MCP601-E/SL Microchip Technology, MCP601-E/SL Datasheet - Page 13

• Manufacturer Part Number: MCP601-E/SL
• Description: 2.7V to 5.5V Single Supply CMOS Op Amps
• Manufacturer: Microchip Technology

3.7.2
Instrumentation amplifiers have a differential input that
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, while one disadvantage is that the
common mode input range is reduced as R
larger.
FIGURE 3-7:
Instrumentation Amplifier.
The two-op amp instrumentation amplifier is shown in
Figure 3-8. While 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.
FIGURE 3-8:
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 both the op amp CMRR and
resistor matching.
2004 Microchip Technology Inc.
V
V
V
V
V
1
2
REF
2
1
V
V
R
R
O UT
+
MCP60X
–
–
MCP60X
+
OU T
G
1
INSTRUMENTATION AMPLIFIER
CIRCUITS
R
R
=
=
2
2
+
MCP60X
-
V
V
1
1
R
–
–
2
V
V
Three-Op Amp
R
Two-Op Amp
2
2
R
R
G
3
3
1
1
+
+
R
R
----- -
R
2R
-------- -
R
–
MCP60X
+
2
1
2
G
2
+
R
R
2R
-------- -
R
R
----- -
R
4
4
G
MCP60X
-
4
3
+
1
+
+
V
R
REF
V
V
1
REF
REF
2
V
/R
V
OUT
G
OUT
gets
3.7.3
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.
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
communications). The design trade-off is increased
diode leakage current and linearity errors. The op amp
needs to have a wide Gain Bandwidth Product
(GBWP).
FIGURE 3-10:
Detector.
Light
Light
I
I
D1
PHOTO DETECTION
D1
V
operation
BIAS
D
D
MCP601/2/3/4
2
) in the feedback loop of the
1
1
2
) sometimes provides stability for
Photovoltaic Mode Detector.
Photoconductive Mode
–
MCP60X
+
MCP60X
–
+
C
R
C
R
(e.g.,
2
2
2
2
V
V
DD
DD
high-speed
DS21314F-page 13
V
V
V
OUT
BIAS
OUT
V
V
= I
OUT
< 0V
= I
OUT
D1
D1
digital
R
R
2
2