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square to sine

Discussion in 'Electronic Basics' started by Sandeep, Nov 4, 2005.

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  1. John Fields

    John Fields Guest

    You're joking, right?

    If you start screwing around with the time constant all you'll wind
    up doing is changing the output amplitude and waveshape, which will
    _never_ resemble a sinewave, no matter what you do.
  2. John Fields

    John Fields Guest

    The OP's query asked for a circuit with a stable sine wave output
    with a frequency equal to that of a squarewave input signal. Since
    he specified a "square wave", I think we can safely assume a 50%
    duty cycle and, therefore, disregard the even harmonics.
  3. Bob Masta

    Bob Masta Guest

    If you can get a good triangle, you can get a very good
    approximation... easily as good as a standard "function
    generator", which are typically 1% THD. Although the
    8038 uses diode breakpoints for shaping, this is not
    a very good method for individual use... too many adjustments,
    even assuming you can figure out how to proceed with the

    My method of choice is an overdriven differential pair.
    You will end up with 2 adjustments: The amount of
    overdrive (input level), and the amount of feedback.
    If you feed the output to an amp and headphones,
    you can adjust this by ear. (Though a scope helps
    to get you in the ballpark.) You will be balancing
    between 2nd and 3rd harmonic levels. 1% THD is
    easy, and I have gotten as low as 0.25% on occasion,
    though I don't know how stable that would be.
    The by-ear method is better than a scope alone for
    distortion adjustment. An FFT spectrum analyzer
    is better still.

    I have seen a paper where the authors used a matched
    pair in a temperature-controlled oven and got
    something like 0.001%. However, if you are shooting
    for these sorts of levels, then the input triangle itself becomes
    more of an issue. It's pretty hard not to have some sort of
    glitch at the peaks.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
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