Scaling Factors for Individual

(e )

ni

2

2

R

G

R +

G

R

S

2

R

G

R

F

+

(18)

(i )

ni

2

R

G

2

(19)

(i )

ii

2

R

G

2

(20)

2

4kTR

F

2 ´

R

G

R

F

(21)

Ni

NA

Rg

Rf

eg

ef

es

Rs

en

No

ini

iii

Rt

et

Ni

Si

No

So

+

−

fully-diff

amp

Rg

Rf

eg

ef

2

4kTR

G

2 ´

R

G

R +

G

R

S

2

(22)

Scaling Factors for Individual

N

i

S

=4kTR

R +

S

2R

T

G

R

R

T

G

+2R

2R

T

G

R

R

T

G

+2R

2

(23)

(e )

ni

2

2

R

G

R +

G

R

S

R

T

2(

)

R +R

S

T

R

G

R

F

+

(12)

N

i

S

=4kTR

2R

G

R

S

G

+2R

2

(24)

(i )

ni

2

R

G

2

(13)

Noise Factor and Noise Figure Calculations

(i )

ii

2

R

G

2

(14)

N =

(NoiseSource

ScaleFactor)

S

´

A

(25)

F=1+

N

A

N

I

(26)

NF=10log(F)

(27)

R +

T

2R

S

G

R

R

S

G

+2R

2R

S

G

R

R

S

G

+2R

2

4kTR

F

(15)

2

4kTR

F

2 ´

R

G

R

F

(16)

4kTR

G

2

R

G

R +

G

R

S

R

T

2(

)

R +R

S

T

2 ´

(17)

THS4504

THS4505

www.ti.com ......................................................................................................................................................... SLOS363D – AUGUST 2002 – REVISED MAY 2008

Noise Sources Assuming No Termination

Resistance is Used (for example, RT is open)

Figure 88. Noise Sources in a Fully

Differential Amplifier Circuit

Input Noise With a Termination Resistor:

Noise Sources Assuming a Finite

Value Termination Resistor

Input Noise Assuming No Termination Resistor:

Copyright © 2002–2008, Texas Instruments Incorporated

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