lt1567 Linear Technology Corporation, lt1567 Datasheet - Page 8

• Manufacturer Part Number: lt1567
• Description: 1.4nv/rt.hz 180mhz Filter Building Block
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LT1567
Functional Description
The LT1567 contains two low noise rail-to-rail output,
wideband operational amplifiers, one of them connected
internally as a unity-gain inverter. These two amplifiers
can form a second order multiple feedback filter configu-
ration (Figure 1) for megahertz signal frequencies, with
exceptionally low total noise. The amplifier in the dedi-
cated inverter (INV) is optimized for better high fre-
quency linearity while the uncommitted operational
amplifier (OA) is optimized for lower input noise voltage,
8
V
IN
R1
R2
C2
R3
U
0.1µF
f
Q =
TRANSFER FUNCTION H(s) =
O
C1
=
3
5
GAIN + 1
2
2π√R2R3 C2
U
LT1567
R2
R3
Figure 1. 2nd Order Lowpass Filter and Gain Response for f
(Butterworth: C1 = C2 = 390pF, R1 = R2 = 576Ω, R3 = 280Ω
Chebyshev: C1 = C2 = 390pF, R1 = R2 = 453Ω, R3 = 174Ω)
1
–
+
150Ω
W
8
V
V
+
+
0.1µF
s
2
7pF
+
1
(2πf
Q
(2πf
O
6
U
600Ω
)
s + (2πf
O
–
+
)
2
O
600Ω
4
)
V
2
–
V
–
0.1µF
GAIN IS MEASURED TO EITHER OUTPUT ALONE.
IF OUTPUT USED DIFFERENTIALLY, V
–18
–21
–24
–27
–30
–12
–15
–3
–6
–9
addressing the different sensitivities to these effects
when used as a filter section. This combination produces
a low noise filter with better distortion performance than
would be possible with identical amplifiers.
LT1567 Free Design Software
A spreadsheet-based design tool is available at
www.linear.com for designing lowpass and bandpass
filters using the LT1567.
3
0
100k
7
1567 F01a
Gain vs Frequency
BUTTERWORTH
V
V
OUT
OUT
FREQUENCY (Hz)
–
+
1M
C
DESIGN EQUATIONS:
GAIN = 1 AND f
f
R1 = R2, C1 = C2, C1 ≤
BUTTERWORTH R2 =
CHEBYSHEV 0.25dB RIPPLE R2 =
C
= 1MHz
IS THE FILTER’S CUTOFF FREQUENCY
OUT
CHEBYSHEV
+
– V
OUT
1567 F01b
C
–
R3 =
≤ 1MHz
= 2× V
10M
4.44 • C1 • f
R2
2
1000 • f
IN
(
GAIN =
1
1
R3 =
C
R2
R1
C
5.65 • C1 • f
2.62
R2
)
1
C
1567fa