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fn the 5O5, tlne value of Rg and Ri used, for the inverLer
is normalfy 1M ohms, therefore:
lM
e o = - - i l
e i n
= - €i - n
Thus a +100 volt
input results
j-n a -100 volt
output,
md
the amplifier
is said to harre a gain of minus one.
The accuracy
of the output to input ratio
depends solely
on the accuracy of
k
-Ene rallo
ltflltin.
(2)
Multiplication
by a Constant
A change in the ratio
of the
resistors
results
in rmrltiplication
by a constant.
ldith R1' equal
to l-I4 and R3 equal to 100K for example, the arnplifier
output is:
]M
oo = -
IOCK
oin = -lu ein
An input
of plus 10 volts
results
ln an output
of minus a
hundred volts.
This operational
amplifier
has a gain of ten.
The multiprying
constant can be made less than one by using a
1OCK feedback resistor
with a LM input resistor.
e^ = '
looK
ein = -0.1 elrt
"
l
M
An input of minus 100 volts
prod,uces an output of 10 volts.
0)
Summation
\^lhen nrultiple
input
resistors
are used with a
feedback resistor
R1, the basic relationship
is ertended to:
/
\
/ R r
R p
R 1
\
€ o = - l j e t +
-
e 2 + . . . +
- e n
i
\ n 1
R 2
R n
I
\
r
u
t
I E
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