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R2
V in
Rl
- -
mend that the power supply pins be
decouplecl with capacitors thai have a
value fhat win produce a vel)' low reactance
path to ground. In most eases,
a value lrom 0.1 ~ F 10 4.7 ~ F Is
usec ror C1 and C2.
Note that in Figure 1 th ere is no
ground connection on the body 01 the
op amp llsell . Input and output signals
are ground reterenced, bu t the only
ground per se is in the DC power supply
circuit (see the Insel to FIQure 1).
mmosl 01 the Circuits in this article
you win flfld the DC power supply ter-
-
V out
VoNI" = Av = -R2IR1
VO
= - Vln R2IRl
rrinals deleted. That is oone for graphic
simpliCity, b1.lt In reatly-worll.lng Cirwits
you would conned V- and V+ as
per Figure 1.
Inverting Followers
Figure 2 shows the Inverting folJower
amplifier circuit. This circuit produces
an output that Is 180 degrees
out of phase (i.e. "inve rted") with
the Inpul signal. Thus, V o '" -A." V...
th e standard notaUon (A" denotes
"closed loop voltage gain1. The value
of the voltage gain is set by the ratiO
"""l
~
+
,
r
- -
FIgUre 3. Unity gam nomnvertmg followe£.
of the resistors in the feedback loop:
R2
/1\,, - - ­ R'
The "0" Sign in the equation deooles
phase inYersiofl taking place. The output
YOita ge. as a function of the input
voltage and gain, is therefore:
Vo = -Vo ( ~ )
For example. lers assume thai we
want a 9aln-ol· 1oo amplifier with an
input impedance 01 at least 10k ohms.
We therefore set input resistor Rl to
10k ohms (or higher), and then caeulate
the value 01 R2 that produces an
A... of 100:
R2 = R1A,. ~ (10k ohms) (1 00) a
l ,OOO,OOO otvnS
For situations where ga in is desired,
make R2 greater than a t. but it
you want to attenuate a signal make
R2 tess than Rl . When Rl _ R2 the
ga .... is umy (1), and Wh8n R2 is a polenliomet
Bl" the ga in Is 0 10 1.
Nonlnverling FDlk)wers
The nonW1veftinQ lo/Iower produces
an output Signal that is in phase with
the input signal, and comes In two varieti
es: un ity gain (Figure 3) and
greater-thall-unity gain (Figure 4). The
unity gain rollowe r is used for butlering,
Isolating and tmoecarce transformation.
It gets the laller job from the
fact that it has a v ery high input
Impedance and a very low (less than
100 ohms) outPut Impedance.
The g reater-than-unity configuration
of Figure 4, like lh8 inverting 101-
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Complete Inventory
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RS--CA RS-7A
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