# Creating a very sharp pulse generator

1. ## Creating a very sharp pulse generator

Hello everyone,
I want to generate a clock with about 4 MHz frequency (should be adjustable) which is very clean and sharp.
I can not access ready oscillators.

I have test a crystal collpits circuit but it is not sharp enough.
Any suggestions?

Best Regards
Ya Montazar

2. ## Re: Creating a very sharp pulse generator

Hi,

Specify "sharp" in values with unit.

Klaus

3. ## Re: Creating a very sharp pulse generator

Originally Posted by KlausST
Hi,

Specify "sharp" in values with unit.

Klaus
I meant fast slew rate. Not a specific v/us is considered.

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4. ## Re: Creating a very sharp pulse generator

Hi,

Complaining about slew rate, but giving no value makes no sense.

Klaus

5. ## Re: Creating a very sharp pulse generator

A quick slew rate requires that a device change immediately from high ohm to low ohm (or vice versa), so that current flow changes immediately.

It's the opposite of a low-pass filter. Which is like saying the highest frequency of a high-pass filter. Therefore a series capacitor is a handy way to create an abrupt spike, since it sharpens a spike into an even more abrupt spike.

6. ## Re: Creating a very sharp pulse generator

Hi,

High pass filter...
What circuit are you thinking of?

A simple C-R high pass filter can't increase dV/dt.

Klaus

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7. ## Re: Creating a very sharp pulse generator

A Colpitts oscillator generates sein wave, the opposite of sharp edges. You surely need to convert the waveform, e.g. by digital logic gates with schmitt trigger function.

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8. ## Re: Creating a very sharp pulse generator

A quick slew rate requires that a device change immediately from high ohm to low ohm (or vice versa), so that current flow changes immediately.

It's the opposite of a low-pass filter. Which is like saying the highest frequency of a high-pass filter. Therefore a series capacitor is a handy way to create an abrupt spike, since it sharpens a spike into an even more abrupt spike.
Thanks, is there any specific known circuit for that.
What I want exactly is to have an oscillator with specific frequency, which an equivalent could be exist in form of oscillator pack.

9. ## Re: Creating a very sharp pulse generator

What's the application? If there are parts already designed for your application you'll want to use them. Don't overthink it.

Otherwise it seems to be a problem of finding a the right driver. Fast gan fet gate drivers come to mind:
http://www.ti.com/document-viewer/LM...28#SNOSD456328

10. ## Re: Creating a very sharp pulse generator

Hi,

Not sure if waveform will be neat enough with either inverter gate-based suggestion and consistent enough with the latter (RC-based), Pierce oscillator (crystal and inverter gate) or a ring oscillator made from 3 inverter gates.

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11. ## Re: Creating a very sharp pulse generator

What is "sharp"?
If it's a rise and fall time of a <20ns you could drive a 5V 74HC14 Schmitt trigger inverting gate with the colpitts signal (if it's 0-5v) to square up the signal.

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12. ## Re: Creating a very sharp pulse generator

Simulation showing how a series capacitor produces a spike-like waveform from a slightly rounded square wave. The series cap performs the differentiation function. (I called it a high-pass filter in post #5 because that is a more common name when used with sinewaves.)

Out2 amplitude is greater than Out1. By mixing or merging or adding the waveforms in some manner, it can sharpen the transistions.

Slew rate is altered further as the capacitor advances the phase (as is characteristic of capacitors). The behavior becomes obvious when Out1 versus Out2 are plotted X-Y fashion.

13. ## Re: Creating a very sharp pulse generator

Originally Posted by FvM
A Colpitts oscillator generates sein wave, the opposite of sharp edges. You surely need to convert the waveform, e.g. by digital logic gates with schmitt trigger function.
It's a good suggestion.

Originally Posted by crutschow
What is "sharp"?
If it's a rise and fall time of a <20ns you could drive a 5V 74HC14 Schmitt trigger inverting gate with the colpitts signal (if it's 0-5v) to square up the signal.
However 74hc14 is too large for me.
I want to replace this circuit with a crystal oscillator so I do not have a large space.
Is there any small package one?

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14. ## Re: Creating a very sharp pulse generator

Hi,

HC1G14

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