Digital electronics interview questions are one of the important part of questions which are generally covered in all electronics related interviews and viva. Here you will find most asked questions in digital electronics.
DIGITAL ELECTRONICS INTERVIEW QUESTIONS AND ANSWERS
Q.1. What do you mean by jitter?
Answer: The short term variations of a signal with respect to its ideal position in time. It is also defined as variation of clock period from edge to edge.
Q.2. What is the difference between bit, nibble, byte and word?
Answer: A bit is a single binary digit, a nibble is a combination of 4 binary digits, a byte is a combination of 8 binary digits while a word is made up of several bytes.
Q.3. What is the main difference between Harvard architecture and Van-Newmen architecture of computer?
Answer: In Harvard architecture model, separate data and instruction memory was used which makes it faster whereas in Van-newmen architecture, model instructions and data were stored in single memory. So this model was simple but slow.
Q.4. What are the characteristics of Flash memory?
Answer: The characteristics of Flash memory are-
- It is a special type of RAM.
- It is a non volatile memory which is powered continuously.
- The erasing and programming of this memory takes place block by block.
- Due to this process, the flash memories are faster than EEPROMs which erase and write new data at byte level.
- Important features of a flash memory are high speed, low operating voltages. Low power consumption and durability.
Q.5. What is CAM?
Answer: CAM is called as content accessible memories. It is a special type of RAM. It can perform association operation in addition to the read/write operations performed by the conventional memories.
Q.6. Which diode is used in HTL logic circuit to increase noise immunity?
Answer: HTL possesses highest noise immunity. In HTL logic circuit zener diode is used in place of normal diode to increase noise immunity.
Q.7. What are the characteristics of Ring counter?
Answer: The characteristics of Ring counter are-
- With n flip flops, there are n-states present in ring counter.
- With n flip flops, maximum count possible in Ring counter is (2n-1).
- Decoding is very easy in Ring counter, because there is no aid of extra circuit.
Q.8. What is MOD number?
Answer: The MOD number indicates the number of states in counting sequence. It indicates the frequency division obtained from the last flip flop.
Q.9. What is lock out condition in counters?
Answer: A counter is supposed to follow the sequence of only the desired states. If it enters into an unused or unwanted state, then it is expected to return back to a desired state. Instead if the next state of an unwanted state is again an unwanted state then the counter is said to be in the lockout conditions.
Q.10. Which shift register is used to convert temporal code into spatial code and vice versa?
Answer: To convert temporal code into spatial code, we use SIPO register while to convert spatial code to temporal code, we use PISO register.
Q.11. What is the difference between Moore and Mealy circuit?
Answer: The synchronous sequential circuit is called as a Moore circuit if the output depends only on the present state of flip flops.
The circuit is called as a Mealy circuit if the output is dependent on the present state of flip flops and the external inputs.
Q.12. Which flip flop is called as universal flip flop?
Answer: JK flip flop is called as universal flip flop because the flip flops like D-FFs, SR-FFs and T-FF can be derived from it.
Q.13. Explain what are preset and clear inputs of flip flops?
Answer: In the flip flops, when the power switch is turned on, the state of outputs is uncertain. But this uncertainty cannot be tolerated in certain applications. In some applications it is necessary to initially set or reset the flip flops.
This can be practically achieved by adding two more inputs to a flip flop, called preset (PR) and Clear (CLR) inputs. These inputs are called as direct or asynchronous inputs because we can apply them any time between clock pulses without thinking about their synchronization with the clock.
Q.14. What is the difference between Flip flop and Latch?
Answer: While gates had to be built directly from transistors, Latches can be built from gates and Flip flops can be built from latches. This fact will make it somewhat easier to understand Latches and Flip flops.
The difference between them are:
- Latch is a combinational logic device while Flip flop is a sequential device.
- Flip flop is a synchronous device while Latch is asynchronous device.
- Latch does not have a clock signal whereas a Flip flop always does.
- Latch is faster than Flip flop.
Q.15. What is the advantage of using open collector output in TTL logic gates rather than using totem pole output?
Answer: With Totem pole output wired-And operation is not possible in TTL gates which may lead to transistor burning. With open collector output wired-AND operation is possible.
Q.16. What do you mean by current hogging and which logic family has this problem?
Answer: Current hogging problem is due to different characteristics of transistor. Owing to these differences, the saturation voltages of the load transistors may be different. So when one transistor enters into saturation it will not allow other transistors to enter saturation and will take whole of the current supplied from the driver gate. This is known as current hogging. DCTL has the problem of current hogging.
Q.17. How microprocessor works without internal memory?
Answer: Microprocessor consists of address, data and control buses with some internal registers to process the task through external memory.
Q.18. Why look ahead carry adder is faster than ripple adder?
Answer: Look ahead carry adder is faster; since carry is generated in parallel at all the stages of addition rather than sequentially as in ripple adder.
Q.19. What is the difference between compiler and interpreter?
Answer: Compiler- Programs that converts English like words of a high level language into the machine language of a computer. It needs a given program called source code and translates the program into the machine language, called object code.
Interpreter- It translates one statement at a time from a source code to an object code.
Q.20. Which code is called as minimum change code and why?
Answer: Gray code is called as minimum change code because it has a very special feature that only one bit will change, each time the decimal number is incremented.
Q.21. What is the difference between digital signal and binary signal?
Answer: A digital signal is defined as a signal which has only a finite number of distinct values. Digital signals are not continuous signal, they are discrete signals.
If a digital signal has only two distinct values, i.e. 0 and 1 then it is called as a binary signal.
Points to be remember for Digital Electronics Interview or Viva
- Gray code is also known as minimum change code
- Common emitter amplifier is used to obtain the logical operation of an INVERTER
- Multiplexer is used for parallel to serial conversion of data
- Parallel addition is fast as compared to serial addition because in parallel adder all bits are added simultaneously
- NAND Gate is known as universal Gate because all the logical functions are realized using it
- NOR Gate with positive logic is always equivalent to NAND Gate with negative logic
- NAND Gate with positive logic is always equivalent to NOR Gate with negative logic
- Gray code is an unweighted code
- BCD code has the advantage that it can be easily converted to and from the decimal code
- BCD code is a weighted code
- BCD code is used in calculators, counters, digital voltmeters, digital clocks etc
- Excess 3 code is an unweighted code
- Excess 3 code is known as self complementing code
- Multiplexer is also known as data selector
- Combinational circuit has no memory elements and output depends only on the current value of the input
- Degenerated functions are those which generates single operation
- The subtraction of two binary numbers is accomplished by taking the complement of subtrahend and adding it to minuend
- Carry look ahead adder is faster, since carry is generated in parallel at all the stages of addition rather than sequentially as in ripple adder
- Demultiplexers is also known as data distributor
- Demultiplexers is used for serial to parallel conversion of data
- JK flip flop is the modification of RS flip flop that the indeterminate state(S = R =1) of the RS flip flop is defined in JK flip flop
- D flip flop is used as a delay switch
- T flip flop is used as a toggle switch
- T flip flop is commonly used as digital counter and frequency divider
- Race around condition is always undesirable
- Race around problem occurs in a circuit because of time delay due to high speed logic
- Race around condition always arises in asynchronous circuits
- Race around condition occurs in JK flip flop to store two bits of information
- The frequency is halved the output of T flip flop
- In shift registers, normally JK flip-flops are used
- A master slave flip flop consists of an RS flip flop followed by a T flip flop
- An asynchronous circuit is generally more difficult to design than a synchronous system
- Asynchronous sequential circuits are difficult to design because of instability
- Shift register can be used to change data from spatial code to temporal code
- Glitch is an unwanted spike in the signal
- Synchronous counter is used for high frequency applications
- Asynchronous counter is used for low frequency applications
- A group of flip flop sensitive to Pulse transition is called as a register
- A group of flip flop sensitive to Pulse duration is usually called as a latch
- For Mod 16 counter Johnson Counter uses 8 flip flops, ring counter uses 16 flip flops and binary counter uses 4 flip flops
- For good IC, propagation delay should be minimum
- Synchronous counter is faster than asynchronous counter
- Ring counter requires N flip flops to design Mod N ring counter
- The temperature range over which logic families works satisfactorily is 0 to 70 degree Celsius
- A SISO shift register is used to introduce delay in the pulse train
- RTL configuration occupies minimum area
- HTL possess highest noise immunity
- DCTL logic circuit perform the operation of NOR Gate
- RTL logic circuit performs the operation of NOR Gate
- A transistor common emitter amplifier configuration is used to obtain the logic of an inverter
- A positive logic OR gate is equivalent to negative logic AND Gate
- A positive logic AND gate is equivalent to negative logic OR gate
- TTL logic circuit performs the operation of NAND Gate
- ECL logic circuit performs the operation of OR or NOR Gate
- IIL possess high packing density that is it allows more circuits to be placed in the given area of the chip
- In HTL logic circuit zener diode is used in place of normal diode to increase noise immunity
- The main disadvantage of DTL is its low fan out capability
- RTL is most expensive among all the logic families
- ECL is non saturated digital logic family
- In ECL differential amplifiers are used
- ECL possess the highest speed of operation among all the digital logic families
- Schottky TTL possess highest speed in a TTL logic family
- CMOS has highest fan out capacity
- NMOS is about twice as fast as PMOS
- Propagation delay of CMOS is highest
- FET is used to design MOS logic families
- Power dissipation of ECL is highest
- NMOS has highest packing density
- Schottky clamped TTL has highest speed among TTL family
- Propagation delay in schottky transistor is lower as compared to normal transistor
- DTL logic circuit performs the operation of NAND Gate
- Dual slope integrating type analog to digital converter provide very good accuracy
- Linearity is the maximum deviation in step size from the ideal step size
- ADC and DAC are used to change the data from spatial code too temporal code and vice versa
- Dual slope converter possess slowest conversion time
- The flash ADC is the highest speed ADC available but it requires complex circuitry
- Accuracy is the maximum deviation of the DACs output from its computed value
- Digital ramp ADC is used for low speed applications
- Settling time is the time required for the DACs output to go from zero to full scale
- Flash ADC is a parallel ADC
- Up down digital ramp ADC is also known as tracking ADC
- Fastest memory cell is semiconductor memory
- RAM is a volatile memory
- ROM is a non volatile memory
- It is possible to have more bits of ROM then of RAM for same chip
- ROM is made up of diodes
- Magnetic bubble memory is a non volatile memory
- ROM consists of a decoder followed by an encoder
- Magnetic tape is a non-volatile memory
- Dynamic MOS memory requires refreshing cycles
- CD ROM is an optical disk that uses a laser beam to store digital information on to it
- Core memory has highest storage capacity
- As compared to MOS memories, bipolar memories have faster access time and are costlier
- Dynamic memory cells are constructed using 4 MOSFET
- Scratchpad memory is a local temporary memory
- PROM is programmed after packaging
- Implementation of BCD to Excess 3 code requires seven AND Gates and three OR Gates
Important Definitions for Digital Electronics Interview
Machine language: The binary medium of communication with the computer through a designed set of instructions specific to each computer that is machine dependent language
Assembly language: A medium of communication with a computer to which programs are written in mnemonics. it is machine independent language
Low level language: It is a machine dependent medium of communication (for example, machine and assembly language). Programs in this language are not transferable
High level language: It is a machine independent medium of communication. Programs in this language can be executed using a translator
Interpreter: It translates one statement at a time from a source code to an object code
Compiler: Program that converts English like words of a high level language into the machine language of a computer. It needs a given program called source code and translates the program into the machine language, called object code
Cross assembler: the program that translates the mnemonics of a particular microprocessor into the mnemonics of other microprocessor is called a cross assembler
Assembler: Program that translates an assembly language program from mnemonics to the binary machine code of a computer
Memory word: A group of BITS in a memory that represents instructions of some type. For example, a register consisting of 8 flip flops can use as a memory for storing an 8 bit word
Memory cell: A device or electrical circuit used to store a single bit (0 or 1). Examples of flip flops, a charged capacitor and a single spot on a Magnetic tape or disk
Direct memory access (DMA): DMA interface is used for transferring data directly between an external device and memory. The busy buffers in the microprocessor are disabled and go into high impedance state during DMA transfer
Programmable Array Logic (PAL): class of Programmable Logic devices. Its AND array is Programmable while it’s OR array is hardwired
Programmable Logic array (PLA): class of Programmable Logic devices. Both its AND and it’s OR arrays are Programmable. Also, called a field Programmable Logic array (FPLA)
Programmable Logic device (PLD): IC that contains a large number of interconnected logic functions. The user can program the IC for a specific function by selectively breaking the appropriate interconnections
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