English
Language : 

THS4505 Datasheet, PDF (27/45 Pages) Texas Instruments – WIDEBAND, LOW-DISTORTION, FULLY DIFFERENTIAL AMPLIFIERS
◁
THS4504
THS4505
www.ti.com ......................................................................................................................................................... SLOS363D – AUGUST 2002 – REVISED MAY 2008
Ni
NA
eg
Rg
Rf
ef
Si
en
Ni
No
Rs
+
Rt
ini
fully-diff
amp
So
No
es
−
et
iii
eg
Rg
Rf
ef
Figure 88. Noise Sources in a Fully
Differential Amplifier Circuit
Scaling Factors for Individual
Noise Sources Assuming a Finite
Value Termination Resistor
2
(eni)2
RG +
R
RG
RR
F
R+
ST
G 2(RS + RT)
(12)
(ini)2
RG2
(13)
(iii)2
RG2
(14)
2
2RSRG
R + 2R
S
G
4kTR
F
2R R
RT
+
RS
SG
+ 2RG
(15)
2
R
G
4kTRF 2 ´ R
F
(16)
2
RG
4kTR
G
2´
RG
+
RSRT
2(RS + RT)
(17)
Scaling Factors for Individual
Noise Sources Assuming No Termination
Resistance is Used (for example, RT is open)
2
R
R
(e )2
G+
G
ni
RF
RG +
RS
2
(18)
(ini)2
RG2
(19)
(i )2
R2
ii
G
(20)
2
RG
4kTRF 2 ´ R
F
(21)
2
R
G
4kTRG
2´
RG +
RS
2
(22)
Input Noise With a Termination Resistor:
2
2RTRG
R + 2R
N = 4kTR
T
G
i
S
2R R
RS
+
RT
TG
+ 2RG
(23)
Input Noise Assuming No Termination Resistor:
Ni = 4kTRS
2RG
RS + 2RG
2
(24)
Noise Factor and Noise Figure Calculations
NA = S (Noise Source ´ Scale Factor)
(25)
NA
F=1+
NI
(26)
NF = 10 log (F)
(27)
Copyright © 2002–2008, Texas Instruments Incorporated
Submit Documentation Feedback
27
Product Folder Link(s): THS4504 THS4505
 ▷