LMV792 datasheet(19/21 Pages) NSC

19 / 21 page

Application Notes (Continued)

SENSOR INTERFACES

The low input bias current and low input referred noise of the

LMV791 and LMV792 make them ideal for sensor interfaces.

These circuits are required to sense voltages of the order of

a few µV, and currents amounting to less than a nA, and

hence the op amp needs to have low voltage noise and low

input bias current. Typical applications include infra-red (IR)

thermometry, thermocouple amplifiers and pH electrode

buffers. Figure 15 is an example of a typical circuit used for

measuring IR radiation intensity, often used for estimating

the temperature of an object from a distance. The IR sensor

generates a voltage proportional to I, which is the intensity of

the IR radiation falling on it. As shown in Figure 15,Kisthe

constant of proportionality relating the voltage across the IR

sensor (V

IN) to the radiation intensity, I. The resistances RA

and R

B are selected to provide a high gain to amplify this

voltage, while C

F is added to filter out the high frequency

noise.

20116872

FIGURE 15. IR Radiation Sensor

LMV792 Datasheet(PDF) 19 Page - National Semiconductor (TI)