Since subtraction can be considered to be the addition of negative numbers, subtraction can be
perform ed by using negative voltages for those quantitities to be subtracted. The circu it shown
in Figure 6 would give the result
o--------------------------------------------------------------------------------
1
Figure 6
OPERATIONAL AMPLIFIER CIRCUIT USED FOR SUBTRACTION
which may be written
where
- i t
and
R f
K2 =
r
7
Division can be perform ed by multiplying by the re cip ro ca l of the number, but since this so m e
tim es requires a ratio of R f/R i of less than unity, which may cause unstable operation of the
am plifier, this method is generally undesirable. The circu it shown in Figure 7 shows a m ore
desirable method.
DIVISION BY A CONSTANT
The voltage e is given by
It is also given by
e = p e 0
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