LMV981-N, LMV982-N

SNOS976L – NOVEMBER 2001 – REVISED MARCH 2013

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In Figure 33 the circuit is referenced to ground, while in Figure 34 the circuit is biased to the positive supply.

These configurations implement the half wave rectifier since the LMV981-N/LMV982 can not respond to one-half

of the incoming waveform. It can not respond to one-half of the incoming because the amplifier can not swing the

output beyond either rail therefore the output disengages during this half cycle. During the other half cycle,

large enough not to load the LMV981-N/LMV982.

Figure 33. Half-Wave Rectifier with Rail-to-Ground Output Swing Referenced to Ground

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 LMV981-N/LMV982 is rail-to-rail and therefore doesn’t have

these disadvantages.

Using three of the LMV981-N/LMV982 amplifiers, an instrumentation amplifier with rail-to-rail inputs and outputs

can be made as shown in Figure 35.

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

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, AN–31, AN–71, and AN–127.

Figure 35. Rail-to-rail instrumentation amplifier

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