This is the summary notes of the important terms and concepts in Chapter 3 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.
PHASE-LOCKED LOOPS, ANDFREQUENCY SYNTHESIZERS
This word means to fluctuate between two states or conditions.
A device that produces oscillations or generates repetitive
waveform. Converts a dc input voltage to an ac output voltage.
A self-sustaining oscillator where the changes in the waveform
are continuous and repetitive; they occur at a periodic rate.
Are oscillators that are not self-sustaining requiring an
external input signal or trigger to produce a change in the output waveform?
Triggered or One-shot
An amplifier with a feedback loop or path for energy to
propagate from the output back to the input.
According to this criterion, for a feedback circuit to sustain
oscillations, the net voltage gain around the feedback loop must be unity or
greater, and the net phase shift around the loop must be a positive integer
multiple of 360º.
Is a positive feedback where the positive means that its phase
aids the oscillation process and does not necessarily indicate a positive or
Is a negative feedback and supplies a feedback signal that
inhibits oscillations from occurring.
Is an untuned RC phase shift oscillator that uses both
positive and negative feedback? The oscillator that Hewlett and Packard used
in their original signal generator design.
Added to the circuit to compensate for imbalances in the
bridge and variations in component values due to heat.
Automatic Gain Control
( AGC )
Are oscillator circuits that utilize LC tank circuits for the
frequency determining components?
An LC oscillator that uses a tapped coil.
The operation of this oscillator is very similar to that of
Hartley except that a capacitive divider is used instead of a tapped coil.
An oscillator circuit identical to the Colpitts except with
the addition of a small capacitor Cs placed in series with L1.
The ability of an oscillator to remain at a fixed frequency.
Frequency stability affected predominantly by fluctuations in
dc operating voltages.
Frequency stability which is a function of component aging and
changes in the ambient temperature and humidity.
Feedback oscillator circuits where a crystal is used for the
frequency determining component.
The study of the form, structure, properties, and
classifications of crystals. It deals with lattices, bonding, and behavior of
slices of crystal material that have been cut at various angles with respect
to the crystal’s axes.
The _______ occurs when oscillating mechanical stresses
applied across a crystal lattice structure generate electrical oscillations
and vice versa.
In this mode the oscillator is tuned at the third, fifth,
seventh, or even the ninth harmonic of the crystal’s fundamental frequency.
The direction of frequency change is the same as the
Positive Temperature Coefficient
The change in frequency is in the direction opposite to the
Is almost a perfect zero-coefficient crystal from freezing to
boiling but is useful only at frequencies below a few hundred kilohertz.
A crystal oscillator circuit that has very good frequency
stability and reasonably simple circuitry.
Discrete Pierce Oscillator
A crystal oscillator circuit that has low cost and simple
digital interfacing capabilities.
IC-based Pierce Oscillator
A crystal oscillator circuit that has best frequency
Consists of a crystal-controlled oscillator and a
voltage-variable component such as a varactor diode.
Crystal Oscillator Module
A specially constructed diode whose internal capacitance is
enhanced when reversed biased, and by varying the reverse-bias voltage, the
capacitance of the diode can be adjusted.
Varactor Diode or Varicap
An oscillator circuit that generates well-defined, stable
waveforms that can be externally modulated or swept over a given frequency
A monolithic function generator integrated circuit
manufactured by EXAR Corporation capable of producing high quality sine,
square, triangle, rap, and pulse waveforms with both a high degree of
stability and accuracy.
A free-running oscillator with a stable frequency of
oscillation that depends on an external timing capacitance, timing
resistance, and control voltage.
A monolithic voltage controlled oscillator (VCO) integrated
circuit featuring excellent frequency stability and a wide tuning range. The
circuit provides simultaneous triangle- and square wave outputs over a
frequency range of from 0.01 Hz to 1 MHz.
A monolithic variable-frequency oscillator circuit featuring
excellent temperature stability and a wide linear sweep range.
A closed-loop feedback control system in which either the
frequency or the phase of the feedback signal is the parameter of interest
rather than the magnitude of the signal’s voltage or current.
Phase Locked Loop
( PLL )
The VCO’s output frequency when the PLL is not locked.
Preset/Natural Free Running
The voltage produced by the phase comparator that is
proportional to the difference in frequency between the two signals.
The PLL state when there is no external input frequency or the
feedback loop is open.
The state when the PLL is in the process of acquiring
The state when the VCO output frequency is locked onto (equal
to) the frequency of the external input signal.
The time required to achieve lock.
The band of frequencies centered around the VCO natural
frequency where the PLL can initially establish or acquire frequency lock
with an external input signal from an unlocked condition. Also known as
The capture range expressed as a peak value.
The band of frequencies centered around the VCO natural
frequency over which a PLL can maintain frequency lock with an external input
signal. Also known as tracking range.
The lock range expressed as a peak value.
An oscillator with a stable frequency of oscillation that
depends on an external bias voltage.
Sometimes called a phase detector which is a nonlinear device
with two input signals: an external input frequency and the VCO output
The difference in phase between an external input frequency
and the VCO output signal.
The product of the individual gains or transfer functions
around the loop for the PLL.
An ultra stable monolithic phase-locked-loop system designed
by EXAR Corporation for a wide variety of applications in both analog and
digital communications systems. Can operate over a relatively wide frequency
range from 0.5 Hz to 35 MHz.
PLL that are used to track digital pulses rather than analog
signals, such as in clock recovery circuits.
This word means to form an entity by combining parts or
Are used to generate many output frequencies through the
addition, subtraction, multiplication, and division, of a smaller number of
fixed frequency sources.
A method of frequency synthesis where multiple output
frequencies are generated by mixing the outputs from two or more
crystal-controlled frequency sources or by dividing or multiplying the output
frequency from a single-crystal oscillator.
A method of frequency synthesis where a feedback-controlled
divider/multiplier such as PLL is used to generate multiple output
Indirect Frequency Synthesis
The minimum frequency separation between output frequencies
for a synthesizer.
An advanced dual-modulus low-power, ECL prescaler manufactured
by Signetics Company. The maximum input signal frequency is 1.2 GHz for
cellular and other land mobile applications.
A bipolar, single-chip frequency synthesizer manufactured in
SUBILO-N technology (components laterally separated by oxide). It performs
all the tuning functions of a PLL radio-tuning system. Also manufactured by Signetics.