Explain why millers theorem cannot be applied to calculate the effect of thermal noise of a floating resistor
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The Miller theorem refers to the process of creating equivalent circuits. It asserts that a floating impedance element that is supplied by two voltage sources connected in series and may be split into two grounded elements with corresponding impedances.
Miller's theorem requires that the floating impedance and the voltage gain be computed at the same frequency. It also allows a floating impedance to be decomposed into to grounded impedances.
The thermal noise from the input impedance of a floating resistor is quite high. The noise voltage at both the nodes are usually high and have the same sign. So, the noise gain is positive and is more than 1. This is called as negative Miller capacitance which cannot be explained by Miller's theorem.
Miller's theorem requires that the floating impedance and the voltage gain be computed at the same frequency. It also allows a floating impedance to be decomposed into to grounded impedances.
The thermal noise from the input impedance of a floating resistor is quite high. The noise voltage at both the nodes are usually high and have the same sign. So, the noise gain is positive and is more than 1. This is called as negative Miller capacitance which cannot be explained by Miller's theorem.
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