What is the Differential Mode The opamp can be connected up in various ways or modes What it does depends on how it is connected up When connected up in the differential mode it finds the ID: 462752
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Slide1
The Differential Mode Op-AmpSlide2
What is the Differential Mode ?
The op-amp can be connected up in various ways or
modes
.
What it does depends on how it is connected up.
When connected up in the
differential mode
, it finds the
difference between the two input voltages
and
multiplies it by the gain
.Slide3
The Differential Mode Op-Amp
+
-
V
1
V
o
R
f
R
1
0 V
+V
s
-V
s
The
feedback resistor
(
R
f
) is used to control the gain of the op-amp.
The input voltages are fed in through the
input resistors
( R
1
and
R
2
).
R
2
R
3
V
2
R
3
is always the same size as Rf.Slide4
Revision – The Gain of an Amplifier
You may remember from Standard Grade that the gain of an amplifier is the ratio of the output and input voltages.
The gain can also be expressed in terms of the resistors used to connect up the op-amp.
Slide5
The Differential
Mode Gain Equation
Slide6
Example 1
Calculate the output voltage from the op-amp below
.
+
-
0.3 V
V
o
150k
Ω
20k
Ω
0 V
+V
s
-V
s
0.5V
20k
Ω
150k
ΩSlide7
Example 1 - Solution
Slide8
Example 2
What size of feedback resistor would be required to produce an output voltage of – 6 volts ?
+
-
0.6 V
- 6 V
R
f
20k
Ω
0 V
+V
s
-V
s
0.3V
20k
Ω
R
3Slide9
Example 2 - Solution