Page 312 - Mechatronics with Experiments

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Then,
i = V ∕R i (5.232)
i
in
i = i in (5.233)
f
V = R ⋅ i = R ⋅ V ∕R (5.234)
f f f f i i
Hence, since the output voltage will have opposite polarity to V ,
f
R f
V =−V =− ⋅ V i (5.235)
o
f
R
i
V = K CL ⋅ V i (5.236)
o
where the gain of the inverting op-amp
R f
K CL =− (5.237)
R i
Noninverting Op-Amp A noninverting amplifier simply amplifies an input voltage
to output voltage with a positive gain. This is accomplished by the feedback connections
−
−
+
shown in Figure 5.34b. Following the same ideal op-amp assumptions (v+= v , i = i =
0), the input–output relationship (neglecting transient response differences) can be derived
as follows,
−
+
v = v = V (5.238)
i
i = V ∕R (5.239)
in i i
i = i in (5.240)
f
V = (R + R ) ⋅ i f (5.241)
f
0
i
Since this is a noninverting amplifier,
R + R f
i
V = ⋅ V i (5.242)
o
R i
= K ⋅ V (5.243)
CL i
where the gain of the noninverting op-amp is
R f
K CL = 1 + (5.244)
R i
which is always larger than one.
Example A special case of the noninverting op-amp is obtained when there are no
resistors in the configuration. Effectively, this is same as R = 0, and R =∞. Hence, the
f
i
gain of the amplifier is unity. Such an op-amp configuration is called the voltage follower
op-amp or buffer op-amp and used to isolate the source and load (Figure 5.27b). The voltage
gain is unity, but the current gain is larger than unity in order to isolate the source from the
load.
Example Let us consider a noninverting op-amp with a saturation output voltage of
V = 13 V, R = 10 kΩ, and R = 10 kΩ. The input voltage and output voltage relationship
sat i f
can be easily determined by
R + R f
i
V = ⋅ V (5.245)
o i
R i
= 2.0 ⋅ V i (5.246)