LMV934MA National Semiconductor, LMV934MA Datasheet - Page 15

• Manufacturer Part Number: LMV934MA
• Description: IC, OP-AMP, 1.5MHZ, 0.42V/µs, SOIC-14
• Manufacturer: National Semiconductor

Specifications of LMV934MA

• Op Amp Type: Low Power
• No. Of Amplifiers: 4
• Bandwidth: 1.5MHz
• Slew Rate: 0.42V/µs
• Supply Voltage Range: 1.8V To 5.5V
• Amplifier Case Style: SOIC
• No. Of Pins: 14
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

INSTRUMENTATION AMPLIFIER WITH RAIL-TO-RAIL
INPUT AND OUTPUT
Some manufactures make a non-“rail-to-rail”-op amp rail-to-
rail by using a resistive divider on the inputs. The resistors
divide the input voltage to get a rail-to-rail input range. The
problem with this method is that it also divides the signal, so
in order to get the obtained gain, the amplifier must have a
higher closed loop gain. This raises the noise and drift by the
internal gain factor and lowers the input impedance. Any mis-
match in these precision resistors reduces the CMRR as well.
The LMV931/LMV932/LMV934 is rail-to-rail and therefore
doesn’t have these disadvantages.
Using three of the LMV931/LMV932/LMV934 amplifiers, an
instrumentation amplifier with rail-to-rail inputs and outputs
can be made as shown in
In this example, amplifiers on the left side act as buffers to the
differential stage. These buffers assure that the input
impedance is very high and require no precision matched re-
sistors in the input stage. They also assure that the difference
amp is driven from a voltage source. This is necessary to
maintain the CMRR set by the matching R
The gain is set by the ratio of R
and R
4
equal R
2
. With both rail-to-rail input and output ranges,
FIGURE 3. Half-Wave Rectifier with Rail-To-Ground Output Swing Referenced to Ground
FIGURE 4. Half-Wave Rectifier with Negative-Going Output Referenced to V
Figure
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2
/R
5.
1
and R
3
1
should equal R
-R
2
with R
3
-R
4
1
.
15
the input and output are only limited by the supply voltages.
Remember that even with rail-to-rail outputs, the output can
not swing past the supplies so the combined common mode
voltages plus the signal should not be greater that the sup-
plies or limiting will occur. For additional applications, see
National Semiconductor application notes AN–29, AN–31,
AN–71, and AN–127.
FIGURE 5. Rail-to-rail Instrumentation Amplifier
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