anyone Know About It

Discussion in 'General Electronics Chat' started by Eplanet, Oct 25, 2007.

  1. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    hello to all
    please tell what is different between Analog Ground and digital Ground?
    thanks Eplanet
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    One's analog and one is digital!

    Actually that does have a consequence, in analog application the ground is a common reference point within the circuit (do a forum search there are several debates on this definition), and in digital applications the ground is also a reference point but additionally is the lower logic-level in the circuit, i.e. ground, denoted GND, is logic value '0'.

    Dave
     
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Analog ground is the ground common to analog circuits (amplifiers, etc). A digital ground is a ground common to digital circuits (logic gates, etc). The main difference resides on how analog and digital circuits work. Digital grounds normally have more noise than analog ones, due to the sudden transitions between on and off states that happen in digital circuitry. So a digital ground is more difficult to decouple, as it needs several capacitors distributed.
    An analog ground will have noise, but in an analog circuit the signal often varies slowly. Decoupling is done using larger capacitors near the most important power amplifier circuits, as these circuits are more prone to introduce noise into ground, since they consume a great deal of energy.
     
  4. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    hi
    Digital circuits may have spikes and high-frequency noise that can propagate into analog circuits if care is not taken.
    as result if we connecting all Ground with together then digital noises can effect to analog circuit.
    i want to know that how can i separate these Grounds and keep in mind that i have one PS (one Ground line) in circuit.
    is there any component that can separate these Grounds?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There has to be a common reference point. Generally, using a star ground that only connects the digital to the analog grounds at one point is effective in controlling noise.

    Is your concern actual, or theoretical?
     
  6. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    both actual and theoretical
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Consider that the connection has to be made in order for things like analog signals to be digitized. A great deal of scientific instrumentation manages to do so with great success

    Grounding techniques are not always cut-and-dried, though. While star grounds and "proper grounding techniques" almost always give good results, eliminating electrical noise sometimes resembles one of the black arts.

    One good start is to insure that no noise is riding in on your analog signal. Do you have a specific application in mind?
     
  8. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    hi
    yes i am making a circuit in radio frequency and in this reason i need to eliminate any digital and analog noises.
     
  9. Eplanet

    Thread Starter Active Member

    Oct 25, 2007
    42
    0
    hello all
    what do you thinking about this attachment for more clearly?
    is there any circuit or component that before connecting Ground to analog section that can preventing digital noise to analog section?
    Eplanet
     
  10. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    You can decouple one ground from the other by using a wire, if you can't use star grounding for both grounds (normally it is complicated in terms of PCB). Then you ground the digital ground to one end of the wire, and the analog ground to the end of the other. Then you use the analog ground as your ground reference. Thus, current spikes generated by the digital circuits will cause the digital ground to float, but the wire has enough resistance to make sure that the analog ground stays rock solid. Floating is tolerated by digital circuits, but not by power analog circuits. This is called a "bus ground", where you ground the higher current circuits first.

    So, the component is a jumper wire (technically it is a shunt), and you connect it in series with the digital circuitry. Then use coupling capacitor. Use a big one to filter the analog ground and small ones near the most important current consuming ICs.
     
  11. chesart1

    Senior Member

    Jan 23, 2006
    269
    1
    The other concern is the actual layout of the circuit on the printed circuit board. You need to keep the analog circuit, digital circuit and power supply circuits [if applicable] in separate sections of the board in order to avoid unintended coupling between the circuits. Don't run a digital connection [clad] under the analog circuitry, etc.
     
Loading...