參數(shù)資料
型號(hào): LM221
廠商: National Semiconductor Corporation
英文描述: LM221/LM321 Precision Preamplifiers
中文描述: LM221/LM321精密前置放大器
文件頁(yè)數(shù): 1/11頁(yè)
文件大?。?/td> 207K
代理商: LM221
TL/H/7769
L
February 1995
LM221/LM321 Precision Preamplifiers
General Description
The LM221 series are precision preamplifiers designed to
operate with general purpose operational amplifiers to dras-
tically decrease dc errors. Drift, bias current, common mode
and supply rejection are more than a factor of 50 better than
standard op amps alone. Further, the added dc gain of the
LM221 decreases the closed loop gain error.
The LM221 series operates with supply voltages from
g
3V
to
g
20V and has sufficient supply rejection to operate from
unregulated supplies. The operating current is programma-
ble from 5
m
A to 200
m
A so bias current, offset current, gain
and noise can be optimized for the particular application
while still realizing very low drift. Super-gain transistors are
used for the input stage so input error currents are lower
than conventional amplifiers at the same operating current.
Further, the initial offset voltage is easily nulled to zero.
The extremely low drift of the LM221 will improve accuracy
on almost any precision dc circuit. For example, instrumen-
tation amplifier, strain gauge amplifiers and thermocouple
amplifiers now using chopper amplifiers can be made with
the LM221. The full differential input and high common-
mode rejection are another advantage over choppers. For
applications where low bias current is more important than
drift, the operating current can be reduced to low values.
High operating currents can be used for low voltage noise
with low source resistance. The programmable operating
current of the LM221 allows tailoring the input characteris-
tics to match those of specialized op amps.
The LM221 is specified over a
b
25
§
C to
a
85
§
C range and
the LM321 over a 0
§
C to
a
70
§
C temperature range.
Features
Y
Guaranteed drift of LM321AD0.2
m
V/
§
C
Y
Guaranteed drift of LM221 seriesD1
m
V/
§
C
Y
Offset voltage less than 0.4 mV
Y
Bias current less than 10 nA at 10
m
A operating current
Y
CMRR 126 dB minimum
Y
120 dB supply rejection
Y
Easily nulled offset voltage
Typical Applications
Thermocouple Amplifier with Cold Junction Compensation
TL/H/7769–1
*
Set for 2.98V at output with LM113
shorted. Output should equal ambi-
ent temperature at 10 mV/
§
K.
2
Adjust for output reading in
§
C.
C
1995 National Semiconductor Corporation
RRD-B30M115/Printed in U. S. A.
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