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    Interpretation of frequency of VCO

    A VCO has a transfer function of 100/s, could this mean, it produces frequency which is 100KHz/V?

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    Re: Interpretation of frequency of VCO

    which VCO?
    what does the data sheet say?
    what do the applicable ap notes say?
    there (likely) is at least one ap note with a sample usage. what does that say?



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    Re: Interpretation of frequency of VCO

    The Laplace model of a vco is given by the expression

    Phase/Vin = Gain/s

    where "s" is the Laplace operator

    then in you case Gain=100. Trasforming into time domain we have dPhase/dt = Gain*Vin that is w = Gain*Vin

    in your case:

    2*pi*frequency = 100*Vin from which frequency/Vin = 100/(2*pi) = 16 Hz/V



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    Re: Interpretation of frequency of VCO

    Hi albbg

    Suppose the VCO produces output say 1KHz/V (square wave)and I connect it to a 10 bit counter. Then it would take 1 second for counter to roll off. So the time constant is 1 second in this case. Would the transfer function of the combo not be 1/s in this case?



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    Re: Interpretation of frequency of VCO

    Hi.

    What you say can be mathematically shown as:

    f = 1 / t
    or
    t = 1 / f

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: Interpretation of frequency of VCO

    Hi KlausST

    Are you confirming that the expression 1/s is correct?



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    Re: Interpretation of frequency of VCO

    Would the transfer function of the combo not be 1/s in this case?
    No. About 6.13/s (2*pi*1000/1024)

    Unless you arbitrarily redefine the commonly understood VCO transfer function definition, you should consider what albbg told. The unit is rad/s rather than Hz.



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    Re: Interpretation of frequency of VCO

    At this point of view, I was wondering the difference between VFC vs VCO?



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    Re: Interpretation of frequency of VCO

    Literally, a VCO is a VFC (voltage to frequency converter) and vice versa. Specifically the term VFC refers to converters with large frequency ratio (e.g. 0 to xx kHz) and high linearity. The frequency ratio of a VCO can range between several 100 ppm (tuned crystal oscillator) to decades (current steered rings oscillator).



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    Re: Interpretation of frequency of VCO

    Quote Originally Posted by garimella View Post
    A VCO has a transfer function of 100/s, could this mean, it produces frequency which is 100KHz/V?
    When the given expression is really the TRANFER FUNCTION (and not thefrequency with s=seconds), it must be interpreted as the PHASE characteristics.
    This is because in a linear PLL model the input and output quantities are given as PHASE values.

    In this case, the transfer function is PHI(s)=Ko/s
    with Ko=VCO constant given in rad/Vs.



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