OP-160_15 Datasheet, PDF (16/24 Pages) Analog Devices – High-Speed, Current Feedback Operational Amplifier

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OP-160
a)
b)
INPUT
OUTPUT
INPUT
OUTPUT
FIGURE11: Settling Time Performance oftheOP-160 to 0.1% (a) and 0.01% (b) Av=-1
SETTLING TIME
The test circuit, built on a copper clad circuit board, has a FET
Settling time is the time between when the input signal begins to
input stage which maintains extremely low loading capacitance
change and when the output permanently enters a prescribed
at the artificial sum node. Preceding stages are complementary
error band. Figure 10 illustrates the artificial summing node test
configuration, used to characterize the OP-160 settling time. The
OP-160isset inagainof-1 with a 10VstepinputThe error bands
on the output are 5mV and 0.5mV, respectively, for 0.1% and
0.01% accuracy.
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emitter follower stages, providing adequate drive current for a
5012 oscilloscope input. The OP-97 establishes biasing for the
input stage, and eliminates excessive offset voltage errors.
TRANSIENT OUTPUT IMPEDANCE
Settling characteristics of operational amplifiers also includes an
amplifier's ability to recover, I.e., settle, from a transient current
output load condition. An example of this includes an op amp
driving the input from a SAR type AID converter. Although the
comparison point of the converter is usually diode clamped, the
input swing of plus-and-minus a diode drop still gives rise to a
significant modulation of input current. If the closed-loop output
impedance is low enough and bandwidth of the amplifier is suf-
ficiently large, the output will settle before the converter makes
a comparison decision which will prevent linearity errors or
missing codes.
Figure 12 shows a settling measurement circuit for evaluating
recovery from an output current transient. An output disturbing
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current generator provides the transient change in output load
current of 1mA. As seen in Figure 13, the OP-160 has extremely
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fast recovery of 80ns, (to 0.01%), for a 1mA load transient. The
performance makes it an ideal amplifier for data acquisition
systems.
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TOGETHER ON GROUND PLANE
WITH SHORT LEAD LENGTHS
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FIGURE12: Transient Output Impedance Test Fixture
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FIGURE 13: OP-160's Extremely Fast Recovery Time from a
1mA Load Transient to 1mV (0.01%)
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