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MCP604T-I/ST 开发手册 - Microchip（微芯）
制造商:
Microchip（微芯）
分类:
运算放大器
封装:
TSSOP-14
描述:
MCP604系列 6V 2.8MHz 单电源 CMOS 运算放大器-TSSOP-14
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MCP604T-I/ST数据手册
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2000 Microchip Technology Inc. DS00682C-page 5
AN682
USING THE FUNDAMENTALS
Instrumentation Amplifier
Instrumentation amplifiers are found in a large variety
of applications from medical instrumentation to process
control. The instrumentation amplifier is similar to the
difference amplifier in that it subtracts one analog sig-
nal from another, but it differs in terms of the quality of
the input stage. A classic, three op amp instrumenta-
tion amplifier is illustrated in Figure 9.
Figure 9: An instrumentation amplifier can be
designed using three amplifiers. The input operational
amplifiers provide signal gain. The output operational
amplifier converts the signal from two inputs to a
single ended output with a difference amplifier.
With this circuit the two input signals are presented to the
high impedance non-inverting inputs of the amplifiers.
This is a distinct advantage over the difference amplifier
configuration when source impedances are high or mis-
matched. The first stage also gains the two incoming sig-
nals. This gain is simply adjusted with one resistor, R
G
.
Following the first stage of this circuit is a difference
amplifier. The function of this portion of the circuit is to
reject the common mode voltage of the two input sig-
nals as well as differentiate them. The source imped-
ances of the signals into the input of the difference
amplifier are low, equivalent and well controlled.
The reference voltage of the difference stage of this
instrumentation amplifier is capable of spanning a wide
range. Most typically this node is referenced to half of
the supply voltage in a signal supply application. A sup-
ply splitter such as the circuit in Figure 5 can be used
for this purpose. The transfer function of this circuit is:
A second instrumentation amplifier is shown in
Figure 10. In this circuit, the two amplifiers serve the
functions of load isolation, and signal gain. The second
amplifier also differentiates the two signals.
Figure 10: An instrumentation amplifier can be
designed using two amplifiers. This configuration is
best suited for higher gains. (gain > 3 V/V)
The circuit reference voltage is supplied to the first op
amp in the signal chain. Typically, this voltage is half of
the supply voltage in a single supply environment.
The transfer function of this circuit is:
Floating Current Source
A floating current source can come in handy when driv-
ing a variable resistance, like an Resistive Temperature
Device (RTD). This particular configuration produces
an appropriate 1mA source for an RTD type sensor,
however, it can be tuned to any current.
Figure 11: A floating current source can be
constructed using two operational amplifiers and a
precision voltage reference.
*Bypass Capacitor, 1µF
V
2
R
4
R
3
V
OUT
R
G
MCP602
V
1
R
2
R
2
R
4
R
3
*
*
V
OUT
V
1
V
2
–()1
2R
2
R
G
---------+
R
4
R
3
------
V
REF
R
4
R
3
------
+=
V
REF
V
DD
V
DD
1
/
2
MCP602
1
/
2
MCP602
1
/
2
V
OUT
V
1
V
2
–()1
2R
2
R
G
---------+
R
4
R
3
------
V
REF
R
4
R
3
------
+=
*
V
OUT
*Bypass Capacitor, 0.1µF
V
REF
V
2
R
G
R
1
V
OUT
V
1
V
2
–()1
R
1
R
2
------
2R
1
R
G
---------++
V
REF
+=
V
1
R
2
R
1
R
2
V
DD
MCP602
1
/
2
MCP602
1
/
2
V
OUT
V
1
V
2
–()1
R
1
R
2
------
2R
1
R
G
---------++
V
REF
+=
I
OUT
R
1
*
R
1
R
1
R
1
V
REF=2.5
V
RTD
V
REF
- 2V
R1
2 (V
REF
- 2V
R1
)
R
l
=2.5kΩ
+V
R1
I
OUT
V
REF
R
L
-------------=
*Bypass Capacitor, 1µF
R
1
=25kΩ
MCP602
1
/
2
MCP602
V
DD
1
/
2
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