# Cleaning up waveform to generate 50% duty cycle

Discussion in 'The Projects Forum' started by robby991, Sep 10, 2010.

1. ### robby991 Thread Starter Active Member

Dec 17, 2007
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Hi everyone. I have a frequency which I need to convert to 50% duty cycle square pulses. The output is from a frequency divider (d-Flip Flops), so the duty cycle should be 50% but it is not. Is there anyway I can help clean this up? The frequency should be oscillating which it is, however it should keeo the 50% duty cycle. It is oscillating however without 50%. The frequency is in the kilohertz range.

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2. ### beenthere Retired Moderator

Apr 20, 2004
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The output from a frequency divider has to be 50% duty cycle, or are you dividing by some factor other than 2?

That said, if the frequency changes, so does the interval between pulses. If the frequency is held constant, does the displayed duty cycle hold at 50%?

Apr 5, 2008
15,539
2,307
Hello,

Can you post the schematic of what you have upto now?

Bertus

4. ### robby991 Thread Starter Active Member

Dec 17, 2007
79
0
It is going through a divide by 4 frequency divider with d-Flip Flops. The input frequency is also not 50%. The input frequency comes from a current to frequency converter. The current is not constant, it varies, so The frequency will not be conatsnt. However wouldn't the pulses still be 50%?

5. ### SgtWookie Expert

Jul 17, 2007
22,182
1,728
First, you need to run your input through a Schmitt-trigger gate to clean it up. A 74HC14, a 4093 or 40106 are a few examples.

You could also use cascaded 74VHCU04's to amplify the signal. It's a very useful technique. See the attached.

• ###### 74HCU04 amp 2.PNG
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Last edited: Sep 10, 2010
6. ### Norfindel Active Member

Mar 6, 2008
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If the frequency varies all the time, how can the duty cycle be 50%? If the flip-flops change state on the rising edge, and the time between rising edges isn't the same every time, the duty cycle won't be 50%.

7. ### robby991 Thread Starter Active Member

Dec 17, 2007
79
0
What I am saying is that my input current is proportional to the output frequency I am getting, which should be 50%. So if my input current is varying, the frequency would vary proportionally, and each pulse period should remain 50% duty. Is this a correct assumption?

Apr 5, 2008
15,539
2,307
Hello,

Again, can you post a schematic?
So we can see what current to frequency converter you use?
Perhaps a link to the datasheet will also give the info.

Bertus

9. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Only correct for a period in which the frequency remains constant. Why is it so important to maintain a 50% duty cycle as the frequency is changing?