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Discrete sampling transfer function ?

Discussion in 'Electronic Design' started by Chris Carlen, Nov 17, 2003.

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  1. Chris Carlen

    Chris Carlen Guest


    The PWM frequency for my solenoid driver is rather close to the open
    loop bandwidth. Of course, this causes the response to differ from what
    I would expect based on an AC model that assumes a continuous time
    system. I don't know yet how to account for the discrete sampling in
    the AC model. I expect it has an effect of introducing a linearly
    increasing phase delay with frequency. I have also not thought a great
    deal about how to model that, as I have only begun thinking about this
    since breakfast.

    I expect a linear phase vs. frequency with unity amplitude gain is what
    we call an "allpass filter." But that's getting ahead of the game since
    I'm not even sure that a linear phase delay vs. frequency is the right
    way to consider discrete sampling.

    How might I go about dealing with (or beginning to learn how to deal
    with) the PWM frequency effect, which is effectively the sampling
    frequency, in modeling the small signal AC response of a control system?

    Thanks for comments.

    Christopher R. Carlen
    Principal Laser/Optical Technologist
    Sandia National Laboratories CA USA
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