參數(shù)資料
型號(hào): LMV324MTX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類(lèi): 運(yùn)動(dòng)控制電子
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: TSSOP-14
文件頁(yè)數(shù): 15/27頁(yè)
文件大?。?/td> 1151K
代理商: LMV324MTX
Application Notes
(Continued)
4.2.1 Three-Op-Amp Instrumentation Amplifier
The quad LMV324 can be used to build a three-op-amp
instrumentation amplifier as shown in
Figure 8
.
The first stage of this instrumentation amplifier is a
differential-input, differential-output amplifier, with two volt-
age followers. These two voltage followers assure that the
input impedance is over 100 M
. The gain of this instrumen-
tation amplifier is set by the ratio of R2/R1. R
3
should equal
R
, and R
equal R
. Matching of R
to R
and R
to R
2
affects the CMRR. For good CMRR over temperature, low
drift resistors should be used. Making R
slightly smaller
than R
and adding a trim pot equal to twice the difference
between R
2
and R
4
will allow the CMRR to be adjusted for
optimum.
4.2.2 Two-op-amp Instrumentation Amplifier
A two-op-amp instrumentation amplifier can also be used to
make a high-input-impedance dc differential amplifier (
Fig-
ure 9
) . As in the three-op-amp circuit, this instrumentation
amplifier requires precise resistor matching for good CMRR.
R
4
should equal to R
1
and R3 should equal R
2
.
4.3 Single-Supply Inverting Amplifier
There may be cases where the input signal going into the
amplifier is negative. Because the amplifier is operating in
single supply voltage, a voltage divider using R
and R
is
implemented to bias the amplifier so the input signal is within
the input common-mode voltage range of the amplifier. The
capacitor C
1
is placed between the inverting input and resis-
tor R
1
to block the DC signal going into theAC signal source,
V
IN
. The values of R
1
and C
1
affect the cutoff frequency, fc =
1/2
π
R
1
C
1
.
As a result, the output signal is centered around mid-supply
(if the voltage divider provides V
+
/2 at the non-inverting
input). The output can swing to both rails, maximizing the
signal-to-noise ratio in a low voltage system.
4.4 ACTIVE FILTER
4.4.1 Simple Low-Pass Active Filter
The simple low-pass filter is shown in
Figure 11
. Its low-
frequency gain (
ω →
0) is defined by -R
/R
. This allows
low-frequency gains other than unity to be obtained. The
filter has a -20dB/decade roll-off after its corner frequency fc.
R
should be chosen equal to the parallel combination of R
1
and R
to minimize errors due to bias current. The frequency
response of the filter is shown in
Figure 12
.
10006085
FIGURE 8. Three-op-amp Instrumentation Amplifier
10006011
10006035
FIGURE 9. Two-Op-amp Instrumentation Amplifier
10006013
10006020
FIGURE 10. Single-Supply Inverting Amplifier
L
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