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How Do I Generate Quarter Sine Waves?

  1. May 6, 2016 #1
    Hello,
    I need to find out how to generate a standing sine wave, or a quarter sine wave. I had no trouble finding out how to create a full or half wave rectifier, but very little generating a quarter wave, & that info mostly dealt with sound waves. I am doing this for experimental purposes. Please not I have a good function generator. Thanks for any help!
     
  2. jcsd
  3. May 6, 2016 #2

    anorlunda

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    You didn't specify the frequency, so maybe a relay.
     
  4. May 6, 2016 #3
    Correction: Please note I have a good function generator.
     
  5. May 6, 2016 #4
    Almost always 100K.
     
  6. May 6, 2016 #5

    Baluncore

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    Which quadrant do you want?
    Draw the waveform you require. Post it as an attachment.
     
  7. May 7, 2016 #6
    If you have a good function generator, you have an advantage, for generating sine wave. What I would do is generate a square wave of duty cycle 75 percent(there are circuits in 555 which enable you to do)....Then, I would connect both this sine wave(amplitude is so low) and the square wave to a bjt transistor network. This network ensures that only quarter of the wave is passed( any quarter section of the full wave)
    For the bjt network(use some bias if needed), use the sine wave as small signal....connect the sine wave to the base(through capacitor). The emitter can be grounded. The large signal is the square wave and you must connect it to the base through a resistor. Take the output from collector or emitter depending on the circuit.
     
  8. May 7, 2016 #7

    davenn

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    the freq is probably irrelevant

    a standing wave ISNT going to come from your generator .... standing waves are generated on a transmission line when
    the transmitted signal hits an impedance mismatch. At that time a reflection of the signal will occur and be reflected back
    towards the transmitter ( generator) and standing waves with be generated when the forward and reflected signals interact

    a 1/2 wave generator is just removing the other 1/2 of the cycle as said with a diode

    the only easy way I could see to produce what looks like a 1/4 sine wave would be to generate a non-linear ramp voltage

    quarterwave.GIF


    maybe you should tell us more about what you are trying to achieve


    cheers
    Dave
     
  9. May 7, 2016 #8

    Baluncore

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    A simple quarter of a sine wave is probably a single quadrant. That suggests both a removal of one polarity and a time dependent elimination of one half of the “pulse”. To split the pulse in two requires a time dependent function. One way to generate that is with a phase shift of 90°. A low or high pass filter will do that. Then the quadrant of the sine wave must be selected based on the polarity of the phase shifted signal.
    Attached is a circuit modelled with LTspice that attempts to do that without integrated components.
    Only R, C and diodes are used. The R1C1 is the phase shifter.
    The diodes form the quadrant data selector. The gate control must be higher than the signal so as to give a steep switching edge.
    Quadrant.png
     
  10. May 7, 2016 #9

    jim hardy

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    I like Balun's thought process - analog phase control.
    I was about to suggest a thyristor lamp dimmer
    http://www.littelfuse.com/~/media/e...rol_using_thyristors_application_note.pdf.pdf

    same phase control principles could be applied at a signal level using precision analog switches like DG614
    https://www.vishay.com/docs/70050/dg411.pdf

    Nowadays one can brute force it - use a μprocessor and D/A to output any function as a stream of numbers from memory......

    [ moderator note: media link removed ]
     
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