E-COMMS (Chapter 2)

Types of inductors

(a) Heavy self-supporting wire coil. (b) Inductor made as copper pattern. (c) Insulating form. (d) Toroidal inductor. (e) Ferrite bead inductor. (f ) Chip inductor.

Inductance

causes a voltage to be self-induced into the coil winding, which has the effect of opposing current changes in the coil

tank circuit

circuit acts as a kind of storage vessel for electric energy

tuned circuits

circuits made up of inductors and capacitors that resonate at specific frequencies

tank current

circulating current

Resonant frequency

is inversely proportional to inductance and capacitance.

Insertion loss

is the loss the filter introduces to the signals in the passband. Passive filters introduce attenuation because of the resistive losses in the components. Insertion loss is typically given in decibels

capacitor

it is used in an ac circuit continually charges and discharges. It tends to oppose voltage changes across it

decade

represents a one-tenth or times-10 relationship

Crystal filters

made from the same type of quartz crystals normally used in crystal oscillator

series resonant circuit

made up of inductance, capacitance, and resistance, such circuits are often referred to as LCR circuits or RLC circuits.

Impedance

resistive value of the load and source terminations of the fi lter. Filters are usually designed for specific driving source and load that must be present for proper operation

Skin Effect

tendency of electrons flowing in a conductor to fl ow near and on the outer surface of the conductor frequencies

Antilog

the number obtained when the base is raised to the logarithm

decibels (dB)

, a unit of measurement that was originally created as a way of expressing the hearing response of the human ear to various sound levels.

quality factor/Q factor

the ratio of inductive power to resistive power (xL/R)

decibels (dB)

It is is one-tenth of a bel.

reactance

Both coils and capacitors offer an opposition to alternating current flow (ohms)

parallel-T or twin-T notch filter

A simple notch filter that is implemented with resistors and capacitors

Ripple

Amplitude variation with frequency in the passband, or the repetitive rise and fall of the signal level in the passband of some types of fi lters, is known as ripple. It is usually stated in decibels.

Types of LC filters

Butterworth,Cauer,Chebyshev,Bessel

half-power points

Current levels at which the response is down 70.7 percent, and the power at the cutoff frequencies is one-half the power peak of the curve

inductive reactance

Opposition to alternating current offered by inductors is continuous and constant

All-pass filter

Passes all frequencies equally well over its design range but has a fixed or predictable phase shift characteristic

High-pass filter

Passes frequencies above the cutoff but rejects those below it

Low-pass filter

Passes frequencies below a critical frequency called the cutoff frequency and greatly attenuates those above the cutoff frequency

Bandpass filter

Passes frequencies over a narrow range between lower and upper cutoff frequencies

Band-reject filter

Rejects or stops frequencies over a narrow range but allows frequencies above and below to pass

Gain

amplification. It is simply the ratio of the output to the input

bandwidth

The narrow frequency range over which the current is highest

Attenuation

This is the amount by which undesired frequencies in the stop band are reduced. It can be expressed as a power ratio or voltage ratio of the output to the input. Attenuation is usually given in decibels.

Passband

This is the frequency range over which the fi lter passes signals. It is the frequency range between the cutoff frequencies or between the cutoff frequency and zero (for low-pass) or between the cutoff frequency and infi nity (for high-pass)

Stop band

This is the range of frequencies outside the passband, i.e., the range of frequencies that is greatly attenuated by the fi lter. Frequencies in this range are rejected.

Zero

This term refers to a frequency at which there is zero impedance in the circuit.

cascaded

When two or more stages of amplifi cation or other forms of signal processing

pole

a frequency at which there is a high impedance in the circuit. It is also used to describe one RC section of a filter

Ceramic

a manufactured crystallike compound that has the same piezoelectric qualities as quar

bandpass filter

allows a narrow range of frequencies around a center frequency fc to pass with minimum attenuation but rejects frequencies above and below this range

Bessel

also called Thomson filters, provide the desired frequency response (i.e., low-pass, bandpass, etc.) but have a constant time delay in the passband

Inductor

also called a coil or choke, is simply a winding of multiple turns of wire

Roll-off

also called the attenuation rate, roll-off is the rate of change of amplitude with frequency in a fi lter

Band-reject filters

also known as bandstop fi lters, reject a narrow band of frequencies around a center or notch frequency

Shape factor

also known as bandwidth ratio, is the ratio of the stop bandwidth to the pass bandwidth of a bandpass filter.

Capacitive Reactance (Xc)

an opposition to alternating current

Notch fi lters

are also referred to as bandstop or band-reject filters

Stray capacitances

are typically small, but they cannot be ignored, especially at the high frequencies used in communication. Stray and distributed capacitances can signifi cantly affect the performance of a circuit

Twin-T notch filters

are used at low frequencies to eliminate power line hum from audio circuits and medical equipment amplifiers.

Band-reject fi lters

are used to greatly attenuate a narrow range of frequencies around a center point

Ceramic filters

are very small and inexpensive and are, therefore, widely used in transmitters and receivers

Henry

basic unit of inductance

octave

defined as a doubling or halving of frequency

Inductance

directly affected by the physical characteristics of the coil, including the number of turns of wire in the inductor, the spacing of the turns, the length of the coil, the diameter of the coil, and the type of magnetic core material.

passive filters

do not amplify

parallel resonant circuit

formed when the inductor and capacitor are connected in parallel with the applied voltage

filter

frequency-selective circuit

Capacitance

generally added to a circuit by a capacitor of a specific value, but it can occur between any two conductors separated by an insulator

Butterworth

has maximum fl atness in response in the pass band and a uniform attenuation with frequency

Chebyshev

have extremely good selectivity; i.e., their attenuation rate or roll-off is high, much higher than that of the Butterworth fi lter.

selectivity

how the circuit responds to varying frequencies

Resonance

occurs when the inductive and capacitive reactances are equal

Cauer filters

produce an even greater attenuation or roll-off rate than do Chebyshev fi lters and greater attenuation out of the passband.

Attenuation

refers to a loss introduced by a circuit or component. Many electronic circuits, sometimes called stages, reduce the amplitude of a signal rather than increase it.

insertion loss

signal attenuation in the passband

Low-pass filter

sometimes referred to as high cut filters

Envelope delay

time it takes for a specifi c point on an input waveform to pass through the fi lter

active filters

use amplifying devices such as transistors and operational amplifiers.

RC filters

use combinations of resistors and capacitors to achieve a desired frequency response

Mechanical Filters

uses resonant vibrations of mechanical disks to provide the selectivity