diffrence between analog voltaj and digital voltaj

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what's the diffrence betwwenn vdda &vdda in circuit both of them is 3.3 v
can we connect them togather.
what about to connect its gnd,how should we connect them,
 

What do you want to ask ? Pls. explain you applicaton more explicitly
 

It is common use if you want to eliminate noise introduced by digital circuit. Basically this noise is current spikes converted into voltages on bonding wires and PCB traces.
 

in some chip like dsp or vga decoderchip we have two kind of vcc one is analog vcc and others is digital vcc vddd,and both of them have the same voltage i want to know what's the diffrence between them,and their gnd,
only for noise problem they separate them or others so what's ?
and what's the best way(attention) to use them in circuit,any experience may be useful thanks
 

analogy Vcc +RC filter to digital VCC.
 

sorry,mistake.
if the digital need large current,LC filter beter than RC filter
 

voltage supplies for digital can be noisy and not affect the operation of the digital circuitry but be totally unacceptable for analog circuits, especially the voltage sensitive type of circuits such as voltage controlled oscillators.

the degree of separation needed varies depending, basically, on what you can get away with. a vga decoder, or a dsp designed to listen for DTMF tones might be unaffected by a few millivolts of noise and using the same supply for both analog and digital would be no big deal. whereas a phase-locked loop might require fanatical attention to separating the analog and digital supplies to get an acceptabe jitter level.
 

Hi there,

it is always advisable to have the digital and the analog grounds separate.
There are problems like noise interference that could send the digital cct into an unknown state, metastable...

Alright the also the digital cct normally switches rapidly this can cause the gnd potential to vary this is not liked by the Analog cct (it mostly depends on the gnd potential)
Now Isolation is the best soln , isolation by optocouplers (low freq) or isolation t/f's for HF is always advisable....thats bacause of Core Saturation Problems in the isolation t/f's

Bye
 

dpeending on ripple size a passive filter may be enough
on one design i had to implement a separate power supply with a lineair regulator to supply the video DAC
 

Use ferrite cores to connect agnd and dgnd and check voltage levels also. İf they are the same no problem but the levels are different you may be step down one of the level to another
 

separate power supply and ground.
for PCB, use separate plane layer for power and ground
the purpose for separating analog and digital is that u don't want noise couple over from digital circuit to analog circuits or the other way.
 

To questioner:

All answerer's answer is right,
But becaful that the digtal and analog power manage are different very deeply depend on your detail cicuit!!


There are commonly recommendation is that use "comman GND" but separate digtal and analog part in your circuit.


I have some document for this question,
But they are all in chinese,
I afraid you don't know chinese
Are you?
If you can use chinese document,
I will show those document to you,
Those document really helpful for you question.
 

CleanAir said:
I have some document for this question,
But they are all in chinese,
I afraid you don't know chinese
Are you?
If you can use chinese document,
I will show those document to you,
Those document really helpful for you question.
Click to expand...
I'm interested. I can read chinese. Would you pls show me how to get the documents? Many thanks.
 

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