Signal Conditioning:
Attenuation, Amplification,
Addition and Subtraction
General Characteristics of Signal Amplification
(p. 35)
► Gain
is the relationship between change in input
and change in output voltages,
► Gain
can be large (1000 or more)
► Gain can be less than 1
ƒ ___________ in this case
What is the “gain” for this data?
0.7
Output Voltage, V
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
4
5
6
Input Voltage, mV
7
8
9
10
Example #1: Miniature Shaker
► Given:
Miniature piezoelectric shaker
ƒ Input: ±100 V
ƒ Output: 0.004 lb/V (0.018 N/V)
Function
Generator
Amplifier
Shaker
► How
do you measure the voltage applied to
the shaker?
ƒ 100 V WELL beyond the range of standard data
acquisition systems
Attenuate
Attenuate the
the signal
signal
Example #1 Continued
► Scale
the ±100 V down to ±10 V
ƒ Use a ____________
±100 V COM
Make sure that your measuring circuit does not draw too much current!
→ Make it’s impedance HIGH
→Make the input impedance of the circuit measuring Vout
even higher!
Limitation: you can only ________ with a voltage divider.
Operational Amplifier (op-amp)
Note the hole
Positive power supply (+12V)
Inverting
input (V-)
Non-inverting
input (V+)
-
1
8
Inverting input
2
7
Positive power
supply (+12V)
Non-inverting input
3
6
Output
Negative power
supply (-12V)
4
Output (Vo)
+
741
5
Negative power supply (-12V)
Electrical Schematic
Symbol
Integrated Circuit
8 Pin DIP
(Dual In-line Package)
Single Input, Inverting amp
► note
Vi connected to inverting input (-)
R1
+
Vi
-
R2
-
V0 =
+12 V
+
-12 V
+
Vo
-
Inverting op-amp amplifier
(Eq. 3.17)
Single-input, Inverting Amplifier
What is the gain of the op-amp that has this input/output?
10
8
6
Output, volts
4
2
0
-2
-4
-6
-8
-10
-3
-2
-1
0
Input, volts
1
2
3
To Maintain Ideal Relationships for all Op-amp
Circuits!
►
Input resistance R1 should be fairly large
R1 > 10kΩ in most cases
ƒ minimizes current drawn from input side of op-amp circuit
Op-Amp Saturation
(±12V power)
15
Output, volts
10
5
0
-5
-10
-15
-6
-4
-2
0
Input, volts
2
4
6
Multiple input, summing amplifier
R2
R1
+
V1
-
R1
+
V2
+
-
+
Vo
-
Vo =
Multiple input, summing amp
Output Eo, volts
What is the gain of the op-amp that has this input/output?
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
-12
E2 = 0 volts
E2 = +0.75 volts
E2 = -1 volt
-3
-2
-1
0
Input E1, volts
1
2
3
Single input, non-inverting amplifier
R2
R1
Vo =
-
+
Vi
-
+
Note connection
+
Vo
-
See anything interesting? Any limitation here?
Single input, non-inverting amp
Output Eo, volts
What is the gain of the op-amp that has this input/output?
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
-12
-4
-3
-2
-1
0
Input E1, volts
1
2
3
4
What op-amp circuit does this?
3
2
#1
Input
Output
Voltage
1
0
-1
-2
-3
0
0.1
0.2
0.3
0.4
0.5
Time, sec
0.6
0.7
0.8
0.9
1
In-Class Exercise #1
► Design
an op-amp circuit to give the input/output
relationship shown in #1
ƒ make ALL necessary connections to op-amp chip
ƒ input connection is yellow, output is orange
► use
the following resistors - 20kΩ, 56kΩ
In-class Exercise #1
+12V
Build a single input,
inverting amplifier,
gain of 2.8
R2 = 56 kΩ
(Gr-Blue-Or)
In
+
R1 = 20 kΩ
Vi
(Red-Blk-Or)
-
Out
+
741
Vo
Com
-12V
What op-amp circuit does this?
#2
3
Input
Output2
2
Voltage
1
0
-1
-2
-3
0
0.1
0.2
0.3
0.4
0.5
Time, sec
0.6
0.7
0.8
0.9
1
In-Class Exercise #2
► Design
an op-amp circuit to give the input/output
relationship shown in #2
ƒ make ALL necessary connections to op-amp chip
ƒ input connection is yellow, output is orange
► use
the following resistors - 20kΩ, 56kΩ
In-Class Exercise #2
► Build
a single input, non-inverting amplifier,
gain of 1.36
► You have 20 kΩ and 56 kΩ resistors
R2
R1
+
Vi
-
+
+
Vo
-
Single input, non-inverting amplifier
R2
R1
Vo =
-
+
Vi
-
+
Note connection
+
Vo
-
What happens if…
This is called a _____________.
Dual input, difference amplifier
R1
i1
R3
i3
+
E1
-
i-
i2
R2
i+
+
+
Eo
E2
R4
Eo =
-
assuming R4=R3 and R2=R1
Dual input, difference amp
Output Eo, volts
What is the gain of the op-amp that has this input/output?
12
10
8
6
4
2
0
-2
-4
-6
-8
-10
-12
-30
-20
-10
0
10
Input (E2-E1), millivolts
20
30
Integrator
R
C
+
Vi
-
Vo =
+
+
Vo
-
(Eq. 3.32)
Differentiator
R
C
+
Vi
-
Vo =
-
(Eqn 3.33)
+
+
Vo
-
reference voltage
Comparator
+12V
-
+
Vref
-
+
Vi
+
-12V
+
Vo
-
input voltage to be compared
Vo =
Instrumentation Amp
+
+
R2
-
R1
R3
V1
-
RG
R3
-
+
Vo =
+
+
R1
R2
Vo
-
Figure 3.14
Note – Formula in text is incorrect
“Buffered” Voltage Divider
+12V
Potentiometer
“low” impedance
+
Vpot
-12V
+
“high”
impedance
+
Vpot
-
Potentiometer - Schematic
Fixed
Resistance
R1-3
1
3
2
Variable
Resistance
R1-2
“wiper”
Variable
Resistance
R2-3
Potentiometer - Physical
Wiper Adjustment