lmv358-mda National Semiconductor Corporation, lmv358-mda Datasheet - Page 15

• Manufacturer Part Number: lmv358-mda
• Description: General Purpose, Low Voltage, Rail-to-rail Output Operational Amplifiers
• Manufacturer: National Semiconductor Corporation

Instrumentation Circuits
The input impedance of the previous difference amplifier is
set by the resistors R
lems of low input impedance, one way is to use a voltage
follower ahead of each input as shown in the following two
instrumentation amplifiers.
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 voltage followers.
These two voltage followers assure that the input impedance
is over 100 MΩ. The gain of this instrumentation amplifier is
set by the ratio of R
R
good CMRR over temperature, low drift resistors should be
used. Making R
pot equal to twice the difference between R
the CMRR to be adjusted for optimum performance.
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
2
4
FIGURE 8. Three-Op-Amp Instrumentation Amplifier
. Matching of R
should equal R
4
3
slightly smaller than R
1
to R
and, R
2
1
/R
, R
1
1
. R
2
and R
, R
3
3
should equal R
3
should equal R
, and R
4
to R
4
2
. To eliminate the prob-
affects the CMRR. For
2
and adding a trim
2
2
and R
.
1
, and R
4
will allow
10006085
4
equal
15
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
R
V
1/2πR
As a result, the output signal is centered around mid-supply
(if the voltage divider provides V
The output can swing to both rails, maximizing the signal-to-
noise ratio in a low voltage system.
IN
1
FIGURE 9. Two-Op-Amp Instrumentation Amplifier
. The values of R
to block the DC signal going into the AC signal source,
FIGURE 10. Single-Supply Inverting Amplifier
1
C
1
.
1
is placed between the inverting input and resistor
1
and C
1
affect the cutoff frequency, fc =
+
10006020
/2 at the non-inverting input).
10006013
10006035
www.national.com
3
and R
10006011
4
is