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  #1  
Old 08-17-2009, 04:39 PM
lalalu lalalu is offline
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Default sine wave shaper

Hello all

I am having trouble understanding a waveform shaping circuit that I found on the internet.

My task is to generate a sine wave (adjustable low frequency range). My plan is to use a vco to generate triangular wave and then change it into a sine wave. I was thinking of using the breakpoint method, and then I found this circuit.

So my question is what is the purpose of the opamp at the end? To smoothen the peak? or is this just aa normal feedback circuit. I also didnt get how the diodes work here, is this just a clipper circuit? I simulated the circuit in spice and found out that the circuit works just fine with only 2 diodes and 1 resistor (+side). Weird


Anyway I would appreciate it if someone could explain to me how the circuit work, or at least just the name of the circuit. Searching sine wave shaper blindly these past few days didnt yield much result. Thank you
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  #2  
Old 08-17-2009, 06:18 PM
jlcstrat jlcstrat is offline
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It would appear the opamp is just used to amplify the signal...The diodes clip the signal to give it more of a sinusoidal shape...I'm only a student myself, but that would be my best guess
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  #3  
Old 08-17-2009, 07:20 PM
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Hello,

The wave shape uses a kind of multiple break points to convert the triangle to a sinawave.
In the two attached PDF's you will find wave shapers with diodes too.

Greetings,
Bertus
Attached Files
File Type: pdf den7_sinewave_shaper.pdf (817.0 KB, 283 views)
File Type: pdf AN-263_sine_wave_generation_techniques.pdf (350.6 KB, 218 views)
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  #4  
Old 08-17-2009, 07:43 PM
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Depending on your purity requirements you don't need a lot of circuits.

I was able to get this with two diodes and an op amp off a triangle wave.





Check this thread out.

http://forum.allaboutcircuits.com/sh...ad.php?t=12405

Nice links Bertus
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Old 08-17-2009, 07:45 PM
Audioguru Audioguru is offline
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A ICL8038 and an XR2206 function generator IC uses multiple breakpoints with diodes to convert a triangle wave into a sine-wave with horrible distortion.

The circuit that has only three breakpoints is much worse.
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  #6  
Old 08-19-2009, 04:44 AM
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The eyeball is not a great harmonic distortion analyzer.
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  #7  
Old 08-19-2009, 08:58 AM
lalalu lalalu is offline
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Ok thanks guys for the speedy response. Especially Brutus .

The pdfs link helps a lot.
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  #8  
Old 08-20-2009, 12:19 AM
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Quote:
Originally Posted by Ron H View Post
The eyeball is not a great harmonic distortion analyzer.
Amen! Makes you appriciate HP equipment when you have access to it.
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  #9  
Old 08-20-2009, 01:09 AM
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You don't need an HP distortion analyser when the distortion is as high as the sine-wave made with a few breakpoints. You can hear the buzzing distortion.
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  #10  
Old 08-20-2009, 01:34 AM
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Quote:
Originally Posted by Audioguru View Post
You don't need an HP distortion analyser when the distortion is as high as the sine-wave made with a few breakpoints. You can hear the buzzing distortion.
I was thinking more about the sine-like shape. All that golders is not glist, etc.
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