AD546

REV. A

–6–

MINIMIZING INPUT CURRENT

The AD546 is guaranteed to have less than 1 pA max input bias

current at room temperature. Careful attention to how the am-

plifier is used will reduce input currents in actual applications.

The amplifier operating temperature should be kept as low as

possible to minimize input current. Like other JFET input am-

plifiers, the AD546’s input current is sensitive to chip tempera-

ture, rising by a factor of 2.3 for every 10

°C rise. This is

illustrated in Figure 24, a plot of AD546 input current versus

ambient temperature.

Figure 24. AD546 Input Bias Current vs

Ambient Temperature

On-chip power dissipation will raise chip operating temperature

causing an increase in input bias current. Due to the AD546’s

low quiescent supply current, chip temperature when the

(unloaded) amplifier is operated with 15 V supplies, is less than

3

°C higher than ambient. The difference in input current is

negligible.

However, heavy output loads can cause a significant increase in

chip temperature and a corresponding increase in input current.

Maintaining a minimum load resistance of 10 k

Ω is recom-

mended. Input current versus additional power dissipation due

to output drive current is plotted in Figure 25.

Figure 25. AD546 Input Bias Current vs.

Additional Power Dissipation

Figure 18. Unity Gain Follower

Figure 21. Unity Gain Inverter

Figure 20. Unity Gain Follower

Small Signal Pulse Response

Figure 23. Unity Gain Inverter

Small Signal Pulse Response

Figure 19. Unity Gain Follower

Large Signal Pulse Response

Figure 22. Unity Gain Inverter

Large Signal Pulse Response