Data Sheet

AD8625/AD8626/AD8627

Rev. F | Page 13 of 20

APPLICATIONS INFORMATION

The AD862x is one of the smallest and most economical

JFETs offered. It has true single-supply capability and has

an input voltage range that extends below the negative rail,

allowing the part to accommodate input signals below ground.

The rail-to-rail output of the AD862x provides the maximum

dynamic range in many applications. To provide a low offset,

low noise, high impedance input stage, the AD862x uses

n-channel JFETs. The input common-mode voltage extends

the amplifier, configured in the unity gain buffer, closer than

2 V to the positive rail causes an increase in common-mode

voltage error, as illustrated in Figure 15, and a loss of amplifier

bandwidth. This loss of bandwidth causes the rounding of the

output waveforms shown in Figure 39 and Figure 40, which

The AD862x does not experience phase reversal with input

signals close to the positive rail, as shown in Figure 29. For

AD862x’s noninverting input prevents phase reversal at the

expense of greater input voltage noise. This current-limiting

resistor should also be used if there is a possibility of the input

voltage exceeding the positive supply by more than 300 mV, or

Either of these conditions damages the amplifier if the

condition exists for more than 10 seconds. A 10 kΩ resistor

allows the amplifier to withstand up to 10 V of continuous

overvoltage, while increasing the input voltage noise by a

negligible amount.

TIME (2

INPUT

OUTPUT

4V

4V

0V

0V

Figure 39. Unity Gain Follower Response to 0 V to 4 V Step

TIME (2

INPUT

OUTPUT

4V

0V

5V

0V

Figure 40. Unity Gain Follower Response to 0 V to 5 V Step