rohandayal Posted February 25, 2005 Report Share Posted February 25, 2005 I want to convert a square wave to a sine wave of same amplitude and frequency.Anybody help me out Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 25, 2005 Report Share Posted February 25, 2005 Hi Ro,Welcome to our forum.To convert a square wave to a sine wave, just filter its harmonics with a low-pass-filter. It must have a steep slope to pass the fundamental but attenuate the 3rd harmonic and above. 50-50 square waves don't have even-numbered harmonics. Use at least a 4-pole Butterworth LPF.The web is full of and I have made converters using a switched-capacitor LPF IC. My extremely low distortion sine-wave generator uses a square-wave with over-sampling and a switched-cap LPF IC. The amplitude of its sine-wave is rock solid. Quote Link to comment Share on other sites More sharing options...
rohandayal Posted February 27, 2005 Author Report Share Posted February 27, 2005 could any one tell anyone tell how to reduce harmonics and noise signals in a sinusoidal wave using a PLL4046 chip? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 27, 2005 Report Share Posted February 27, 2005 Hi Ro,A PLL has a square-wave output so you would lose any amplitude changes of a sine-wave it is locked in frequency with. A PLL is useful to recover a sine-wave that is buried in noise or has frequency jitter.A PLL output might have frequency overshoot and decaying frequency hunting with quick frequency changes of the sine-wave, or follow the frequency changes too slowly. Then you just filter-out the PLL's square-wave's harmonics with a low-pass-filter like previously to end up with a pure sine-wave. ;D Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted February 27, 2005 Report Share Posted February 27, 2005 If you could modify the square wave beforehand you would be better off. It requires that you use logic to insert a DC level of zero volts for a time at the zero crossing. There is a reason for converting a square wave to a sine wave and the applications are limited. It would seem very appropriate to construct a sine wave from an oscillator. I would like someone to tell me how it is done. I mean how do they actually get the value of the sine wave right. As I understand it, the output of an oscillator is basically a single rate of change. Sort of like a triangle. How do they accomplish the effect that gives rise to the rounding at the peak. Quote Link to comment Share on other sites More sharing options...
gg4rest Posted February 28, 2005 Report Share Posted February 28, 2005 Here is a good article I found on constructing sinewave oscillators.http://www.web-ee.com/primers/files/AN-263.pdfHope it helps. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 28, 2005 Report Share Posted February 28, 2005 Thanks GG, I forgot about that appl note. Here's a modern one: http://www-s.ti.com/sc/psheets/sloa060/sloa060.pdf Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted March 1, 2005 Report Share Posted March 1, 2005 What frequency?Try this circuit the formula for the frequency is 1.38/(RC) Just make sure the capacitors and resistors drawn in pink and labeled R and C are the same value.The 555 generates a square and sort of triangle wave the first op-amp amplifies this, the R and C on the output low pass filters the triangle wave to give a sine wave, and the last amplifies this again. There are simpler ways to do this but I desined this circuit a long time ago, I used a dual sterio pot for R and a gang rotary switch to switch the value of C. I recomend you use 10 Quote Link to comment Share on other sites More sharing options...
gg4rest Posted March 1, 2005 Report Share Posted March 1, 2005 Thanks for the appl note audioguru. That one is very good. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted March 1, 2005 Report Share Posted March 1, 2005 Great app-note Audioguru! Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 1, 2005 Report Share Posted March 1, 2005 Thanks Guys,When I first saw that new appl note, I built a buffered phase-shift osc and fixed its problems with a 4th opamp. I used 3/4th of a 4-gang pot I got out of a toy. It works great. Using a little low-droppout regulator, its amplitude is rock-solid and its distortion is very low. ;D Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted March 5, 2005 Report Share Posted March 5, 2005 HEY GUYS!WHATS THE PROBLEM IN USING AN INTEGRATOR CIRCUIT WITH FEEBLE AMPLIFICATION USING OPAMPS?PRATEEK Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 5, 2005 Report Share Posted March 5, 2005 Hi Prateek,A single integrator won't convert a square-wave to a sine-wave. Many integrator stages will attenuate the fundamental frequency as well as its harmonics. That's why I recommended using a multi-pole Butterworth low-pass-filter, because of its sharp cutoff.Opamps don't have feeble amplification. They have an open-loop gain of hundreds of thousands and with negative feedback have almost any amplification you need. Quote Link to comment Share on other sites More sharing options...
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