MOSFETs

Discussion in 'General Electronics Chat' started by Mazaag, Sep 7, 2006.

  1. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
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    In relation to MOSFETs, what do VSS, VDD, VCC, and Vref refer to ? and what is the difference between them

    Thanks
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Vss is the voltage at the "source" terminal.
    Vdd is the voltage at the "drain" terminal.
    Vcc is the voltage at the collector of a bipolar junction transistor, and doesn't strictly have any meaning in a MOSFET circuit.
    Vref is usually and A/D converter reference or a comparator referenc voltage, and strictly speaking has no meaningful connection with MOSFETS.

    In many circuits with a mix of discrete parts and ICs you will see Vdd and Vcc connected together and be at some voltage between say 1.8 and 5.0 volts.

    FYI Vgg is the gate voltage on a MOSFET.
     
  3. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
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    Hi Papa,
    Thank you for your reply..


    Vref here is refered to as the Reference Voltage. Now i'm looking right now at a DDR I/O block, which uses SSTL.

    Would that help determine what Vref is used for..?

    Thanks
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    Sorry, I don't know what a DDR I/O block is, nor do I know what SSTL is. Can you elaborate?
     
  5. Dave

    Retired Moderator

    Nov 17, 2003
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    SSTL stands for Stub-Series-Terminated-Logic.

    DDR I/O block I would assume is something to do with Double Data Rate RAM (most likely SDRAM), of which SSTL devices are used to drive in computer memory structures.

    A bit more clarity may be of use here.

    Dave
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    Then I'm completely out-of-gas because I have encountered neither one of those animals.
     
  7. Dave

    Retired Moderator

    Nov 17, 2003
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    It will also help if you can upload the DDR I/O block diagram you are looking at.

    Dave
     
  8. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
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    The problem is that I am working directly from a netlist, and have no schematic to refer to. To add to that, I am not familiar with the components that would be found in such a block. In other words, I have no clue what the inside of this block looks like :S

    But anyway, I do know that it Vref happens to be a port on the this, so was wondering if anyone knows what it would be used for.. but appearently its not such a common block.. So no worries :D

    Thanks anyways guys
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I would recommend you post your netlist as an attachment. Then we all can be on the same page.
     
  10. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    VREF is the reference voltage used at the receiving end of the SSTL as the threshold voltage between logic high and low. Usually, VREF is set at half of VDDQ - VSSQ over external variations such as voltage, process, temperature, etc. It is also highly desirable for VREF to be symmetrical between VOH and VIL. The VTT (termination voltage) also has to very closely match VREF.
     
  11. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    VREF is the reference voltage used at the receiving end of the STTL as the threshold voltage between logic high and low. Usually, VREF is set at half of VDDQ - VSSQ over external variations such as voltage, process, temperature, etc. It is also highly desirable for VREF to be symmetrical between VOH and VIL. The VTT (termination voltage) also has to very closely match VREF.
     
  12. Dave

    Retired Moderator

    Nov 17, 2003
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    This link goes some way to diagramatically explaining what n9352527 has described.

    Dave
     
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