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#1
08-17-2009, 04:39 PM
 lalalu New Member Join Date: Aug 2009 Posts: 3
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
#2
08-17-2009, 06:18 PM
 jlcstrat Member Join Date: Jun 2009 Posts: 58

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
#3
08-17-2009, 07:20 PM
 bertus Administrator Join Date: Apr 2008 Location: Amsterdam,Holland (GMT + 1) Posts: 12,261

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
 den7_sinewave_shaper.pdf (817.0 KB, 283 views) AN-263_sine_wave_generation_techniques.pdf (350.6 KB, 218 views)
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#4
08-17-2009, 07:43 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,045 Blog Entries: 5

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.

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"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#5
08-17-2009, 07:45 PM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

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.
#6
08-19-2009, 04:44 AM
 Ron H E-book Developer Join Date: Apr 2005 Location: Idaho, USA (GMT-7) Posts: 7,050

The eyeball is not a great harmonic distortion analyzer.
#7
08-19-2009, 08:58 AM
 lalalu New Member Join Date: Aug 2009 Posts: 3

Ok thanks guys for the speedy response. Especially Brutus .

The pdfs link helps a lot.
#8
08-20-2009, 12:19 AM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,045 Blog Entries: 5

Quote:
 Originally Posted by Ron H The eyeball is not a great harmonic distortion analyzer.
Amen! Makes you appriciate HP equipment when you have access to it.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#9
08-20-2009, 01:09 AM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

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.
#10
08-20-2009, 01:34 AM
 Ron H E-book Developer Join Date: Apr 2005 Location: Idaho, USA (GMT-7) Posts: 7,050

Quote:
 Originally Posted by Audioguru 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.

 Tags shaper, sine, wave

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