Data Acquisition ET 228 Chapter 3.0 - 3.10

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Subjects Covered
• Inverting Amplifier
• Inverting Adder and Audio Mixer
• Multichannel Amplifier
• Inverting Averaging Amplifier
• Noninverting Amplifier
• Voltage Follower
• Ideal Voltage Source
• Noninverting Adder
• Single Supply Operation
• Difference Amplifiers
• Inverting Amplifier
• See Figure 3-1 on page 46

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Inverting Amplifier
• Simplifying Assumptions
• Ed is essentially 0 if Vout is not in saturation
• Input terminal currents in negligible
• Formulas for Figures 3-1, 3-2, 3-3
• On Pages 46, 48, and 50
• I Ei/Ri
• I determined by the input voltage and input
  resistor
• Voltage drop across the feedback resistor
• Vrf I x Rf Ei/Ri Rf
• Output voltage - Across the load
• VOut - EiRf / Ri
• Output Current
• IOut I IL

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Inverting Amplifier
• Example Problems
• Examples 3-1 and 3-2 on page 47
• Example 3-3 on page 49
• Walk through applying Ei per Figure 3-3
• Example Problems
• 3-4 on page 49
• 3-5 on page 50
• 3-6 on page 51
• Design Procedure
• Choose Circuit type
• Pick Ri (10k? is a safe choice)
• Calculate Rf from (gain)(R )
• Analysis Procedure
• Find Ri
• Find gain from Ri and Rf
• VOut has the opposite polarity of the input

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Inverting Adder and Audio Mixer
• Formulas for Figure 3-4 on page 52
• I1 E1 /R I2 E2 /R I3 E3 /R
• VOut - E1/R E2/R E3/RR - E1 E2 E3
• Fig 3-4 Walk through and Example Problems
• Example Problems 3-8 and 3-9 starting on page 52
• Audio Mixer
• The input currents and voltages dont interact
• Replace the DC voltage sources with audio sources
• Add an adjustable resistor in series with the
  input R
• Approximately 1/10 of R
• DC offset of AC signals
• Usually used to supply bias voltage levels needed
  on the output
• Walk through Figure 3-5 using different levels
  for Edc

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Multichannel Amplifier
• Formulas for Figure 3-6 on page 55
• I1 E1 /R I2 E2 /R I3 E3 /R
• VOut - E1 (Rf /R) E2 ( Rf/R) E3 ( Rf/R)
• Acl1 - Rf /R1 Acl2 - Rf /R2 Acl3
  - Rf /R3
• Walk Through Fig 3-6
• Example Problem 3-11 on page 56
• Inverting Averaging Amplifier
• Make all the input resistors equal
• Make the feedback resistor R/n, with n of
  inputs
• Example 3-12
• Noninverting Amplifier
• Input voltages applied directly to input

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Noninverting Amplifier
• Formulas for Figure 3-7
• I Ei/R1
• Vrf I Rf (Rf /R1) Ei
• VOut Ei (Rf /R1) Ei (1 Rf /R1) Ei
• Walk through Figure 3-7
• Use 5V and -5V
• Example Problems 3-13 and 3-14
• Page 59
• Voltage Follower
• Commonly called
• Source Follower
• Unity-Gain Amplifier
• Buffer Amplifier
• Isolation Amplifier

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Voltage Follower
• Formulas
• VOut Ei
• Acl VOut /Ei 1
• Example 3-15 on page 62
• Uses of the Voltage Follower
• Isolation of the quantity being measured from the
  measurement
• Walk though both circuits in Figure 3-11 on page
  63
• Ideal Voltage Source
• Characteristics
• Output doesnt change regardless of the load
• No resistance in series with the voltage
• Walk through Figure 3-12
• The b figure shows the loading due to a
  inverting amplifier
• The c figure shows a practical Ideal Voltage
  Source

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Noninverting Adder
• Typical Circuit in Figure 3-14
• Assume R RA
• Inputs could be buffered with Voltage Followers
• Formulas
• VOut E1 E2 E3
• Rf R(n-1), where n the number of inputs
• Ein E1 E2 E3/3
• Figure 3-14 Walk Through
• Single-Supply Operation
• Figure 3-15
• Characteristics
• Usually used in battery operated devices
• Inputs can go to ground and close to the supply
  voltage
• Usually wired as Noninverting since there is only
  one supply

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Single-Supply Operation
• If the input signal goes below ground (referenced
  to supply voltage)
• The input must be biased
• See b figure
• Difference Amplifiers
• Variations reviewed
• Subtractor
• Inverting-Noninverting
• Subtractor
• Figure 3-16a
• First an inverter inverts E1
• Then it and E2 are feed to an inverting adder
• Results in VOut E1 - E2

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Data Acquisition ET 228Chapter 3.0 - 3.10

• Difference Amplifiers
• Inverting-Noninverting
• Figure 3-16b
• Can solve using supper positioning
• If E2 0V then VOut 2 x E1
• If E1 0V then VOut - E2