LMV716_15 Datasheet, PDF (16/24 Pages) Texas Instruments – LMV716 5 MHz, Low Noise, RRO, Dual Operational Amplifier with CMOS Input

LMV716
SNOSAT9B – APRIL 2006 – REVISED MARCH 2013
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finite and fairly low closed loop gain. This is while the high frequency signal on the input is still gained up by the
open loop gain of the first amplifier. This makes the first amplifier a high pass filter. The high pass signal is then
fed into a low pass filter. The outcome is a band pass signal, meaning the second amplifier is a band pass filter.
This signal is then fed into the third amplifiers input and so, the third amplifier behaves as a simple low pass
filter.
R₄
R₁
C₂
C₃
V_IN
R₅
-
A₁
+
R₂
V_HP
-
A₂
+
R₃
-
V_BP
A₃
+
V_LP
R₆
Figure 38. State Variable Active Filter
The transfer function of each filter needs to be calculated. The derivations will be more trivial if each stage of the
filter is shown on its own.
The three components are:
R₄
R₁
V_O
R₅
V_IN
R₆
V_O2
R₂
V_O1
-
A₁
+
C₂
-
A₂
+
R₃
V_O2
C₃
-
A₃
+
V_O1
V_O2
VO
For A₁ the relationship between input and output is:
-R₄
R₆ R₁ + R₄
R₅
V_O1 = _{R1 V0} + _{R5 + R6}
R₁
V_IN + _{R5 + R6}
R₁ + R_{4 VO2}
R₁
(22)
16
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