Data Sheet

ADA4001-2

Rev. B | Page 11 of 12

INPUT BIAS CURRENT

Because the ADA4001-2 has a JFET input stage, the input bias

current, due to the reverse-biased junction, has a leakage

current that approximately doubles every 10°C. The power

dissipation of the part, combined with the thermal resistance of

the package, results in the junction temperature increasing 30°C

above ambient. This parameter is tested with high speed ATE

equipment, which does not result in the die temperature

reaching equilibrium. This is correlated with bench

measurements to match the guaranteed maximum at room

temperature in Table 1.

The input current can be reduced by keeping the temperature as

low as possible and using a light load on the output.

NOISE CONSIDERATIONS

The JFET input stage offers very low input voltage noise and

input current noise. The thermal noise of a 1 kΩ resistor at

room temperature is 4 nV/√Hz, thus low values of resistance

should be used for dc-coupled inverting and noninverting

amplifier configurations. In the case of transimpedance

amplifiers (TIAs), current noise is more important.

The ADA4001-2 is an excellent choice for both of these

applications. Analog Devices, Inc., offers a wide variety of low

voltage noise and low current noise op amps in a variety of

processes optimized for different supply voltage ranges. Refer

to the AN-940 Application Note for a complete discussion of

noise, calculations, and selection tables for more than three

dozen low noise, op amp families.