Z
o =
1
R1R2C1C2
fc =
1
2S
Q =
R1C1+R2C1+(1-K)R1C2
R1R2C1C2
VS = 4.75V to 5.5V
OUT
LMP8270
+
-
A1
GND
+IN
-IN
A2
GAIN = 2
A1
A2
R1 =
100 k:
GAIN = 10
PROPRIETARY
LEVEL - SHIFT
CIRCUITRY
C2
C1
R2
1
AVOL
+
R3
R3 + R4
=
1
K
M = s
2C
1C2R1R2 + s(R1C1+R1C2+C1R2) + 1
N = sC2R1
=
VO
VIN
K
M - KN
OBSOLETE
SNOSAK1K – DECEMBER 2004 – REVISED APRIL 2013
With the general transfer function:
where
and
(3)
K represents the sum of DC closed loop gain and the non-ideality behavior of the operational amplifier. Assuming
ideal behavior, the equation for K simply reduces to the DC gain, which is +2 for the LMP8270.
The LMP8270 can be used to realize this configuration as shown in
Figure 29:Figure 29. Low-Pass Filter With LMP8270
Using the filter parameters can be calculated as follows:
(4)
for the LMP8270, R1 = 100 k. Setting R1 = R2 and C1 = C2 results in a low-pass filter with Q = 1. Since the
values of resistors are predetermined, the corner frequency of this implementation of the filter depends on the
capacitor values.
Copyright 2004–2013, Texas Instruments Incorporated
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