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    pulse width stretching

    i want to design a circuit for stretching the "0" output of my signal. I have seen the Monostable multivibrator but it stretches the "1" output. is there anyway flipping it or another topology for realizing that?

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    Re: pulse width stretching

    Could you give us more information? Is this a digital system? Is there a clock? You could use a schmitt-trigger AND gate where the signal goes directly to one input and through an RC to the other input.

    "Is there anyway of flipping it?" Of course; use an inverter.



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    Re: pulse width stretching

    In addition, most monostable chips have trigger inputs for both polarities. Pulse stretching refers to retriggerable monoflop, otherwise the pulse width would be also limited.



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    Re: pulse width stretching

    Quote Originally Posted by barry View Post
    Could you give us more information? Is this a digital system? Is there a clock? You could use a schmitt-trigger AND gate where the signal goes directly to one input and through an RC to the other input.

    "Is there anyway of flipping it?" Of course; use an inverter.
    it's a digital output of a d-flipflop which is clocked by a 50MHz clock. Adding an inverter will invert the "1" to "0" which is not the goal.



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    Re: pulse width stretching

    Adding an inverter will invert the "1" to "0" which is not the goal.
    barry answered your question in post #1 (how can we use a monoflop with inverse input polarity), you apparently forgot your question.



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    Re: pulse width stretching

    Quote Originally Posted by FvM View Post
    In addition, most monostable chips have trigger inputs for both polarities. Pulse stretching refers to retriggerable monoflop, otherwise the pulse width would be also limited.
    I#m designing the circuit so i don't have a ready to use multivibrator



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    Re: pulse width stretching

    I#m designing the circuit so i don't have a ready to use multivibrator
    Fine, than just design it with correct polarity and don't forget the retrigger point if you expect input pulses longer than the monoflop period.



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    Re: pulse width stretching

    Quote Originally Posted by barry View Post
    Could you give us more information? Is this a digital system? Is there a clock? You could use a schmitt-trigger AND gate where the signal goes directly to one input and through an RC to the other input.

    "Is there anyway of flipping it?" Of course; use an inverter.
    sorry didn't get it. am i supposed to have two inputs?



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    Re: pulse width stretching

    Quote Originally Posted by iaf View Post
    sorry didn't get it. am i supposed to have two inputs?
    I don't think there are any one-input AND gates.



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    Re: pulse width stretching

    Quote Originally Posted by FvM View Post
    Fine, than just design it with correct polarity and don't forget the retrigger point if you expect input pulses longer than the monoflop period.
    how do i change the polarity? i just want to extend the 0 output for some ms as an example. The design i used was a NOR gate connected to a capacitor and resister with an inverter in the end giving the output



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    Re: pulse width stretching

    Low Going Pulse Stretcher using two NAND Gates ...
    NAND_GATE
    scroll down for schematic
    Use "High Speed" and right hand device, best if, "Schmidt Trigger" Input
    Width of trigger pulse must be wider than gate delays


    Or use something like 74AHC123A or 74AHCT123A Monostable ...
    MONO-STABLE
    Has both Rising Edge & Falling Edge Triggers

    - - - Updated - - -

    Can your Low-Going Pulse discharge a small Capacitor ?

    Click image for larger version. 

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    Last edited by andre_teprom; 13th June 2019 at 13:38. Reason: resize picture - removed wasting area


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    Re: pulse width stretching

    Bad idea. Use this:

    Click image for larger version. 

Name:	stretch.jpg 
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ID:	153653

    Have to consider pulse width, etc. in selecting RC. Can also put diode across R for narrow input pulse.


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    Re: pulse width stretching

    Quote Originally Posted by barry View Post
    Bad idea. Use this:

    Click image for larger version. 

Name:	stretch.jpg 
Views:	6 
Size:	498.4 KB 
ID:	153653

    Have to consider pulse width, etc. in selecting RC. Can also put diode across R for narrow input pulse.
    why is it bad idea?
    is there any schematic of this schmitt trigger? as i have to design it in that case



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    Re: pulse width stretching

    Quote Originally Posted by iaf View Post
    it's a digital output of a d-flipflop which is clocked by a 50MHz clock. Adding an inverter will invert the "1" to "0" which is not the goal.
    Would I be wrong in assuming that you are on the scope of a programmable logic circuit design? In this case, it would make little sense to implement this circuit with an analog approach.
    --------------------------------------------------------------------------------------------------
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    Re: pulse width stretching

    Quote Originally Posted by andre_teprom View Post
    Would I be wrong in assuming that you are on the scope of a programmable logic circuit design? In this case, it would make little sense to implement this circuit with an analog approach.
    no it's actually an analog design just having a digital output



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    Re: pulse width stretching

    Quote Originally Posted by iaf View Post
    why is it bad idea?
    is there any schematic of this schmitt trigger? as i have to design it in that case
    It's a bad idea because you'll never pull the input lower than one diode drop+Vlo of the source. This may not be low enough to effect a logic '0'.
    .



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    Re: pulse width stretching

    so how would i design this schmitt trigger with 2 inputs?

    - - - Updated - - -

    another problem with this design is that the pulse will be stretched in a constant time regardless how long the input takes, which is applicable in case if the input is longer the RC time constant, so is there a solution to add this time constant to the original width?



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    Re: pulse width stretching

    is there any schematic of this schmitt trigger? as i have to design it in that case
    Two single ST gates and an AND.



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    Re: pulse width stretching

    Quote Originally Posted by FvM View Post
    Two single ST gates and an AND.
    What'S an ST gate?



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    Re: pulse width stretching

    ST= Schmitt Trigger.
    My batteries are recharged by "Helpful Post" ratings.
    If you feel that I've helped you, please indicate it as a Helpful Post



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