Correct Answer : Only restricted to communication between computers
Explanation : Digital data communication was only restricted to communication between computers. Since analog signals can now be easily converted into digital signals using analog to digital converter, digital transmission can now transmit voice, video and other analog signals in digital form.
Correct Answer : Cannot easily change binary 1 to 0
Explanation : Noise is inevitable in a signal transmission. In a digital transmission the amplitude of the noise must be higher than the amplitude of the signal at binary ’1’, which is generally not the case, and vice versa. The receiver can differentiate between binary ‘1’ and ‘0’ with a significant amount of noise.
Correct Answer : Signal regeneration
Explanation : In the process of signal regeneration a cut off value or threshold value is set in the receiver so that the noise can be clipped off. When the values are set properly only the binary data would pass through the circuit. This produces a clean output pulse.
Correct Answer : Bit error rate
Explanation : Bit rate error(BER) is the number of error bits that are present for a given number of bits transmitted. It depends on several factors like the environment, equipment and other considerations. BER is calculated for a particular set of conditions.
Correct Answer : 0.819
Explanation : Total number of bits = 512 x 8 = 4096 bitsAverage number of errors = (2/10,000) x 4096 = 0.819.
Correct Answer : Discrete data
Explanation : Digital data is discrete and hence can be transmitted via time division multiplexing, whereas analog data is continuous and can only be transmitted as a whole. However, analog data can be converted into digital by analog to digital converters and then be transmitted via time division multiplexing. Time division multiplexing is one of the biggest advantages of digital communication.
Correct Answer : True
Explanation : In a parallel transmission each bit is transmitted in a separate wire. Since each bit is transmitted individually, each bit requires a separate transmitter and a receiver.
Correct Answer : Data bus
Explanation : In a parallel transmission multiwire cables are used. These cables carry a bit in each wire and are referred as data bus.
Correct Answer : Low speed
Explanation : One of the major disadvantages of using parallel transmission for long distance is that laying the data bus is costly. To cover a distance of 10km for an 8 bit system, we need a cable of 80km length. Parallel data are usually faster than serial since all the bits are transmitted simultaneously.
Correct Answer : Serializer/Deserializer
Explanation : Parallel transmission is high speed and serial data can cover longer distances. Hence they are used interchangeably and the devices which convert serial to parallel and parallel to serial transmission is called serializer/deserializer device (SERDES).
Correct Answer : Inductive and capacitance effects
Explanation : As the speed of transmission or the frequency of transmission increases the wavelength of transmission becomes comparable with the length of the data bus. This causes inductive and capacitance effects which degrade the signal.
Correct Answer : Least significant bit
Explanation : In serial transmission, the bits are transmitted one after the other in a specific order. The least significant bit is transmitted first and the most significant bit is transmitted in the end.
Correct Answer : 80μs
Explaination : Total transmission time = time for each bit x total number of bits = 8 x 10μs = 80μs.
Correct Answer : Convert analog to digital
Explanation : ADC corresponds to Analog to Digital Converter which is used to convert an analog signal into a digital. Digital signal can be processed and manipulated.
Correct Answer : Stairstep wave
Explanation : The Digital to analog converter takes the binary number as an input and produces the analog voltage proportional to the binary number. These analog voltages represent specific analog voltage levels and have stairstep characters.
Correct Answer : 70kHz
Explanation : Fifth harmonic = 5 x signal frequency = 5 x 14kHz = 70kHz.
Correct Answer : 1.7mV
Explanation :
Correct Answer : Quantization error
Explanation : When the number of bits is not sufficient enough to represent the analog voltage levels, quantization error occurs. The greater the number of bits, the greater the number of increments over the analog range and the smaller the quantizing error.
Correct Answer : 12000Hz
Explanation : Minimum sampling frequency= Nyquist frequency = 2x(frequency of analog waveform)= 2x 6000Hz = 12000Hz.
Correct Answer : 255
Explanation : The number of voltage increments that can be in an N bit system is given by 2N-1 = 28-1 =255.
Explanation : The modulator acts like a gating circuit that allows the analog wave for a particular time period producing a pulse. The amplitude of the pulse is the input to the ADC which converts the voltage into binary numbers.
Correct Answer : Low pass
Explanation : The antialiasing filter is basically just a low pass filter which allows signals with frequencies less than the cut off value to pass through. The cut off frequency is usually half of the sampling frequency.
Correct Answer : Single stage RC or LC circuits
Explanation : An antialiasing filter must have good selective characteristics. The roll off rate of a single stage RC or LC circuit is too low and hence Multistage LC circuits, RC active filter and High order switched capacitor filter circuits are used.
Correct Answer : Less accuracy
Explanation : Accuracy of the conversion increases with an increase in sampling rate since discretization is reduced and we get a better digital replica of the original signal. As the frequency is high and the time period between samples are very low huge amounts of data are recorded and hence require high power and storage space eventually leading to high costs.
Correct Answer : Improvement in SNR
Explanation : One of the major advantages of oversampling is that it increases the signal to noise ratio(SNR). It decreases the quantization noise by spreading it over a wider frequency. The increase in SNR is called the processing gain.
Correct Answer : Use low pass filters
Explanation : Undersampling causes aliasing which at the output of the ADC results in a wave with much lower frequency than the original signal. To reduce aliasing effects, antialiasing filters are used which acts as a low pass filter.
Correct Answer : Downconverter
Explanation : In radio receivers, a high-frequency signal is converted to a lower mixed frequency called an intermediate frequency (IF) where it can be more adequately filtered for improved frequency selection. A downconverter is a circuit that performs this equivalent of aliasing.
Correct Answer : Fast microprocessors
Explanation : Since in undersampling the time period between samples is sufficiently large, this allows slower processors to be used for ADC. This also allows low memory capacity for storage and less power consumption.
Correct Answer : 72.24dB
Explanation : 20 log( 212-1) = 20 log (4096-1) = 20 log (4095) = 72.24dB.
Correct Answer : Flash conversion
Explanation : The flash converter produces an output as fast as the comparators can switch and the signals can be translated to binary levels by the logic circuits. Comparator switching and logic propagation delays are extremely short. Thus, flash converters are the fastest type of A/D converter.
Correct Answer : 10MHz
Explanation : Operational frequency = 1 / (100 x 10-9)= 10MHz. Operational frequencies higher than this would produce errors.
Correct Answer : False
Explanation : Settling time is the amount of time it takes for the output voltage of a DAC, after a change in binary input, to stabilize to within a specific voltage range. The output is thus not an accurate representation of the binary input; it is not usable until it settles down.
Correct Answer : 1.25V
Explanation : Resolution = reference voltage / 2N = 10/23 = 1.25V.
Correct Answer : Pulse modulation
Explanation : In pulse modulation, the information to be transmitted is represented by a series of binary pulses. Since the pulse information is binary in nature analog signal shave to be converted to digital before transmitting.
Correct Answer : 1.02V
Explaination :
Correct Answer : Pulse code modulation
Explanation : The most widely used technique for digitizing information signals for electronic data transmission is pulse code modulation. It has uniform transmission quality and also can be used when the signal traffic is high.
Correct Answer : Companding
Explanation : To reduce the effects of noise and distortion in pulse modulation, a process called companding is done. Companding is a process of signal compression and expansion.
Correct Answer : Communication of airplane with ATC
Explanation : Pulse modulation is used in telemetry systems to monitor spacecraft or missile, RC models, for switching power supplies like regulators and also as audio switching power amplifiers. Communication of airplane with ATC is amplitude modulated waves.
Correct Answer : Pulse frequency modulation
Explanation : There are four basic forms of pulse modulation. They are: pulse amplitude modulation, pulse width modulation, pulse position modulation pulse code modulation. In any form of pulse modulation, the frequency of the signal is not changed.
Correct Answer : 2
Explanation : The amplitude of PWM is binary in nature meaning that it has only two levels. The amplitude of the modulating signals varies the width of the pulses generated.
Correct Answer : Pulse amplitude modulation
Explanation : Out of all the pulse modulation techniques, Pulse amplitude modulation is the least expensive and simplest to implement. In pulse amplitude modulation, the amplitude of the pulse varies with the amplitude of the modulating signal.
Correct Answer : Pulse width changes in accordance with the amplitude of modulating signal
Explanation : In PPM, the pulses change position according to the amplitude of the analog signal. The pulses are very narrow. These pulse signals may be transmitted in a baseband form, but in most applications, they modulate a high-frequency radio carrier.
Explanation : DSP is the use of a fast digital computer or digital circuitry to perform processing on digital signals. Any digital computer with sufficient speed and memory can be used for DSP.
Correct Answer : Stored in a RAM
Explanation : When the signal is converted from analog to digital it is a sequence of binary numbers which is stored in the RAM. A user defined code that is usually stored in the ROM performs mathematical and other manipulations after which it is converted back into analog signals.
Correct Answer : John Von Neumann
Explanation : Physicist John Von Neumann is generally credited with creating the stored program concept that is the basis of operation of all digital computers. Binary words representing computer instructions are stored sequentially in a memory to form a program. The instructions are fetched and executed one at a time at high speed.
Correct Answer : Data compression
Explanation : Data compression is done by checking redundancy in data. Data redundancy checking is only possible when the data is in digital form and hence data compression cannot be done in analog signals.
Correct Answer : Fast Fourier transforms
Explanation : The DFT is a complex program that is long and time-consuming to run. In general, computers are not fast enough to perform DFT in real time as the signal occurs. Therefore, a special version of the algorithm has been developed to speed up the calculation. Known as the fast Fourier transform (FFT), it permits real-time signal spectrum analysis.
Correct Answer : Spectrum analysis
Explanation : Spectrum analysis is the process of examining a signal to determine its frequency content. Algorithms such as discrete Fourier transform (DFT) and FPGA is used to analyze the frequency content of an input signal.
Correct Answer : High sampling frequency
Explanation : The time taken for input/output and the processing time together must be smaller than the sampling period to ensure the continuous flow of data. Since high sampling frequencies are needed for accurately converting the analog signal to digital, high speed DSP is a must.
Correct Answer : Von Neumann bottleneck
Explanation : The accessibility limitation of only one data or instruction set at a time from the memory is called as Von Neumann bottleneck. This has the effect of greatly limiting the execution speed.
Correct Answer : Harvard architecture
Explanation : In a Harvard architecture microprocessor, there are two memories, a program or instruction memory, usually a ROM, and a data memory, which is a RAM. Also, there are two data paths into and out of the CPU between the memories. Because both instructions and data can be accessed simultaneously, very high-speed operation is possible.
