Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

pulse width stretching

Status
Not open for further replies.
I

iaf

Member level 3
Member level 3
Joined
Apr 11, 2019
Messages
57
Helped
0
Reputation
0
Reaction score
0
Trophy points
6
Activity points
433
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?
 

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.
 

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.
 

barry said:
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.
Click to expand...

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.
 

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

FvM said:
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.
Click to expand...

I#m designing the circuit so i don't have a ready to use multivibrator
 

I#m designing the circuit so i don't have a ready to use multivibrator
Click to expand...
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.
 

barry said:
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.
Click to expand...

sorry didn't get it. am i supposed to have two inputs?
 

FvM said:
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.
Click to expand...

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
 

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 ?

Stretch.jpg
 
Last edited by a moderator:
  • Like
Reactions: iaf

    I

    iaf

    Points: 2
    Helpful Answer Positive Rating
Bad idea. Use this:

stretch.jpg

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

    I

    iaf

    Points: 2
    Helpful Answer Positive Rating
barry said:
Bad idea. Use this:

View attachment 153653

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

why is it bad idea?
is there any schematic of this schmitt trigger? as i have to design it in that case
 

iaf said:
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.
Click to expand...

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.
 

andre_teprom said:
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.
Click to expand...

no it's actually an analog design just having a digital output
 

iaf said:
why is it bad idea?
is there any schematic of this schmitt trigger? as i have to design it in that case
Click to expand...

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'.
.
 

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?
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top