ADC VIVA QUESTIONS
ADC VIVA QUESTIONS
The process of reconstructing a continuous time signal from it's samples is known as interpolation.
The process of converting continuous time signal into equivalent time signal can be termed as sampling.
in another way
The sampling theorem can be defined as the conversation of an analog signal into a discrete form by taking samples of analog signals at specific frequency.
Modulation is the process of converting data into radio waves by adding information to an electronic or optical carrier signal.
or shifting a signal from lower frequency to higher frequency.
It is the process by which amplitude of high frequency signal is varying according to the instataneous amplitude of information.
It is the process by which frequency of high frequency signal is varying according to the instataneous amplitude of information.
It is the process by which phase of high frequency signal is varying according to the instataneous amplitude of information.
Quantization is the process of representing the sampled value of the amplitude by a finite set of levels, which means converting a continuous amplitude sample into a Discrete time signal.
There are two types of Quantization - Uniform Quantization and Non-uniform Quantization. The type of quantization in which the quantization levels are uniformly spaced is termed as a Uniform Quantization. The type of quantization in which the quantization levels are unequal and mostly the relation between them is logarithmic, is termed as a Non-uniform Quantization.
Again in Uniform Quantization there are two types.
The Mid-Rise type is so called because the origin lies in the middle of a raising part of the stair-case like graph. The quantization levels in this type are even in number.
The Mid-tread type is so called because the origin lies in the middle of a tread of the stair-case like graph. The quantization levels in this type are odd in number.
It is the ratio of amplitude of modulating signal to amplitude of carrier signal.
The transmission of such a signal which contains a carrier along with two side-bands, can be termed as DSB-FC.
The form of AM signal in which carrier signal is suppressed and transmitting only two sidebands is termed as DSB-SC.
Power-Saving in DSB-SC is 66.66% of the total transmitting power at 100% Modulation.
The process of suppressing one of the sideband along with the carrier and transmitting a signal sideband is called as SSB-SC or SSB signal.
Power saving in SSB-SC or SSB is 83.32% of the total transmitting power at 100% modulation.
In telecommunication Bit rate is the number of bits that are processed per unit of time.
Bit-length is the number of binary digits, called Bits
Communication is the process of exchange of data between transmitter and receiver though transmission medium.
It is a process by which information /message is transmitted from one person to another in the form of electrical signals.
In analog communication, the message or the information to be transmitted is analog in nature. This analog message is obtained from the source such as speech, video, audio etc.
In Digital communication, the message or the signal are transmitted in Digital form. that means digital communication involves transmission of data or information in Digital form.
1. height of Antenna
2. Multiplexing
3. High Bandwidth
4. Narrow Bandwidth
Vestigial Sideband Modulation or VSB Modulation is the process where a part of the signal called as vestige is modulated, along with one sideband.
Slope of Analog signal is greater than delta modulator can maintain is called slope overload.
If input is slowly varies another error occurs that is granular noise
The rate at which a signal can be sampled without introducing errors, which is twice the highest frequency present in input signal is called Nyquist Rate. [Fs>=2fmax]
It is an effect that causes different signals to become indistinguishable while sampling.?
In another way we can say that the overlapping of the frequency spectrum of the sampled signal is known as the aliasing effect.
spreading of a pulse beyond it's interval causes to interfere with neighboring pulses, which is known as Internal symbol interference.
It is the process of sampling of the band limited signal below the Nyquist rate. [Fs<=2fm]
Companding is a non-linear technique used in PCM which compresses the data at the transmitter and expands the same data at the receiver. The effects of noise and crosstalk are reduced by using Companding.
Pulse-code modulation (PCM) is a method used to represent sampled analog signals digitally.
Advantages
1 .it provides secure Data transmission.
2. It offers efficient regeneration.
3. easy to add or drop channels.
Disadvantages
1.Large bandwidth is required for transmission.
2.overload appears when modulating signal changes between samplings.
Differential pulse code modulation (DPCM) is a procedure of converting an analog into a digital signal in which an analog signal is sampled and then the difference between the actual sample value and its predicted value (predicted value is based on previous sample or samples) is quantized and then encoded forming a digital value.
The type of modulation, where the sampling rate is much higher and in which the stepsize after quantization is of smaller value Δ, such a modulation is termed as delta modulation.
Advantages
1.consumption of low bandwidth.
2.cost effective technique.
3.Data can be timely delivered by using it.
Disadvantages
1.production of Granular noise
2.slope overload distortion which occur due to large dynamic ranges of the input signal.
The ADM is a type of Delta Modulation in which the step size is variable, also known as continuously variable slope Delta Modulation.
Output of multiplexer is coded in to electrical pulses for the purpose of transmission over the channel.This process is known as line coding or transmission coding.
In another way
A line code is the code used for data transmission of a digital signal over a transmission line. This process of coding is chosen so as to avoid overlap and distortion of signal such as inter-symbol interference.
It's a line code technique in which a High in data represented by a Mark pulse, its duration is less than the symbol bit duration. Half of the bit duration remains high but it immediately returns to zero and shows the absence of pulse during the remaining half of the bit duration and low in data represented by a no pulse.
It's a line code technique in which a High in data represented by a Mark pulse, its duration is less than the symbol bit duration. Half of the bit duration remains high but it immediately returns to zero and shows the absence of pulse during the remaining half of the bit duration and for Low input, a negative pulse represents the data, and the zero level remains same for the other half of the bit duration.
It's a line coding technique in which a High in data is represented by a positive pulse and Low in data has no pulse.
It's a line coding technique in which a high in data is represented by a positive pulse while a Low in data is represented by negative pulse.
This technique is also called AMI(alternative mark inversion). in this technique For a 1, the voltage level gets a transition from + to – or from – to +, having alternate 1s to be of equal polarity. A 0 will have a zero voltage level.
1. Transmission bandwidth should be minimum.
2. Transmitted power for given BW and BER should be minimum.
3. It should be possible to easily detect and correct the error.
4. PSD should be zero at ω=0(dc) because AC coupling and transformers are used at repeaters.
5. It should be possible to extract timing or clock information from the signal.
In telecommunication eye diagram, is an oscilloscope display in which a digital signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep.
The source encoder converts information waveforms to bits, while the decoder converts bits back to waveforms. ... Channel coding: The channel encoder converts bits to signal waveform, while the decoder converts received waveform back to bits.
Scrambling is a rearrangement of data sequence. It manipulates a data stream before transmitting. Scrambling is widely used in satellite communication.
Small deviation of incoming pulse from it's ideal location is known as Timing Jitter.
A regenerative repeater amplifies and reconstructs such a badly distorted digital signal and develops a nearly perfect replica of the original signal at its output.
Regenerative repeaters are the major source of timing jitter in a digital transmission system.
Equalizer eliminates dispartion but preamplifier enhances the received channel noise by boosting noise Signal.This undesirable phenomena is known as Noise Amplification.
number of possible digital values to represent each sample.
Daata transmission for a given amount of time is called Bandwidth.
It is the Ratio of output signal to noise ratio to input signal to noise ratio.
The disturbance caused in nearby channel or circuit due to transmitted signal.
If the highest frequency in the signal is B, then the signal can be reconstructed from it's samples if sampling frequency is greater than or equal to twice the highest frequency of the information signal.
Amplitude Shift Keying ASK is a type of Amplitude Modulation which represents the binary data in the form of variations in the amplitude of a signal.
if binary signal when ASK modulated, gives a zero value for Low input while it gives the carrier output for High input.
Frequency Shift Keying FSK is the digital modulation technique in which the frequency of the carrier signal varies according to the digital signal changes. FSK is a scheme of frequency modulation.
The output of a FSK modulated wave is high in frequency for a binary High input and is low in frequency for a binary Low input.
Phase Shift Keying PSK is the digital modulation technique in which the phase of the carrier signal is changed by varying the sine and cosine inputs at a particular time.
This is also called as 2-phase PSK or Phase Reversal Keying. In this technique, the sine wave carrier takes two phase reversals such as 0° and 180°.
This is the phase shift keying technique, in which the sine wave carrier takes four phase reversals such as 0°, 90°, 180°, and 270°.
The Nyquist criterion states that a repetitive waveform can be correctly reconstructed provided that the sampling frequency is greater than double the highest frequency to be sampled.
In delta modulation step size is fixed for the whole signal. whereas in adaptive delta modulation the step size is varies depending upon the input signal.
The high frequency signal, which has a certain amplitude, frequency and phase but contains no information is called as a carrier signal.
The signal which contains a message to be transmitted, is called as a message signal.
The resultant signal after the process of modulation is called as a modulated signal.
The electrical equivalent of the original message signal is called as baseband signal.
In analog and digital communication SNR is a measure of signal strength relative to background noise.
A Sideband is a band of frequencies, containing power, which are the lower and higher frequencies of the carrier frequency.
A continuous time varying signal, which represents a time varying quantity can be termed as an Analog Signal.
A signal which is discrete in nature or which is non-continuous in form can be termed as a Digital signal.
In Pulse Amplitude Modulation (PAM) technique, the amplitude of the pulse carrier varies, which is proportional to the instantaneous amplitude of the message signal.
In pulse width modulation (PWM) technique, the width of the pulse carrier varies, which is proportional to the instantaneous amplitude of the message signal.
In pulse position modulation (PPM) technique, the position of the pulse carrier varies, which is proportional to the instantaneous amplitude of the message signal.
Multiplexing is the process of combining multiple signals into one signal, over a shared medium.
The process is called as analog multiplexing if these signals are analog in nature.
If digital signals are multiplexed, it is called as digital multiplexing.
The reverse process, extracting the number of channels from one, which is done at the receiver is called as demultiplexing.
The effect of distortion, noise, and interference is much less in digital signals as they are less affected.
Digital circuits are more reliable.
Digital circuits are easy to design and cheaper than analog circuits.
The hardware implementation in digital circuits, is more flexible than analog.
The occurrence of cross-talk is very rare in digital communication.
An M-ary transmission is a type of digital modulation where instead of transmitting one bit at a time, two or more bits are transmitted simultaneously.
The process of extracting a modulating or baseband signal from the modulated signal is called demodulation or detection.
It is the ratio of transmitted power which contains information to the total transmitted power.
Due to power saving, reduced channel bandwidth and reduced interference of noise, SSB is preferred.
It is the minimum sampling rate required to represent the continuous time signal faithfully in its sampled form.
When the sampling rate is chosen much higher than the Nyquist rate than a small space occures between the samples. this space said to be a Guard band.
If the frequency spectrum of a signal is centered around a non-zero frequency fc, then the signal is called as a band pass signal.
It is a signal, the spectrum of which extends over a finite frequency range.
It is a signal which is present only over a finite interval of time is called as a time limited signal.
Modulator and De-modulator packaged in one unit as modem is called as duplex system.
FDM is an analog technique that can be applied when the bandwidth of a link is greater than the bandwidth of the signal to be transmitted.
Time division multiplexing (TDM) is a technique of multiplexing, where the users are allowed the total available bandwidth on time sharing basis. Here the time domain is divided into several recurrent slots of fixed length.
The bit error rate is a number of bit errors per unit of time.
No. of pulses per second.
The envelop is a resulting sum of LSB.
If information is transmitted without modulation, it is called baseband communication.
Under modulation occurs when the maximum amplitude of the message signal or modulating signal is less than the maximum amplitude of the carrier signal.[Am < Ac]
Perfect modulation occurs when the maximum amplitude of the message signal or modulating signal is exactly equal to the maximum amplitude of the carrier signal.[Am = Ac]
Over modulation occures when the maximum amplitude of the message signal or modulating signal is greater than the maximum amplitude of the carrier signal.[Am > Ac]
Guided medium is a wired communication it transmits data either using twisted pair cable, coaxial cable or fibre optics; it requires maintenance charge.
The unguided medium is a wireless communication it transmits signal by broadcasting it through the air.
in communication channel is mediums through which you can send a message to its intended audience.
Pulse Width (PW) is the elapsed time between the rising and falling edges of a single pulse.
it is the measure of the percentage (%) that what percent of the circuit is ON compared to circuit OFF.
In ideal sampling technique the sampling function is a train of impulses and the principle used is known as multiplication principle.
Natural sampling is similar to ideal sampling, except the impulse train is replaced by pulse train of period T.
During transmission, noise is introduced at top of the transmission pulse which can be easily removed if the pulse is in the form of flat top. this type of sampling is known as flat top sampling.
It is the ratio of largest to smallest measurable amplitude.
Compressor provides amplification to lower value and attenuation to higher value.
Expander provides amplification to higher value and attenuation to lower value.
To process these signals in computers, we need to convert the signals to "digital" form. While an analog signal is continuous in both time and amplitude, a digital signal is discrete in both time and amplitude. To convert a signal from continuous time to discrete time, a process called sampling is used.
Angle modulation is the type of modulation in which either frequency or phase of a sinusinusoidal carrier is varied in proportion with the message signal amplitude, keeping the carrier amplitude constant.
The Modulation index corresponding to the maximum deviation and maximum modulating frequency is called as the Deviation ratio.
The sensitivity of a radio receiver is defined as it's ability to amplify weak signals.
The selectivity of a receiver is defined as its ability to reject unwanted signals.
The Fidelity is a ability of a receiver to reproduce all the modulating frequency equally.
QPSK is a type of PSK in which the phase shift of analog carrier can take one of the four different values such as 90,180,270 and 360 to represent four different input symbols.
The unwanted signal at frequency Fsi is known as the image frequency.
Double spoting is the phenomenon in which, the same stations gets picked up at two different nearby points, on the receiver dial.
Transducers are used in electronic communications systems to convert signals of various physical forms to electronic signals, and vice versa.
Digital signals can be regenerated using repeaters in order to travel longer distances before weakening and becoming unusable because of attenuation. Baseband supports bidirectional communication. It means, this technology can send and receive data simultaneously.
As the coding is done to make more bits transmit on a single signal, the bandwidth used is much reduced.
For a given bandwidth, the power is efficiently used.
The probability of error is much reduced.
Error detection is done and the bipolar too has a correction capability.
Power density is much favorable.
in the application like telecommunication system, there are large number of users involved.
it is not possible to use a separate pair of wires from each subscriber to all the other subscribers.
instead we use the principle of multiplexing, then we can use a common communication medium such as a coaxial cable.
The communication system in which the information is communicated in only one direction are known as simplex system.
The system that can transmit as well as receive but not simultaneously are known as half duplex system.
The truly bidirectional system that allow the communication to take place in both the direction simultaneously
are known as Full duplex system.
A constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying.
In wireless communication we are using Free space or Air as a transmission medium. signal are transmitted in the form of EM waves in Air or Free space. (Antenna is used to convert electrical signal into EM waves)
The noise generated internally by the devices and components is called as a thermal noise.
The transmitted power can be defined as the average power of the transmitted signal.
The channel bandwidth is defined as the band of frequencies allotted for the transmission of message signal.
Transmitters and receivers are simple.
Low bandwidth requirement
FDM can be used
Noise affects the signal quality
It's not possible to separate noise and signal.
Repeaters can not be used between transmitter and receiver
Coding is not possible
Radio broadcasting
TV broadcasting
Telephones
The effect of distortion, noise, and interference is much less in digital signals as they are less affected.
Digital circuits are more reliable.
Digital circuits are easy to design and cheaper than analog circuits.
The hardware implementation in digital circuits, is more flexible than analog.
The occurrence of cross-talk is very rare in digital communication.
TDM technique can be used
The bit rate of digital system is high.
Digital modulation needs synchronization in case of synchronous modulation.
Satellite communication
Military communications
Telephone systems
Data and computer communications
Select the desired signal from all the other unwanted signal.
Amplify the desired signal.
Demodulate the amplified signal.
After demodulation, the original modulating signal is obtained which must be amplified.
Apply the demodulated signal to the loudspeaker.
The operating frequencies in FM are much higher than in AM.
The FM demodulators are different from AM detectors.
The method to obtain the AGC(Automatic gain control) is different in FM receivers.
The FM receivers need the circuit like Limiter and De-emphasis.