This is the summary notes of the important terms and concepts in Chapter 10 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Is the transmittal of digital signals between two or more
points in a communications system.
_________ developed the first digital transmission system for
the purpose of carrying digitally encoded analog signals, such as human
voice, over metallic wire cables between telephone offices.
The primary advantage of digital transmission over analog
Digital signals are also better suited than analog signals for
processing and combining using a technique called _____.
Is the processing of analog signals using digital methods and
includes bandlimiting the signal with filters, amplitude equalization, and
Digital Signal Processing ( DSP )
Digital transmission systems are more resistant to analog
systems to additive noise because they use ________ rather than signal
Consist essentially of sampling analog information signals and
then converting those samples into discrete pulses and transporting the
pulses from a source to a destination over a physical transmission medium.
The four predominant methods of pulse modulation.
PWM, PPM, PAM and PCM
Sometimes called pulse duration modulation (PDM) or pulse
length modulation (PLM), as the width (active portion of the duty cycle) of a
constant amplitude pulse is varied proportional to the amplitude of the
analog signal at the time the signal is sampled.
Pulse Width Modulation ( PWM )
The position of a constant-width pulse within a prescribed
time slot is varied according to the amplitude of the sample of the analog
Pulse Position Modulation ( PPM )
The amplitude of a constant-width, constant-position pulse is
varied according to the amplitude of the sample of the analog signal.
Pulse Amplitude Modulation
The analog signal is sampled and then converted to a serial
n-bit binary code for transmission.
Pulse Code Modulation ( PCM )
__________ is credited with inventing PCM in 1937 while
working for AT&T at its Paris laboratories.
Alex H. Reeves
A circuit that periodically samples the analog input signal
and converts those samples to a multilevel PAM signal.
The transmission line ________ are placed at prescribed
distances to regenerate the digital pulses.
An integrated circuit that performs the PCM encoding and
Codec ( Coder / Decoder )
The function of a _________ in a PCM transmitter is to
periodically sample the continually changing analog input voltage and convert
those samples to a series of constant-amplitude pulses that can more easily
be converted to binary PCM code.
The sampling process alters the frequency spectrum and
introduces an error called _________.
The ________ of the capacitor is called the A/D conversion
time because it is during this time that the ADC converts the sample voltage
to a PCM code.
If the input to the ADC is changing while it is performing the
conversion, _______ results.
_________ theorem establishes the minimum sampling rate (fs)
that can be used for a given PCM system.
The binary codes used for PCM are _________, where n may be
any positive integer greater than 1.
The sign bit in a sign-magnitude code.
Most Significant Bit ( MSB )
Is the process of converting an infinite number of
possibilities to a finite number of conditions. Is the process of rounding
off the amplitudes of flat-top samples to a manageable number of levels.
A type of code where the codes on the bottom half of the table
are a mirror image of the codes on the top half, except for the sign bit.
Folded Binary Code
The magnitude difference between adjacent steps.
Quantization Interval or Quantum
If the magnitude of the sample exceeds the highest
quantization interval, ________ (also called peak limiting) occurs.
Any round-off errors in the transmitted signal are reproduced
when the code is converted back to analog in the receiver.
Quantization Error (Qe ) Quantization
Is the ratio of the largest possible magnitude to the smallest
possible magnitude (other than 0V) that can be decoded by the
digital-to-analog converter in the receiver.
During times when there is no analog input signal, the only
input to the PAM sampler is random, thermal noise also called as __________,
that is converted to a PAM sample just as if it were a signal.
Idle Channel Noise
A way to reduce idle channel noise wherein the first
quantization interval is made larger in amplitude than the rest of the steps.
Is the process of compressing and then expanding.
Two methods of companding:
μ-Law and A-law Companding
Involves compression in the transmitter after the input sample
has been converted to a linear PCM code and then expansion in the receiver
prior to PCM decoding.
When digitizing speech signals only, special voice
encoders/decoders called _______ are often used
A _________ coder extracts the most significant portions of
speech information directly from the time waveform rather than from the
frequency spectrum as with the channel and formant vocoders.
_________ modulation uses a single-bit PCM code to achieve
digital transmission of analog signals.
Two problems associated with delta modulation that do not
occur with conventional PCM.
Slope Overload and Granular Subdivision
With ________, the difference in the amplitude of two
successive samples is transmitted rather than the actual sample.
Differential PCM ( DPCM )
The secondary lobes are called __________.
_________ causes crosstalk between channels that occupy
adjacent time slots in a time-division-multiplexed carrier system.
Inter symbol interference ( ISI )
Special filters called _________ are inserted in the
transmission path to “equalize” the distortion for all frequencies, creating
uniform transmission medium reducing transmission impairments.
A ________ is simply the superposition of a series of
harmonically related sine waves with specific amplitude and phase
The decision levels for the regenerator are represented by
The _______ has an effect on the symbol timing (clock)
recovery circuit and, if excessive, may significantly degrade the performance
of cascaded regenerative sections.