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TV Tuner

Mar 1 2005

By Eric Yang

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Television (TV):

A form oftelecommunication for the transmission oftransient images of fixed or moving objects.

Signal: Detectable transmitted energy that can be usedto carryinformation.

A time-dependent variation of a characteristic of

a physical phenomenon, used to conveyinformation. As applied to electronics, any transmitted

electrical impulse.
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Radio frequency (RF) :

Any frequency within the electromagnetic spectrumnormally associated with radio wavepropagation.

Electromagnetic spectrum :The range of frequencies ofelectromagnetic radiation

from zero to infinity.

Note: The electromagnetic spectrum was, by custom and practice,

formerly divided into 26 alphabetically designated bands. Thisusage still prevails to some degree. However, the ITU formally

recognizes 12 bands, from 30 Hz to 3000 GHz. New bands, from 3

THz to 3000 THz, are under active consideration for recognition.

Refer tothe figure below.
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Electromagnetic radiation (EMR) :

Radiation made up of oscillating electric and magneticfields and propagated with the speed of light. Includes

gamma radiation, X-rays, ultraviolet, visible, and

infrared radiation, and radarand radio waves.

Modulation:The process, or result of the process, of varying a

characteristic of a carrier, in accordance with aninformation-bearing signal.
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Amplitude Modulation (AM):Modulation in which the amplitude of a carrierwave is varied in accordance with somecharacteristic of the modulating signal.Note: Amplitude modulation implies the modulation of acoherent carrier wave by mixing it in a nonlinear devicewith the modulating signal to produce discrete upper andlower sidebands, which are the sum and differencefrequencies of the carrier and signal. The envelope of theresultant modulated wave is an analog of the modulatingsignal. The instantaneous value of the resultant

modulated wave is the vector sum of the correspondinginstantaneous values of the carrier wave, upper sideband,and lower sideband. Recovery of the modulating signalmay be by direct detection or by heterodyning.
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NTSC standard:Abbreviation forNational Television StandardsCommittee standard. The North American standard

(525-line interlaced raster-scanned video) for the

generation, transmission, and reception oftelevision

signals.

Note 1: In the NTSC standard, picture information is transmitted in

vestigial-sideband AM and sound information is transmitted in FM.

Note 2: In addition to North America, the NTSC standard is used inCentral America, a number of South American countries, and

some Asian countries, including Japan. Contrast withPAL, PAL-M

, SECAM.
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PAL:Acronym forphase alternation by line. A television

signalstandard (625 lines, 50 Hz, 220 V primary power) used in the United Kingdom, much of the rest of

western Europe, several South American countries,

some Middle East and Asian countries, several African

countries, Australia, New Zealand, and other Pacific

island countries.

PAL-M:A modified version of the phase-alternation-by-line (PAL) televisionsignalstandard (525 lines, 50 Hz, 220

V primary power), used in Brazil.
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SECAM:Acronym for

systme electronique couleur avec memoire.

A televisionsignalstandard (625 lines, 50 Hz, 220 V

primary power) used in France, eastern European

countries, the former USSR, and some African

countries.

Necessary bandwidth:For a given class of emission, the width of the frequency

band which is just sufficient to ensure the transmission

ofinformation at the rate and with the quality requiredunder specified conditions.Note: Emissions useful for the adequate functioning of the receiving

equipment, e.g., the emission corresponding to the carrierof

reduced carrier systems, must be included in the necessary

bandwidth.

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Signal level:In a communications system, the signalpoweror

intensity at a specified point and with respect to aspecified reference level, e.g., 1 mW.

Sensitivity:

In an electronic device, e.g., a communications systemreceiver, ordetection device, e.g.,PIN diode, the

minimum inputsignal required to produce a specified

output signal having a specified signal-to-noise ratio, or

other specified criteria.Note 1: The signal input may be expressed as powerin dBm or as

field strength in microvolts per meter, with input network

impedance stipulated.

Note 2: "Sensitivity"is sometimes improperly used as a synonym

for"responsivity."
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Selectivity:A measure of the ability of a receiver to discriminate

between a wanted signal on one frequency andunwanted signals on other frequencies.

Signal-to-noise ratio (SNR):The ratio of the amplitude of the desired signal to the

amplitude ofnoise signals at a given point in time.Note 1: SNR is expressed as 20 times the logarithm of the amplitude

ratio, or 10 times the logarithm of the powerratio.

Note 2: SNR is usually expressed in dB and in terms of peak values

forimpulse noise and root-mean-square values forrandom noise. In

defining or specifying the SNR, both the signal and noise should be

characterized, e.g., peak-signal-to-peak-noise ratio, in order to avoid

ambiguity.

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Impedance matching:

The connection of an additional impedance to an existingone in order to accomplish a specific effect, such as to

balance a circuit or to reduce reflection in a

transmission line.

Resonance:

In anelectrical circuit, the condition that exists when theinductive reactance and the capacitive reactance are of

equal magnitude, causing electrical energy to oscillatebetween the magnetic field of the inductor and the

electric field of the capacitor.
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Note 1: Resonance occurs because the collapsing magnetic field of

the inductor generates an electric current in its windings that charges

the capacitor and the discharging capacitor provides an electric

current that builds the magnetic field in the inductor, and the process

is repeated.

Note 2: At resonance, the series impedance of the two elements is at

a minimum and the parallel impedance is a maximum. Resonance is

used fortuning and filtering, because resonance occurs at a

particularfrequency for given values of inductance andcapacitance. Resonance can be detrimental to the operationofcommunications circuits by causing unwanted sustainedand transient oscillations that may cause noise, signaldistortion, and damage to circuit elements. Note 3: At

resonance the inductive reactance and the capacitivereactance are of equal magnitude. Therefore, L = 1/C ,where = 2f , in which f is the resonant frequency in hertz,L is the inductance in henrys, and C is the capacity in faradswhen standard SI units are used. Thus,
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Tuning:Adjusting the parameters and components of a circuit so

that it resonates at a particularfrequency or so that the

current or voltage is either maximized or minimized at a

specific point in the circuit. Note: Tuning is usuallyaccomplished by adjusting the capacitance or the

inductance, or both, of elements that are connected to or

in the circuit.
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Filter:

In electronics, a device that transmits only part of theincident energy and may thereby change the spectral

distribution of energy:

(c) high-pass filters transmit energy above a certain

frequency;(d) low-pass filters transmit energy below a certain

frequency;

(e) bandpass filters transmit energy of a certain

bandwidth;

(f) band-stop filters transmit energy outside a specificfrequency band.
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Bandpass filter:A filterthat ideally passes all frequencies between two

non-zero finite limits and bars all frequencies not withinthe limits. Note: The cutoff frequencies are usually taken

to be the 3-dB points.

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Heterodyne:

To generate new frequencies by mixing two or more

signals in a nonlinear device such as a vacuum tube,

transistor, or diode mixer.

Note: A superheterodyne receiver converts any selected incomingfrequency by heterodyne action to a common

intermediate frequency where amplification and selectivity

(filtering) are provided.

6. A frequency produced by mixing two or more signalsin a nonlinear device.
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Heterodyne Principle

Heterodyning is a method for transferring a broadcast

signal from its carrier to a fixed local intermediate

frequency in the receiver so that most of the receiver

does not have to be retuned when you change channels.

The interference of any two waves will produce a

beat frequency, and this technique provides for the tuning

of a radio by forcing it to produce a specific beat

frequency called the "intermediate frequency" or IF.
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Heterodyne PrincipleAn electromagnetic carrierwave which is carrying a signal by means of

amplitude modulation orfrequency modulation can transfer that signal to acarrier of different frequency by means of a process called heterodyning. This

transfer is accomplished by mixing the original modulated carrier with a sine

wave of another frequency. This process produces a beat frequency equal to

the difference between the frequencies, and this difference frequency

constitutes a third carrier which will be modulated by the original signal.

Heterodyning is extremely important in radio transmission -- in fact, the

development of heterodyning schemes was one of the major developments

which led to mass communication by radio. By fixing the beat frequency

between the incoming carrier and the local oscillator to a fixed intermediate

frequency (IF), most of a radio receiver can be constructed so that it can be

used by any incoming radio signal. Only the local oscillator is tuned toproduce a beat frequency equal to the fixed IF frequency. We now take for

granted that one radio receiver can be tuned to any of the locally broadcast

radio stations, but if it were not for heterodyning, you would have to have one

receiver for each broadcast station.
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Sum and Difference FrequenciesWhen you superimpose two sine waves of different frequencies, you

get components at the sum and difference of the two frequencies.

This can be shown by using a sum rule from trigonometry. For equal

amplitude sine waves

The first term gives the phenomenon ofbeats with a beat frequency

equal to the difference between the frequencies mixed. The beat

frequency is given by

since the first term above drives the output to zero (or a minimum forunequal amplitudes) at this beat frequency. Both the sum and

difference frequencies are exploited in radio communication, forming

the upper and lowersidebands and determining the transmitted

bandwidth.

When you say that the beat frequency is f1-f2 rather than (f1-f2)/2, thatrequires some explanation. For the difference frequency you can just

say that you get a minumum when the modulating term reaches zero,

which it does twice per cycle, so that the number of minima per

second is f1-f

2.
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Envelope of Beat ProductionBeats are caused by the interference of two waves

at the same point in space. This plot of thevariation of resultant amplitude with time showsthe periodic increase and decrease for two sinewaves.
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The image below is the beat pattern produced by a

London police whistle, which uses two short pipes to

produce a unique and piercing three-note sound.
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Oscillator:

An electronic circuit designed to produce an ideally stablealternating voltage or current.

Mixer:A nonlinearcircuit or device that accepts as its input two

different frequencies and presents at its output

(c) a signal equal in frequency to the sum of the

frequencies of the input signals,

(d) a signal equal in frequency to the difference betweenthe frequencies of the input signals, and, if they are

not filtered out,

(e) the original input frequencies.
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Intermediate frequency (IF):

A frequency to which a carrier frequency is shifted as anintermediate step in transmission or reception.

Image frequency:In radio reception using heterodyning in the tuningprocess, an undesired inputfrequency that is capable of

producing the same intermediate frequecy (IF) that the

desired input frequency produces.

Note: The term image arises from the mirror-like symmetry ofsignal

and image frequencies about the beating-oscillatorfrequency.

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Note: The term image arises from the mirror-like symmetry ofsignal

and image frequencies about the beating-oscillatorfrequency.

Image frequency:

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Image rejection ratio:In reception using heterodyning in the tuning process, the

ratio of (a) the intermediate-frequency (IF) signal levelproduced by the desired input frequency to (b) that

produced by the image frequency.

Note 1: The image rejection ratio is usually expressed in dB.

Note 2: When the image rejection ratio is measured, the input signallevels of the desired and image frequencies must be equal for the

measurement to be meaningful. Synonym image frequency rejection

ratio.

Demodulation:The recovery, from a modulated carrier, of a signal having

substantially the same characteristics as the original

modulating signal.

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Detector: A device that is responsive to the presence or

absence of a stimulus. In an AM radio receiver, a circuit or device that

recovers the signal of interest from the modulated

wave.Note: In FM reception, a circuit called a discriminatoris used to

convert frequency variations to amplitude variations.

Phase-locked loop (PLL):An electronic circuit that controls an oscillatorso that it

maintains a constant phase angle relative to a referencesignal.Note: Phase-locked loops are widely used in space communications

forcoherentcarriertracking and threshold extension,

bit synchronization, and symbol synchronization.
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Phase Locked Loop BasicsAn Introduction To Phase Locked Loops

Phase Locked Loops (PLL) circuits are used for frequency control.

They can be configured as frequency multipliers, demodulators,tracking generators or clock recovery circuits. Each of these

applications demands different characteristics but they all use the

same basic circuit concept.

Figure 1 Block diagram of a PLL frequency multiplier

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Figure 1 contains a block diagram of a basic PLL frequency

multiplier. The operation of this circuit is typical of all phase locked

loops. It is basically a feedback control system that controls the

phase of a voltage controlled oscillator(VCO). The input signal is

applied to one input of a phase detector. The other input is

connected to the output of a divide by N counter. Normally the

frequencies of both signals will be nearly the same. The output of the

phase detector is a voltage proportional to the phase difference

between the two inputs. This signal is applied to the loop filter. It is

the loop filter that determines the dynamic characteristics of the PLL.

The filtered signal controls the VCO. Note that the output of the VCOis at a frequency that is N times the input supplied to the frequency

reference input. This output signal is sent back to the phase

detector via the divide by N counter.

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Normally the loop filter is designed to match the characteristics

required by the application of the PLL. If the PLL is to acquire and

track a signal the bandwidth of the loop filter will be greater than if it

expects a fixed input frequency. The frequency range which the PLL

will accept and lock on is called the capture range. Once the PLL is

locked and tracking a signal the range of frequencies that the PLL will

follow is called the tracking range. Generally the tracking range is

larger than the capture range. The loop filter also determines how

fast the signal frequency can change and still maintain lock. This is

the maximum slewing rate. The narrower the loop filter bandwidth

the smaller the achievable phase error. This comes at the expense

of slower response and reduced capture range.

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Figure 2 - The response of a PLL to a step in frequency input

A l f t i l t f PLL d i i

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An example of typical measurement of PLL dynamic response is

shown in figure 2. This PLL is used in a frequency synthesizer and

shows the response to an 80 kHz step in the 10 MHz reference

input. This circuit has a capture range of about +/- 5% of center

frequency.

Figure 3

Locating the largest cycle to cycle period in a 100 MHz clock

Note that the

frequency of the

PLL, the vertical

axis, shows a 50 %

overshoot.This slightly under

damped response is

a compromise which

achieves faster slew

rate tolerance andmoderate capture

range.

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Frequency synthesizer:A device that produces frequencies that are phasecoherent with a reference frequency.Note: The reference frequency may be derived from an internal or

external source.

Automatic gain control (AGC):A process or means by which gain is automatically

adjusted in a specified manner as a function of aspecified parameter, such as received signal level.
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mar 1 2005 by eric yang

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