lt1568 Linear Technology Corporation, lt1568 Datasheet - Page 11

• Manufacturer Part Number: lt1568
• Description: Very Low Noise, High Frequency Active Rc, Filter Building Block
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
The following filter examples are provided to make it easy
to design a variety of filter stages. Both 2nd and 4th order
filters are shown. For each filer, a table of external resistor
values (standard 1% tolerance) is provided. These resistor
values have been adjusted to compensate for the finite
gain bandwidth product of the LT1568 amplifiers.
To implement a filter, simply connect the resistor values
shown in the table for the cutoff frequency desired. If the
desired cutoff frequency is not shown in the table of
values, use interpolation as recommended in the next
section.
DESIGNING FOR ANY CUTOFF FREQUENCY
To implement a lowpass filter with a cutoff frequency not
included in the design table, resistor values can be inter-
polated in the following manner:
For a Cutoff Frequency, f
Start with the resistor values for f
them up by the ratio of (1MHz/f
U
U
C
, Less Than 1MHz
C
C
).
= 1MHz and then scale
W
U
Example: Implement a 2nd order lowpass Chebyshev filter
with an f
1MHz are R11 = R21 = 976 and R31 825 .
Scaling for f
For a Cutoff Frequency, f
Design Table
Start with the resistor values for the cutoff frequency
closest to the desired one and scale the values up or down
accordingly.
Example: Implement a 2nd order lowpass Chebyshev filter
with an f
for f
Scaling for f
R11 = R21 = 976 • (1MHz/256kHz) 3.83k
R31 = 825 • (1MHz/256kHz) 3.24k
R11 = R21 = 316 • (3MHz/3.2MHz) 294
R31 = 274 • (3MHz/3.2MHz) 255
C
of 3MHz and are R11 = R21 = 316 and R31 = 274 .
C
C
of 3.2MHz. From Table 2 the closest values are
of 256kHz. From Table 2 the values for f
C
C
= 256kHz:
= 3.2MHz:
C
, Between Values Given in a
LT1568
11
C
1568f
of