unable to understand a symbol

Discussion in 'Homework Help' started by rohit75, Nov 28, 2013.

  1. rohit75

    Thread Starter New Member

    Nov 28, 2013
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    In this circuit, there is a current source Ib.
    Its one end is connected to the circuit.
    While the other end goes out to an arrow.
    What does this arrow signify?
    Should I connect it to Vcc i.e. +5 V DC or AC GND or if not, then where?
     
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  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Ib is a constant current source
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    You are not really planning on building this, are you?
     
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
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    This looks like a representation of part of the internal circuitry of an op amp or comparator but it's not a complete (buildable) schematic.
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    Looks like some sort of an analog multiplier function
     
  6. WBahn

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    Mar 31, 2012
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    Ib is a current source and all that matters, as far as this circuit is concerned, is the current coming out of it and going into the input transistor. So you can use any circuit that will produce Ib. That might be as simple as a resistor to Vcc.

    This circuit relies on close matching of the transistor parameters and, hence, is only suitable for fabrication on an IC. If you want to build a circuit like this using discrete parts, you need to us ballast resistors in a number of places to force adequate matching in the mirrors.
     
  7. #12

    Expert

    Nov 30, 2010
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    I interpret the current supply to be a negative supply (electrons arriving at the arrow in question) because M7 is a P type, so drain voltage will be negative.

    Do you think I am correct?
     
  8. WBahn

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    Mar 31, 2012
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    M7 is an NFET. M5 is a PFET.

    Note that the diode arrow that is part of the symbol is not going from the channel to the bulk, but rather from the channel to the source.
     
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  9. #12

    Expert

    Nov 30, 2010
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    Oh, I get it. The placement of the arrow is as important as the direction of the arrow. Thank you.
     
  10. Ramussons

    Active Member

    May 3, 2013
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    It's not an arrow - It's a ground symbol upside down :D - the substrate.

    Ramesh
     
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  11. WBahn

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    That could well be. The image doesn't have enough resolution for me to tell if it is a ground symbol or an arrow. It doesn't really matter -- it's just signifying that the other side of the current source goes somewhere. Ground is as good a place as any, although the substrate, in general, is NOT a good place for it to go. While there are exceptions -- and processes designed for those exceptions -- you generally try to keep signal currents out of the substrate.
     
  12. Ramussons

    Active Member

    May 3, 2013
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    Agreed, but since there is no "ground" terminal shown, it will have to be the substrate.

    Ramesh
     
  13. WBahn

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    Mar 31, 2012
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    Why? It's just a generic schematic. Gives no indication of what type of process it is. Might be N-Well, might be P-Well, might be Twin-Well, might be epi or non-epi. Heck, might be SOS.

    The current source is just there to indicate a programming current going into M7. As I said before, it might well be nothing more than a resistor to Vcc.
     
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