MCP602

Manufacturer Part NumberMCP602
DescriptionMCP601-2-3-4
ManufacturerN/A
MCP602 datasheet
 


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3.7.2
INSTRUMENTATION AMPLIFIER
CIRCUITS
Instrumentation amplifiers have a differential input,
which subtracts one input voltage from another and
rejects common mode signals. These amplifiers also
provide a single-ended output voltage.
The three op amp instrumentation amplifier is
illustrated in Figure 3-7. One advantage of this
approach is unity-gain operation. A disadvantage is
that the common mode input range is reduced as
R
/R
gets larger.
2
G
V
1
R
R
3
4
MCP60X
MCP60X
R
2
R
G
R
R
R
2
3
4
MCP60X
V
2
2R
R
2
4
V
= (V
- V
)
1 +
OUT
1
2
R
R
G
3
FIGURE 3-7:
Three op amp
instrumentation amplifier.
The two op amp instrumentation amplifier is shown in
Figure 3-8. Its power consumption is lower than the
three op amp version. Its main drawbacks are that the
common mode range is reduced with higher gains and
it must be configured in gains of two or higher.
R
G
R
R
R
1
2
2
V
REF
MCP60X
MCP60X
V
2
V
1
R
2R
1
1
V
= (V
- V
)
1 +
+
OUT
1
2
R
R
2
G
FIGURE 3-8:
Two op amp instrumentation
amplifier.
Both instrumentation amplifiers should use a bulk
bypass capacitor of at least 1 µF. The CMRR of these
amplifiers will be set by the op amp CMRR and by
resistor matching.
2003 Microchip Technology Inc.
3.7.3
PHOTO DETECTION
The MCP601/2/3/4 op amps can be used to easily
convert the signal from a sensor that produces an
output current (such as a photo diode) into a voltage (a
transimpedance amplifier). This is implemented with a
single resistor (R
amplifiers shown in Figure 3-9 and Figure 3-10. The
optional capacitor (C
these circuits.
A photodiode configured in the photovoltaic mode has
zero voltage potential placed across it (Figure 3-9). In
this mode, the light sensitivity and linearity is
maximized, making it best suited for precision
applications. The key amplifier specifications for this
application are: low input bias current, low noise,
common mode input voltage range (including ground)
and rail-to-rail output.
V
OUT
V
REF
I
D1
Light
+ V
REF
FIGURE 3-9:
In contrast, a photodiode that is configured in the
photoconductive mode has a reverse bias voltage
across the photo sensing element (Figure 3-10). This
decreases the diode capacitance, which facilitates
high-speed
operation
communications). The design trade off is increased
diode leakage current and linearity errors. The op amp
V
OUT
needs to have a wide Gain Bandwidth Product.
R
1
I
D1
Light
+ V
REF
V
FIGURE 3-10:
Detector.
MCP601/2/3/4
) in the feedback loop of the
2
) sometimes provides stability for
2
C
2
R
2
V
OUT
V
DD
D1
MCP60X
V
= I
R
OUT
D1
2
Photovoltaic mode detector.
(e.g.,
high-speed
digital
C
2
R
2
V
OUT
V
DD
D
1
MCP60X
V
= I
R
OUT
D1
2
BIAS
V
< 0V
BIAS
Photoconductive Mode
DS21314E-page 13