參數(shù)資料
型號(hào): MCP6241U
廠商: Microchip Technology Inc.
英文描述: 50 uA, 550 kHz Rail-to-Rail Op Amp
中文描述: 50微安,550千赫軌至軌運(yùn)算放大器
文件頁數(shù): 10/28頁
文件大小: 378K
代理商: MCP6241U
MCP6241/2/4
DS21882C-page 10
2005 Microchip Technology Inc.
4.7
Application Circuits
4.7.1
MATCHING THE IMPEDANCE AT
THE INPUTS
To minimize the effect of offset voltage in an amplifier
circuit, the impedances at the inverting and non-
inverting inputs need to be matched. This is done by
choosing the circuit resistor values so that the total
resistance at each input is the same. Figure 4-7 shows
a summing amplifier circuit.
FIGURE 4-7:
To match the inputs, set all voltage sources to ground
and calculate the total resistance at the input nodes. In
this summing amplifier circuit, the resistance at the
inverting input is calculated by setting V
IN1
, V
IN2
and
V
OUT
to ground. In this case, R
G1
, R
G2
and R
F
are in
parallel. The total resistance at the inverting input is:
Summing Amplifier Circuit.
At the non-inverting input, V
DD
is the only voltage
source. When V
DD
is set to ground, both R
X
and R
Y
are
in parallel. The total resistance at the non-inverting
input is:
To minimize offset voltage and increase circuit
accuracy, the resistor values need to meet the
condition:
4.7.2
COMPENSATING FOR THE
PARASITIC CAPACITANCE
In analog circuit design, the PCB parasitic capacitance
can compromise the circuit behavior; Figure 4-8 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 4-8:
Capacitance at the Input.
Effect of Parasitic
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
.
MCP624X
+
V
OUT
V
IN2
V
IN1
R
G2
R
G1
R
F
R
Z
V
DD
R
X
R
Y
R
VIN
R
G1
---------
R
G2
---------
R
F
------
+
+
---------------------------------------------
=
Where:
R
VIN–
= total resistance at the inverting input
R
VIN+
R
X
------
1
R
Y
-----
+
------------------------
R
Z
+
=
Where:
R
VIN+
= total resistance at the inverting
input
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
------
=
MCP624X
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MCP6242-E/MS 制造商:Microchip Technology Inc 功能描述:; LEADED PROCESS COMPATIBLE:YES; PEAK RE