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How to make a pure two sided sine wave generator with astable multivibrator?

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sr13579

Member
Hello again,
I wanted to make an oscillator that provodes a sine wave. I don't have an oscilloscope with me but I simulated this and found that the sine wave is always at positive side. I want to make sonething that can give me half positive side and half negative side sine wave using one sided square wave. Can you show me a circuit please?
 

audioguru

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Most Helpful Member
There are many circuits that produce a sine wave. Please show your schematic.

Please sketch what you said:
1) sine wave is always at positive side.
2) half positive side.
3) half negative side.
4) one sided square wave.
 

dknguyen

Well-Known Member
Most Helpful Member
If you square wave was unipolar (0V to some +V) and you filtered it to produce a sine-wave, then your sine-wave will also be 0V to some +V.

Assuming this, use an series capacitor to DC-block your output sine-wave or the source square-wave and that should fix the issue.

There words you are looking for are:
Two-sided => bipolar (-V to +V)
One-sided => unipolar (0V to +V)
 

sr13579

Member
If you square wave was unipolar (0V to some +V) and you filtered it to produce a sine-wave, then your sine-wave will also be 0V to some +V.

Assuming this, use an series capacitor to DC-block your output sine-wave or the source square-wave and that should fix the issue.

There words you are looking for are:
Two-sided => bipolar (-V to +V)
One-sided => unipolar (0V to +V)
I want the bipolar one.(Thanks for the information I am totally new at this)
 

dknguyen

Well-Known Member
Most Helpful Member
Yeah, stick a largeish capactiro in series with the output. If it's a polarized capacitor, mind the polarity.
 

audioguru

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A capacitor blocks DC but passes AC. That is what you want, a coupling capacitor. Its value is simply calculated for the lowest frequency to pass without much loss.
 

crutschow

Well-Known Member
Most Helpful Member
Yeah, stick a largeish capactiro in series with the output. If it's a polarized capacitor, mind the polarity.
You also need a resistor to ground at the capacitor output.
10kΩ is a typical value.
 

carbonzit

Active Member
Output sine wave is Half negative side and half positive side(2 and 3 both). I have added the circuit I was working on.
So that's what, a square-wave generator with a third-order low pass filter? Is that right? Not sure the quality of the sine wave you'll get out of this.
 

audioguru

Well-Known Member
Most Helpful Member
Some sinewave oscillators use a squarewave filtered by an 8th-order switched capacitor lowpass filter IC. I made a stepped sinewave from a CD4018 with a few resistors and filtered it with two 4th-order switched capacitor lowpass filter ICs and the distortion was so low I could not measure it.
 
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