linear integrated circuits interview questions and answers P-4

1.   Briefly explain the block diagram of PLL and derive the expression for Lock
range and capture range.

Block diagram of PLL

Explanation for each block.

Derivation for capture range and lock range.

2.   With a neat functional diagram, explain the operation of VCO. Also derive
an expression for fo.

Internal diagram for VCO IC.

Explanation

Derivation for fo.

3.   Analyse the Gilbert's four quadrant multiplier cell with a neat circuit
diagram.Discuss its applications.

Circuit diagram

Analysis

Expression for output current Applications.

      4.   In detail dicuss the applications of PLL:

AM detection

FM demodulation

FSK demodulation

Frequency multiplication/division.

1.   List the broad classification of ADCs.

1.    Direct type ADC.

2.    Integrating type ADC.

2.   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

3.   List out some integrating type converters.

1.      Charge balancing ADC

2.      Dual slope ADC

4.   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.

5.   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.

6.   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.

7.   Where are the successive approximation type ADC's used?

The Successive approximation ADCs are used in applications such as data loggers & instrumentation where conversion speed is important.

8.   What is the main drawback of a dual-slop ADC?

The dual slope ADC has long conversion time. This is the main drawback of dual slope ADC.

9.   State the advantages of dual slope ADC:

It provides excellent noise rejection of ac signals whose periods are integral multiples of the integration time T.

10. 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

11. 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.

12.       Define accuracy of converter.

Absolute accuracy:

It is the maximum deviation between the actual converter output & the ideal converter output.

Relative accuracy:

It is the maximum deviation after gain & offset errors have been removed. The accuracy of a converter is also specified in form of LSB increments or % of full scale voltage.

13.       What is settling time?

It represents the time it takes for the output to settle within a specified band i^LSB of its final value following a code change at the input (usually a full scale change). It depends upon the switching time of the logic circuitry due to internal parasitic capacitance & inductances. Settling time ranges from 100ns. 10^s depending on word length & type circuit used.

14.       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.

15.       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 +V2LSB.

16.       What is monotonic DAC?

A monotonic DAC is one whose analog output increases for an increase in digital input.

17.       What is multiplying DAC?

A digital to analog converter which uses a varying reference voltage V_R is called a multiplying DAC(MDAC). If the reference voltage of a DAC, Vr is a sine wave give by

V(t)=Vm Cos 2nft Then, Vo(t)=V_omCos(2nft + 180°)

18.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

19.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.

20.What is meant by delta modulation?

Delta modulation is a technique capable of performing analog signal quantisation with smaller bandwidth requirements. Here, the binary output representing the most recent sampled amplitude will be determined on the basis of previous sampled amplitude levels.

1.  What is integrating type converter?Explain the operation of dual slope ADC:

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.

Functional diagram of Dual slope ADC.

Explanation, Derivation.

2.  Explain 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. Functional diagram Operation

Truth table, Output graph.

3 . Explain the operation of sample and hold circuit .

Circuit diagram Operation Output waveforms.

4. Explain the various types of digital to analog converters:

Weighted resistor DAC

R-2R ladder DAC

Inverted 

R-2R ladder DAC

Circuit diagram & operation for each

5. What is delta sigma modulation?Explain the A/D conversion using Delta modulator.

Delta modulation is a technique capable of performing analog signal quantisation with smaller bandwidth requirements. Here, the binary output representing the most recent sampled amplitude will be determined on the basis of previous sampled amplitude levels. Functional diaaagram Operation.