MCP6241_08 Datasheet, PDF (14/38 Pages) Microchip Technology – 50 μA, 550 kHz Rail-to-Rail Op Amp

MCP6241/1R/1U/2/4
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.
V_AC
R_G
V_DC
+
MCP624X
–
R_F
V_OUT
C_PARA
C_F
C_F
=
C_PARA
•
R_----G--
R_F
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.
DS21882D-page 14
© 2008 Microchip Technology Inc.