Datasheet

MCP6231/1R/1U/2/4
DS21881E-page 14 © 2009 Microchip Technology Inc.
To minimize output offset voltage and increase circuit
accuracy, the resistor values need to meet the
conditions:
EQUATION 4-3:
4.7.2 COMPENSATING FOR THE
PARASITIC CAPACITANCE
In analog circuit design, the PCB parasitic capacitance
can compromise the circuit behavior; Figure 4-9 shows
a typical scenario. If the input of an amplifier sees
parasitic capacitance of several picofarad (C
PARA
,
which includes the common mode capacitance of 6 pF,
typical), and large R
F
and R
G
, the frequency response
of the circuit will include a zero. This parasitic zero
introduces gain-peaking and can cause circuit
instability.
FIGURE 4-9: Effect of Parasitic
Capacitance at the Input.
One solution is to use smaller resistor values to push
the zero to a higher frequency. Another solution is to
compensate by introducing a pole at the point at which
the zero occurs. This can be done by adding C
F
in
parallel with the feedback resistor (R
F
). C
F
needs to be
selected so that the ratio C
PARA
:C
F
is equal to the ratio
of R
F
:R
G
.
R
VIN
+
R
VIN
–=
V
OUT
C
F
V
DC
+
–
V
AC
R
G
R
F
C
PARA
C
F
C
PARA
R
G
R
F
-------
•=
MCP623X