Understanding electronic noise, and root hertz

Discussion in 'General Electronics Chat' started by szehowe, Oct 28, 2009.

  1. szehowe

    Thread Starter New Member

    Oct 28, 2009
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    Hi all,

    I'm struggling to get my head around some concepts of noise. In an assignment, I'm told given the following characteristics of a transistor:

    i) Input voltage noise = 1.8 nV/√Hz (under the conditions that I_C is 100μA and the frequency range is 100 Hz - 100 kHz)
    ii) Base current noise = 0.2 pA/√Hz (I_C = 100μA, frequencies from 1 Hz - 100 kHz)
    iii) Beta = 550 (I_C = 100μA) (I've omitted the other betas listed for other I_C values)

    From the above, is it correct to say that:
    1) For the given conditions, the area under the voltage noise PSD vs. frequency curve, from 100 Hz - 100 kHz, is 1.8^2 = 3.24 nV^2?
    2) The noise values will change, if we specify different frequency ranges?

    Also, I'm asked to derive other transistor parameters (such as base-spreading resistance r_x, and 1/f noise parameters) from the given data, for SPICE analysis. Are these parameters dependent on frequency ranges too?

    I do realize this is quite a list of questions; thanks in advance for your help!
     
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