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
    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!