# Sine Wave Circuit

Discussion in 'Homework Help' started by danny2, Nov 15, 2009.

1. ### danny2 Thread Starter New Member

Oct 28, 2009
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my modulation index,Ma=0.9,Mf=9.
theoretically,my sinewave frequency is 50Hz,my Triangular wave frequency is 450Hz.
When i simulate it,the output do not show the accurate result for me.
Voltage Output peak of the sinewave form apporximately 2.0V,and 1 cycle of the sine wave is 1.260ms which i think is wrong.

can any1 help me?

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2. ### Wendy Moderator

Mar 24, 2008
21,352
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Uhhh, no. This is a shapper circuit, it leaves the fundimental frequency unchanged. It converts the shape of a triangle wave (which is easy to make, and oscillates reliably over a extremely wide range) into an approximation of a sine wave.

It is possible you mis spoke, and meant some other unit of measurement, but the frequency doesn't change. There are lots of other types of converters that do change the frequency out there, which is why I bring it up.

3. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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which converter that change frequency and amplitude?mind to suggest a few circuit?

my university supervisor need me to convert the triangular wave to sine wave with variable modulation index,Mf and Ma.
By changing the value of variable resistance,R9,i do get the different timing on the simulation result.Is that mean the fundamental frequency changing?

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4. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,177
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Yes, but the "earball" is quite good at it!

Eric

5. ### Ron H AAC Fanatic!

Apr 14, 2005
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You need to look up Pulse Width Modulation (PWM), and study and understand it. This is what your supervisor is referring to.

6. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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yes,i did study the PWM For Power Converter,analog signal processing and analog electronics .I understand the different in harmonic and frequency spectrum graph of the bipolar spwm and unipolar spwm.theoretically,i understand,but when come to the circuit diagram as i attach,i got a little bit confuse whether the circuit can varaible the amplitude and frequency or not.haiz...my task is to generate the sine waveform and triangular waveform without using the IC chip,555timer,and i found a suitable waveform at this topic,but then it is only fixed frequency as told by bill marsden.

7. ### Ron H AAC Fanatic!

Apr 14, 2005
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Do you understand how, theoretically, a PWM waveform at 450 Hz can create a sine wave at 50 Hz?

8. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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theoritically,to generate the pwm waveform...i need 1 carrier waveform(triangular) and 1 reference waveform(sinusoidal waveform) to generate it.let said the Mf=9,the carrier waveform frequency is 450hz,so it will generate the 50Hz sinusoidal waveform.correct?

9. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
673
Maybe we are confused here. Are you just trying to figure out how to create the sinusoidal reference waveform, or are you trying to figure out how to create the PWM waveform?

10. ### Wendy Moderator

Mar 24, 2008
21,352
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It does sound like there are couple of missing steps here. You use a high frequency to PWM modulate (both words together are different than just modulate), and it can create almost anything you want. This is the basis for a Class D amplifier.

The triangle wave is just one process that does it, there are several out there, including synthisise with a µC, or you can do it with a sequencer. You can PWM modulate a 450Hz waveform, but you're still going to need the 50Hz waveform to modulate it with. Two oscillators, separate and then merged.

11. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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i wan to generate the pwm waveform.

12. ### danny2 Thread Starter New Member

Oct 28, 2009
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i think i get your point.initially i thought with 1 circuit that i attached before can generate the pwm waveform by connecting the output of the U1(triangular) and U3(sinusoidal),i realize that the frequency for the triagular and sinusoidal are the same because whenever the triangular frequency change,the sinusoidal will change accordingly.
now i know what is wrong with the circuit,i need to make seperately for the triangular circuit and the sinusoidal circuit in order to get the pwm.i attach with my file.now i wonder how to indicate the Ma,Mf on this circuit.

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14. ### lovlyman3030 Member

Apr 28, 2008
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i read your post about the sine wave and the tringular wave generator and im having the same problem i want to generate 50hz sive wave and 1050hz tringular wave i used a function generator chips (icl8031) but it gives me a dc offset so i was wondering if you can help . and if you have the schematics of your circuit i will be greatful
regards

15. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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i didnt work on the IC chip to generate the waveform,as i know you can try on 555timer chip to generate such a waveform.i generate the triangular and sine waveform base on the op-amp.
may i know why you choosing your triangular frequency as 1050Hz?you want to make the Mf=21?

16. ### lovlyman3030 Member

Apr 28, 2008
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i will use that wave to modulate a pmw . im building a statcom for my senior project using FACTS and the carrier signal must be retangular with frequency 1050hz and i must have a sine wave with frequency 50 hz and when i was usig the chip i get that signals but it has dc offset which is not likely to got it

17. ### lovlyman3030 Member

Apr 28, 2008
10
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do you have the schematics for the circuit you build?

18. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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i have post all my circuit in this topic.check it out. triangular generator circuit and sinusoinal generator only.

19. ### danny2 Thread Starter New Member

Oct 28, 2009
29
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could somebody tell me how to perfrom 1,3,5,7,9th harmonic for this circuit?how to setup in pspice?