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sine to square wave converter

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Newbie level 6
Dec 17, 2012
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i am trying to understand how to convert sine wave to square wave:

i found this over the internet:

**broken link removed**

however i didnt understand some points and i will be happy for explanations:

1. where is connect the second input of the operational amplifier? (i see that it has only one input, however as i know the operational amplifier has 2 inputs)

2. why do we need the capacitor?

thanks alot

That's not an opamp. If you read the text, it tells you it's a schmitt trigger, it said nothing about opamps.

You need to the capacitor so that the input to the schmitt trigger doesn't go below the negative rail.
to get the square wave from sinusodial wave you can simply connect input waveform to two pins + and - of a comparator i.e. LM324
as u can c, pin1 of the device is grounded. so when the voltage at pin3 is positive, the output goes to +Vsat; 'n when the voltage at pin3 is negative, the output goes to -Vsat. thus, the sine wave at the input is converted to a square wave at the output of the op-amp (oh yes, the schmitt trigger is an application of the op-amp).
hope this helped :)
thanks you all my friends!

soi want to understand something..can i connect the capacitor derectly to op-amp that the second input to zero and then i will have a sine to square wave converter...

only to be right?

If you are going to use an opamp, you MIGHT want to add a little positive feedback to avoid oscillation. It may not be necessary depending on your application, your input an d your opamp.

@barry: did u mean 'negative feedback to avoid oscillations'? 'cause i believe positive feedback makes oscillations, rather than preventing them!

i think he meant 'hysteresis'.

In general, though you CAN use an opamp like a comparator, (and it often is) it is always better to use an IC which is designed to be a comparator. Like LM311 & similar.

@barry: did u mean 'negative feedback to avoid oscillations'? 'cause i believe positive feedback makes oscillations, rather than preventing them!

No, I meant POSITIVE feedback (or hysteresis, if you prefer). And, I agree with rohitkhanna that a comparator might be better; but in many applications an opamp will work just fine.

sorry but i lost u guys there..! can u please elaborate on how hysteresis can be reduced by positive feedback?

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