AMP02E 데이터 시트보기 (PDF) - Analog Devices
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AMP02E Datasheet PDF : 12 Pages
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AMP02
+IN
3
RG2
8
RG
RG1
1
–IN
2
V1 25k⍀
R
25k⍀
R
25k⍀
25k⍀
V2
25k⍀
25k⍀
SENSE
(SOIC-16 ONLY)
6
OUT
5
REFERENCE
Figure 4. Triple Op Amp Topology
Figure 4 shows the triple op amp configuration of the AMP02.
With all instrumentation amplifiers of this type, it is critical not
to exceed the dynamic range of the input amplifiers. The ampli-
fied differential input signal and the input common-mode volt-
age must not force the amplifier’s output voltage beyond ± 12 V
(VS = ± 15 V) or nonlinear operation will result.
The input stage amplifier’s output voltages at V1 and V2 equal:
V1
=
–1
+
2R VD
RG 2
+ VCM
=
–G VD
2
+ VCM
V2
=
1
+
2R VD
RG 2
+ VCM
=
G VD
2
+ VCM
where:
VD = Differential input voltage
= (+IN) – (–IN)
VCM = Common-mode input voltage
G = Gain of instrumentation amplifier
If V1 and V2 can equal ± 12 V maximum, the common-mode
input voltage range is:
CMVR
=
±
12 V
−
GVD
2
Grounding
The majority of instruments and data acquisition systems have
separate grounds for analog and digital signals. Analog ground may
also be divided into two or more grounds that will be tied together
at one point, usually at the analog power supply ground. In
addition, the digital and analog grounds may be joined—normally
at the analog ground pin on the A/D converter. Following this
basic practice is essential for good circuit performance.
Mixing grounds causes interactions between digital circuits and the
analog signals. Since the ground returns have finite resistance
and inductance, hundreds of millivolts can be developed between
the system ground and the data acquisition components. Using
separate ground returns minimizes the current flow in the sensitive
analog return path to the system ground point. Consequently, noisy
ground currents from logic gates interact with the analog signals.
Inevitably, two or more circuits will be joined together with
their grounds at differential potentials. In these situations, the
differential input of an instrumentation amplifier, with its high
CMR, can accurately transfer analog information from one
circuit to another.
Sense and Reference Terminals
The sense terminal completes the feedback path for the instrumen-
tation amplifier output stage and is internally connected directly
to the output. For SOIC devices, connect the sense terminal to
the output. The output signal is specified with respect to the refer-
ence terminal, which is normally connected to analog ground.
The reference may also be used for offset correction level shift-
ing. A reference source resistance will reduce the common-mode
rejection by the ratio of 25 kΩ/RREF. If the reference source resis-
tance is 1 Ω, the CMR will be reduced 88 dB (25 kΩ/1 Ω = 88 dB).
REV. E
–9–
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