rajkumar palwai
Community Member
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Posts: 46
Sunnyvale, California
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@Raja, summi took an assumption that the conductance and currents are same in resistor and mosfet. Ideally the mosfet noise current is 4kt(gamma)(gds@vds=0). But as gds@vds=0 is same as gm, we use typical equation of 4ktgm. So in the case of mosfet & resistor conductances being same, both of them produce same amount of noise current.
@summi But if we see the noise voltages, the resistor noise voltage is 4kt/r*r^2 = 4ktr. Where as the noise voltage at mosfet o/p is 4ktgm*ro^2 , which is much greater than resistor noise voltage.
However, as you may be aware that all these equations hold true only when the mos is in saturation. If mosfet is in linear region than all the noise currents and voltages are same for both mosfet and resistor.
-rajkumar
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