Datasheet

LMV931-N, LMV931-N-Q1, LMV932-N, LMV932-N-Q1
LMV934-N, LMV934-N-Q1
www.ti.com SNOS993M –NOVEMBER 2001–REVISED NOVEMBER 2013
Figure 31. Half-Wave Rectifier with Negative-Going Output Referenced to V
CC
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 mismatch in these
precision resistors reduces the CMRR as well. The LMV931-N/LMV932-N/LMV934-N is rail-to-rail and therefore
doesn’t have these disadvantages.
Using three of the LMV931-N/LMV932-N/LMV934-N amplifiers, an instrumentation amplifier with rail-to-rail inputs
and outputs can be made as shown in Figure 32.
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 resistors 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
1
-R
2
with R
3
-R
4
. The gain is set by the ratio of R
2
/R
1
and R
3
should equal R
1
and R
4
equal R
2
. With both rail-to-
rail input and output ranges, 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 supplies or limiting will occur. For additional applications, see Texas
Instruments application notes AN–29 (SNOA625), AN–31 (SNLA140), AN–71 (SNOA652), and AN–127
(SNVA516).
Figure 32. Rail-to-rail Instrumentation Amplifier
Copyright © 2001–2013, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: LMV931-N LMV931-N-Q1 LMV932-N LMV932-N-Q1 LMV934-N LMV934-N-Q1