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OP285GP

Dual 9 MHz Precision Operational Amplifier

Analog Devices 

OP285

+15V

0.1␮F

3+ 8

1/2

1

OP285

2–

4

0.1␮F

*

–15V

+ 7A13 PLUG-IN

– 7A13 PLUG-IN

TTL

INPUT

300pF

15V

1.5k⍀

1k⍀

2N3904

⌬IOUT

|VREF|

1k⍀

1N4148

1.8k⍀

15V

2N2907

1k⍀

220⍀

10␮F

+

0.1␮F

*NOTE

DECOUPLE CLOSE

TOGETHER ON GROUND PLAN

WITH SHORT LEAD LENGTHS.

0.01␮F

0.47␮F

VREF

(–1V)

Figure 5. Transient Output Load Current Test Fixture

A1

100

TTL CTRL 90

(5V/ DIV)

1,2 V

10V

VOUT 10

(2MV/ DIV) 0%

5V

2MV

T

138.9NS

50NS

Measuring Settling Time

The design of OP285 combines high slew rate and wide gain-

bandwidth product to produce a fast-settling (ts < l µs) amplifier

for 8- and 12-bit applications. The test circuit designed to measure

the settling time of the OP285 is shown in Figure 7. This test

method has advantages over false-sum node techniques in that

the actual output of the amplifier is measured, instead of an

error voltage at the sum node. Common-mode settling effects

are exercised in this circuit in addition to the slew rate and

bandwidth effects measured by the false-sum-node method. Of

course, a reasonably flat-top pulse is required as the stimulus.

The output waveform of the OP285 under test is clamped by

Schottky diodes and buffered by the JFET source follower.

The signal is amplified by a factor of ten by the OP260 and

then Schottky-clamped at the output to prevent overloading

the oscilloscope’s input amplifier. The OP41 is configured as

a fast integrator which provides overall dc offset nulling.

High Speed Operation

As with most high speed amplifiers, care should be taken with

supply decoupling, lead dress, and component placement. Rec-

ommended circuit configurations for inverting and noninverting

applications are shown in Figures 8 and Figure 9.

+15V

10␮F

+

0.1␮F

2– 8

1/2

1

VOUT

VIN

3

OP285

+

4

RL

15k⍀

0.1␮F

Figure 6. OP285’s Output Load Current Recovery Time

10␮F

16–20V

–+

0.1␮F

V+

DUT

V–

0.1␮F

+–

16–20V

؎5V

RL

1k⍀

D1

–15V

Figure 8. Unity Gain Follower

+15V

1k⍀

D3

2N4416 1/2 OP260AJ

D2

RF

2k⍀

RG

222⍀

10k⍀

10k⍀

OUTPUT

(TO SCOPE)

D4

1␮F

IC2

1N4148

2N2222A

15k⍀

–15V

750⍀

SCHOTTKY DIODES D1–D4 ARE

HEWLETT-PACKARD HP5082-2835

IC1 IS 1/2 OP260AJ

IC2 IS PMI OP41EJ

Figure 7. OP285’s Settling Time Test Fixture

–8–

REV. A

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