Datasheet

MCP6H01/2/4
DS22243D-page 20  2010-2011 Microchip Technology Inc.
4.7.2 TWO OP AMP INSTRUMENTATION
AMPLIFIER
The MCP6H01/2/4 op amps are well suited for
conditioning sensor signals in battery-powered
applications. Figure 4-9 shows a two op amp
instrumentation amplifier using the MCP6H02, which
works well for applications requiring rejection of
common mode noise at higher gains.
To ensure proper operation, the op amp common mode
input voltage must be kept within the allowed range.
The reference voltage (V
REF
) is supplied by a low-
impedance source. In single-supply applications, V
REF
is typically V
DD
/2.
FIGURE 4-9: Two Op Amp
Instrumentation Amplifier.
To obtain the best CMRR possible, and not limit the
performance by the resistor tolerances, set a high gain
with the R
G
resistor.
4.7.3 PHOTODETECTOR AMPLIFIER
The MCP6H01/2/4 op amps can be used to easily
convert the signal from a sensor that produces an
output current (such as a photo diode) into voltage (a
trans-impedance amplifier). This is implemented with a
single resistor (R
2
) in the feedback loop of the
amplifiers shown in Figure 4-10. The optional capacitor
(C
2
) sometimes provides stability for these circuits.
A photodiode configured in Photovoltaic mode has a
zero voltage potential placed across it. 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, common mode input voltage range (including
ground), and rail-to-rail output.
FIGURE 4-10: Photodetector Amplifier.
V
OUT
V
1
V
2
–1
R
1
R
2
------
2R
1
R
G
---------++


V
REF
+=
V
REF
R
1
R
2
R
2
R
1
V
OUT
R
G
V
2
V
1
½
MCP6H02
½
MCP6H02
D
1
Light
V
OUT
V
DD
R
2
C
2
I
D1
V
OUT
= I
D1
*R
2
–
+
MCP6H01