AD8610/AD8620

Slew Rate (Unity Gain Inverting vs. Noninverting)

Amplifiers generally have a faster slew rate in an inverting unity

G= –1

gain configuration due to the absence of the differential input

SR = 54V/µs

TIME (400ns/DIV)

capacitance. Figure 49 through Figure 52 show the performance

of the AD8610/AD8620 configured in a gain of –1 compared to

the OPA627. The AD8610/AD8620 slew rate is more symmetrical,

and both the positive and negative transitions are much cleaner

than in the OPA627.

V

R

G = –1

SR = 54V/µs

Figure 51. –Slew Rate of AD8610/AD8620 in Unity Gain of –1

G= –1

SR = 56V/µs

TIME (400ns/DIV)

Figure 49. +Slew Rate of AD8610/AD8620 in Unity Gain of –1

G= –1

TIME (400ns/DIV)

SR = 42.1V/µs

Figure 52. –Slew Rate of OPA627 in Unity Gain of –1

The AD8610/AD8620 have a very fast slew rate of 60 V/μs even

when configured in a noninverting gain of +1. This is the toughest

condition to impose on any amplifier since the input common-

mode capacitance of the amplifier generally makes its SR appear

worse. The slew rate of an amplifier varies according to the voltage

difference between its two inputs. To observe the maximum SR,

a voltage difference of about 2 V between the inputs must be

TIME (400ns/DIV)

ensured. This is required for virtually any JFET op amp so that

Figure 50. +Slew Rate of OPA627 in Unity Gain of –1

one side of the op amp input circuit is completely off, thus maxi­

mizing the current available to charge and discharge the internal

compensation capacitance. Lower differential drive voltages

produce lower slew rate readings. A JFET input op amp with a

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