LTC1563-2_15 Datasheet, PDF (14/20 Pages) Linear Technology – Active RC, 4th Order Lowpass Filter Family

LTC1563-2/LTC1563-3
APPLICATIONS INFORMATION
4th Order Filter Responses Using the LTC1563-3
R31
R21
R11
V_IN
LTC1563-3
1
LP
2
SA
3
NC
4
INVA
5
NC
6
LPA
7
AGND
8 _V–
V^{+ 16}
15
LPB
14
NC
13
INVB
12
NC
11
SB
10
NC
9
EN
R22
V_OUT
R32
R12
1563 F06
Figure 6. 4th Order Filter Connections (Power Supply, Ground,
EN and LP Connections Not Shown for Clarity). Table 2 Shows
Resistor Values
10
0
–20
–40
BESSEL
TRANSITIONAL
–60
GAUSSIAN TO 12dB
TRANSITIONAL
GAUSSIAN TO 6dB
–80
NORMALIZED TO f_C = 1Hz
–90
0.1
1
10
FREQUENCY (Hz)
1563 F06a
Figure 6a. Frequency Response
1.2
1.0
0.8
0.6
0.4
0.2
0
0
BESSEL
TRANSITIONAL
GAUSSIAN TO 12dB
TRANSITIONAL
GAUSSIAN TO 6dB
NORMALIZED TO f_C = 1Hz
0.5 1.0 1.5 2.0
TIME (s)
2.5 3.0
1563 F06b
Figure 6b. Step Response
1.05
BESSEL
TRANSITIONAL
GAUSSIAN TO 12dB
TRANSITIONAL
GAUSSIAN TO 6dB
1.00
0.95
0
NORMALIZED TO f_C = 1Hz
0.5
1.0
1.5
2.0
TIME (s)
1563 F06c
Figure 6c. Step Response—Settling
14
Table 2. Resistor Values, Normalized to 256kHz Cutoff Frequency (f_C), Figure 6. The Passband
Gain, of the 4th Order LTC1563-3 Lowpass Filter, Is Set to Unity. (Note 1)
BESSEL
TRANSITIONAL
GAUSSIAN TO 6dB
TRANSITIONAL
GAUSSIAN TO 12dB
LP Mode Max f_C
HS Mode Max f_C
R11 = R21 =
R31 =
R12 = R22 =
R32 =
25.6kHz
256kHz
10k(256kHz/f_C)
10k(256kHz/f_C)
10k(256kHz/f_C)
10k(256kHz/f_C)
20kHz
175kHz
17.4k(256kHz/f_C)
13.3k(256kHz/f_C)
14.3k(256kHz/f_C)
6.04k(256kHz/f_C)
21kHz
185kHz
15k(256kHz/f_C)
11.8k(256kHz/f_C)
10.5k(256kHz/f_C)
6.19k(256kHz/f_C)
Note 1: The resistor values listed in this table provide good approximations of the listed transfer functions. For the
optimal resistor values, higher gain or other transfer functions, use FilterCAD Version 3.0 (or newer) or contact the
Linear Technology Filter Applications group for assistance.
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