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From: ssave@caen.engin.umich.edu (Shailendra Anant Save)
Newsgroups: sci.electronics
Subject: Re: schmitt trig. nand configurations
Summary: Difference in schmitt trig. nand configurations
Message-ID: <1990Dec2.223748.28062@engin.umich.edu>
Date: 2 Dec 90 22:37:48 GMT
References: <48711@eerie.acsu.Buffalo.EDU>
Sender: news@engin.umich.edu (CAEN Netnews)
Organization: The University of Michigan, Ann Arbor
Lines: 63

In article <48711@eerie.acsu.Buffalo.EDU>, blw@acsu.buffalo.edu (brian l wybaillie) writes:
> i have a circuit which uses a 74xx13 schmitt triggered dual 4 input
> nand in the following configurations;
> 
>                                     74xx13
>                                       |
>                                       | 
>      input ___________                v
>                      |
>                   ___|______       ___________
>                   |  |  |  |______|            \
>                   |  |  |_________| _______     \
>                   |  |____________|   \____\__   )o-------- output
>                   |_______________|             /
>                                   |____________/ 
> 
> 
> 
>                                    ___________
>     input ________________________|            \
>                      _____________| _______     \
>                      |  __________|   \____\__   )o-------- output
>                      |  |  _______|             /
>                      |  |  |      |____________/
>                     _|__|__|_  
>                         |
>                         | 
>                         + Vcc
> 
> 
> 	can anyone tell me the difference, if any, these two circuits have
> with each other?  the way i see it they are the same, the top one has all
> it's inputs tied to one which produces an inverted output.  the bottom one
> is only dependant upon one of it's inputs since the other 3 are tied to Vcc.
> thus since it is a nand gate it will have the same outcome as the
> as the first circuit, (an inverter).
> 	is there any special reason for configuring it in the two different
> ways, i.e. faster responce, or sinking more current?  


        I'd say that the fan-out of the gate that is producing the input
would be used up (?) if method 1 is used.
        Also, in method 2, the schmitt sees a pure high voltage (5V) as 
opposed to a logic high of the input for the three inputs tied together.
Hence faster?        
   
> 
> 	thanks in advance for any cunstructive input.
> 
> 				brian wybaillie
> 
> 
> 	ps.  sorry for the poor graphics.

        Quite good graphics actually. :-)

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