LMV321M5X National Semiconductor, LMV321M5X Datasheet - Page 12

• 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

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Application Notes
4.2 Instrumentation Circuits
The input impedance of the previous difference amplifier is
set by the resistors R
problems of low input impedance, one way is to use a volt-
age follower ahead of each input as shown in the following
two instrumentation amplifiers.
4.2.1 Three-op-amp Instrumentation Amplifier
The quad LMV324 can be used to build a three-op-amp in-
strumentation 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 R
R
fects the CMRR. For good CMRR over temperature, low drift
resistors should be used. Making R
2
R
1
and adding a trim pot equal to twice the difference between
2
FIGURE 8. Three-op-amp Instrumentation Amplifier
, and R
and R
4
4
equal R
will allow the CMRR to be adjusted for optimum.
FIGURE 7. Difference Amplifier
2
. Matching of R
1
, R
2
, R
3
(Continued)
, and R
4
3
2
slightly smaller than R
to R
/R
4
1
. To eliminate the
1
. R
DS100060-7
and R
DS100060-19
3
should equal
4
DS100060-85
to R
2
af-
12
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.
R4 should equal to R1 and R3 should equal R2.
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
implemented to bias the amplifier so the input signal is within
the input common-mode voltage range of the amplifier. The
capacitor C
tor R
V
= 1/2 R
As a result, the output signal is centered around mid-supply
(if the voltage divider provides V
put). 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 (
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
R
sponse of the filter is shown in Figure 12 .
IN
3
FIGURE 9. Two-Op-amp Instrumentation Amplifier
. The values of R
to minimize errors due to bias current. The frequency re-
1
FIGURE 10. Single-Supply Inverting Amplifier
to block the DC signal going into the AC signal source,
1
C
1
1
.
is placed between the inverting input and resis-
1
0) is defined by -R
and C
DS100060-20
1
affect the cutoff frequency, fc
+
/2 at the non-inverting in-
3
/R
1
. This allows low-
DS100060-13
DS100060-35
3
and R
DS100060-11
1
and
4
is
2