LMV321M5X National Semiconductor, LMV321M5X Datasheet - Page 13

• Manufacturer Part Number: LMV321M5X
• Description: IC,Operational Amplifier,SINGLE,BICMOS,TSOP,5PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LMV321M5X

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Notes
Note that the single-op-amp active filters are used in to the
applications that require low quality factor, Q(
quency ( 5 kHz), and low gain ( 10), or a small value for
the product of gain times Q ( 100). The op amp should have
an open loop voltage gain at the highest frequency of inter-
est at least 50 times larger than the gain of the filter at this
frequency. In addition, the selected op amp should have a
slew rate that meets the following requirement:
where
output peak-to-peak voltage.
4.4.2 Sallen-Key 2nd-Order Active Low-Pass Filter
The Sallen-Key 2nd-order active low-pass filter is illustrated
in Figure 13 . The dc gain of the filter is expressed as
Its transfer function is
FIGURE 12. Frequency Response of Simple Low-Pass
FIGURE 11. Simple Low-Pass Active Filter
H
SlewRate
is the highest frequency of interest, and V
Active Filter in Figure 11
0.5 x (
DS100060-37
H
V
(Continued)
OPP
) x 10
−6
DS100060-15
DS100060-14
V/µsec
10), low fre-
opp
is the
(1)
(2)
13
The following paragraphs explain how to select values for
R
as A
The standard form for a 2nd-order low pass filter is
where
Comparison between the Equation (2) and Equation (3)
yields
To reduce the required calculations in filter design, it is con-
venient to introduce normalization into the components and
design parameters. To normalize, let
C
(4) and Equation (5) . From Equation (4) , we obtain
From Equation (5) , we obtain
For minimum dc offset, V+ = V-, the resistor values at both
inverting and non-inverting inputs should be equal, which
means
From Equation (1) and Equation (8) , we obtain
1
1
Q: Pole Quality Factor
FIGURE 13. Sallen-Key 2nd-Order Active Low-Pass
, R
= C
C
LP
: Corner Frequency
2
, R
, Q, and f
2
= C
3
, R
n
4
= 1F, and substitute these values into Equation
, C
1
c
, and C
.
2
for given filter requirements, such
Filter
C
=
n
= 1rad/s, and
DS100060-16
www.national.com
(3)
(4)
(5)
(6)
(7)
(8)
(9)