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The potentiometer
having a l-ower n:mber has priority.
trihen two
buttons are pushed, the lower numbered potentioineter
r^r111 be selected.
5.
OIERATIONAL AMFT,IFIER
a.
General Consi-derations
I,lhen a high-gain
d-c arnplifier
is used in conjunction
with input
a3d feedback networks to perforrn mathematical operations,
the resu-lt-
ing systen is generally
referred
to as an operational
amplfier.
The
operational
amplifier
is the basic and most versatile
unit
in the
analog computer.
It
can be used for
inversion,
summation, multipli-
cation by a cr,rnstant, integration,
anil used in conjurrction with spe-
cial
networks for
squaring,
erbracting
square root,
generating
1 ^ ^ ^ a i + h m i a
f r r n n i i n n <
a t a
! v 5 4 f ! u r l r r
To understand the basic concept of the operational
amplifier,
consider the simplified
block diagram of Figgre 2.5-L where a high-
gain arnplifier
(gain of -A) has a feedback i-rnpedance Zg Egß, an input
impedance Zin.
The amplifier
is designed so that it
has three basie
and essential characteristics.
(1)
The amplifier
output
(eo) is related
to the summi.ng iunc-
tion
voltage
(es) ry t,he gain of the araplifier:
eo = -Aes
(Z)
T;e input
stage of the amplifier
draws neglisible
current:
l - O - U
(3)
The open loop gain of the amplifier
is extremely high:
A >> 1 (on the order of 10? at d-c ).
''
using Kirchhoffts
laws, the nodal current equation at the sum-
ming junction
(S.l) is:
i t =
1€
e i n - e s
F
r
r
r
t
t
t
r
t
f
r
f
t
r
t
io
*
ir-
I
U
€ s - € o
-
- L
; ,
, & n
A a
4 L
t
r
t
t
or
v . .
-l_n
- l a -
( E Q . 2 . 5 - 1 )
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