LM194 LM394 Supermatch Pair
December 1994
LM194 LM394 Supermatch Pair
General Description
The LM194 and LM394 are junction isolated ultra well-
matched monolithic NPN transistor pairs with an order of
magnitude improvement in matching over conventional tran-
sistor pairs This was accomplished by advanced linear pro-
cessing and a unique new device structure
Electrical characteristics of these devices such as drift ver-
sus initial offset voltage noise and the exponential relation-
ship of base-emitter voltage to collector current closely ap-
proach those of a theoretical transistor Extrinsic emitter
and base resistances are much lower than presently avail-
able pairs either monolithic or discrete giving extremely low
noise and theoretical operation over a wide current range
Most parameters are guaranteed over a current range of
1
mA
to 1 mA and 0V up to 40V collector-base voltage
ensuring superior performance in nearly all applications
To guarantee long term stability of matching parameters
internal clamp diodes have been added across the emitter-
base junction of each transistor These prevent degradation
due to reverse biased emitter current the most common
cause of field failures in matched devices The parasitic iso-
lation junction formed by the diodes also clamps the sub-
strate region to the most negative emitter to ensure com-
plete isolation between devices
The LM194 and LM394 will provide a considerable improve-
ment in performance in most applications requiring a closely
matched transistor pair In many cases trimming can be
eliminated entirely improving reliability and decreasing
costs Additionally the low noise and high gain make this
device attractive even where matching is not critical
The LM194 and LM394 LM394B LM394C are available in
an isolated header 6-lead TO-5 metal can package The
LM394 LM394B LM394C are available in an 8-pin plastic
dual-in-line package The LM194 is identical to the LM394
except for tighter electrical specifications and wider temper-
ature range
Features
Y
Y
Y
Y
Y
Y
Y
Y
Emitter-base voltage matched to 50
mV
Offset voltage drift less than 0 1
mV
C
Current gain (h
FE
) matched to 2%
Common-mode rejection ratio greater than 120 dB
Parameters guaranteed over 1
mA
to 1 mA collector
current
Extremely low noise
Superior logging characteristics compared to
conventional pairs
Plug-in replacement for presently available devices
Typical Applications
Low Cost Accurate Square Root Circuit
I
OUT
e
10
b
5
0
10 V
IN
Low Cost Accurate Squaring Circuit
I
OUT
e
10
b
6
(V
IN
)
2
TL H 9241 鈥?2
TL H 9241 鈥?1
Trim for full scale accuracy
C
1995 National Semiconductor Corporation
TL H 9241
RRD-B30M115 Printed in U S A
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