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NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Building, Aguinaldo Highway Dasmariñas City, Cavite ASSIGNMENT # 1 OPERATIONAL AMPLIFIERBani, Arviclyn C. July 26, 2011Electronics 3/BSECE 41A1 Score: Engr. Grace Ramones Instructor
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Operational AmplifiersAs well as resistors and capacitors, Operational Amplifiers, or Op-amps as they are more commonlycalled, are one of the basic building blocks of Analogue Electronic Circuits.Operational amplifiers are linear devices that have all the properties required for nearly ideal DCamplification and are therefore used extensively in signal conditioning, filtering or to performmathematical operations such as add, subtract, integration and differentiation.An ideal Operational Amplifier is basically a three-terminal device which consists of two highimpedance inputs, one called the Inverting Input, marked with a negative sign, ("-") and the otherone called the Non-inverting Input, marked with a positive plus sign ("+").The third terminal represents the op-amps output port which can both sink and source either avoltage or a current. In a linear operational amplifier, the output signal is the amplification factor,known as the amplifiers gain (A) multiplied by the value of the input signal and depending on thenature of these input and output signals, there can be four different classifications of operationalamplifier gain. Voltage – Voltage "in" and Voltage "out" Current – Current "in" and Current "out" Transconductance – Voltage "in" and Current "out" Transresistance – Current "in" and Voltage "out"
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Equivalent Circuit for Operational AmplifiersCharacteristics of Operational AmplifiersThe Operational Amplifier, or Op-amp as it is most commonly called, is an ideal amplifier withinfinite Gain and Bandwidth when used in the Open-loop mode with typical d.c. gains of 100,000,or 100dB.The basic Op-amp construction is of a 3-terminal device, 2-inputs and 1-output.An Operational Amplifier operates from either a dual positive (+V) and an correspondingnegative (-V) supply, or they can operate from a single DC supply voltage.The two main laws associated with the operational amplifier are that it has an infinite inputimpedance, (Z∞) resulting in "No current flowing into either of its two inputs" and zero inputoffset voltage "V1 = V2".An operational amplifier also has zero output impedance, (Z = 0).Op-amps sense the difference between the voltage signals applied to their two input terminalsand then multiply it by some pre-determined Gain, (A).This Gain, (A) is often referred to as the amplifiers "Open-loop Gain".
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The Two Basic Operational Amplifier CircuitsOp-amps can be connected into two basic configurations, Inverting and Non-inverting.The Open-loop gain called the Gain Bandwidth Product, or (GBP) can be very high and is ameasure of how good an amplifier is.Very high GBP makes an operational amplifier circuit unstable as a micro volt input signal causesthe output voltage to swing into saturation.By the use of a suitable feedback resistor, (Rf) the overall gain of the amplifier can be accuratelycontrolled.
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Gain Bandwidth ProductFor negative feedback, were the fed-back voltage is in "anti-phase" to the input the overall gainof the amplifier is reduced.For positive feedback, were the fed-back voltage is in "Phase" with the input the overall gain ofthe amplifier is increased.By connecting the output directly back to the negative input terminal, 100% feedback is achievedresulting in a Voltage Follower (buffer) circuit with a constant gain of 1 (Unity).Changing the fixed feedback resistor (Rf) for a Potentiometer, the circuit will have AdjustableGain.
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Differential and Summing Operational Amplifier CircuitsThe Differential Amplifier produces an output that is proportional to the difference between the2 input voltages.Adding more input resistor to either the inverting or non-inverting inputs Voltage Adders orSummers can be made.Voltage follower op-amps can be added to the inputs of Differential amplifiers to produce highimpedance Instrumentation amplifiers.
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Differentiator and Integrator Operational Amplifier CircuitsThe Integrator Amplifier produces an output that is the mathematical operation of integration.The Differentiator Amplifier produces an output that is the mathematical operation ofdifferentiation.Both the Integrator and Differentiator Amplifiers have a resistor and capacitor connected acrossthe op-amp and are affected by its RC time constant.In their basic form, Differentiator Amplifiers suffer from instability and noise but additionalcomponents can be added to reduce the overall closed-loop gain.
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Comparator Compares two voltages and switches its output to indicate which voltage is larger. . Voltage follower (Unity Buffer Amplifier) Used as a buffer amplifier to eliminate loading effects(e.g., connecting a device with a high source impedance to a device with a low input impedance).Inverting integrator - Integrates the (inverted) signal over timeInverting differentiator- Differentiates the (inverted) signal over time.Schmitt trigger - A bistable multivibrator implemented as a comparator with hysteresis.
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Relaxation oscillator - By using an RC network to add slow negative feedback to theinverting Schmitt trigger, a relaxation oscillator is formed. The feedback through the RC networkcauses the Schmitt trigger output to oscillate in an endless symmetric square wave (i.e., theSchmitt trigger in this configuration is an astable multivibrator). Inductance gyrator - Simulates an inductor (i.e., provides inductance without the use of apossibly costly inductor). The circuit exploits the fact that the current flowing through a capacitorbehaves through time as the voltage across an inductor. The capacitor used in this circuit is smallerthan the inductor it simulates and its capacitance is less subject to changes in value due toenvironmental changes. Zero level detector - Voltage divider reference; Zener sets reference voltage; Acts as acomparator with one input tied to ground; When input is at zero, op-amp output is zero (assumingsplit supplies.) Negative impedance converter (NIC) - Creates a resistor having a negative value for any signalgenerator
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Wien bridge oscillator - Produces a very low distortion sine wave. Uses negative temperaturecompensation in the form of a light bulb or diode . Precision rectifier - The voltage drop VF across the forward biased diode in the circuit of a passiverectifier is undesired. In this active version, the problem is solved by connecting the diode in thenegative feedback loop. The op-amp compares the output voltage across the load with the inputvoltage and increases its own output voltage with the value of VF. As a result, the voltage drop VF iscompensated and the circuit behaves very nearly as an ideal (super) diode with VF = 0 V. Logarithmic output Exponential output
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