TL087, TL088, TL287, TL288

JFET-INPUT OPERATIONAL AMPLIFIERS

SLOS082A – D2484, MARCH 1979 – REVISED JANUARY 1993

POST OFFICE BOX 655303

19

TYPICAL APPLICATION DATA

input characteristics

These amplifiers are specified with a minimum and a maximum input voltage that, if exceeded at either input,

could cause the device to malfunction.

Because of the extremely high input impedance and resulting low bias current requirements, these amplifiers

are well suited for low-level signal processing; however, leakage currents on printed circuit boards and sockets

can easily exceed bias current requirements and cause degradation in system performance. It is good practice

to include guard rings around inputs (see Figure 45). These guards should be driven from a low-impedance

source at the same voltage level as the common-mode input.

+

–

VO

VO

VO

VI

VI

(a) NONINVERTING AMPLIFIER

(b) INVERTING AMPLIFIER

(c) UNITY–GAIN AMPLIFIER

VI

Figure 45. Use of Guard Rings

noise performance

The noise specifications in op amp circuits are greatly dependent on the current in the first-stage diflferential

amplifier. The low input bias current requirments of these amplifiers result in a very low current noise. This

feature makes the devices especially favorable over bipolar devices when using values of circuit impedance

greater than 50 k

Ω.