Figure 18. Unity Gain Follower
Figure 19. Unity Gain Follower Large Signal Pulse Response
Figure 20. Unity Gain Follower Small Signal Pulse Response
Figure 21. Unity Gain Inverter
Figure 22. Unity Gain Inverter Large Signal Pulse Response
Figure 23. Unity Gain Inverter Small Signal Pulse Response
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.
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 amplifier 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 amplifiers, the AD546’s input current is sensitive to chip temperature, 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.
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 kΩ is recommended. Input current versus additional power dissipation due to output drive current is plotted in Figure 25.
Figure 24. AD546 Input Bias Current vs Ambient Temperature
Figure 25. AD546 Input Bias Current vs. Additional Power Dissipation