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since es = eo,/A,
to obtain:
and since iuAl 0, Equation 2.5-I can be rewritten
e i n
e o
e o
e O
- +
= a -
Zin
LZ]n
LZt
Z1
e ^ t - . i - d
f n r
a
2 1
ö !
D U I V - L I I ä
r v a
v O .
- - - - Z i -
s A I l
4 l n
t
t
t
e o =
Z r
e^ = -------1
ein
.J]-rl
1nq. 2.5-z)
(tQ. 2.5-3)
' . 1 ]
In most applications
the ratio
of z1 to zi., is less than 30 and
since I/1, approaches zero, Equation 2.5-2 becomes:
t
t
t
t
Equation 2.5-3
illustrates
one of the most important
considera-
tions
of the operational
amplifier:
The inpgl_g1lput
rela!i9ne4!!1)f
Orl LY
the operational
arnplifier
is so1e1y de
t on the ratio of the
feedback to the input
imPedance.
using Equation 2.5-3 as the basis of discussion,
the following
subparagraphs describe the various uses of the operational
amplifier.
/- \
r
|
|
l h r t A h d a ^ h
\ !
/
ir,lhen the same value resi-stor
is used for both the feedback and
the input
impedance, the amplifier
output voltage
has the same ampli-
tude as the input voltage but is opposite in polarity.
'l
R1'
o o = - = . -
e l n
r L - l
Y t
t
t
T
t
(
t
t
t
t
- /'J, '
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