BRIDGE CONFIGURATION AMPLIFIER

Some applications may benefit from doubling the voltage

across the load. With V

providea2V

300

Ω. The output stage of the LMV951 enables it to drive a

load of 120

Ω and still swing at least 70% of the supply rails.

The bridge configuration shown in Figure 4 enables the

amplifier to maintain a low dropout voltage thus maximizing

its dynamic range. It has been configured in a gain of 1 and

uses the fewest number of parts.

Resistor values have been selected to keep the current

consumption to a minimum and voltage errors due to bias

currents negligible. Using the selected resistor values makes

this circuit quite practical in a battery operated design. R

and R

the accuracy of the resistor values will establish how well the

two virtual grounds match. Any errors in the virtual grounds

will show as current across R

AC coupling the input signal sets the DC bias point of this

signal to the virtual ground of the circuit. Using the large

resistor values witha1µF capacitor (C

rolloff of this circuit below 10 Hz.

•

C

located as close as possible to pin 6, the V

covered in the power supply bypassing section these

capacitors must have low ESR and a self resonant fre-

quency above 15 MHz.

•

C

also be located close to the supply pin.

•

To use the shutdown feature tie pin 5 of the two parts

together and connect through a 470 k

Add a switch between pin 5 and ground. Closing the

switch keeps the parts in the active mode, opening the

switch sets the parts in the shutdown mode without add-

ing any additional current to V

VIRTUAL GROUND CIRCUIT

The front page of this data sheet shows the LMV951 being

used in a system establishing a virtual ground. Having a

buffered output stage gives this part the ability to handle load

currents higher than 35 mA at 1V.

R

To maintain low noise the values should be between 1 k

Ω

and 10 k

Ω.C

for the LMV951. These caps must be placed as close as

possible to pins 2 and 6.

TWO WIRE LINE TRANSMISSION

The robust output stage of the LMV951 makes it an excellent

choice for driving long cables. The circuit shown below in

Figure 5 can drive a long cable using only two wires; power

and ground.

When many sensors are located remotely from the control

area the wiring becomes a significant expense. Using only

two wires helps minimize the wiring expense in a large

project such as an industrial plant. Figure 6 shows a 25 kHz

signal after passing though 1000 ft. of twisted pair cable.

Figure 7 shows a 200 kHz signal after passing through 50 ft.

of twisted pair cable.

20123144

FIGURE 4. Bridge Amplifier

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