DEE 509�AD&TVE Theory

Unit 1

Lecture 4

ADDER/ SUMMING AMPLIFIER USING OP-AMP

• The Voltage adder or summing amplifier is an electronic circuit that produces an output, which is equal to the sum of the applied inputs (in form of voltage signals) on either of its terminal.

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Inverting Adder

Non-inverting Adder

• In this simple summing amplifier circuit, the output voltage, ( Vout ) now becomes proportional to the sum of the input voltages, V₁, V₂, V₃, etc. Then we can modify the original equation for the inverting amplifier to take account of these new inputs thus:

For Inverting Adder

• For a 2-input non-inverting summing amplifier the currents flowing into the input terminals can be defined as:

Applications of Adder

• It can be used to add the signals.
• It can be used as an averaging amplifier with the proper input and feedback resistor values a summing amplifier can be modified to provide an output voltage which is equal to the average input values.
• Summing Amplifier Audio Mixer
• Can be used to produce an audio mixer for adding or mixing together individual waveforms (sounds) from different source channels (vocals, instruments, etc) before sending them combined to an audio amplifier.
• Digital to Analogue Converter

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SUBTRACTOR/ DIFFERENTIAL AMPLIFIER USING OP-AMP

• The differential amplifiers amplify the difference between two voltages making this type of operational amplifier circuit a subtractor unlike a summing amplifier which adds or sums together the input voltages.

• By connecting each input in turn to 0v ground we can use superposition to solve for the output voltage Vout. Then the transfer function for a Differential Amplifier circuit is given as:

• It is used as a series negative feedback circuit by using op-amp
• Generally, we use differential amplifier that acts as a volume control circuit.
• The differential operational amplifier can be used as an automatic gain control circuit.
• Some of the differential operational amplifier can be used for Amplitude modulation.

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Applications of Subtractor

WAVE SHAPING CIRCUITS

• A wave shaping circuit is designed to modify some specific portions of a wave (with respect to magnitude or time).
• A wave shaping circuit can be made to vary either the current or voltage characteristics.
• Wave shaping Circuits are commonly used in digital computers and Communication such as TV and FM Receivers.

Need of Wave shaping

• To Generate one wave from the other.
• To limit the voltage level of the waveform to some preset value and suppressing all other voltage levels in excess of the preset value.
• To cut off the +ve and –ve portions of the input waveform.
• To hold the waveform to a particular DC level.

Types of Wave Shaping Circuits

Clippers

• In Electronics, a Clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage level without distorting the remaining part of the applied waveform.
• In Op-Amp Clipper circuits, a rectifier diode may be used to clip off a certain portion of the I/P signal to obtain a desired O/P waveform.
• The diode works as a switch in the circuit.

Positive Clipper

• A positive clipper is a clipper that clips only the positive portion(s) of the input signal.
• V_i is connected to the Non-inverting terminal of Op-Amp. V_ref can be chosen by varying the potentiometer 

R₂ and connected to +V_CC

• If V_i is less than the value of V_ref then the diode D₁ conducts (ON). Then, the circuit given above behaves as a voltage follower.

i.e. V_O= V_i for V_i < V_ref

• If V_i is greater than the value of reference voltage  V_ref , then the diode D₁ will be OFF. Now, the Op-Amp operates in an open loop since the feedback path was open.

i.e. V_{O =} V_ref for V_i > V_ref

Negative Clipper

• A negative clipper is a clipper that clips only the negative portion(s) of the input signal.
• Diode is reversely connected and reference voltage V_ref will be taking from -V_EE
• If V_i is greater than the value of V_ref then the diode D₁ conducts (ON). Then, the circuit given above behaves as a voltage follower.

i.e. V_O= V_i for V_i > V_ref

• If V_i is less than the value of the reference voltage V_ref then the diode D₁ will be OFF. Now, the Op-Amp operates in an open loop since the feedback path was open.

i.e. V_{O =} V_ref for V_i < V_ref

Applications of Clippers

• In the separation of synchronizing signals existing from the composite color picture signals.
• In generation of new waveforms or shaping existing waveform.
• The excessive noise spikes above a certain level can be limited or clipped in FM transmitters by using the series clippers
• Frequently used half wave rectifier in power supply kits is a typical example of a clipper. It clips either positive or negative half wave of the input.
• Used in speech processing for communications (radio) applications. 

Clampers

• A clamper is an electronic circuit that produces an output, which is similar to the input but with a shift in the DC level.
• The output of a clamper is an exact replica of the input.
• Clampers are used to introduce or restore the DC Level of Input signal at the output.
• It pushes the signal towards the positive or the negative side

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• Need Of Clamping.
• Certain applications in electronics require that the upper or lower extremity of a wave be fixed at a specific value. In such applications, a CLAMPING (or CLAMPER) circuit is used.
• There are two types of clampers based on the DC shift of the input.
• Positive Clampers
• Negative Clampers

Positive Clamper

• A positive clamper is a clamper circuit that produces an output in such a way that the input signal gets shifted vertically by a positive DC value.
• V_i  is applied to the inverting terminal of op-amp through a network that consists of a capacitor C1 and a resistor R1. The V_ref is applied to the non-inverting terminal of the op-amp whose can be chosen by varying the resistor R2
• The clamper circuit produces an output in such a way that the sinusoidal voltage signal  V_i  gets shifted vertically upwards by the value of reference voltage V_ref.�

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Negative Clamper

• A negative clamper is a clamper circuit that produces an output in such a way that the input signal gets shifted vertically by a negative DC value.
• In this case, we will get reference voltage  V_ref  of a negative value.
• The above circuit produces an output, which is the combination (resultant sum) of sinusoidal voltage signal  V_i and reference voltage  V_ref.
• That means, the clamper circuit produces an output in such a way that the sinusoidal voltage signal  V_i  gets shifted vertically downwards by the value of reference voltage  V_ref.

Applications of Clampers

• Clampers are frequently used in test equipment, sonar and radar systems.
• Clampers can be used for removing distortions
• To improve overdrive recovery time clampers are used.
• Clampers can be used as voltage doublers or voltage multipliers.