AD8698 데이터 시트보기 (PDF) - Analog Devices
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AD8698 Datasheet PDF : 20 Pages
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10M
1M
100k
10k
1k
1
10
100
LOAD CAPACITANCE (nF)
Figure 52. Unity Gain Bandwidth vs. Load Capacitance
Figure 52 shows the unity gain bandwidth as a function of load
capacitance.
INSTRUMENTATION AMPLIFIER
Instrumentation amplifiers are used in applications requiring
precision, accuracy, and high CMRR. One popular application
is signal conditioning in process control, test automation, and
measurement instrumentation, where the amplifier is used to
amplify small signals.
The triple op amp implementation uses the AD8698 at the
front end with the OP184 for optimum accuracy.
The circuit in Figure 53 enjoys a high overall gain, excellent dc
performance, high CMRR, as well as the benefit of an output
that swings to the supplies.
The CMRR of the in-amp will be limited by the choice of
resistor tolerance. R5 is an optional potentiometer that can be
used to calibrate the circuit for maximum gain. R7 can be
trimmed for optimum CMRR.
The output voltage is given by:
VO
=VIN ⎜⎝⎛1 +
2R3
R4
⎟⎠⎞⎜⎝⎛
R2
R1
⎟⎠⎞
AD8698
R1
V1
V+
1kΩ
V–
1/2 AD8698 R3
9kΩ
R2
10kΩ
R4
2kΩ
R5
10kΩ
V+
V–
OP184
R3
9kΩ
V–
V2
V+
1/2 AD8698
R1
9.8kΩ
R7
400Ω
Figure 53. Three Op Amp In-Amp
COMPOSITE AMPLIFIER
The dc accuracy of the AD8698 and the ac performance of the
OP184 are combined in the circuit shown in Figure 54. The
composite amplifier provides a higher bandwidth, a lower offset
voltage, and a higher loop, thereby reducing the gain error
substantially.
The circuit shown exhibits a total output rms noise of less than
500 µV, corresponding to less than 3 mV of peak-to-peak noise
over approximately a 3 MHz bandwidth. Cf is used to minimize
peaking.
The circuit has an inverting gain of 10. In applications with
higher closed-loop gains, Cf is necessary to maintain a
sufficient phase margin and ensure stability. This results in a
narrower closed-loop bandwidth.
R1
1kΩ
VIN
R2
10kΩ
Cf
20pF
V–
V–
V+
V+
1/2 AD8698
OP184
Figure 54. Composite Amplifier Circuit
Rev. 0 | Page 15 of 20
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