Number of gates in simple circuts

Discussion in 'General Electronics Chat' started by FDewhirst, Feb 8, 2008.

  1. FDewhirst

    Thread Starter New Member

    Feb 8, 2008
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    Just starting to think about digital circuits after a 30 year break. I want to know how many gate are in typical 16 bit: 1) full adder 2) counter 3) shift register?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Well, I thought about picking up my vintage '76 TI TTL book up off of the floor, but you could do the same thing ;)
     
  3. FDewhirst

    Thread Starter New Member

    Feb 8, 2008
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    I no longer have my books on TTL and seriously want to know for current designs the minimum number of transisters it takes to make a 16 bit full adder a 16 bit counter, and a 16 bit shift register. I did a Google search and got to this forum. Hopefully, someone can give me a numerical answer to my question. Like 1000, 800, 64. I know this is a simple question for someone. Sorry for using gates for transisters in my original question--I had fuzzed them together.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    It is a question that has no ready answer without a great deal of work for a vanishingly small payoff. Only a chip designer would care about the answer. We are mostly hobbyists who put chips on boards. Since the advent of the integrated circuit in the late sixties and early seventies nobody except a chip designer would count transistors for a logic circuit. The optimization parameter of choice has been package count.
     
  5. FDewhirst

    Thread Starter New Member

    Feb 8, 2008
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    This is a chip design/logic design question. Can anyone point me to where I could find the answer--web accessable books, other forums? I'm particularly interested in how much simpler a counter is than an adder. It doesn't need the look ahead components because it just adds 1.
     
  6. FDewhirst

    Thread Starter New Member

    Feb 8, 2008
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    Papabravo & SgtWookie--Thanks for your comments. I've spent some time going through the All About Circuits online books and find a rough answer to my question. Counters are simple compared to adders--a string of flip flops for each bit will do for a counter. You have an interesting forum/site that I will keep bookmarked.
     
  7. Salgat

    Active Member

    Dec 23, 2006
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    Keep in mind that inside an IC can be many more components than you might think (due to making it more reliable, etc).
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    I also question the utility of a notion like "complexity measured by transistor count or gate count". An adder is a pure combinatorial circuit with no memory and no feedback. A counter on the other hand is a syncronous circuit. A basic flip-flop has feedback and can suffer from problems like metastability. Working with counters can be difficult, designing them might be even harder.

    In chip design real estate is everything. Pickin' picoacres is the name of the game.
     
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