Topic 12 Op-Amp Applications

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Topic 12 Op-Amp Applications

• Comparators
• Integrators and Differentiators
• Summing Amplifiers
• Other Op-Amp Circuits
• Active Filters
• Low-Pass and High-Pass
• Band-Pass Filters

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Op-Amp Integrator

• The op-amp provides a constant-current source for
  the capacitor, causing it to charge at a linear
  rate.

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Reduced Gain Op-Amp Integrator

• A feedback resistor limits the gain at low
  frequency since the reactance of Cf increases,
  causing an increase in voltage gain.
• Any output offset voltage can also be reduced.

Rf is normally gt 10 Rin
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12.2.2 Differentiator

• Differentiator A circuit whose output is
  proportional to the rate of change of its input
  signal.

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Reduced Gain Op-Amp Differentiator

• The added Rin resistor limits the gain at high
  frequency since the reactance of Cf is extremely
  low at higher frequencies

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12.3 Summing Amplifiers

• Summing amplifier An op-amp circuit that
  produces an output proportional to the sum of its
  input voltages.

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Summing Amplifiers Example (1)

• Example 16.4 Determine the output voltage.

Solution
Voltage gain equals -1 for all the inputs.
(-1)(3V 6V 4V) -13V
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Summing Amplifiers Example (2)

• Example 16.5 Determine the output voltage.

Solution
Voltage gain equals -0.1 for all the inputs.
(-0.1)(10V8V7V) -2.5V
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General Summing Circuits

• General-class equation An equation derived for
  a summing amplifier that is used to predict the
  circuit output for any combination of input
  voltages.
• Determine the Rf / R ratio for each branch.
• Represent each branch as the product of its
  resistance ratio and input voltage.
• Write the equation as the sum of these products.

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Summing Amplifiers Example (3)

• Example 16.6 Determine the output voltage for
  the 3 sets of inputs.

V1(V) V2(V) V3(V)
10 0 10
0 10 10
10 10 10
Solution
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Simplified D/A Converter

• One summing amplifier application is as a
  digital-to-analog (D/A) converter.
• Digital-to-analog (D/A) converter A circuit
  that converts digital circuit outputs to
  equivalent analog voltages.

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Averaging Amplifier

• By using the proper input and feedback resistors,
  a summing amplifier can be an averaging
  amplifier.
• Averaging amplifier A summing amplifier that
  provides an output proportional to the average of
  the input voltages.

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Difference Amplifier (Subtractor)

• Difference amplifier A summing amplifier that
  provides an output proportional to the difference
  between two input voltages. Also called a
  subtractor.

In order to work properly, a difference amplifier
must have values of R1 R2 and R3 R4
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12.4 Other Op-Amp Circuits

• Instrumentation amplifier A high-gain and
  high-CMRR circuit used to amplify low-level
  signals in process control and measurement
  applications.

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Audio Amplifier

• Audio amplifier The final audio stage in
  low-power communications receivers, used to drive
  the speakers.

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Voltage-Controlled Current Source

• Voltage-controlled current source A circuit
  with a constant-current output controlled by the
  circuit input voltage.

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Precision Rectifier

• Precision rectifier A clipper that consists of
  a diode and an op-amp. The circuit can clip
  extremely low-

level input signals.
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Op-Amp Applications (1)

• A comparator is a circuit used to compare two
  voltages.
• Most comparators use a voltage-divider to set the
  reference voltage.
• An op-amp integrator provides a linear/ramp
  output waveform with a square-wave input.
• A differentiator is a circuit whose output is
  proportional to the rate of change of its input
  signal.
• A summing amplifier produces an output
  proportional to the sum of its input voltages.
• A averaging amplifier provides an output
  proportional to the average of the input
  voltages.
• A difference amplifier (subtractor) provides an
  output proportional to the difference between two
  input voltages.
• Chapter 16 Problems (min.) 1, 3, 5, 7, 11, 13,
  15, 17, 19