data acquisition et 228 chapter 3.0 - 3.10 subjects covered inverting amplifier inverting adder and...
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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
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 = - Ei{Rf / Ri }
• Output Current• IOut = I + IL
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)(Ri )
• Analysis Procedure• Find Ri • Find gain from Ri and Rf
• VOut has the opposite polarity of the input
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/R}R = - {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 don’t 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
Data Acquisition ET 228Chapter 3.0 - 3.10
• Multichannel Amplifier• Formulas for Figure 3-6 on page 55
• I1 = E1 /R1 I2 = E2 /R2 I3 = E3 /R3
• VOut = - {E1 (Rf /R1) + E2 ( Rf/R2) + E3 ( Rf/R3)}
• 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
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
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 doesn’t 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
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
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
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