Discussion in 'The Projects Forum' started by shirketteyim, Aug 16, 2013.

Aug 16, 2013
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2. ### shirketteyim Thread Starter New Member

Aug 16, 2013
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I don't want to use amplifier. Is it possible without using amplifier?

3. ### wayneh Expert

Sep 9, 2010
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Your circuit is wired as a peak detector and will ensure no square wave is output. What is the purpose of R1 and R4?

R2 and R5 may be too large for your op-amp. I'd drop them by 10X and see if that helps.

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4. ### wayneh Expert

Sep 9, 2010
11,937
2,864
Why not just use a comparator. LM339 (quad comparator) is widely available and would work fine here.

What do you mean by "very small amplitude"? 1mV? 1nV?

5. ### shirketteyim Thread Starter New Member

Aug 16, 2013
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This is simplest version of another circuit-- http://imageshack.us/photo/my-images/43/5k7u.jpg/ -- I transformed this to file in upward to understand how this circuit works. Original circuit has R4 and R1 so i didn't change them. Actually my goal is to create an system such that it will give a reaction similar to square(square+triangle or whatever likes it is hard to describe but not a line. My system gives a line under 1.9mv at 600mHz sinusoidal. I want a reaction even at 0.1mV is this possible?
I don't have an information about LM339 but i will research it thank you.

6. ### wayneh Expert

Sep 9, 2010
11,937
2,864
Yes, but that is small enough to be more difficult. At that level, I would first use an op-amp at a voltage gain of 50X or so, to take that 0.1mV up to 5mV or more. Then the comparator will easily square it up.

What exactly are you trying to do? Fluctuation at that small amplitude can easily come form all sorts of noise sources. Why square up the "noise"?

The biasing in the circuit shown may be causing you problems as well. I haven't done the math but it may be overwhelming your tiny signal, so that it cannot come through. I would use an op-amp that can sense to the negative rail and then use circuit ground on one of the inverting input.

7. ### shirketteyim Thread Starter New Member

Aug 16, 2013
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"What exactly are you trying to do? Fluctuation at that small amplitude can easily come form all sorts of noise sources. Why square up the "noise"?"
You are probably right, i didn't think in this way. Experiment will show this and i will do on monday.
"The biasing in the circuit shown may be causing you problems as well. I haven't done the math but it may be overwhelming your tiny signal, so that it cannot come through. I would use an op-amp that can sense to the negative rail and then use circuit ground on one of the inverting input."
I couldn't understand what exactly you mean in this part please forgive me. Can you give a little more detail? Thank you