schmitt trigger question

Discussion in 'Homework Help' started by Ron Potashnik, Feb 9, 2016.

  1. Ron Potashnik

    Thread Starter New Member

    Dec 27, 2015
    15
    0
    i have the next circuit
    1.png

    what will happen if i replace all the 4093nand component with similar component but have no histeresis? what is the need of histeresis component here?
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    The circuit will not work. Circ1 and Circ2 form a astable generator. And this type of a generator needs schmitt trigger gates.
     
    Ron Potashnik likes this.
  3. WBahn

    Moderator

    Mar 31, 2012
    17,751
    4,797
    The resistor and capacitor result in a relatively slowly changing waveform. As a result, the circuit does not pass through the transition region (which is rather poorly defined to begin with) quickly. The noise in the signal can result in the output of the logic gate flailing (switching back and forth many times which it should only change once).
     
  4. Ron Potashnik

    Thread Starter New Member

    Dec 27, 2015
    15
    0
    thank you, great explain
     
  5. RBR1317

    Active Member

    Nov 13, 2010
    232
    48
    It appears that Circ1 and Circ2 are configured as 4093 oscillators. As such, the input voltage is meant to hover between the switching threshold points. The time it takes for the capacitor voltage to slowly traverse the middle region is what determines the oscillator frequency. A regular input gate does not have this wide region between the switching points (since there is generally only a single switching threshold) so any oscillations will be of much higher frequency and totally unpredictable.

    Figure is taken from Fairchild Semiconductor Application Note 140, June 1975.

    4093-oscillator.png
     
Loading...