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[SOLVED] Function Generator Design

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OsmanH

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I have an assignment that I should design a function generator in pspice. It converts square wave to sine wave by using schmitt trigger and an intergrator. Firstly, I should take square wave output from schmitt trigger than convert it sine wave by integrator but I cannot do the design. Also, I should use LM158JG for opamps. Can I use LM158 instead of LM158JG? Anyone can give me idea for making design?

Thank you for helping
 

I don't see, how you want to generate a sine wave by integrating a square wave. Obviously, you can expect a triangle wave. Sine function generators are usually based on non-linear diode networks. Low pass filters are another method.

LM158JG isn't but a specific case variant.
 

I think I should use two integrator circuit first convert triangle wave then convert sine wave is it true?
 

The waveform will look nearer to a sine after passing the second integrator, but still have considerable distortion.
 

Is there a way to clear off the distortion or I should make any other design for it
 

OsmanH said:
Is there a way to clear off the distortion or I should make any other design for it
Click to expand...

As mentioned by FvM - the most logical way is to use only the fundamental frequency of the squarewave by lowpass filtering.
 

Integrating a triangle wave does get pretty close to a sine wave. But the main problem with using integrators is that the gain of the output will be inversely proportional to the frequency. If you want to vary frequency without changing amplitude, then that won't work (unless you put some automatic gain control in somewhere, which would be a big step up in complexity).

And using filters on a square or triangle wave has issues too when varying frequency, since your filters will probably have fixed characteristics (unless you again have very sophisticated automatic controls).
 

Hi mtwieg,

I am sure you know that integrating is nothing else than a special form of lowpass filtering - however only of first order!
Therefore, integrating can never reach the degree of harmonic suppression of - let's say - a second order lowpass.
 

Right, an integrator is a filter. But the difference is that other filters will generally have a flat passband, so as long as you operate in that passband your amplitude won't vary with frequency (but the amplitude of the harmonics will). But an integrator will at least give you a constant THD vs frequency.
 

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