DIGITAL ELECTRONICS QUESTION AND ANSWER

Q.Define combinational logic 
When  logic  gates  are  connected  together  to  produce a  specified  output  for  certain 
specified combinations of  input  variables,  with no  storage  involved, the  resulting  circuit is called combinational logic. 

Q. Define Half adder and full adder 
The logic circuit that performs the addition of two bits is a half adder. The circuit that 
performs the addition of three bits is a full adder. 

Q. Define Decoder
 A decoder is a multiple - input multiple output logic circuit that converts coded inputs into coded outputs where the input and output codes are different. 

Q. What is binary decoder? 
 A  decoder  is  a  combinational  circuit  that  converts binary  information  from  n  input 
lines to a maximum of 2ⁿ out puts lines. 

Q. Define Encoder? 
 An encoder has 2ⁿ input lines and n output lines. In encoder the output lines generate 
the binary code corresponding to the input value. 

Q. What is priority Encoder? 
 A priority encoder is an encoder circuit that includes the priority function. In priority 
encoder,  if  2  or  more  inputs  are  equal  to  1  at  the  same  time,  the  input  having  the  highest priority will take precedence.

Q. Define multiplexer
 Multiplexer is a digital switch. If allows digital information from several sources to be 
routed onto a single output line. 

Q. What do you mean by comparator 
 A comparator is a special combinational circuit designed primarily to compare the 
relative magnitude of two binary numbers. 

Q. What are the classification of sequential circuits? 
 The sequential circuits are classified on the basis of timing of their signals into two 
types. They are, 
  1)Synchronous sequential circuit. 
  2)Asynchronous sequential circuit. 

Q. Define Flip flop. 
 The basic unit for storage is flip flop. A flip-flop maintains its output state either at 1 
or 0 until directed by an input signal to change its state. 

Q.What are the different types of flip-flop? 
 There are various types of flip flops. Some of them are mentioned below they are, 
RS flip-flop 
SR flip-flop 
D flip-flop 
JK flip-flop 
T flip-flop 

Q.What is the operation of D flip-flop? 
 In D flip-flop during the occurrence of clock pulse if D=1, the output Q is set and if 
D=0, the output is reset. 

Q. What is the operation of JK flip-flop? 
•  When K input is low and J input is high the Q output of flip-flop is 
set. 
•  When K input is high and J input is low the Q output of flip-flop is 
reset. 
•  When both the inputs K and J are low the output does not change 
•  When both the inputs K and J are high it is possible to set or reset the 
flip-flop (ie) the output toggle on the next positive clock edge. 

Q. What is the operation of T flip-flop? 
 T flip-flop is also known as Toggle flip-flop. 
•  When T=0 there is no change in the output. 
•  When T=1 the  output  switch to  the  complement  state  (ie)  the output 
toggles. 

Q. Define race around condition. 
 In JK flip-flop output is fed back to the input. Therefore change in the output results 
change in the input. Due to this in the positive half of the clock pulse if both J and K are high 
then output toggles continuously. This condition iscalled ‘race around condition’. 

Q. What is edge-triggered flip-flop? 
 The  problem  of  race around  condition  can  solved  by edge  triggering  flip  flop.  The 
term  edge  triggering  means  that  the  flip-flop  changes  state  either  at  the  positive  edge  or negative edge of the clock pulse and it is sensitive to its inputs only at this transition of the clock. 

Q. What is a master-slave flip-flop? 
 A master-slave flip-flop consists of two flip-flops where one circuit serves as a master 
and the other as a slave. 

Q.Define registers. 
A register is a group of flip-flops flip-flop can store one bit information. So an n-bit register 
has  a  group  of  n  flip-flops  and  is  capable  of  storing  any  binary  information/number 
containing n-bits. 

Q.Define shift registers. 
 The  binary  information  in  a  register  can  be  moved from  stage  to  stage  within  the 
register  or  into  or  out  of  the  register  upon  application  of  clock  pulses.  This  type  of  bit movement  or  shifting  is  essential  for  certain  arithmetic  and  logic  operations  used  in microprocessors. This gives rise to group of registers called shift registers. 

Q.What are the different types of shift type? 
 There are five types. They are, 
Serial In Serial Out Shift Register 
Serial In Parallel Out Shift Register 
Parallel In Serial Out Shift Register 
Parallel In Parallel Out Shift Register 
Bidirectional Shift Register  

 Q.Define synchronous sequential circuit 
 In synchronous sequential circuits, signals can affect the memory elements only at 
discrete instant of time. 

Q. Define Asynchronous sequential circuit? 
 In  asynchronous  sequential  circuits  change  in  input  signals  can  affect  memory 
element at any instant of time. 

MICROPROCESSOR QUESTION AND ANSWER

Q.What is Microprocessor? Give the power supply & clock frequency of 8085 
A microprocessor is a multipurpose, programmable logic device that reads 
binary  instructions  from  a  storage  device  called  memory  accepts  binary  data  as 
input  and  processes  data  according  to  those  instructions  and  provides  result  as 
output. The power supply of 8085 is +5V and clock frequency in 3MHz. 

Q. List few applications of microprocessor-based system. 
It is used: 
i. For  measurements,  display  and  control  of  current,  voltage, temperature, pressure, etc. 
ii.  For traffic control and industrial tool control. 
iii.  For speed control of machines. 

Q. What are the functions of an accumulator? 
The  accumulator  is  the  register  associated  with  the  ALU  operations  and sometimes I/O operations. It is an integral part of ALU. It holds one of data to be processed by ALU. It also temporarily stores the result of the operation performed by the ALU. 

Q. List the 16 – bit registers of 8085 microprocessor. 
Stack pointer (SP) and Program counter (PC).

Q.  List the allowed register pairs of 8085. 
•  B-C register pair 
•  D-E register pair 
•  H-L register pair 

Q.  Mention the purpose of SID and SOD lines 
SID (Serial input data line): 
It is an input line through which the microprocessor accepts serial data. 
SOD (Serial output data line): 
It is an output line through which the microprocessor sends output serial data. 

Q.  What is an Opcode? 
The part of the instruction that specifies the operation to be performed is called the Operation code or opcode. 

Q.  What is the function of IO/M signal in the 8085? 
It is a status signal. It is used to differentiate between memory locations and  I/O  operations.  When  this  signal  is  low  (IO/M  =  0)  it  denotes the memory related operations. When this signal is high (IO/M = 1) it denotes an I/O operation. 

Q.  What is an Operand? 
The data on which the operation is to be performed is called as an Operand. 

Q.  How  many  operations  are  there  in  the  instruction  set  of 8085 microprocessor? 
There are 74 operations in the 8085 microprocessor. 

Q. List  out  the  five  categories  of  the  8085  instructions.  Give  examples  of  the instructions for each group. 
•  Data transfer group – MOV, MVI, LXI. 
•  Arithmetic group – ADD, SUB, INR. 
•  Logical group –ANA, XRA, CMP. 
•  Branch group – JMP, JNZ, CALL. 
•  Stack I/O and Machine control group – PUSH, POP, IN, HLT. 

Q. Explain the difference between a JMP instruction and CALL instruction. 
A  JMP  instruction  permanently  changes  the  program  counter.  A  CALL instruction  leaves  information  on  the  stack  so  that  the  original  program  execution sequence can be resumed. 

Q.  Explain the purpose of the I/O instructions IN and OUT. 
The  IN  instruction  is  used  to  move  data  from  an  I/O  port  into  the accumulator. 
The OUT instruction is used to move data from the accumulator to an I/O port. 
The IN & OUT instructions are used only on microprocessor, which use a separate address space for interfacing. 

Q.  What is the difference between the shift and rotate instructions? 
A rotate instruction is a closed loop instruction. That is, the data moved out at one end is put back in at the other end. The shift instruction loses the data that is moved out of the last bit locations. 

Q.  How many address lines in a 4096 x 8 EPROM CHIP? 
12 address lines. 

Q.  Control signals used for DMA operation are ____________ 
HOLD & HLDA. 

Q.  What is meant by Wait State? 
This state is used by slow peripheral devices. The peripheral devices can 
transfer the data to or from the microprocessor by using READYinput line. The 
microprocessor remains in wait state as long as READY line  is low. During the 
wait  state,  the  contents  of  the  address,  address/data  and  control  buses  are  held 
constant. 

Q.  List the four instructions which control the interrupt structure of the 8085 
microprocessor. 
•  DI ( Disable Interrupts ) 
•  EI ( Enable Interrupts ) 
•  RIM ( Read Interrupt Masks ) 
•  SIM ( Set Interrupt Masks ) 

Q.  What is meant by polling? 
Polling or device polling is a process which identifies the device that has interrupted the microprocessor. 

Q.  What is meant by interrupt? 
Interrupt is an external signal that causes a microprocessor to jump to a specific subroutine. 

Q.  Explain priority interrupts of 8085. 
The 8085 microprocessor has five interrupt inputs. They are TRAP, RST 7.5,  RST  6.5,  RST  5.5,  and  INTR.  These  interrupts  have  a  fixed  priority  of interrupt service. 
If two or more interrupts go high at the same time, the 8085 will service them on priority basis. The TRAP has the highest priority followed  bye RST 7.5, RST 6.5, RST 5.5. The priority of interrupts in 8085 is shown in the table. 
Interrupts  Priority 
TRAP 
RST 7.5 
RST 6.5 
RST 5.5 
INTR 

Q.  What is a microcomputer? 
 A computer that is designed using a microprocessor as its CPU is called microcomputer. 

Q.  What is the signal classification of 8085 
All the signals of 8085 can be classified into 6 groups 
•  Address bus 
•  Data bus 
•  Control and status signals 
•  Power supply and frequency signals 
•  Externally initiated signals 
•  Serial I/O ports 

Q.  What are operations performed on data in 8085 
The various operations performed are 
•  Store 8-bit data 
•  Perform arithmetic and logical operations 
•  Test for conditions 
•  Sequence the execution of instructions 
•  Store data temporarily during execution in the defined R/W memory locations called the stack 

Q.  Steps involved to fetch a byte in 8085 
i.  The PC places the 16-bit memory address on the address bus 
ii.  The  control  unit  sends  the  control  signal  RD  to  enable  the  memory chip 
iii.  The byte from the memory location is placed on the data bus 
iv.  The byte is placed in the instruction decoder of the microprocessor and 
the task is carried out according to the instruction 

Q.  How many interrupts does 8085 have, mention them 
The 8085 has 5 interrupt signals; they are INTR, RST7.5, RST6.5, RST5.5 
and TRAP 

Q.  Basic concepts in memory interfacing 
The  primary  function  of  memory  interfacing  is  that  the  microprocessor 
should be able to read from and write into a given register of a memory chip. To 
perform these operations the microprocessor should 
•  Be able to select the chip 
•  Identify the register 
•  Enable the appropriate buffer 

Q.  Define instruction cycle, machine cycle and T-state 
Instruction cycle is defined, as the time required completing theexecution of an instruction. Machine cycle is defined as the time required completing one operation  of  accessing  memory,  I/O  or  acknowledging  an  external  request.  Tcycle is defined as one subdivision of the operation performed in one clock period 

Q.  What is an instruction? 
An  instruction  is  a  binary  pattern  entered  through  an  input  device  to command the microprocessor to perform that specific function 

Q.  What is the use of ALE 
The ALE is used to latch the lower order address so that it can be available in T2 and T3 and used for identifying the memory address. During T1 the ALE goes  high,  the  latch  is  transparent  ie,  the  output  changes  according  to  the  input data, so the output of the latch is the lower order address. When ALE goes low the lower order address is latched until the next ALE. 

Q.  How many machine cycles does 8085 have, mention them 
The 8085 have seven machine cycles. They are 
•  Opcode fetch 
•  Memory read 
•  Memory write 
•  I/O read 
•  I/O write 
•  Interrupt acknowledge 
•  Bus idle 

Q.  Explain the signals HOLD, READY and SID 
HOLD  indicates  that  a  peripheral  such  as  DMA  controller  is  requesting 
the  use  of  address  bus,  data  bus  and  control  bus.  READY  is  used  to  delay  the 
microprocessor read or write cycles until a slow responding peripheral is ready to 
send or accept data. SID is used to accept serial data bit by bit 

Q.  Mention  the  categories  of  instruction  and  give  two  examples  for  each 
category 
The instructions of 8085 can be categorized into the following five 
•  Data transfer   MOV Rd,Rs STA 16-bit 
•  Arithmetic   ADD R  DCR M 
•  Logical   XRI 8-bit  RAR 
•  Branching   JNZ   CALL 16-bit 
•  Machine control  HLT   NOP 

Q.  Explain LDA, STA and DAA instructions 
LDA  copies  the  data  byte  into  accumulator  from  the  memory  location 
specified by the 16-bit address. STA copies the data byte from theaccumulator in 
the  memory  location  specified  by  16-bit  address.  DAA  changes  the  contents  of 
the accumulator from binary to 4-bit BCD digits. 

Q.  Explain the different instruction formats with examples 
The instruction set is grouped into the following formats 
•  One byte instruction   MOV C,A 
•  Two byte instruction   MVI A,39H 
•  Three byte instruction  JMP 2345H 

Q.  What is the use of addressing modes, mention the different types 
The various formats of specifying the operands are called addressing modes, it is used to 
access the operands or data. The different types are as follows 
•  Immediate addressing 
•  Register addressing 
•  Direct addressing 
•  Indirect addressing 
•  Implicit addressing 

Q. What is the use of bi-directional buffers? 
It is used to increase the driving capacity of the data bus. The data bus of a 
microcomputer system is bi-directional, so it requires a buffer that allows the data 
to flow in both directions. 

Q.  Define stack and explain stack related instructions 
The stack is a group of memory locations in the R/W memory thatis used 
for  the  temporary  storage  of  binary  information  during  the  execution  of  the 
program. The stack related instructions are PUSH & POP 

Q.  Why do we use XRA A instruction 
The XRA A instruction is used to clear the contents of the Accumulator and store the value 00H. 

Q.  What is Microcontroller and Microcomputer 
Microcontroller is a device that includes microprocessor; memory and I/O 
signal lines on a single chip, fabricated using VLSI technology. Microcomputer is 
a  computer  that  is  designed  using  microprocessor  as  its  CPU.  It includes 
microprocessor, memory and I/O. 

Q. Define Flags
The flags are used to reflect the data conditions in the accumulator. The 8085 
flags  are  S-Sign  flag,  Z-Zero  flag,  AC-Auxiliary  carry flag,  P-Parity  flag,  CYCarry flag 
D7 D6 D5 D4 D3 D2 D1 D0 
S  Z   AC   P   CY 

Q. How does the microprocessor differentiate between data and instruction 
When  the  first  m/c  code  of  an  instruction  is  fetched  and  decoded  in  the 
instruction register, the microprocessor recognizes the number of  bytes required 
to  fetch  the  entire  instruction.  For  example  MVI  A,  Data,  the  second  byte  is 
always considered as data. If the data byte is omitted by mistake whatever is in 
that memory location will be considered as data & the byte after the “data”will be 
treated as the next instruction. 


Q.  What is assembler 
The assembler translates the assembly language program text which is given as input 
to the assembler to their binary equivalents known as object code. The time required to 
translate the assembly code to object code is called access time. The assembler checks for 
syntax errors & displays them before giving the object code. 

Q.  What is loader 
The  loader  copies  the  program  into  the  computer’s  main  memory  at load time and begins the program execution at execution time. 

Q.  What is linker 
A linker is a program used to join together several object files into one large object 
file.  For  large  programs  it  is  more  efficient  to  divide  the large  program  modules  into 
smaller modules. Each module is individually written, tested &  debugged. When all the 
modules work they are linked together to form a large functioning program. 

Q.  Explain ALIGN & ASSUME 
The ALIGN directive forces the assembler to align the nextsegment at an address 
divisible by specified divisor. The format is ALIGN number where number can be 2, 4, 8 
or 16. Example ALIGN 8. 
The ASSUME directive assigns a logical segment to a physical segment at any given 
time.  It  tells  the  assembler  what  address  will  be  in  the  segment  registers  at  execution 
time. Example ASSUME CS: code, DS: data, SS: stack 

BASIC ELECTRONICS QUESTION AND ANSWER

Q.What are semiconductors?
The materials whose electrical property lies between those of conductors and insulators 
are known as Semiconductors. Ex germanium, silicon.
It has two types.
1. Intrinsic semiconductor 2. Extrinsic semiconductor.

Q.What is the order of energy gap in a conductor, semi conductor, and 
insulator?. 
Conductor - no energy gap 
Semi Conductor - It is of the order of 1 ev. 
Insulator - 6 ev (or) more than 6 ev. 

Q. Zener effect and avalanche effect are the two possible break down mechanisms that helps the external current . Why ?
Zener effect : The electric field in the depletion layer reach a point that it can break the covalent bonds and generate electron–hole pairs. 
Avalanche breakdown : The minority carriers that cross the depletion layer under the influence of the electric field gain sufficient kinetic energy to be able to break covalent bond in atoms which they collide. 

Q.Why does the conductivity of a semi conductor change with the rise in 
temperature ? 
When a semi conductor is heated more & more electrons get enough energy to jump across the forbidden energy gap from valence band to the conduction band, where they are free to conduct electricity. Thereby increasing the conductivity of a semi conductor. 

Q.Differentiate between intrinsic and extrinsic semiconductor
Pure form of semiconductors are said to be intrinsic semiconductor.
Ex: germanium, silicon.
It has poor conductivity
If certain amount of impurity atom is added to intrinsic semiconductor the resulting 
semiconductor is Extrinsic or impure Semiconductor
It has good conductivity.

Q.Define drift current?
When an electric field is applied across the semiconductor, the holes move towards the 
negative terminal of the battery and electron move towards the positive terminal of the battery. 
This drift movement of charge carriers will result in a current termed as drift current.

Q.Define the term diffusion current?
A concentration gradient exists, if the number of either electrons or holes is greater in one
region of a semiconductor as compared to the rest of the region. The holes and electron
tend to move from region of higher concentration to the region of lower concentration.
This process in called diffusion and the current produced due this movement is diffusion
current.

Q.Differentiate between drift and diffusion currents.
Drift current
1. It is developed due to potential gradient.
2. This phenomenon is found both in metals and semiconductors
Diffusion current
1. It is developed due to charge concentration gradient.
2. This phenomenon is found only in metals 

Q.What is depletion region in PN junction?
The region around the junction from which the mobile charge carriers ( electrons and
holes) are depleted is called as depletion region.since this region has immobile ions, which are electrically charged , the depletion region is also known as space charge region.

Q.What is barrier potential?
Because of the oppositely charged ions present on both sides of PN junction an electric
potential is established across the junction even without any external voltage source which is 
termed as barrier potential.

Q.What is Reverse saturation current?
The current due to the minority carriers in reverse bias is said to be reverse saturation
current. This current is independent of the value of the reverse bias voltage.

Q.Define PIV. 
Peak inverse voltage is the maximum reverse voltage that can be applied to the PN junction without damage to the junction.

Q. Write some applications of PN junction diode
1. Rectifier circuit 
ii. clipping and clamping
iii voltage multiplier
iv AM detection
v. Feedback diodes
vi Freewheeling diode

Q: What is clipper? 
 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. Series clippers are employed as noise limiters in FM transmitters by clipping excessive noise peaks above a specified level. 

Q Can you explain clipping circuit? 
A clipping circuit consists of linear elements like resistors and non-linear elements like junction diodes or transistors. Thus a clipper circuit can remove certain portions of an arbitrary waveform near the positive or negative peaks. Clipping may be achieved either at one level or two levels Clipping Circuits are also called as Slicers, amplitude selectors or limiters. 

Q Explain Clipping using Zener Diode? 
one or two zener diodes are used to clip the voltage VIN. In the first circuit, the voltage is clipped to the reverse breakdown voltage of the zener diode. In the second, it is limited to the reverse breakdown voltage plus the voltage drop across one zener diode. 

Q. Classification of clipper? 
Practical clippers may be classified into two types: (a) Shunt Clippers, and (b) Series Clippers. The series configuration is defined as one where diode is in series with the load In a shunt clipper which uses a diode in conjunction with a resistor the diode forms a parallel path across the output. The network must have capacitor, a diode, and a resistive element, but it also employs an independent dc supply to introduce an additional shift. 

Q. Application of clipper? 
It is used in television sets and FM receivers. It is also used for amplifier and different types of opamps through which we can do some mathematical operations. 

Q What is positive and negative clipping? 
Depending on the orientation of the diode, the positive or negative region of the input signal is “clipped” off and accordingly the diode clippers may be positive or negative clippers. 

Q. What is Positive Clipper circuit?
Positive Clipper: The clipper which removes the positive half cycles of the input voltage is called the positive clipper. The positive series clipper circuit (that is, diode in series with the load). while the input is positive, diode D is reverse biased and so the output remains at zero that is, positive half cycle is clipped off. During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. 

Q. What is negative clipper circuit? 
 If the positive clipper circuit is reconnected with reversed polarity, the circuits will become for a negative clipper and the operation will be same. 

Q. What is Combination Clipper?
When a portion of both positive and negative of each half cycle of the input voltage is to be clipped (or removed), combination clipper is employed. 

Q. Drawbacks of Series Diode Clippers?
In series clippers, when diode is in ‘off’ position, there should be no transmission of input signal to output. But in case of high frequency signals transmission occurs through diode capacitance which is undesirable. This is the drawback of using diode as a series element in such clippers.

Q. What is the rectifier? 
The process of converting A.C. voltage into D.C. voltage which is in only one direction,  is called rectification and it is done by rectifier. 

Q. What is the application of rectifier? 
Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other components. Rectifiers also find a use in detection of amplitude modulated radio signals 

Q.What is the type of rectifier? 
There are two type of rectifier:- 
1. Half wave rectifier 2. Full wave rectifier:- center tape full wave  Bridge full wave 

Q. What is the ripple factor of the rectifier? 
A4: The ripple factor of the rectifier: - Half wave recitifer:-1.21, Center tape wave rectifier:-0.48 
Bridge full wave:-0.48 

Q. What is the PIV of all type rectifiers? 
 The PIV of rectifier: - Half wave rectifier=Vm, Center tape wave rectifier=2Vm 
 Bridge full wave=Vm 

Q. Half wave rectifier? 
In a half wave rectifier only one half cycle of ac voltage is taken.Here only one diode is used. During the positive half cycle of ac voltage the diode conducts. So current flows through 
load. During the negative half cycle, the diode is reverse biased .So no current flows through the diode. Half-wave rectification can be achieved with a single diode in a one-phase supply, or with three diodes in a three-phase supply. 

Q. Full wave bridge rectifier? 
Full wave bridge rectifier: In full wave bridge rectifiers 4 diodes are using. During positive half cycle, D1 and D4 are in forward biased condition. In the negative half cycle of ac D3 and D2 are in forward biased condition. So in both the half cycles current through the load is in single direction. This circuit does not need a centre tap rectifier. But it requires more number of diodes than centre tap and half wave rectifiers 

Q. Full wave centre tap rectifier? 
 In this method only two diodes are used. But it requires a center tap transformer. During the positive half cycle diode D1 conducts. In the negative half cycle diode D2 conducts. So in both half cycles current flowing through load in same direction. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. 

Q.What are the types of filter circuits? 
The types of filter circuits are Inductor filter Capacitor filter LC filter CLC or π filter

Q. Why we use Filter? 
While half-wave and full-wave rectification suffice to deliver a form of DC output, neither produces constant-voltage DC. In order to produce steady DC from a rectified AC supply, a smoothing circuit or filter is required. In its simplest form this can be just a reservoir capacitor or smoothing capacitor, placed at the DC output of the rectifier. There will still remain an amount of AC ripple voltage where the voltage is not completely smoothed. 

Q. Difference between half wave and full wave rectifier? 
A10: The efficiency of half wave rectifier is not so good as that of full wave rectifier Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. The ripples are maximum in the single phase half-wave rectifier and being reduced in the full-wave rectifier and being reduced further with the increase in the number of phases. 

Q.For faster action which transistor is used and why? 
For faster action NPN Transistor is used .In an NPN transistor, current conduction is mainly by free electron ,whereas in PNP type transistor .it is mainly holes Since electron are more mobile than holes we prefer NPN for faster action as well as high conduction current.

Q. What do you mean by operating point?

The zero signal values of collector current Ic and collector to emitter voltage Vce are known as operating point.

Q. What are the methods of transistor biasing?

1. fixed bias

2.collector to base bias

3. self bias or voltage divider bias

4. emitter bias

Q. Why an ordinary transistor is called bipolar transistor?

Because transistor operation is carried out by both majority and minority carriers

Q. Why transistor is called current controlled device?

The output voltage , current or power is controlled by the input current

Q.What would happen if the base resistor has zero resistance?
If the base resistance is zero, then the base current is very high. Since, we know that the base current is directly proportional to the collector current with the multiplying factor of current gain. So, the value of collector current is enormously getting high. In this time, the transistor operates in saturation region and finally it is being destroyed.

Q. why silicon type transistor are more often used than germanium?

because silicon has smaller cutoff current Icbo, small variations in Icbo due to variation in temperature as compared to those in case of germanium.

Q.Key point for its proper functioning of base region in a transistor depends upon the thickness of the base Why ? Base region in a transistor controls the current. The majority charge carriers supplied by the emitter do not combine in the same region due to its thin size and light doping and most of them pass on to the collector. This is the key point for its proper functioning.

Q. Why do we choose q point at the center of the loadline?

The operating point of a transistor is kept fixed usually at the center of the active region in order that the input signal is well amplified. If the point is fixed in the saturation region or the cut off region the positive and negative half cycle gets clipped off respectively.

Q. What do you meant by thermal runway? Due to the self heating at the collector junction, the collector current rises. This causes damage to the device. This phenomenon is called thermal runway.

Q. Define current amplification factor? It is defined as the ratio of change in output current to the change in input current at constant other side voltage.

Q. What are the requirements for biasing circuits? · The q point must be taken at the Centre of the active region of the output characteristics. · Stabilize the collector current against the temperature variations. · Make the q point independent of the transistor parameters. · When the transistor is replaced, it must be of same type.

Q. When does a transistor act as a switch? The transistor acts as a switch when it is operated at either cutoff region or saturation region.

Q. What is biasing? To use the transistor in any application it is necessary to provide sufficient voltage and current to operate the transistor. This is called biasing.

Q. What is operating point? For the proper operation of the transistor a fixed level of current and voltages are required. This values of currents and voltages defined at a point at which the transistor operate is called operating point.

Q. What is stability factor? Stability factor is defined as the rate of change of collector current with respect to the rate of change of reverse saturation current.

Q. What is d.c load line? The d.c load line is defined as a line on the output characteristics of the transistor which gives the value of Ic & Vce corresponding to zero signal condition.

Q. What are the advantages of fixed bias circuit? This is simple circuit which uses a few components. The operating point can be fixed any where on the Centre of the active region

Q. Explain about the various regions in a transistor? The three regions are active region saturation region cutoff region.

Q. Explain about the characteristics of a transistor? Input characteristics: it is drawn between input voltage & input current while keeping output voltage as constant. Output characteristics: It is drawn between the output voltage &output current while keeping input current as constant.

Q. What is the necessary of the coupling capacitor? It allows a c &blocks the d c.

Q What is reverse saturation current? The current due to the minority carriers is called the reverse saturation current.

Q. Why is the operating point selected at the Centre of the active region? The operating point is selected at the Centre of the active region to get to perfect amplification. Moreover there is no distortion.

Q. What is JFET? 
 A junction FET is a three terminal semiconductor device in which current conduction is by one type of carrier (i.e.) electrons or holes.

Q..What is pinch off voltage in JFET? 
Pinch off voltage (VP): It is the minimum drain source voltage at which the drain current essentially becomes constant.

Q.What is the importance of JFET?
 A JFET acts like a voltage controlled device i.e. input voltage controls the output current. This is different from ordinary transistor where input current controls the output current. JFET has higher input impedance than that of a conventional transistor.

Q.Why JFET is called a unipolar transistor?
In JFET, the current conduction is either by electrons or holes and controlled by means of an electric field between the gate electrode and the conducting channel of the device, So it is called as a unipolar transistor.

Q. Why is input impedance of the FET very high?
BECAUSE its input circuit (gate to source) is reverse biased and input gate current is very small.

Q.What is MOSFET?

 MOSFET stands for Metal oxide Semiconductor field effect transistor. A type of transistor that is controlled by voltage rather than current. 

Q. Explain working of MOSFET.

MOSFET  is a special type of field-effect transistor ( FET ) that works by electronically varying the width of a channel along which charge carriers  flow. The wider the channel, the better the device conducts. The charge carriers enter the channel at the source , and exit via the drain . The width of the channel is controlled by the voltage on an electrode called the gate , which is located physically between the source and the drain and is insulated from the channel by an extremely thin layer of metal oxide.

Q. Explain how MOSFET functions?

Ans:There are two ways in which a MOSFET can function.

• The first is known as depletion mode . When there is no voltage on the gate, the channel exhibits its maximum conductance . As the voltage on the gate increases (either positively or negatively, depending on whether the channel is made of P-type or N-type semiconductor material), the channel conductivity decreases.

• The second way in which a MOSFET can operate is called enhancement mode . When there is no voltage on the gate, there is in effect no channel, and the device does not conduct. A channel is produced by the application of a voltage to the gate. The greater the gate voltage, the better the device conducts.

Q. What are the basic rules of an operating amplifier? The operating point should be fixed on the load line. The upper end of the load line lies on the saturation region &lower end lies on the cutoff region.

Q. What is an amplifier? An amplifier is a device which produces a large electrical output of similar characteristics to that of the input parameters.

Q. How are amplifiers classified according to the input? 1. Small – signal amplifier 2. Large – signal amplifier

Q. How are amplifiers classified according to the transistor configuration? 1. Common emitter amplifier 2. Common base amplifier 3. Common collector amplifier

Q. What is the different analysis available to analyze a transistor? 1. AC analysis 2. DC analysis

Q. How can a DC equivalent circuit of an amplifier be obtained? By open circuiting the capacitor.

Q. How can a AC equivalent circuit of a amplifier be obtained? By replacing dc supply by a ground and short- circuiting capacitors.

Q. What are feed back amplifiers? Amplifiers which uses feed back principle is called as feed back amplifiers.

Q. What are the types of feed back? 1. Positive feedback 2. Negative feedback.

Q. What is positive feedback? If the feed back signal is applied in such a way that it is in phase with the input signal and thus increases it is said to be positive feedback.

Q. What is negative feed back? If the feed back signal is applied in such a way that it is out of phase with the input signal and thus decreases it is said to be positive feedback.

Q. Which feedback decreases the gain of the amplifier? Negative feed back

Q. Which feedback increases the gain of the amplifier? Positive feedback

Q. What is the advantage of negative feed back? 1. increased stability 2. Increased bandwidth 3. Decreased noise 4. Less frequency distortion

Q. What is the disadvantage of negative feed back? Reduces amplifier gain.

Q. What is an op-amp? The operational amplifier is a multi-terminal device, which is quite complex internally. An operational amplifier is a direct coupled high gain amplifier usually consisting of one or more differential amplifiers and usually followed by a level translator and an output stage. An operational amplifier is available as a single integrated circuit package. It is a versatile device that can be used to amplify dc as well as ac input signals and was originally designed for computing such mathematical functions.

Q. What are the characteristics of ideal op-amp? a. Open loop voltage gain, (AOL) = ’ b. Input impedance (Ri) = ’ c. Output impedance (Ro) = 0 d. Bandwidth (BW) = ’ e. Zero offset Vo = 0, when V1 = V2 = 0

Q. Define loading? A large value of Rc cannot be used in a circuit since,a large value of resistance requires a large chip area.For large Rc, quiescent drop across it increases and hence a large power supply is required.These difficulties removed by using a current source. Hence, a current source can also be used as an active load for an amplifier to obtain a very large voltage gain.

Q. Define input offset voltage? It is defined as the voltage that must be applied between the input terminals of an op-amp to nullify the output.

Q. Define input offset current? It is defined as the algebraic difference between the current entering the inverting and non-inverting terminal of an op-amp.

Q. Define input bias current? It is defined as the average of the currents entering into the input terminals of an op-amp.

Q. What are the two compensating techniques used in frequency compensation? Two types of compensating techniques are used, they are, a. External compensation b. Internal compensation

Q. What is compensated op-amp? Op-amp, which uses a capacitor internally for compensation, is called a compensated op-amp. This op-amp has a high gain stability and low bandwidth.

Q. What are the methods used in external compensation technique? a. Dominant-pole compensation b. Pole-zero compensation

Q. Define slew rate? Slew rate can be defined as the maximum rate of change of output voltage of op-amp with respect to time.

Q. How can the slew rate be made faster? The slew rate can be made faster by having a high charging current or a small capacitance value.

Q. What are the methods to improve slew rate? a. The slew rate can be improved with higher closed-loop gain and dc supply voltage. But the slew rate also varies with temperature. i.e., slew rate decreases with increase in temperature. b. Another method for improving slew rate is, the rate at which voltage across the capacitor increases is gain by, dVc/dt = I / C. where, I is the maximum current furnished by the op-amp to the capacitor

C. From the equation it is clear that for a higher slew rate, op-amp should have either a higher current or a small value of capacitor.

Q. What are the AC characteristics of an op-amp? a. Frequency response b. Slew rate

Q. What are the DC characteristics of an op-amp? a. input bias current b. Input offset current c .Input offset voltage d. Thermal drift

Q. What is the type of feedback employed in the inverting op-amp amplifier? Negative feedback is employed in the inverting op-amp amplifier.
Q. List the applications of instrumentation amplifier. a. Temperature indicator b. Temperature controller c. Light intensity meters d. Water flow meter c. Thermal conductivity meter f. Analog weight scale
Q. What is the basic building block of an op-amp? The basic building block of an op-amp is differential amplifier.
Q. Define non-inverting amplifier? The input is applied to the non-inverting input terminal and the inverting terminal connected to the ground.
Q. What is meant by voltage follower? If the output voltage of an op-amp follows the input i.e., if the output voltage is equal to the input voltage it is called as a voltage follower.
Q. What is a Multivibrator? Multivibrator is a wave shaping circuit which gives symmetric or asymmetric square wave output. It has two states. They may be either stable or quasi stable depends upon the type of the Multivibrator.
Q. What is Astable Multivibrator? Astable Multivibrator is a square wave circuit. It has two quasi stable states. It is also referred as free running Multivibrator.
Q. What is a monostable Multivibrator? A monostable Multivibrator is a square wave shaping circuit having one stable state and another quasi stable state. It is often referred as single shot Multivibrator. It is also used as gating circuit and delay circuit.
Q. What is the type of feedback used in an op-amp Schmitt trigger? The type of feedback used in an op-amp Schmitt trigger is positive feedback.

Q. What is Oscillator circuit? Oscillators produce a waveform (mostly sine or square waves) of desired amplitude and frequency. They can take input from the output itself. For a complete oscillator circuit we require a feedback device, amplifier and feedback factor.

Q. What are the classifications of Oscillators? *Based on wave generated: i. Sinusoidal Oscillator, ii. Non-sinusoidal Oscillator or Relaxation Oscillator Ex: Square wave, Triangular wave, Rectangular wave etc. *According to principle involved: i. Negative resistance Oscillator, ii. Feedback Oscillator. *According to frequency generated: i. Audio frequency oscillator 20 Hz – 20 kHz ii. Radio frequency Oscillator 30 kHz – 30 MHz iii. Ultrahigh frequency Oscillator 30 MHz – 3 GHz iv. Microwave Oscillator 3 GHz – above. * Crystal Oscillators.
* RC-Phase shift Oscillator, * LC-Oscillators i. Tuned collector Oscillator ii. Tuned emitter Oscillator iii. Tuned collector base Oscillator iv. Hartley Oscillator v. Colpits Oscillator vi. Clap Oscillator
Q. What are the conditions for oscillation? The total phase shift of an oscillator should be 360 degree. For feedback oscillator it should satisfy Barhausen criterion.
Q. Application of electronic oscillator? An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in innumerable electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games. 
Q. Types of electronic oscillator? There are two main types of electronic oscillator: the harmonic oscillator and the relaxation oscillator. 
Q: What is Harmonic oscillator? The harmonic, or linear, oscillator produces a sinusoidal output. The basic form of a harmonic oscillator is an electronic amplifier with the output attached to an electronic filter, and the output of the filter attached to the input of the amplifier, in a feedback loop. When the power supply to the amplifier is first switched on, the amplifier's output consists only of noise. The noise travels around the loop, being filtered and re-amplified until it increasingly resembles the desired signal. 
Q: Types of Harmonic oscillator? A5: There are many ways to implement harmonic oscillators, because there are different ways to amplify and filter. Some of the different circuits are: • Hartley oscillator • Colpitts oscillator • Cross-coupled LC oscillator • crystal oscillator • Phase-shift oscillator • RC oscillator (Wien Bridge and "Twin-T") • Q. What are LC oscillators? Inductive oscillators also known as LC oscillators are built of an tank circuit, which oscillates by charging and discharging a capacitor through an inductor. These oscillators are typically used when a tunable precision frequency source is necessary, such as with radio transmitters and receivers 
Q What is phase-shift oscillator? A phase-shift oscillator is a simple electronic oscillator. It contains an inverting amplifier, and a feedback filter which 'shifts' the phase of the amplifier output by 180 degrees at the oscillation frequency. The filter produces a phase shift that increases with frequency. It must have a maximum phase shift of considerably greater than 180° at high frequencies, so that the phase shift at the desired oscillation frequency is 180°.
Q. How to produced 180° phase shift? The most common way of achieving this kind of filter is using three identical cascaded resistor capacitor filters, which together produce a phase shift of zero at low frequencies, and 270 degrees at high frequencies. At the oscillation frequency each filter produces a phase shift of 60 degrees and the whole filter circuit produces a phase shift of 180 degrees. 

Q. Define Piezoelectric effect. When applying mechanical energy to some type of crystals called piezoelectric crystals the mechanical energy is converted into electrical energy is called piezoelectric effect.
Q. What is Miller crystal oscillator? Explain its operation. It is nothing but a Hartley oscillator its feedback Network is replaced by a crystal. Crystal normally generate higher frequency reactance due to the miller capacitance are in effect between the transistor terminal.
Q. .List the important characteristics of a voltage regulator. The output voltage is fixed at a specified value, The unregulated voltage must be at least 2V more than the regulated voltage.
Q. What is a Schmitt trigger? Schmitt trigger is a regenerative comparator. It converts sinusoidal input into square wave output. The output of Schmitt trigger swings between upper threshold voltage and lower threshold voltage, the reference voltages of the input waveform.

Q.What would happen if the base resistor has zero resistance?

If the base resistance is zero, then the base current is very high. Since, we know that the base current is directly proportional to the collector current with the multiplying factor of current gain. So, the value of collector current is enormously getting high. In this time, the transistor operates in saturation region and finally it is being destroyed.