Datasheet
MCP6441/2/4
DS22257C-page 16 © 2010-2012 Microchip Technology Inc.
4.6.2 PRECISION HALF-WAVE
RECTIFIER
The precision half-wave rectifier, which is also known
as a super diode, is a configuration obtained with an
operational amplifier in order to have a circuit behaving
like an ideal diode and rectifier. It effectively cancels the
forward voltage drop of the diode in such a way that
very low level signals can still be rectified, with minimal
error. This can be useful for high-precision signal
processing. The MCP6441/2/4 op amp has high input
impedance, low input bias current and rail-to-rail
input/output, which makes this device suitable for
precision rectifier applications.
Figure 4-8 shows a precision half-wave rectifier and its
transfer characteristic. The rectifier’s input impedance
is determined by the input resistor R
1
. To avoid the
loading effect, it must be driven from a low-impedance
source.
When V
IN
is greater than zero, D
1
is OFF, D
2
is ON, and
V
OUT
is zero. When V
IN
is less than zero, D
1
is ON, D
2
is OFF, and V
OUT
is the V
IN
with an amplification of
-R
2
/R
1
.
The rectifier circuit shown in Figure 4-8 has the benefit
that the op amp never goes in saturation, so the only
thing affecting its frequency response is the
amplification and the gain bandwidth product.
.
FIGURE 4-8: Precision Half-Wave
Rectifier.
4.6.3 INSTRUMENTATION AMPLIFIER
The MCP6441/2/4 op amp is well suited for condition-
ing sensor signals in battery-powered applications.
Figure 4-9 shows a two op amp instrumentation
amplifier, using the MCP6441/2/4 device, that works
well for applications requiring rejection of Common
Mode noise at higher gains. The reference voltage
(V
REF
) is supplied by a low-impedance source. In sin-
gle supply applications, V
REF
is typically V
DD
/2.
FIGURE 4-9: Two Op Amp
Instrumentation Amplifier.
V
OUT
R
2
D
1
D
2
R
1
V
IN
V
OUT
V
IN
-R
2
/R
1
Transfer Characteristic
Precision Half-Wave Rectifier
MCP6441
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
1/2 MCP6442
1/2 MCP6442