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enter image description here

I have 2 signal (signal on the left) and how to combine those 2 signal into the signal on the right, I have try using lm 741 op amp, but unfortunately the output signal is different from the signal(not as expected) on the right picture..

Since i use 4kHz of frequency and 4V of voltage input, What the comparator circuit i should use to generate signal like on the right picture? Should i change the 741 op-amp??thanks

here is my output signal, it look different from the signal i wanted

enter image description here

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  • \$\begingroup\$ Start with your requirements. What are the voltage ranges for the inputs? What (exactly) do you need for the output? What time scale are you showing? What power supplies do you have available? What (exactly, use the schematic entry icon or ctrl-m) does your 741 circuit look like, and how (exactly) is it different from what you want? Until you have supplied this information, you are asking us to be psychics, and learn the details telepathically from your mind. We're not. \$\endgroup\$ – WhatRoughBeast Apr 12 '16 at 15:37
  • \$\begingroup\$ @WhatRoughBeast No, i just ask simply, how to generate those signal from the signal on the left.. how circuit i should use to generate the signal output like on the right picture.. \$\endgroup\$ – rezhart Apr 12 '16 at 15:41
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    \$\begingroup\$ Show us your 741 circuit then. It's entirely possible that your basic idea is correct. Tell us exactly what you expected, and why the real output is different. \$\endgroup\$ – WhatRoughBeast Apr 12 '16 at 16:00
  • \$\begingroup\$ @WhatRoughBeast i have upload image from my output signal \$\endgroup\$ – rezhart Apr 12 '16 at 16:35
  • \$\begingroup\$ Please. Get a grip. Your new trace shows 2 traces, not one. Which one is your output? How did you expect us to know? Do you think we're psychic? And one more time - exactly how is the output different from what you expect? Don't just say it's different. Explain what you expect. \$\endgroup\$ – WhatRoughBeast Apr 12 '16 at 17:02
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The 741 won't do what you are trying to do, at least not if you are using it with a single supply voltage.

The 741 cannot handle input signals that go within about 2 volts of the supply rails. So, for a single voltage supply that would be input from about 2V to about Supplyvoltage - 2V.

Since your input signals go to zero volts, you won't get what you expect at the output.

The 741 also cannot drive its output to the voltage rails, within about the same range - so, output from 2V to about supplyvoltage -2V.

Any modern rail-to-rail op amp made for single supply operation, and which has enough bandwidth, would be better than the 741.


Aside from the obvious limitations of the 741, there's not much else that anyone can tell you since you haven't posted a schematic.

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  • \$\begingroup\$ Can you recommend me what type of op amp for this problem? \$\endgroup\$ – rezhart Apr 12 '16 at 15:45
  • \$\begingroup\$ Nope. I'm not an expert, and even they need basic information that you haven't supplied. You need to know what frequencies and voltages you are dealing with. \$\endgroup\$ – JRE Apr 12 '16 at 15:47
  • \$\begingroup\$ frequency is about 4kHz and voltage input 4v \$\endgroup\$ – rezhart Apr 12 '16 at 15:49
  • \$\begingroup\$ @rezhart - Update your question with this extra information. That helps the community understand the same question without having to read all of the comments. \$\endgroup\$ – gbulmer Apr 12 '16 at 15:51
  • \$\begingroup\$ Is the 4kHz for the triangle or for the sine? To do what you want, the triangle probably ought to be of a higher frequency than the sine. (At least twice as high, probably more.) \$\endgroup\$ – JRE Apr 12 '16 at 15:59

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