Datasheet

C
C2
R
B1
R
B2
C
F
C
C1
V
+
A
V
= 1 +
R
2
R
1
+
-
V
IN
+
-
R
1
1 k:
R
2
1 M:
V
OUT
+
-
= 1001
C
C1
+
V
OUT
+
-
-
C
F
V
IN
+
-
R
B1
V
+
R
B2
C
C2
R
2
R
1
A
V
=
-
R
2
100 k:
R
1
1 k:
= -100
LMV651, LMV652, LMV654
www.ti.com SNOSAI7J –SEPTEMBER 2005–REVISED MARCH 2013
Figure 42. High Gain Inverting Amplifier
Figure 43. High Gain Non-Inverting Amplifier
ACTIVE FILTERS
With a wide unity gain bandwidth of 12 MHz, low input referred noise density and a low power supply current, the
LMV651/LMV652/LMV654 are well suited for low-power filtering applications. Active filter topologies, like the
Sallen-Key low pass filter shown in Figure 44, are very versatile, and can be used to design a wide variety of
filters (Chebyshev, Butterworth or Bessel). The Sallen-Key topology, in particular, can be used to attain a wide
range of Q, by using positive feedback to reject the undesired frequency range.
In the circuit shown in Figure 44, the two capacitors appear as open circuits at lower frequencies and the signal
is simply buffered to the output. At high frequencies the capacitors appear as short circuits and the signal is
shunted to ground by one of the capacitors before it can be amplified. Near the cut-off frequency, where the
impedance of the capacitances is on the same order as R
g
and R
f
, positive feedback through the other capacitor
allows the circuit to attain the desired Q. The ratio of the two resistors, m
2
, provides a knob to control the value of
Q obtained.
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