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DEE 509�Analog, Digital &TV Engg.�

Unit 1

Lecture 2

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Applications of Op-Amp

  • Differentiator Amplifier
  • Integrator Amplifier
  • Op-Amp as Comparator
  • Summing Amplifier (Adder)
  • Differential Amplifier (Subtactor)
  • Op-Amp as Multivibrator

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  • An Op-Amp can be operated in Two configurations:
    • Inverting Amplifier Configuration
    • Non-Inverting Amplifier Configuration
  • Output Voltage of Op-Amp will be:
    • For Inverting Amplifier

Vout= -(Rf/Rin)*Vin

    • For Non-Inverting Amplifier

Vout= (1+Rf/Rin)* Vin

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Inverting Amplifier configuration

  • An inverting amplifier using Op-Amp is a type of amplifier where, the output waveform will be phase opposite to the input waveform.
  • The input waveform will be amplified by the factor Av (voltage gain of the amplifier) in magnitude and its phase will be inverted.
  • In the inverting amplifier circuit, the signal to be amplified is applied to the inverting input of the Op-Amp through the input resistance R1.
  • Rf is the feedback resistor. Rf and R1 together determine the gain of the amplifier.

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Op-Amp in inverting amplifier configuration

Input and output waveform of inverting amplifier

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  • The Non-inverting amplifier using Op-Amp is a type of amplifier where, the output waveform will be in same phase to the input waveform.
  • In this electronic circuit design, the signal is applied to the non-inverting input of the Op-Amp. In this way the signal at the O/P is not inverted when compared to the input.
  • The feedback is taken from the O/P of the Op-Amp via a resistor Rf to the inverting input of the operational amplifier where another resistor R1 is taken to ground. It has to be applied to the inverting input as it is negative feedback. Rf and R1 together determine the gain of the amplifier.
  • The non-inverting amplifier circuit provides a high input impedance along with all the advantages gained from using an Op-Amp.

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Non-Inverting Amplifier configuration

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Op-Amp in Non-inverting amplifier configuration

Input and output waveform of Non-inverting amplifier

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OP-AMP AS DIFFERENTIATOR

  • The basic operational amplifier differentiator circuit produces an output signal which is the first derivative of the input signal.
  • This operational amplifier circuit performs the mathematical operation of Differentiation, that is it “produces a voltage output which is directly proportional to the input voltage’s rate-of-change with respect to time“

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OP-AMP as Differentiator

  • The capacitor C blocks any DC content only allowing AC type signals to pass through and whose frequency is dependent on the rate of change of the input signal.
  • At low frequencies the reactance of the capacitor is "High" resulting in a low gain (Rf/Xc) and low output voltage from the op-amp.
  • Problems in an Ordinary op-amp differentiator are instability and high frequency noise.
  • A Resistor is added in series with the capacitor at the input and a capacitor is added in parallel to the resistor in the feedback circuit in the practical differentiator to eliminate the above problems.
  • The output Voltage of Differentiator will be:

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OP-AMP AS AN INTEGRATOR

  • The integrator Op-Amp produces an output voltage that is both proportional to the amplitude and duration of the input signal.
  • the Op-Amp Integrator is an operational amplifier circuit that performs the mathematical operation of Integration.
  • the Op-Amp integrator produces an output voltage which is proportional to the integral of the input voltage.

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OP-AMP as an Integrator

  • In Op-Amp, the magnitude of the output signal is determined by the length of time a voltage is present at its input as the current through the feedback loop charges or discharges the capacitor as the required negative feedback occurs through the capacitor.
  • The gain of an integrator at low frequency is very high and the circuit goes to saturation.
  • The feedback capacitor is shunted with a resistor in the practical integrator to overcome the above problem.
  • The Output Voltage of the Integrator will be:

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Fig: A practical Op-Amp Integrator circuit

Integrator waveforms

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OP-AMP AS COMPARATOR

  • The Op-Amp comparator compares one analogue voltage level with another analogue voltage level, or some preset reference voltage, VREF and produces an output signal based on this voltage comparison.
  • In other words, the Op-Amp voltage comparator compares the magnitudes of two voltage inputs and determines which is the largest of the two.
  • Voltage comparators can either use positive feedback or no feedback at all (open-loop mode) to switch its output between two saturated states, because in the open-loop mode the amplifiers voltage gain is basically equal to AVO.

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OP-AMP AS A NON- INVERTING COMPARATOR

  • The sinusoidal input signal VIN is applied to the non-inverting terminal. The fixed reference voltage VREF is given to the inverting terminal (-) of the op-amp.
  • When VIN is greater than VREF, the output voltage Vo goes to positive saturation.
  • When VIN is lesser than VREF, the output voltage Vo goes to negative saturation.

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OP-AMP AS AN INVERTING COMPARATOR

  • The sinusoidal input signal VIN is applied to the inverting terminal. The fixed reference voltage VREF is given to the non-inverting terminal (+) of the op-amp.
  • When VIN is lesser than VREF the output voltage Vo goes to positive saturation.
  • When VIN is greater than VREF, the output voltage Vo goes to negative saturation.

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For Non-Inverting Comparator

For Inverting Comparator

Fig: Output Waveforms

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OP-AMP IC PIN CONFIGURATION