# sine wave shaper

Discussion in 'Homework Help' started by lalalu, Aug 17, 2009.

1. ### lalalu Thread Starter New Member

Aug 16, 2009
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0
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. ### jlcstrat Active Member

Jun 19, 2009
58
3
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

Apr 5, 2008
19,912
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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

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• ###### AN-263_sine_wave_generation_techniques.pdf
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umarfarooqleo likes this.

Mar 24, 2008
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5. ### Audioguru Expert

Dec 20, 2007
11,251
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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.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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681
The eyeball is not a great harmonic distortion analyzer.

Miguel Angel Gullon likes this.
7. ### lalalu Thread Starter New Member

Aug 16, 2009
3
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Ok thanks guys for the speedy response. Especially Brutus .

The pdfs link helps a lot.

8. ### Wendy Moderator

Mar 24, 2008
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Amen! Makes you appriciate HP equipment when you have access to it.

9. ### Audioguru Expert

Dec 20, 2007
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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.

10. ### Ron H AAC Fanatic!

Apr 14, 2005
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I was thinking more about the sine-like shape. All that golders is not glist, etc.

11. ### Audioguru Expert

Dec 20, 2007
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A Cmos digital inverter that is self-biased can be used to smooth a triangle-wave into a pretty good looking sine-wave but its even harmonics are not as low as they should be.
The inverter "compresses" the peaks of the triangle-wave.

12. ### danny2 New Member

Oct 28, 2009
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by setting the Vsin is 50Hz,and VAMPL is 14V,AC=10V passing through the 1k ohm resistor.what is the frequency spectrum should be?is my simulate correct?

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Mar 24, 2008
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14. ### danny2 New Member

Oct 28, 2009
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ops..ya.wrong post.

15. ### danny2 New Member

Oct 28, 2009
29
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how to generate the 50Hz frequency of this sine waveform?

i had connect triangular waveform circuit to your circuit,i get the frequency of the 100Hz at the output of U3 in the schematic.

i have done the calculation for the triangular generator.the formular is F=R1/4(C1)(R9)(R3).the value for R1=100k,C1=0.1u,R9=417k,R3=12k,the frequency obtain is 50Hz,but then when i simulate this circuit,i get the sinewave of 100Hz,doen't it suppose to follow the triangular frequency?I need help on this.

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Dec 20, 2007
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