connections. Certainly what adds a bit to the confusion is that there is only one power supply, +5 volts, feeding pin #1. My advice will only apply to this particular circuit built up on a breadboard similar to the one pictured in post #4. My suggestion is to connect the power supply negative terminal to that section that connects to pin #4, and then use a short jumper lead to tie that section to the negative strip, as identified by the blue color in that picture. Then the resistors from pin #6 would also connect to that short section with pin #4.
ALL of the other ground connections will be to the section with the blue strip. Also, the input and output connection common sides (grounds) will tie to that same blue strip section.
The advice from the others is correct, but it does not seem to answer your question. Hopefully this suggestion does provide an answer. Other circuits may need different considerations.
 

Joël Huser

Joined Jun 30, 2019
42
Hello A will to power,

As Rsjsouza rightly said, "The separation between AGND (analog ground) and DGND (digital ground) is useful to improve the separation between the noisy part of the device (the digital) and the sensitive (the analog)". Nothing to say more.

In every circuit, you usually have a "big capacitor" around the power input section.... you theoretically connect every GND to 1 single point "like a star" , exactly on the GND pad of the main cap.

Some people say, like me, that if you have a very low impedance ground plane, you can use it as "THE UNIQUE GND".

In another way, as you can see attached with a piece of a schematic, I created the 5VD / GNDD and the 5VA / GNDA from an USB plug in a "linear way". This means that I successively with different LDOs / voltage doubler isolated next power supply / voltage reference from the perturbations of the previous power supply. It's possible to reduce a lot of voltage perturbations with successible LDOs without heathink because analog power supplies often don't need a lot of power.

All polarized caps are tantale. I begin to say after an LC filtration that the "5 [VDC] USB line" is the "5VD" = "the digital 5 [VDC]", referenced to the "GNDD". I put it very close to the input, because with digital power rails, usually you don't care about perturabations and use noisy power rails.

After that, I connected a voltage doubler U2 after the 5VD to make the "10VD", to where all perturbations from the 5VD will be transmitted.

Finally, with the LDO U3, I remove all the perturbations from the 10VD to make the "5VA" = "the analog 5 [VDC]", which should be free from any perturbations.

And at the end, with U4, I create the 2,5 [VDC] reference voltage.

with 16bitsADCSection.png you can see how I connect analog and digital power rails to the 16 [bits] ADC.

Joël
 

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