OPAMP Basics

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OP-AMP Basics
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The purpose of OP-AMP

• The Operational Amplifier (Op-Amp) was developed
  many years ago for_________.
• For instance, OP-AMP used to provide voltage
  amplitude changes, oscillator, filter circuit.
• Analogue computing
• Calculator
• Video Player
• cell phone

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Answer is

• Analogue Computing

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OP-AMP

• Op-Amp is nothing more than a differential
  _______that amplifies the difference between two
  inputs. Where it contains a number of
  differential stages to achieve very high voltage
• Resistors
• Semiconductor
• Amplifier
• circuit

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Answer

• Amplifier

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Or defined as

• a very high gain amplifier having very high
  input impedance (typically a few mega ohms) and
  low output impedance (less than 100 ohms).

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Basic OP-AMP

• Basic OP-AMP has two input and at least one
  output

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The components of an OP-AMPOne input has a
_____effect on the output signal, the other input
has a ______ effect on the output.

• positive, negative
• negative, positive
• positive, positive
• Negative, negative

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The answer

• a) positive, negative

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OP-AMP
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Types of OP-AMP

• Single ended input one input connected to the
  signal input and the other input connected to
  ground
• Double ended input (differential) each input
  applied to a signal ( niether input is at
  ground). Same action to the signal when the two
  separate signal applied to inputs

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Types of OP-AMP

• Double ended (output) OP-AMP operated with the
  opposite output. An input applied to either input
  results an outputs from both output terminals,
  and these outputs always being opposites in
  polarity.
• Common-mode operation same input signals are
  applied to both inputs.
• Common mode rejection signals which are opposite
  at the input are highly amplified. While common
  signal applied to two inputs are slightly
  amplified.

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Differential and Common-mode operation

• -Differential inputs has separate inputs
• Vd Vi1 Vi2
• -Common inputs input signal are the same
• Vc ½ ( Vi1Vi2)
• -Output voltage any signal applied to OP-AMP
  have both in-phase and out-phase
• Vo AdVd AcVc

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Differential and Common-mode operation

• Opposite polarity input if opposite polarity
  inputs applied to an OP-AMP are ideally opposite
  signals, Vi1 -Vi2 Vs
• Vd 2Vs
• Same polarity input if the same polarity are
  applied to an OP-AMP, Vi1 Vi2 Vs
• Vd 0

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Ideal OP-AMP

• We can describe ideal OP-AMP having infinite
  input impedance, zero output impedance, and
  infinite voltage gain.

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Ideal Op Amp
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Basic op-amp
UNITY GAIN IF RF R1 THE GAIN IS
VOLTAGE GAIN RF/R1 -1 So that the
circuit provides a unity voltage gain with 180
degrees phase inversion. If RF is exactly R1 the
voltage gain is 1.
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Basic op-amp
CONSTANT MAGNITUDE GAIN If rf is some multiple
of r1, the overall amplifier gain is a constant.
For example if rf 10r1. Then
voltage gain rf/r1 -10 And the circuits
provides a voltage gain of exactly 10 along with
an 180 degrees phase inversion from the input
signal.
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Basic op-amp
VIRTUAL GROUND The output voltage is limited by
the supply voltage of,typically a few volts.
Voltage gains are very high. Example Vo -10V
and Ax 20000 the input voltage would then be
Vi -Vo/Ax 10V /20000 0.5mV
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Practical OP-AMP Circuit

• - Inverting
• - Non-inverting
• - unity follower
• - Summing
• - Difference Amplifier
• - Integrator

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Practical OP-AMP Circuit

• Inverting Amplifier output is obtained by
  multiplying the input by fixed or constant gain.
• Non-inverting amplifier.
• Unity follower provides gain of unity (1) with
  no polarity or phase reversal. The circuit
  operates like emitter.

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Practical OP-AMP Circuit

• Summing 3 inputs summing amplifier circuit which
  provides means of algebraically summing 3
  voltages, each can multiplied by a constant gain
  factor.
• Integrator feedback component used is a
  capacitor.
• Differential.

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Example of non-inverting op-amp
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Example of inverting op-amp