Datasheet

LTC6403-1
16
64031fa
Noise Considerations
The LTC6403-1’s input referred voltage noise is on the
order of 2.8nV/√Hz. Its input referred current noise is on
the order of 1.8pA/√Hz. In addition to the noise generated
by the amplifi er, the surrounding feedback resistors also
contribute noise. A noise model is shown in Figure 9.
The output noise generated by both the amplifi er and the
feedback components is governed by the equation:
e
e
R
R
IR
e
no
ni
F
I
nF
n
=
+
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
+
()
+•••
•
12
2
2
2
RRI
F
I
nRF
R
R
e••
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
+
2
2
2
A plot of this equation, and a plot of the noise generated
by the feedback components for the LTC6403-1 is shown
in Figure 10.
The LTC6403-1’s input referred voltage noise contributes
the equivalent noise of a 480Ω resistor. When the feedback
network is comprised of resistors whose values are less
than this, the LTC6403-1’s output noise is voltage noise
dominant (See Figure 10.):
ee
R
R
no ni
F
I
≈+
⎛
⎝
⎜
⎞
⎠
⎟
•1
Feedback networks consisting of resistors with values
greater than about 1k will result in output noise which is
resistor noise and amplifi er current noise dominant.
eIR
R
R
kTR
no n F
F
I
F
≈
()
++
⎛
⎝
⎜
⎞
⎠
⎟
214
2
•• ••••
Lower resistor values (<400Ω) always result in lower noise
at the penalty of increased distortion due to increased
loading of the feedback network on the output. Higher
APPLICATIONS INFORMATION
Figure 9. Noise Model of the LTC6403-1
–
+
1
SHDN
5 6
–IN
7
+OUT
8
+OUTF
16 15
+IN
NC
NC
14
–OUT
13
–OUTF
e
no
2
R
F2
2
V
+
3
V
–
V
+
V
+
V
–
V
+
V
–
V
OCM
V
OCM
12
V
–
11
V
+
10
V
+
9
V
–
V
–
V
–
64031 F09
LTC6403-1
e
nof
2
e
nRI2
2
SHDN
R
F1
R
I2
R
I1
V
–
V
+
V
–
4
e
nRF2
2
e
nRI1
2
e
ncm
2
e
ni
2
e
nRF1
2
i
n
+2
i
n
–2