Datasheet

NOISE
e =A ´
O VMAX
2 (R i ) +e +2 4kTR´ ´ ´
S n n S
2 2
(5)
R
F
+V
IN
R
G+
R
G-
-V
IN
FB
R
G
R
S
e
O
VCA821
*
e
O
i
n
4kTR
S
R
S
*
i
n
4kTR
S
NOTE:R andR arenoiseless.
F G
*
*
e
nOUTPUT
i
niOUTPUT
i
inOUTPUT
I
CORE
e
nINPUT
i
nINPUT
R
F
4kTR
F
*
R
S2
4kTR
S2
*
R
F
4kTR
F
e
O
FB
GND
V
OUT
V
REF
V
G
V
G
x1
*
e
nINPUT
i
nINPUT
*
x1
R
G
(Noiseless)
+R
G
-R
G
V-
-V
IN
+V
IN
*
R
S1
4kTR
S1
i
nINPUT
V+
VCA821
SBOS407B – DECEMBER 2007 – REVISED DECEMBER 2008 ....................................................................................................................................... www.ti.com
This model is formulated in Equation 5 and Figure 86 .
The VCA821 offers 6nV/ √ Hz input-referred voltage
noise density at a gain of 20dB and 2.6pA/ √ Hz
input-referred current noise density. The
A more complete model is shown in Figure 87 . For
input-referred voltage noise density considers that all
additional information on this model and the actual
noise terms (except the input current noise but
modeled noise terms, please contact the High-Speed
including the thermal noise of both the feedback
Product Application Support team at www.ti.com .
resistor and the gain resistor) are expressed as one
term.
Figure 86. Simple Noise Model
Figure 87. Full Noise Model
26 Submit Documentation Feedback Copyright © 2007 – 2008, Texas Instruments Incorporated
Product Folder Link(s): VCA821