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Chapter: Linear Integrated Ciruits : Application of Op-Amp

Important Short Questions and Answers: Applications of Op Amp

Linear Integrated Ciruits - Application of Op-Amp - Important Short Questions and Answers: Applications of Op Amp

Applications of Op Amp


1.What is the need for an instrumentation amplifier?


In a number of industrial and consumer applications, the measurement of physical quantities is usually done with the help of transducers. The output of transducer has to be amplified So that it can drive the indicator or display system. This function is performed by an instrumentation amplifier.



2.List the features of instrumentation amplifier:


¯          high gain accuracy


¯          high CMRR


¯          high gain stability with low temperature co-efficient


¯          low dc offset


¯          low output impedance


3.What is a comparator?


A comparator is a circuit which compares a signal voltage applied at one input of an op-amp with a known reference voltage at the other input. It is an open loop op - amp with output + Vsat .



4.What are the applications of comparator?


¯          Zero crossing detector


¯          Window detector


¯          Time marker generator


¯          Phase detector


5.What is a Schmitt trigger?


Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square wave output. The output of Schmitt trigger swings between upper and lower threshold voltages, which are the reference voltages of the input waveform.


6.What is a multivibrator?


Multivibrators are a group of regenerative circuits that are used extensively in timing applications. It is a wave shaping circuit which gives symmetric or asymmetric square output. It has two states either stable or quasi- stable depending on the type of multivibrator.


7.What do you mean by monostable multivibrator?


Monostable  multivibrator  is  one  which  generates  a  single  pulse  of specified duration in response to each external trigger signal.  It has only one stable state.  Application of a trigger causes a change to the quasi-stable state.An external


trigger signal generated due to charging and discharging of the capacitor produces the transition to the original stable state.



8.What is an astable multivibrator?


Astable multivibrator is a free running oscillator having two quasi-stable states. Thus, there is oscillations between these two states and no external s i g n a l a r e required to produce the change in state.



9.What is a bistable multivibrator?


Bistable multivibrator is one that maintains a given output voltage level unless an external trigger is applied . Application of an external trigger signal causes a change of state, and this output level is maintained indefinitely until an second trigger is applied . Thus, it requires two external triggers before it returns to its initial state



10.What are the requirements for producing sustained oscillations in feedback circuits?

For sustained oscillations,


¯          The total phase shift around the loop must be zero at the desired frequency of oscillation, fo. ie, LAB =0 (or) 360°


¯          At fo, the magnitude of the loop gain | A b | should be equal to unity


11.What are the different types of filters?

Based on functions:  Low pass filter,High pass  filter,Band pass filter, Band reject filter

Based on order of transfer function: first ,second,third higher order filters.

Based on configuration: Bessel,Chebychev,Butterworth  filters.


12.List the broad classification of ADCs.


1.        Direct type ADC.

2.        Integrating type ADC.


13.List out the direct type ADCs.

1.        Flash (comparator) type converter


2.        Counter type converter

3.        Tracking or servo converter

4.        Successive approximation type converter

14.   List out some integrating type converters.


1.        Charge balancing ADC

2.        Dual slope ADC


15.What is integrating type converter?


An ADC converter that perform conversion in an indirect manner by first changing the analog I/P signal to a linear function of time or frequency and then to a digital code is known as integrating type A/D converter.


16.Explain in brief the principle of operation of successive Approximation ADC.


The circuit of successive approximation ADC consists of a successive approximation register (SAR), to find the required value of each bit by trial & error.With the arrival of START command, SAR sets the MSB bit to 1. The O/P is converted into an analog signal & it is compared with I/P signal. This O/P is low or High. This process continues until all bits are checked.


17.What are the main advantages of integrating type ADCs?


i.          The integrating type of ADC’s do not need a sample/Hold circuit at the input.


ii.        It is possible to transmit frequency even in noisy environment or in an isolated form.


18.Define conversion time.


It is defined as the total time required to convert an analog signal into its digital output. It depends on the conversion technique used & the propagation delay of circuit components.


The conversion time of a successive approximation type ADC is given by T(n+1)

where T---clock period

Tc---conversion time n----no. of bits


19.Define resolution of a data converter.


The resolution of a converter is the smallest change in voltage which may be produced at the output or input of the converter.


Resolution (in volts)= VFS/2n-1=1 LSB increment. The resolution of an ADC is defined as the smallest change in analog input for a one-bit change at the output.


20.Explain in brief stability of a converter:


The performance of converter changes with temperature age & power supply variation. So all the relevant parameters such as offset, gain, linearity error & monotonicity must be specified over the full temperature & power supply ranges to have better stability performances.


21.What is meant by linearity?


The linearity of an ADC/DAC is an important measure of its accuracy & tells us how close the converter output is to its ideal transfer characteristics. The linearity error is usually expressed as a fraction of LSB increment or percentage of full-scale voltage. A good converter exhibits a linearity error of less than ±½LSB.


22.What is a sample and hold circuit? Where it is used?


A sample and hold circuit is one which samples an input signal and holds on to its last sampled value until the input is sampled again. This circuit is mainly used in digital interfacing, analog to digital systems, and pulse code modulation systems.


23.Define sample period and hold period.


The time during which the voltage across the capacitor in sample and hold circuit is equal to the input voltage is called sample period.The time period during which the voltage across the capacitor is held constant is called hold period.


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