參數(shù)資料
型號: LMC6042
廠商: National Semiconductor Corporation
英文描述: CMOS Dual Micropower Operational Amplifier
中文描述: CMOS雙微功耗運(yùn)算放大器
文件頁數(shù): 9/13頁
文件大?。?/td> 401K
代理商: LMC6042
Applications Hints
(Continued)
The designer should be aware that when it is inappropriate
to lay out a PC board for the sake of just a few circuits, there
is another technique which is even better than a guard ring
on a PC board: Don’t insert the amplifier’s input pin into the
board at all, but bend it up in the air and use only air as an in-
sulator. Air is an excellent insulator. In this case you may
have to forego some of the advantages of PC board con-
struction, but the advantages are sometimes well worth the
effort of using point-to-point up-in-the-air wiring. See Figure
6
Typical Single-Supply Applications
(V
+
= 5.0 V
DC
)
The extremely high input impedance, and low power con-
sumption, of the LMC6042 make it ideal for applications that
require battery-powered instrumentation amplifiers. Ex-
amples of these types of applications are hand-held pH
probes, analytic medical instruments, magnetic field detec-
tors, gas detectors, and silicon based pressure transducers.
The circuit in Figure 7 is recommended for applications
where the common-mode input range is relatively low and
the differential gain will be in the range of 10 to 1000. This
two op-amp instrumentation amplifier features an indepen-
dent adjustment of the gain and common-mode rejection
trim, and a total quiescent supply current of less than 20 μA.
To maintain ultra-high input impedance, it is advisable to use
ground rings and consider PC board layout an important part
of the overall system design (see Printed-Circuit-Board Lay-
out for High Impedance Work). Referring to Figure 7 the in-
put voltages are represented as a common-mode input V
CM
plus a differential input V
D
.
Rejection of the common-mode component of the input is
accomplished by making the ratio of R1/R2 equal to R3/R4.
So that where,
A suggested design guideline is to minimize the difference of
value between R1 through R4. This will often result in im-
proved resistor tempco, amplifier gain, and CMRR over tem-
perature. If RN = R1 = R2 = R3 = R4 then the gain equation
can be simplified:
Due to the “zero-in, zero-out” performance of the LMC6042,
and output swing rail-rail, the dynamic range is only limited to
the input common-mode range of 0V to V
2.3V, worst
case at room temperature. This feature of the LMC6042
makes it an ideal choice for low-power instrumentation sys-
tems.
A complete instrumentation amplifier designed for a gain of
100 is shown in Figure 8 Provisions have been made for low
sensitivity trimming of CMRR and gain.
DS011137-11
(Input pins are lifted out of PC board and soldered directly to components.
FIGURE 6. Air Wiring
DS011137-12
FIGURE 7. Two Op-Amp Instrumentation Amplifier
www.national.com
9
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