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Signal Conditioning:Attenuation, Amplification, Addition and Subtraction
General Characteristics of Signal Amplification (p. 35)
Gain is the relationship between change in inputand change in output voltages,
Gain can be large (1000 or more)Gain can be less than 1
___________ in this case
What is the “gain” for this data?
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5 6 7 8 9 10
Input Voltage, mV
Out
put V
olta
ge, V
Example #1: Miniature Shaker
Given: Miniature piezoelectric shakerInput: ±100 VOutput: 0.004 lb/V (0.018 N/V)
How do you measure the voltage applied to the shaker?
100 V WELL beyond the range of standard data acquisition systems
Function Generator Amplifier Shaker
Attenuate the signalAttenuate the signal
Example #1 Continued
Scale the ±100 V down to ±10 VUse 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 Vouteven higher!
Limitation: you can only ________ with a voltage divider.
Operational Amplifier (op-amp)
Note the hole
741
4
1
2
3
5
6
7
8
Positive power supply (+12V)
Positive powersupply (+12V)
Negative powersupply (-12V)
Inverting input
Non-inverting inputNon-invertinginput (V+) +
-Output (Vo)
Invertinginput (V-)
Output
Negative power supply (-12V)
Integrated Circuit8 Pin DIP (Dual In-line Package)
Electrical SchematicSymbol
Single Input, Inverting amp
note Vi connected to inverting input (-)
+
-+12 V
-12 V
R1 R2
-Vi
+ (Eq. 3.17)=0V
Vo-
+
Inverting op-amp amplifier
Single-input, Inverting Amplifier
-10
-8
-6
-4
-2
0
2
4
6
8
10
-3 -2 -1 0 1 2 3
Input, volts
Out
put,
volts
What is the gain of the op-amp that has this input/output?
To Maintain Ideal Relationships for all Op-amp Circuits!
Input resistance R1 should be fairly large
R1 > 10kΩ in most casesminimizes current drawn from input side of op-amp circuit
Op-Amp Saturation (±12V power)
-15
-10
-5
0
5
10
15
-6 -4 -2 0 2 4 6
Input, volts
Out
put,
volts
Multiple input, summing amplifier
=oV
V1
+R1
-
V2
+-
R1
+
-
Vo
+
-
R2
Multiple input, summing amp
-12-10-8-6-4-202468
1012
-3 -2 -1 0 1 2 3
Input E1, volts
Out
put E
o, v
olts
E2 = 0 voltsE2 = +0.75 voltsE2 = -1 volt
What is the gain of the op-amp that has this input/output?
Single input, non-inverting amplifierR2R1
=oV
+
-
+
Note connection-
VoVi
+
-
See anything interesting? Any limitation here?
Single input, non-inverting amp
-12-10
-8-6-4-202468
1012
-4 -3 -2 -1 0 1 2 3 4
Input E1, volts
Out
put E
o, v
olts
What is the gain of the op-amp that has this input/output?
What op-amp circuit does this? #1
-3
-2
-1
0
1
2
3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Time, sec
Vol
tage
InputOutput
In-Class Exercise #1
Design an op-amp circuit to give the input/output relationship shown in #1
make ALL necessary connections to op-amp chipinput connection is yellow, output is orange
use the following resistors - 20kΩ, 56kΩ
In-class Exercise #1+12V
Com
Out
Vi
-
+
Vo
+
Build a single input,inverting amplifier,gain of 2.8
R2 = 56 kΩ(Gr-Blue-Or) In 741
-R1 = 20 kΩ(Red-Blk-Or)
-12V
-3
-2
-1
0
1
2
3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Time, sec
Vol
tage
InputOutput2
What op-amp circuit does this? #2
In-Class Exercise #2
Design an op-amp circuit to give the input/output relationship shown in #2
make ALL necessary connections to op-amp chipinput 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
R1
+
R2
-
+Vo+
Vi --
Single input, non-inverting amplifierR2R1
=oV
+
-
+
Note connection-
VoVi
+
-
What happens if…
This is called a _____________.
Dual input, difference amplifier
E2
E1
-i2 R2
i-
i1
+
R1
+
R4
-
i+
Eo
-
+
R3
i3
=oE assuming R4=R3 and R2=R1
Dual input, difference amp
-12-10-8-6-4-202468
1012
-30 -20 -10 0 10 20 30
Input (E2-E1), millivolts
Out
put E
o, v
olts
What is the gain of the op-amp that has this input/output?
Integrator
+
CR
-
+=oV
-Vi
(Eq. 3.32)+
Vo
-
Differentiator
+
RC
-
+=oV
-Vi
(Eqn 3.33)+
Vo
-
Comparatorreference voltage
input voltage to be compared
-
- +
+
+
-+12V
-12V+Vref
VoVi -
=oV
Instrumentation Amp
-
+
R2 -Vo
+
-
+
R3
-
+
R3
+ R2R1V1
RGR1
-
Figure 3.14
=oV Note – Formula in text is incorrect
“Buffered” Voltage Divider
+12V “low” impedancePotentiometer
-+ +
+VpotVpot “high”
impedance --
-12V
Potentiometer - Schematic
1
2
3
“wiper”Variable
ResistanceR1-2
VariableResistance
R2-3
FixedResistance
R1-3
Potentiometer - Physical
Wiper Adjustment
