HO15_214W09_Noise_fb_2pp

HO15_214W09_Noise_fb_2pp - Handout #15 EE 214 Winter 2009...

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Handout #15 EE 214 Winter 2009 Noise in Feedback Circuits B. Murmann and B. A. Wooley Stanford University Ideal Feedback ± Consider an amplifier with input referred noise sources placed into an ideal series-shunt feedback configuration (no loading effects) ± We can identify the equivalent input noise generators for the overall circuit in the same way we have done this previously Short-circuit the input, find input noise voltage generator that yields the same output noise in both circuits – Open-circuit the input, find input noise current generator that yields the same output noise in both circuits B. A. Wooley, B. Murmann EE214 Winter 2008-09 2

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Input Shorted ± Equal output noise in both circuits is obtained for 22 vv = ii a B. A. Wooley, B. Murmann EE214 Winter 2008-09 3 Input Open ± Equal output noise in both circuits is obtained for = a B. A. Wooley, B. Murmann EE214 Winter 2008-09 4
Observation ± For the idealized example studied on the previous slides, we see that the equivalent input noise generators of the amplifier can be moved hd tid th f db k l unchanged outside the feedback loop – Applying feedback has no effect on the circuit’s noise performance – Note that this is very different from the effect of feedback on distortion performance ± This results holds for all four possible (ideal) feedback configurations – Prove this as an exercise ± In practical feedback configurations, the input referred generators must be computed while taking loading effects into account – Loading makes the calculations more complicated, and generally worsens the noise performance – In the best possible design outcomes, the noise performance can approach (but not surpass) that of an idealized configuration B. A. Wooley, B. Murmann EE214 Winter 2008-09 5 Including Loading and Noise from the Feedback Network ±

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This note was uploaded on 08/13/2009 for the course EE EE214 taught by Professor Borismurmann during the Winter '08 term at Stratford.

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HO15_214W09_Noise_fb_2pp - Handout #15 EE 214 Winter 2009...

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