LMV324M National Semiconductor, LMV324M Datasheet - Page 15

• Manufacturer Part Number: LMV324M
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LMV324M

• No. Of Amplifiers: 1
• Slew Rate: 1V/µs
• No. Of Pins: 14
• Amplifier Type: Operational
• Mounting Type: Surface Mount
• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Notes
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 MΩ. The gain of this instrumen-
tation amplifier is set by the ratio of R2/R1. R
R
affects the CMRR. For good CMRR over temperature, low
drift resistors should be used. Making R
than R
between R
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
1
4
FIGURE 8. Three-op-amp Instrumentation Amplifier
, and R
FIGURE 9. Two-Op-amp Instrumentation Amplifier
should equal to R
2
and adding a trim pot equal to twice the difference
4
2
equal R
and R
4
2
will allow the CMRR to be adjusted for
1
. Matching of R
and R3 should equal R
(Continued)
3
to R
4
1
slightly smaller
3
and R
2
should equal
10006035
.
10006085
4
10006011
to R
2
15
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
1/2πR
As a result, the output signal is centered around mid-supply
(if the voltage divider provides V
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
low-frequency gains other than unity to be obtained. The
filter has a -20dB/decade roll-off after its corner frequency fc.
R
and R
response of the filter is shown in Figure 12.
IN
2
. The values of R
should be chosen equal to the parallel combination of R
1
FIGURE 10. Single-Supply Inverting Amplifier
3
1
to block the DC signal going into the AC signal source,
C
to minimize errors due to bias current. The frequency
1
.
1
is placed between the inverting input and resis-
1
and C
1
affect the cutoff frequency, fc =
10006020
+
/2 at the non-inverting
3
/R
10006013
1
. This allows
3
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and R
4
is
1