lt1567 Linear Technology Corporation, lt1567 Datasheet - Page 9

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

APPLICATIO S I FOR ATIO
The simple-to-use spreadsheet requires the user to de-
fine the desired corner (or center) frequency, the pass-
band gain and a capacitor value for a choice of second or
third order Chebyshev or Butterworth lowpass or second
order bandpass filters.
The spreadsheet outputs the required external standard
component values and provides a circuit diagram.
Signal Ground
Both operational amplifiers within the LT1567 are de-
signed for inverting operation (constant common mode
V
IN
R1
R2
C2
C1
U
0.1µF
R3
3
5
2
U
LT1567
Figure 2. 2nd Order Bandpass Filter and Gain Response for f
Gain = 10 (C1 = C2 = 1000pF, R2 = R3 = 1.05k, R1 = 105Ω)
–
+
150Ω
8
W
V
V
+
+
0.1µF
GAIN IS MEASURED TO EITHER OUTPUT ALONE.
IF OUTPUT USED DIFFERENTIALLY, V
–10
–15
–5
25
20
15
10
7pF
5
0
1
50k
6
600Ω
U
–
+
Gain vs Frequency
600Ω
4
V
FREQUENCY (Hz)
–
V
–
0.1µF
500k
input) and they share a single reference node on the chip.
Two pins permit access to this node: DC BIAS and
BYPASS. For a clean reference over a wide bandwidth, the
normal procedure is to connect DC BIAS to a DC potential
or ground and BYPASS to a decoupling capacitor that
returns to a ground plane.
Differential Output Feature
The multiple feedback filter section of Figure 1 inherently
includes two outputs of opposite signal polarity: a DC
inverting output from the OA (Pin 1) and a DC noninverting
OUT
7
+
– V
1567 F02a
OUT
V
V
1567 F02b
OUT
OUT
–
= 2× V
5M
–
+
IN
DESIGN EQUATIONS FOR f
f
MAXIMUM f
GN IS GAIN AT f
f
C1 ≤
CENTER
CENTER
C
= 500kHz,
√GN + 1
2500 • f
IS THE FILTER’S CENTER FREQUENCY
=
2 • π • R2 • C1
CENTER
√GN + 1
C
CENTER
R3 =
= 5MHz/GAIN
2π • C1 • f
= R3/R1, R2 = R3, C1 = C2
CENTER
–3dB BANDWIDTH =
√GN + 1
CENTER
≤ 1MHz
LT1567
f
√GN + 1
CENTER
1567fa
9