參數(shù)資料
型號(hào): LMV324M
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 運(yùn)算放大器
英文描述: General Purpose, Low Voltage, Rail-to-Rail Output Operational Amplifiers
中文描述: QUAD OP-AMP, 9000 uV OFFSET-MAX, 1 MHz BAND WIDTH, PDSO14
封裝: SOIC-14
文件頁數(shù): 17/27頁
文件大?。?/td> 1151K
代理商: LMV324M
Application Notes
(Continued)
For minimum dc offset, V
+
= V
, the resistor values at both
inverting and non-inverting inputs should be equal, which
means
(8)
From
Equation (1)
and
Equation (8)
, we obtain
(9)
(10)
The values of C
1
and C
2
are normally close to or equal to
As a design example:
Require: A
LP
= 2, Q = 1, fc = 1KHz
Start by selecting C
1
and C
2
. Choose a standard value that
is close to
From
Equations (6), (7), (9), (10)
,
R
1
= 1
R
2
= 1
R
3
= 4
R
4
= 4
The above resistor values are normalized values with
ω
=
1rad/s and C
= C
= C
= 1F. To scale the normalized cut-off
frequency and resistances to the real values, two scaling
factors are introduced, frequency scaling factor (k
f
) and im-
pedance scaling factor (k
m
).
Scaled values:
R
2
= R
1
= 15.9 k
R
3
= R
4
= 63.6 k
C
1
= C
2
= 0.01 μF
An adjustment to the scaling may be made in order to have
realistic values for resistors and capacitors. The actual value
used for each component is shown in the circuit.
4.4.3 2nd-order High Pass Filter
A 2nd-order high pass filter can be built by simply inter-
changing those frequency selective components (R
1
, R
2
,
C
1
, C
2
) in the Sallen-Key 2nd-order active low pass filter. As
shown in
Figure 14
, resistors become capacitors, and ca-
pacitors become resistors. The resulted high pass filter has
the same corner frequency and the same maximum gain as
the previous 2nd-order low pass filter if the same compo-
nents are chosen.
4.4.4 State Variable Filter
A state variable filter requires three op amps. One conve-
nient way to build state variable filters is with a quad op amp,
such as the LMV324 (
Figure 15
).
This circuit can simultaneously represent a low-pass filter,
high-pass filter, and bandpass filter at three different outputs.
The equations for these functions are listed below. It is also
called "Bi-Quad" active filter as it can produce a transfer
function
which
is
quadratic
denominator.
in
both
numerator
and
10006083
FIGURE 14. Sallen-Key 2nd-Order Active High-Pass
Filter
L
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