GATE Electronics|Electrical

Why only h-parameter model is taken for a BJT application as an amplifier? Ans. H-parameter of a transistor are real numbers at audio frequency range. Therefore, the reactive part of parameters are absent in h-parameter representation and thus it is computationally simple. h-parameter can be measure from the static characteristic of a transistor.

Explain the difference between ‘Access Time’ and ‘Turnaround Time’. Ans. Access time is the time taken to fetch data from an address within the computer is asked to bring data to the moment data is ready. Access time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned. Turn around time is the total time in which a job submitted to the computer is ready i.e. time between job submission and return of results

Assertion (A):  The data bus and address bus of 8085 are multiplexed. Reason (R):  Multiplexing reduces the number of pins. A. Both A and R are correct and R is correct explanation of A B. Both A and R are correct but R is not correct explanation of A C. A is correct R is wrong D. A is wrong R is correct Answer: Option A Explanation: In 8085 signal lines AD7 - AD0 are used for address bits in some T states and for data in some other T states.

What do you mean by Gibbs phenomenon? Ans. Gibbs phenomenon says that whenever there is an abrupt discontinuity in the signal which is being sampled, the reconstructed signal will always have high, frequency oscillations and as the number of samples increases the oscillations compress towards discontinuity but their maximum value remains the same. The nth partial sum of the Fourier series has large oscillations near the jump, which might increase the maximum of the partial sum above that of the function itself. The overshoot does not die out as n increases but approaches a finite limit.

Why we use only sinusoid wave and no other signals for signal analysis? Ans. we use only sinusoid wave because: (i) The response of a sine wave to an LTI (linear time-invariant) system is also sinusoidal. (ii) The sinusoidal analysis of electric network is simple and convenient.

What is basic difference between channel coding and source coding? And why they are done. Ans. Channel coding is done to reduce the error during the transmission of information in the channel, usually done by adding redundancy to the information. Ex:  Hamming codes. Sources coding is done to reduce the bandwidth requirement for communication. Redundancy is removed using this coding. Ex: Shannon coding, Huffman coding.

What is bandwidth efficiency? What should be its value ,high or low? Ans. Spectral efficiency, spectrum efficiency orbandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system. Or Bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth expressed in bps/Hz. It should be optimum because as the number of bits per symbol are increases probability of error also increases. So it should neither be too high nor too low.

Which of these has highly doped p and nregion? A.PIN diode B.Tunnel diode C.Schottky diode D.Photodiode Answer: Option B Explanation: Tunnel diode has heavily doped p and nregions leading to very thin depletion layer.

In which of these is reverse recovery time nearly zero? A.Zener diode B.Tunnel diode C.Schottky diode D.PIN diode Answer: Option C Explanation: In schottky diode there is no charge storage and hence almost zero reverse recovery time.

Which of the following oscillators is suitable for frequencies in the range of mega hertz? A.RC phase shift B.Wien bridge C.Hartley D.Both (a) and (c) Answer: Option C

Which is the fastest logic family? Ans. Emitter coupled logic family. Since in ECL transistor operates in active region and cut-off region rather saturation and  cut-off region as in other logic gates and recovery time for storage charge carrier is more.

Which interrupt is not level sensitive in 8085 microprocessor? Ans. RST 7.5 which is rising edge triggered interrupt & TRAP is level and edge sensitive both.

What are the types of general purpose registers in 8085? Sol. There are 6 general purpose registers in 8085 microprocessor. They are designated by the letters – B, C, D, E, H and L. These are 8-bit registers and are used to store data temporarily during the execution of any program. These registers can also be used to store 16-bit data by using them in pairs i.e., BC, DE and HL. These pairs cannot be changed as B cannot pair with any other register other than C.

Write code to generate a square wave in the 8085 microprocessor. Ans. REPEAT: MVI A, FFH            CALL DELAY            OUT XXH             MVI A, 00H             CALL DELAY             OUT XXH            JMP REPEAT DELAY: MVIC, (N)16 LOOP: DCRC JNZLOOP RET

Define XCHG, SHLD command of 8085? Explain. Ans. XCHG: In 8085 Instruction set, there is one mnemonic XCHG, which stands for eXCHanGe. This is an instruction to exchange contents of HL register pair with DE register pair. This instruction uses the implied addressing mode. As it is1-Byte instruction, so It occupies only 1-Byte in the memory. After the execution of this instruction, the content between H and D registers and L and E registers will get swapped respectively. SHLD: In 8085 Instruction set, SHLD is a mnemonic, which stands for Store HLpair using Direct addressing in memory location whose 16-bit address is denoted as a16. As HL pair has to be stored, so it has to be stored in two consecutive locations starting at the address a16. We know that H and L are 8-bit registers. So their contents will be stored in two consecutive memory locations as each memory location can hold 8-bits of data. This instruction uses absolute addressing mode for specifying the destination. It occupies 3-Bytes in the memory.

What is cache memory? Why are they used? Ans. Cache memory is a random access memory that a computer microprocessor can access more quickly than regular RAM. This memory is typically integrated directly with the CPU chip or placed on a separate chip with separate bus interconnect with CPU. Advantages of Cache Memory : 1. Cache memory is faster than main memory. 2. It stores the program that can be executed within a short period of time. 3. It consumes less access time as compared to main memory. 4. It stores data for temporary use.

What is companding? Ans. Companding is used as a complement to the process of modulation and demodulation. In this process a voice signal is compressed, then changed from analog to digital, transmitted and converted back from digital to analog before it is expanded again.  For audio analog signals, the amplitude of weak signals is raised and the amplitude of strong signals is decreased, thereby altering (compressing and expanding) the dynamic range of the signals. The technique is used in AM, FM and single-sideband modulation radio and is helpful in improving the quality of amplified voice and musical instrument sounds. Dolby and dbx noise reduction also employ companding. 

Why the ABCD parameters termed 'transmission parameters'?  (IES-10) Ans. The ABCD parameters represent the relation between the input quantities and the output quantities in a two-port network. They are thus voltage-current pairs. These parameters are known as transmission parameters as  in a transmission line, the currents enter at one end and leave at the other end, and we need to know a relation between the sending-end quantities and the receiving-end quantities.