how to make a clean square wave?

sss · 28th August 2004, 08:27 AM

i wonder how to make a square wave with no overshoots like the frequency generator .

plus
what type of input buffer/op amp used in scopes that can show a clean square wave (or any other)?

Pabo · 28th August 2004, 05:37 PM

Build an oscillator with a schmittrigger inverter, a resistor and a capacitor. Set the frequency by altering the resistance. Put a flip-flop after for generating 50% duty cycle.

sss · 28th August 2004, 05:54 PM

will that be as good as the freq generator?
i got many op amps and when the input signal is a square wave theres always an overshoot , i guess thats because they are too slow right?

what type of amps/buffers used in scopes that shows the wave as it is?

sajti · 28th August 2004, 06:08 PM

Audio amplifiers/buffers are not the best solution for square wave amplification. So for this, use non feedback swithcing type output stage. Use low impedance and high current..

sajti

sss · 28th August 2004, 06:12 PM

does feedback causes the overshoots?

sajti · 28th August 2004, 06:18 PM

Quote:

Originally posted by sss
does feedback causes the overshoots?

Yes. I had a schematic for one HP scope. It contains 10kHz squarewave generator. In this generator there was no any feedback, and it produced extremly perfect squarewave

sajti

sss · 28th August 2004, 06:25 PM

so what kind of amp do they use at scopes input?
it should amplify / attenuate all types of signals

pinkmouse · 28th August 2004, 06:38 PM

Have you seen the MAX038? It is a very good chip that needs few external components to give a frequency generator, with nice even square waves.

OliverD · 28th August 2004, 06:48 PM

Quote:

Originally posted by sss
so what kind of amp do they use at scopes input?
it should amplify / attenuate all types of signals

The trick is bandwidth.

Remember a perfect square wave of frequency f is a sum of several sine waves: 1 x f + 1/3 x 3f + 1/5 x 5f + 1/7 x 7f.... up to infinity. To correctly amplify a mixture of sinewaves with frequency up to infinity, you need of course an infinite bandwidth.

There's nothing special about the input amplifier of a scope, except that it is a very sophisticated and very fast one.

In your case, where you limit yourself to squarewaves only, you could use a fast comparator at the final stage to square things up.

sss · 28th August 2004, 07:01 PM

Quote:

Originally posted by OliverD
There's nothing special about the input amplifier of a scope, except that it is a very sophisticated and very fast one.

yeah but those fast amplifiers also can amplify "slow" signals with no distortion - thats special

28th August 2004, 08:27 AM	#1
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	how to make a clean square wave? i wonder how to make a square wave with no overshoots like the frequency generator . plus what type of input buffer/op amp used in scopes that can show a clean square wave (or any other)?

28th August 2004, 05:37 PM	#2
Pabo diyAudio Member Join Date: Feb 2003 Location: Helsingborg, southern sweden	Build an oscillator with a schmittrigger inverter, a resistor and a capacitor. Set the frequency by altering the resistance. Put a flip-flop after for generating 50% duty cycle. __________________ If something that measures good doesn´t sound good, measure again!

28th August 2004, 06:38 PM	#8
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Have you seen the MAX038? It is a very good chip that needs few external components to give a frequency generator, with nice even square waves. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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28th August 2004, 05:54 PM	#3
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	will that be as good as the freq generator? i got many op amps and when the input signal is a square wave theres always an overshoot , i guess thats because they are too slow right? what type of amps/buffers used in scopes that shows the wave as it is?

28th August 2004, 06:08 PM	#4
sajti diyAudio Member Join Date: Apr 2003 Location: Vác, Hungary	Audio amplifiers/buffers are not the best solution for square wave amplification. So for this, use non feedback swithcing type output stage. Use low impedance and high current.. sajti

28th August 2004, 06:12 PM	#5
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	does feedback causes the overshoots?

28th August 2004, 06:25 PM	#7
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	so what kind of amp do they use at scopes input? it should amplify / attenuate all types of signals

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