week_10 - 79 Noise in Resistors Thermal noise (+ maybe...

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Unformatted text preview: 79 Noise in Resistors Thermal noise (+ maybe flicker noise) ~ R f kTR ∆ 4 . . R f R kT ∆ ⋅ 4 . or . Noise in Diode Shot noise (+ thermal noise from contact resistance + maybe flicker noise) . ~ f kTR S ∆ 4 . . S R D T d I V r = f f I k f qI i D D d ∆ ⋅ + ∆ = α 2 2 Noise in MOS transistor Thermal noise (in channel) + flicker noise in gate region Model for saturation region: 80 2 d i ds r gs m v g G 2 g v . . . gd C gs C D S gs v + _ ~ This thermal noise is not due to . ds r ← ∆ = f f WLC k v ox g . 2 flicker noise (Experimentally they have found that flicker noise in MOS is not a function of drain current) devices channel short devices channel long f g kT i m d − → = − → = ∆ = 3 ~ 2 3 2 . 4 2 γ γ γ Noise in Bipolar ternsistors Thermal noise in base (contact and intrinsic base) bb r + shot noise in base + shot noise in collector + flicker noise in base 81 bb r 2 c i o r be m v g B . . . µ C π C C E 2 b v ~ π r 2 B i f qI i f f I k qI i f g kT kTr v C c B B B m bb g ∆ = ∆ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ′ + = ∆ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + = 2 2 2 1 4 4 2 2 2 ow H to calculate total Noise? Consider the following circuits In the book you have ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + + ... 2 f kI I q B B so k and are related. k ′ Noisy Network . . . . . . S R Measure noise 82 . . . . S R Noiseless 2 i v ~ 2 i i . . Measure noise Circuit ny noise 2-port network can be represented by a noiseless network and two input A voltage and current noise sources. Æ (there might be some correlation between them) Why do we need both 2 i v and 2 i i ? Æ 2 i i shorts out but 2 i v R → S still represents the noise. Æ 2 i v cannot generate any noise at the output but 2 i i R ∞ → S does. ne more thing O o measure noise at the output, it may be easier to consider output current noise when T output is short-circuited. 83 Example alculate C 2 i v and 2 i i for a bipolar transistor. oisy Network N o measure output noise we will short circuit collector. T Noiseless Network bb r 2 c i o r be m v g . . µ C π C C 2 b v ~ π r 2 B i S R f kTR S ∆ 4 noise o i i = 1 E ~ . bb r o r be m v g . µ C π C 2 i v ~ π r 2 i i S R f kTR S ∆ 4 ~ noise o i i = 2 E To find Æ 2 i v short-circuit input ( = S R ) and measure output noise in both circuits. To find Æ 2 i i open-circuit input ( ∞ = S R ) and measure output noise in both circuits. 84 Noisy network with : ssuming noise sources are un-correl ffect of = S R bb r 2 c i be m v g ....
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This note was uploaded on 02/19/2012 for the course ECE 455 taught by Professor Mohammadi during the Fall '10 term at Purdue University.

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week_10 - 79 Noise in Resistors Thermal noise (+ maybe...

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