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