Datasheet

 2012-2013 Microchip Technology Inc. DS20002322C-page 19
MCP6481/2/4
4.7.3 PH ELECTRODE AMPLIFIER
The MCP6481/2/4 op amps can be used for sensing
applications where the sensor has high output
impedance, such as a pH electrode sensor; its output
impedance is in the range of 1 M to 1G. The key op
amp specifications for these kinds of applications are
low-input bias current and high input impedance.
A typical sensing circuit is shown in Figure 4-12, it is
implemented with a non-inverting amplifier which has a
gain of 1+R
2
/R
1
. The input voltage error due to input
bias current is equal to I
B
*R
OUT
, which is amplified by
1+R
2
/R
1
at the output. To minimize the voltage error
and get the V
OUT
with better accuracy, the I
B
must be
small enough.
FIGURE 4-12: pH Electrode Amplifier.
V
OUT
R
1
R
2
V
IN
+
–
pH electrode
V
SEN
V
SEN
is the sensed voltage by pH electrode
R
OUT
is the pH electrode’s output impedance
+
–
R
OUT
MCP648X