REV. D

–12–

AD8610/AD8620

diodes greatly interfere with many application circuits such as

precision rectifiers and comparators. The AD8610 is free from

these limitations.

V1

–13V

3

2

7

4

+13V

14V

0

6

AD8610

Figure 16. Unity Gain Follower

No Phase Reversal

Many amplifiers misbehave when one or both of the inputs are

forced beyond the input common-mode voltage range. Phase

reversal is typified by the transfer function of the amplifier,

effectively reversing its transfer polarity. In some cases, this can

cause lockup and even equipment damage in servo systems, and

may cause permanent damage or nonrecoverable parameter

shifts to the amplifier itself. Many amplifiers feature compensation

circuitry to combat these effects, but some are only effective for

the inverting input. The AD8610/AD8620 is designed to prevent

phase reversal when one or both inputs are forced beyond their

input common-mode voltage range.

TIME – 400 s/DIV

0

Figure 17. No Phase Reversal

THD Readings vs. Common-Mode Voltage

Total harmonic distortion of the AD8610/AD8620 is well below

0.0006% with any load down to 600

Ω. The AD8610/AD8620

outperforms the OPA627 for distortion, especially at frequen-

cies above 20 kHz.

FREQUENCY – Hz

0.01

0.0001

10

80k

0.001

0.1

100

1k

10k

OPA627

AD8610

13V

BW = 80kHz

TIME – 400ns/DIV

13V

G = +1

SR = 23V/ s

Figure 14. (+SR) of OPA627 in Unity Gain of +1

The slew rate of an amplifier determines the maximum frequency

at which it can respond to a large signal input. This frequency

(known as full-power bandwidth, or FPBW) can be calculated

from the equation:

FPBW

SR

V

PEAK

=

×

()

2

π

for a given distortion (e.g., 1%).

0V

0V

TIME – 400ns/DIV

Figure 15. AD8610 FPBW

Input Overvoltage Protection

through the negative supply (V–) or the positive supply (V+),

respectively, to the input pins, which can destroy the device. If the

input source can deliver larger currents than the maximum forward

current of the diode (>5 mA), a series resistor can be added to

protect the inputs. With its very low input bias and offset current, a

large series resistor can be placed in front of the AD8610 inputs to

limit current to below damaging levels. Series resistance of 10 k

Ω

will generate less than 25

µV of offset. This 10 kΩ will allow input

voltages more than 5 V beyond either power supply. Thermal noise

generated by the resistor will add 7.5 nV/

√Hz to the noise of the

AD8610. For the AD8610/AD8620, differential voltages equal to

the supply voltage will not cause any problem (see Figure 15).

In this context, it should also be noted that the high breakdown

voltage of the input FETs eliminates the need to include clamp

diodes between the inputs of the amplifier, a practice that is

mandatory on many precision op amps. Unfortunately, clamp