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NOISE ANALYSIS Goal: a) To evaluate the thermal and 1/f noises in a MOSFET, for a given biasing condition. b) Effect of Feedback on those Noises. Set up: +10 V r 100k To Spec. Analyzer 100k Procedure: Always use a compensated 10X probe for the noise analysis. 1) Look at the RMS voltage in the Analyzer. Let it be X 2) Now this X = Vr2 +Vfet2 3) Now Vfet2 = X - Vr2 4) The reflection on the Input side =>Vfet2/gain = Y, say 5) Now this Y = Vr2 +4kT(2/3) (1/gm) + k Id (1/f) 6) Obtain the Noise Bandwidth from the Analyzer. 7) Now draw [approximately from the Analyzer output], i2/f 1/f Frequency 8) Get the 1/f, from the graph. 9) The thermal noise can thus be obtained by substituting this 1/f in the formula in 5. [Approximate value] Now add a feedback of 1k [series–shunt] +10 V 100k To Spec. Analyzer 100k 1k Repeat the procedure, 1 through 7 but here 2 resistors are in series with the MOSFET. RESULTS: Without feedback, 1) The 1/f Noise is ___. 2) The Thermal Noise is ___. 3) The Noise Bandwidth is ___. With feedback, 1) The 1/f Noise is ___. 2) The Thermal Noise is ___. 3) The Noise Bandwidth is ___.