logic circuit

Discussion in 'The Projects Forum' started by Xufyan, Jul 29, 2011.

  1. Xufyan

    Thread Starter Member

    Aug 3, 2010
    114
    0
    Hello,
    i am very good in DLD and can design some of the very good DLD project myself , i have cleared DLD exam in last semester,
    now i am in my fourth semester and one of my course is Operational Amplifiers and Osciallators , i am in search of some kind of good project that uses Opamp ic.

    anybody have an idea on using an Opamp ic in a completely logical circuit ?

    for example,

    as this is a logic circuit,

    http://www.allaboutcircuits.com/vol_6/chpt_7/7.html

    what new i can add in this circuit so that opamp must be use in this circuit.

    Thankyou
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Op Amps are linear, not digital. What you are after is more of a comparator circuit.

    We occasionally see people use op amps as comparators, this is usually a bad idea.

    Voltage comparator
     
  3. simo_x

    Member

    Dec 23, 2010
    200
    6
    Normally oscillator circuits that use Op Amps are for sine-wave output. See here and here for more informations..

    In digital electronics, as you maybe already know, oscillators are mainly used to generate square wave output for clock source, and op amps are generally not used for this purpose, as Bill already said.. Take a look here

    If you would like to generate a square wave oscillator using only operational amplifiers, you should create a circuit that would have a
    sine-wave output oscillator >> op amp Schmitt trigger
    (with threshold voltage reference on inverting input, depending your need).

    Regards
     
  4. Xufyan

    Thread Starter Member

    Aug 3, 2010
    114
    0
    why its not good to use Opamp as a comparator ? what is the need of connecting to potentiometer in the circuit you linked ?

    what would be the basic and good project of opamp ?
     
    Last edited: Jul 31, 2011
  5. Xufyan

    Thread Starter Member

    Aug 3, 2010
    114
    0
    we've just started learning about Opamp so i don't know much about it , i couldn't create a circuit myself

     
    Last edited: Jul 31, 2011
  6. simo_x

    Member

    Dec 23, 2010
    200
    6
    Perhaps Bill didn't want to say that comparator circuit is a bad idea as op amp circuit, because it describes simply the "basic" operation of Op Amps.. Maybe is not a good idea use them for a digital purpose.

    As a potentiometer connected between Vcc & Gnd is nothing more than a variable voltage regulator, the potentiometers, one connected to non inverting input (+) and the other to the inverting input (-), are just needed to permit you to vary the voltage to the associated input. In this moment the op amp it self will vary the output voltage from Gnd to something less than Vcc & vice-versa, depending on which of the two input terminals is more positive. That is the simple function of a comparator circuit.

    The 2nd link I reported should be very useful. ;)

    Regards
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Op amps are a deeper subject than digital. If you want to learn you are going to have to read, lots and lots of reading. They can be simple amplifiers for audio and RF, they were invented to make analog computers. They can (if properly designed) simulate inductors, capacitors, and more, which leads to complex filters (active filters). They are the heart of analog voltage regulators.

    Audio amplifiers and voltage regulators are two of their biggest uses, but that doesn't come close to touching all the jobs they can do.

    The early op amps, such as 741 and 1548, were extremely slow. People are still trying to use these old parts (created almost 50 years ago) for jobs they simply were never meant to do. However, during that time many, many new parts were created, each generation better than the last. Again, much reading is required.

    The concept of op amps is much older though. They were selling tube (valve) versions almost as soon as tubes were created, and making analog computers out of them. Analog computers are much older than digital, and have some unique properties it took a very long time for digital to come close to emulate (and still doesn't approach the basic simplicity). You can make a circuit that is X + Y, or create a circuit that does advanced calculus accurately. The math is measured in volts (analog of course, such the number 2.2 is 2.2 volts), the circuit is wired to create the formula.

    A comparator is a true digital gate. It has been called a single bit A-D converter. Most of the cheap and common units, such as the LM393 and LM399, have a uniquely digital design called open collector. If you haven't studied this in digital then you have yet more reading in front of you. The gist is they are fast, their outputs are true digital, while an op amp tries to smoothly transition between power supply rails with no blips or bumps, which is a lot harder than you can imagine.
     
    Last edited: Jul 31, 2011
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