LTC6605-10 Linear Technology, LTC6605-10 Datasheet - Page 15

• Manufacturer Part Number: LTC6605-10
• Description: Dual Matched 10MHz Filter
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
Noise
When comparing the LTC6605-10’s noise to that of
other amplifi ers, be sure to compare similar specifi -
cations. Standalone op amps often specify noise re-
ferred to the inputs of the op amp. The LTC6605-10’s
internal op amp has input referred voltage noise of
only 2.1nV/√Hz. In addition to the noise generated by
e
e
no
no
=
=
⎡
⎢
⎣
⎡
⎢
⎣
e
e
ni
ni
• 1+
• 1+
⎛
⎜
⎝
⎛
⎜
⎝
R2
R1
R2
R1
⎞
⎟
⎠
⎞
⎟
⎠
⎤
⎥
⎦
⎤
⎥
⎦
2
2
+ 2 • I
+ 2 • I
⎡
⎢
⎣
⎡
⎢
⎣
n
n
• R2 + R3 • 1+
• R2 + R3 • 1+
⎛
⎜
⎝
⎛
⎜
⎝
e
e
nR1
nR1
2
2
R1
R1
Figure 7a. Differential Noise Model
⎡
⎢
⎣
⎡
⎢
⎣
e
e
nR3
nR3
R2
R2
R1
R1
2
2
I
I
⎤
⎥
⎦
n
n
⎤
⎥
⎦
Figure 7b
Figure 7c
R3
R3
+ 2
– 2
⎞
⎟
⎠
⎞
⎟
⎠
⎤
⎥
⎦
⎤
⎥
⎦
2
2
+ 2 • e
+ 8 • k • T • R2 • 1+
the amplifi er, the surrounding feedback resistors also
contribute noise. A noise model is shown in Figure 7a.
The output spot noise generated by both the amplifi er
and the feedback components is given in Figure 7b.
Substituting the equation for Johnson noise of a resistor
(e
ing gives the result shown in Figure 7c.
e
ni
e
e
nR2
2
nR2
2
⎡
⎢
⎣
nR
2
2
nR1
+
–
= 4kTR) into the equation in Figure 7b and simplify-
R2
R2
•
⎡
⎢
⎢
⎣
⎛
⎜
⎝
660510 F07a
R2
R1
⎞
⎟
⎠
⎤
⎥
⎦
⎛
⎜
⎝
2
e
+ 2 • e
no
2
R2
R1
⎡
⎢
⎣
⎞
⎟ + R3 • 1+
⎠
nR3
• 1+
⎛
⎜
⎝
⎛
⎜
⎝
LTC6605-10
www.DataSheet4U.com
R2
R1
R2
R1
⎞
⎟
⎠
⎞
⎟
⎠
⎤
⎥
⎦
2
2
⎤
⎥
⎥
⎦
+ 2 • e
nR2
15
2
660510f