LTC6605-7 Linear Technology, LTC6605-7 Datasheet - Page 15

• Manufacturer Part Number: LTC6605-7
• Description: Dual Matched 7MHz Filter
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
Noise
When comparing the LTC6605-7’s noise to that of other
amplifi ers, be sure to compare similar specifi cations. Stand-
alone op amps often specify noise referred to the inputs of the
op amp. The LTC6605-7’s internal op amp has input referred
voltage noise of only 2.1nV/√Hz. In addition to the noise gen-
erated by 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.
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
R2
e
e
R2
R1
R1
nR3
nR3
2
2
I
I
n
n
Figure 7b
2
Figure 7c
R3
R3
2
+ 2
– 2
+ 2 • e
+ 8 • k • T • R2 • 1+
Substituting the equation for Johnson noise of a resistor
(e
ing gives the result shown in Figure 7c.
Board Layout and Bypass Capacitors
For single-supply applications it is recommended that a
high quality X5R or X7R, 0.1μF bypass capacitor be placed
directly between V
including the Exposed Pad, should be tied directly to a low
impedance ground plane with minimal routing.
e
ni
e
e
nR2 2
2
nR2
2
nR1
nR
2
+
–
= 4kTR) into the equation in Figure 7b and simplify-
•
R2
R2
R2
R1
66057 F07a
2
+ 2 • e
R2
e
R1
no
+
2
and the adjacent V
+ R3 • 1+
nR3
• 1+
R2
R1
R2
R1
www.DataSheet4U.com
LTC6605-7
2
2
+ 2 • e
–
pin. The V
nR2
2
15
–
pins,
66057f