SSM2275/SSM2475

REV. A

–11–

FREQUENCY – kHz

–100

–130

–160

022

10

20

–110

–120

–140

–150

FREQUENCY – kHz

–100

–130

–160

022

10

20

–110

–120

–140

–150

Figure 31. Spectral Graph of Amplifier Outputs

Settling Time

The high slew rate and wide gain-bandwidth product of the

SSM2275 and SSM2475 amplifiers result in fast settling times

µs) that are suitable for 16- and 20-bit applications. The

test circuit used to measure the settling time of the SSM2275/

SSM2475 is shown in Figure 32. This test method has advan-

tages over false-sum node techniques of measuring settling times

in that the actual output of the amplifier is measured, instead of

an error voltage at the sum node. Common-mode settling ef-

fects are also taken into account in this circuit in addition to

slew rate and bandwidth factors.

The output waveform of the device 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 current feed-

back amplifier and then Schottky-clamped at the output to the

oscilloscope. The 2N2222 transistor sets up the bias current for

the JFET and the OP41 is configured as a fast integrator, pro-

viding overall dc offset nulling at the output.

SETTLING TIME – ns

10

6

–10

400

600

800

1000

1200

2

–2

–6

8

4

0

–4

–8

–0.01%

0.1%

0.01%

Figure 33. Settling Time vs. Step Size

Overdrive Recovery

The overdrive, or overload, recovery time of an amplifier is the time

required for the output voltage to return to a rated output voltage

from a saturated condition. This recovery time can be important in

applications where the amplifier must recover quickly after a large

transient event, or overload. The circuit in Figure 34 was used to

evaluate the recovery time for the SSM2275/SSM2475. Also shown

are the input and output voltages. It takes approximately 0.5

µs for

the device to recover from output overload.

R1

1k

909

10k

+5V

–5V

10k

2V p-p

10kHz

Figure 34. Overload Recovery Time Test Circuit

9V–15V

0.1 F

V+

5V

1k

D1

D2

+15V

2N4416

1k

D3

D4

OUTPUT

(TO SCOPE)

1 F

10k

IC2

2k

750

2N2222A

15k

–15V

1N4148

DUT

1/2 OP260AJ

9V–15V

0.1 F

10k

–+

+

–

SCHOTTKY DIODES D1–D4 ARE

HEWLETT-PACKARD HP5082-2835

IC1 IS 1/2 OP260AJ

IC2 IS PMI OP41EJ

V–

222

Figure 32. Settling Time Test Fixture