MAX038 Sine Wave

Bengali · 14th August 2008, 06:01 PM

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.

jan.didden · 14th August 2008, 06:48 PM

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

Bengali · 14th August 2008, 09:14 PM

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.

Elvee · 15th August 2008, 07:11 AM

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.

Bengali · 15th August 2008, 08:45 AM

it could very likely be my layout. I'll look into it further when time permits. thanks.

jan.didden · 15th August 2008, 10:53 AM

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

Bengali · 15th August 2008, 03:38 PM

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.

jan.didden · 15th August 2008, 04:10 PM

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

14th August 2008, 06:48 PM	#2
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	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 __________________ /Yes! Its out: Linear Audio Vol 5! I'm not an "accademic", just a plodder who loves a challenge - Ian Hegglun

15th August 2008, 10:53 AM	#6
jan.didden diyAudio Member Join Date: May 2002 Location: Great City of Turnhout, Belgium Blog Entries: 6	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 __________________ /Yes! Its out: Linear Audio Vol 5! I'm not an "accademic", just a plodder who loves a challenge - Ian Hegglun

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14th August 2008, 09:14 PM	#3
Bengali diyAudio Member Join Date: Oct 2006	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.

15th August 2008, 07:11 AM	#4
Elvee diyAudio Member Join Date: Sep 2006	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.

15th August 2008, 08:45 AM	#5
Bengali diyAudio Member Join Date: Oct 2006	it could very likely be my layout. I'll look into it further when time permits. thanks.

15th August 2008, 03:38 PM	#7
Bengali diyAudio Member Join Date: Oct 2006	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.