Difference between Digital and Analog ground ?

[spherulite]

analog ground and digital ground

what is the difference between digital and analog ground ?

 

[bastos4321]

analog ground

The diference is the noise. The digital gnd is much more noiser that analog agnd, so they should not be mix up to avoid coupling from digital noise to analog.

Bastos

 

[videohu]

difference between analog and digital ground

Usually, digital ciricuits are more robust to noise, which have only two value 0,1. The analog circuits work on specific working points depending on requirements. the working point is easy to drift due to noise. So the best way is to avoid the large current circle from digital section runing across analog circuit. point connection between digital gnd and analog gnd is usually preferred.

 

[djalli]

digital ground analog ground

The diference is the noise. The digital gnd is much more noiser that analog agnd, so they should not be mix up to avoid coupling from digital noise to analog.

Bastos

Use decoupling capacitors (for IC...etc) and in real life you can use analog ground for digital ground at the same time. I know it works pretty good.

 

[bastos4321]

analog ground digital ground

In IC design (inside chip) the decoulpling values avaible are very limitted so it does not work. You have to separate grounds.

Obviosly in discrete you can use good decoulpling and coexist only with one ground, but that is not the best way to do it.

Bastos

 

[tlihu]

digital and analog ground

Digital GND is noisy because the well/sub are locally connected to the sources of P/N mos and the mos are switching from rail to rail. On the contrary, analog GND is relatively quiet because the it deals with small signal mostly.

 

[djalli]

analog and digital ground

In IC design (inside chip) the decoulpling values avaible are very limitted so it does not work. You have to separate grounds.

Obviosly in discrete you can use good decoulpling and coexist only with one ground, but that is not the best way to do it.

Bastos

Bastos, you can place decoupling capacitors in IC socket (not inside the IC chip). Connect them from first pin to last pin of IC with cap (sometimes these caps can be called bypass capacitors). Although I have not tried with high speed signal.

I tried one common ground for both analog/digital ground but working signals up to 40khz and it worked good. I digitized and recorded in 10mb memory and played back the recorded digitized signal. Everything a big circuit, just 1 ground.

 

[maharshi_qis]

digital ground and analog ground

difference is interms of noise,design etc......

 

[Kral]

difference between digital and analog ground

spherulite,
In an ideal world, there is no difference. In the real word, ground connections have both resistance and inductance. Good practice dictates that the layout be arranged such that ground currents from the digital circuits do not flow through the ground path for the analog circuits. Ultimately, the two grounds must be connected together. This should be done at the power supply.
Regards,
Kral

 

[eelinker]

analog and digital grounds

I highly recommand reading behzad razavi's book (analog cmos ic design) he has described the difference under the title substrate noise page 663.

 

[STOIKOV]

analog digital ground

if there are analog and digital grounds, what would the return path be at the moment of communicating 2 signals between the analog and digital block? Both grounds should be connected in one point ?

 

[Kral]

separate analog and digital ground

STOIKOV,
Yes, the two grounds must be connected together at one point. In many ICs, such as A/D converters, the two grounds are brought out to separate pins on the IC package. In this case, the terms "analgo ground" and "digital ground" refer to internal functions of the chip. In this case, most manufacturers recommend that the two grounds be connected together at the chip, with as short a connection as possible.
Regards,
Kral

 

[waqas85]

difference between analog digital ground

the main difference between digital & analoge signal is the digital signals are in the form of 0 & 1 that is there is continous chain of zeros & ones that form digital signal
but the analoge signal is in the form of a wave just like ups & downs with certain amplitude & frequrency
the example of digtal signal is the signal from the DC source
while example of the analoge sinal is domestic electricity supply

 

[srieda]

digital analog ground

I agree with the above posts that digital ground is noisier than analog ground. And as it is suggested, it is a good and safe practice to have separate grounds for analog and digital circuits. These are usually brought out as separate pins which are finally connected together on the board. This actually lowers the effects of coupling as the connection is outside the chip.

 

[melc]

analog ground digital

STOIKOV,
Yes, the two grounds must be connected together at one point. In many ICs, such as A/D converters, the two grounds are brought out to separate pins on the IC package. In this case, the terms "analgo ground" and "digital ground" refer to internal functions of the chip. In this case, most manufacturers recommend that the two grounds be connected together at the chip, with as short a connection as possible.
Regards,
Kral

Kral&Stoikov,

Imagine the following situation: a speedy A2D/D2A input/output connected to an 100MHz bus.
The A2D/D2A analogic ground is also a RF ground for some transcievers running at 2.5Ghz and 5Ghz.
The 100MHz bus is connected with a 2GHz DSP.

How do you separe the RF ground, the analogic ground and the digital ground ?

 

[STOIKOV]

analogue and digital ground

good and real example to think about,

:?:

 

[Kral]

analog ground vs digital ground

melc,
I don't have a perfect solution, but here goes:
Isolate the RF section with its own ground plane. Use heavy local bypassing to this isolated RF ground plane. Call this "Gnd 1"
.
A/D chips often have separate Digital, Analog ground pins. These are indications of the internal chip functions. Manufacturers usually recommend that these two grounds be connected together as close to the chip as possible, and treated as an analog ground. Call this "Gnd 2"
.
D/A chips almost never have separte grounds, so treat this ground as an analog ground also. If the currents for the A/D and D/A sections are small, they could share the same ground or ground plane. Call this "Gnd 3" This could also be an isolated ground plane.
.
Call the digital ground for the DSP and its associated parts "Gnd 4". This could also be an isolated ground plane.
.
Connect the 3 (or 4) grounds or ground planes together at one point only. This is ideally done at the common ground for the power supplies for the 3 (or 4) sections of the circuit.
.
Use adequate supply bypassing for all 3 (or 4) sections.
.
Regards,
Kral