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Old 14th August 2008, 06:01 PM   #1
Bengali is offline Bengali  United States
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Default MAX038 Sine Wave

Hi,

I built up a MAX038. I get a sine wave with the peaks slightly skewed. Does not matter what frequency it is set to.
The supply voltages are +/- 4.92V.

What causes this slight shift? Any ideas what to look for?


I used this circuit:

www.kitsrus.com/pdf/k101.pdf

Thanks.
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File Type: jpg sine1.jpg (17.4 KB, 152 views)
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Old 14th August 2008, 06:48 PM   #2
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You need to lift pin 7 (DADJ) from GND and make it adjustable between a volt or so pos and neg - something like the FINE adjust but then between + and -. That will let you adjust the symmetry of the waveform.
One way to test it is to look at the square wave output (NOT the sync output - that is always 50%) and adjust as best as possible for 50% duty cycle.

It's all in the data sheet, by the way...

Jan Didden
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Old 14th August 2008, 09:14 PM   #3
Bengali is offline Bengali  United States
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thanks. I will give that a try. I wonder how the kits they sell get away without having to make that adjustment. I'm using all the same values and parts.
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Old 15th August 2008, 07:11 AM   #4
Elvee is online now Elvee  Belgium
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Doesn't look like a symmetry problem. I'd rather say there is some leak from the square wave to the sinewave, perhaps caused by charge injection or something similar.
Might be caused by a poor layout, or it could happen internally in the MAX038. Even if this is the case you could correct it by injecting a square of opposite phase into the sine output, through a high value resistor f.e.
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Old 15th August 2008, 08:45 AM   #5
Bengali is offline Bengali  United States
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it could very likely be my layout. I'll look into it further when time permits. thanks.
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Old 15th August 2008, 10:53 AM   #6
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Looking at it again, it may well be the graph itself. The line is quite thick and jumps one or two pixels at the time.
What equipment/program did you use to make it? If you look on the scope, do you still see those jumps? Probably not!

Jan Didden
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Old 15th August 2008, 03:38 PM   #7
Bengali is offline Bengali  United States
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actually, I just cut and pasted a sine wave from the wave
to show as an example of what I see on the oscilloscope :-)

my respects to your great attention to detail.

I had the max 038 part so I wanted to give it a try.
it's working but not great so I need to spend some more
time on it.
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Old 15th August 2008, 04:10 PM   #8
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Quote:
Originally posted by Bengali
actually, I just cut and pasted a sine wave from the wave
to show as an example of what I see on the oscilloscope :-)

my respects to your great attention to detail.

I had the max 038 part so I wanted to give it a try.
it's working but not great so I need to spend some more
time on it.

So maybe there isn't a problem at all. Maybe a pic of the scope screen would be more clear.

Jan Didden
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