mosfet AGND or DGND

Discussion in 'The Projects Forum' started by vivek20055, Feb 13, 2013.

  1. vivek20055

    Thread Starter Member

    Nov 4, 2012
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    Hi,

    Is Mosfet analog component or digital component???

    I need to seperate the gnds for the circuits based on components(like AGND and DGND)

    I am attaching the circuit in with some circuit and controller and joystick,push bottons dataflash,current sensor is there


    In these components which are analog and which are digital???

    Regards,
    Vivek
     
  2. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hi,


    I am using AGND and DGND in my circuit

    So, For microcontroller I have both AGND and DGND in datasheet.

    But for MOSFET it is not given in datasheet as AGND or DGND.

    Can anyone suggest me something about this???


    Regards
    Vivek
     
  3. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    Must have schematic. A MOSFET is not, by its nature, digital or analog. The circuit it is used in is analog or digital.
     
    vivek20055 likes this.
  4. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hi,

    Thanks for your reply

    In my circuit Mosfet receives the input from micro controller and is used for ON/OFF(SWITCHING)

    so, I must use AGND or DGND for grounding the Mosfet

    I am adding schematic for the circuit here
     
    Last edited: Feb 13, 2013
  5. #12

    Expert

    Nov 30, 2010
    16,298
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    The top, left circuit is where I found MOSFETs. That is an analog circuit, except for the switching power supply, but the power supply doesn't have a MOSFET that I could see.
     
  6. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hi,

    Thanks for your reply

    Exactly the MOSFETS are in top left

    they are used for alternative switching of current from the LC circuit.

    Yes,exactly it is analog circuit

    So, can I use AGND for the Mosfets
     
  7. DickCappels

    Moderator

    Aug 21, 2008
    2,653
    632
    All components in the analog section go to the analog ground, and all the components in the digital section use the digital ground. This includes MOSFETs.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Now you have three threads on the same subject. What gives?
     
  9. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    The more I look, the more I think I might be wrong. It depends on the inputs to the op-amps. If they are used for fast switchers, the MOSFETs are in a digital circuit.
     
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  10. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hi,

    Then what about gate drivers connected to Mosfets.

    I think obviously they are also digital ground.

    I have used a switch for converting 24V supply to 5V .

    what about that circuit. Is it AGND or DGND
     
  11. #12

    Expert

    Nov 30, 2010
    16,298
    6,808
    Digital circuits use the digital ground. Analog circuits use the analog ground.
     
  12. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hi,

    what about LDO(LINEAR REGULATOR)?

    which converts the voltage ?

    Is it a digital circuit or analog circuit?
     
  13. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Analog is separated out for a time varying signal you wish to process. It is kept in a separate section for amplification/filtering prior to ADC or other operation to reduce digital switching noise being added onto the signal.

    Digital is separated out for clocks, it tends to need a higher current power supply, sometimes at a different voltage than the analog side.

    All of these are dependent on the power supply, which can be linear (analog, poor efficiency), or Switching (pwm on/off control, very efficient). The power supply needs to be filtered very well by caps for both the analog and digital portions of the circuit, and is connected to both Analog Ground and Digital Ground (unless an isolator is used, then they can be entirely separate).

    All of the DSP/Logiic/Controller ICs use the digital ground for supply, and Analog Ground for signal input (Signal must be referenced to something). All of the analog amplifier and filtering components are connected to the Analog ground.

    You cannot look at a component and decide "Is this analog or digital"? While some, like certain logic ICs are obviously digital, other ICs in the "digital family" are actually analog. Same for MOSFETs. The context of the circuit in which it is used determines which ground to use for each sub-circuit.
     
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  14. MrChips

    Moderator

    Oct 2, 2009
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    Is an ADC (Analog to Digital Converter) and DAC (Digital to Analog Converter) analog or digital? Where do you connect the GND, to analog ground or digital ground?
     
  15. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Both ADC and DACs and other Mixed Signal ICs usually have VDD/VSS and AVDD/AVSS (or similar names) So the "wall" between digital functions and analog output is still isolated.

    The distinction between analog and digital is more important when dealing with millivolt analog signals going into a DSP, interference at that level becomes a problem after amplification. If the incoming analog signal is already at the level required, the signal/noise ratio lowers, and is less of a concern, but still a strong enough concern to warrant separate supplies in a critical application.
     
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