Color Television - Receive Channel 1Channel 2Channel 3 8 MHz Multi-channel Broadcast Frequency Specturm Tuner Luminance Chrominance Sound

Color Television - ReceiveColor Television - Receive

Channel 1 Channel 2 Channel 3

8 MHz 8 MHz 8 MHz

Multi-channel Broadcast Frequency Specturm

Tuner

Luminance

Chrominance

Sound


TUNER

Video Detector

Syn Sep

Amplifier Y

Syn

Color Decoder

U,VFigure 21

Color Television - DecodeColor Television - Decode

AmplifierY

Syn SepSyn

Color Decoder

U,V

R

G

YUVTO

RGB

GBRTime

Base

R

G

B

V scan

H scanFigure 22


Bandwidth of TV stations are very wide – a few hundred MHz

The entire Spectrum is divided into many channels

Each channel has a bandwidth of around 8 MHz

Building circuits to process the entire TV bandwidth is expensive

Translate the viewing channel to a fix Intermediate Frequency

A circuit to process a fix bandwidth of 8 MHz will suffice

A Better solution


TUNER IF Stage

565.25-575.25 31.5-41.5MHz

565.25+41.5 MHz

=

606.75MHz (LO)

Vision Carrier IF Vision Carrier

LPF

Low Pass Filter

Noted that the downconvert process also inverted the spectrum

31.5-41.5MHz

565.25+41.5 MHz

=

606.75MHz (LO)


LPF

Low Pass Filter

565.25-575.25

Video Spectrum

Inverted Video Spectrum



TUNER IF Stage

CH33 575.25-585.25 31.5-41.5MHz

575.25+41.5 MHz

=

616.75MHz (LO)


Tuning and I.F.Tuning and I.F.

f

f

Tune

f

Figure 23a

31.5 MHz 41.5 MHz


f

f

Tune

f

Figure 24b

31.5 MHz 41.5 MHz


f

f

Tune

f

Figure 25c

31.5 MHz 41.5 MHz

I.F. filter responseI.F. filter response

f

db

0

Adj

, vis

ion

31.5

MH

z

Sou

nd 3

3.5M

Hz

Chr

oma

35.0

7MH

z

Vis

ion

39.5

MH

z

Adj

, sou

nd 4

1.5M

Hz


TUNER IF Stage

Video Detector

Syn Sep

Amplifier Y

Syn

Color Decoder

U,VFigure 21


TUNER IF Stage

Video Detector

Syn Sep

Amplifier Y

Syn

Color Decoder

U,VFigure 21

YUV Frequency DistributionYUV Frequency Distribution

freq

Line frequency = 1/T = 15.6kHz

Line duration = T = 64s

Color Subcarrier frequency fsc = 283.5/T = 4.43MHz

Y

U

V

fsc

284/T

1/T

1/2T

Figure 26

Y-C SeparationY-C Separation

Figure 27

Notch Filter

fsc +100KHz-100KHz

Y

Gain

Supress all frequency components around the color subcarrier.

A simple method to suppress chrominance component with a notch filter. Luminance signal is suppressed as well, but it is stronger than the chrominance.

U-V SeparationU-V Separation

freq

Y

U

V

fsc

284/T

1/T

1/2T

Figure 28





freq

fsc

Desire Filter to Extract the V Component Figure 29

U V





freq

fsc

Desire Filter to Extract the U Component Figure 30

U V





freq

fsc

Desire Filter to Extract the U Component Figure 31

U V




Comb FilterComb Filter

The ideal Filters are not available in practice

Solution: Approximated by ‘Comb Filters’

T = 283.5/fsc

Delay+

+

+

_

+

_

-1Vi Vo1

Vo2

0.5

0.5

Sum Output

Diff erence Output

Figure 32

Response of Comb FilterResponse of Comb Filter

f

f

Sum Output

Difference Output

283.5fsc

U-V Separation with Comb FiltersU-V Separation with Comb Filters

f

f

Sum Output

Difference Output

fsc = 283.5/T

fsc

Figure 33

U V

Where are We?Where are We?

Notch Filter

fsc +100KHz-100KHz

Y

YUV

Diff. Comb Filters U

Sum Comb Filters V

0o

+90o

Gain

Supress all frequency components around the color subcarrier.


TUNER IF Stage

Video Detector

Syn Sep

Amplifier Y

Syn

Color Decoder

U,V

Envelop DetectorEnvelop Detector

Figure 34

R

Inverter

Figure 35

Automatic Gain Control (AGC)Automatic Gain Control (AGC)

Transmitted signal

Received signal

Figure 36

Amplitudes of transmitted and received signals

are generally different.

Automatic Gain Control (AGC) is employed to

recover the original signal

amplitude


300mV

150mV

Transmitted signal

Received signal

Required Amplification = 2Figure 37

Reference voltage obtained from syn pulse (0.7V)


TUNER IF Stage

Video Detector

Syn Sep

Amplifier Y

Syn

Color Decoder

U,V


Received signal

Figure 38

Gate

I.F Amplifier

Gain Control

I.F. Video Signal

Output

Clamping - DC RestorationClamping - DC Restoration

DC

AMP

100% brightness

50% brightness

DC

Figure 39

Vc

R

-Vs

0

-+

Vo = Vi -Vc

Vi

Vi

Vc gradually charged to -Vs

Steady State: Vo = Vi -Vc = Vi +Vs Figure 40


TUNER IF Stage

Video Detector

Syn Sep

Amplifier Y

Syn

Color Decoder

U,V

U-V DemodulationU-V Demodulation

YUV-Y

cos c t (LO – Inphase component)

cos ( c t + 90o) (LO – Quadrature component)

U

V

Figure 10

LPF

LPF

Multipliers Low Pass Filters

UV components only

• The frequency and phase of the Local Oscillators (LO) has to be identical to that in modulation

• The LO and its quadrature component are not fully sent to the receiver

• Only a few cycles of the LO (color burst) is included at the start of each video line

Problems in U-V DemodulationProblems in U-V Demodulation

Color Subcarrier RegenerationColor Subcarrier Regeneration

Color Burst Detector

Subcarrier Regenerator

Figure 41

.Basic TransformationBasic Transformation

Y = 0.3R + 0.59G + 0.11BU = B - YV = R - Y

RGB to YUV transform

R = V + YG = (Y - 0.3R - 0.11B)/0.59B = U + Y

YUV to RGB transform

Note: no Gamma correction or UV weighting

YUV-RGBYUV-RGB

Y

Figure 41

U

V

w1

w2

w3

R

G

B

Color Bar PatternsColor Bar Patterns

Useful in testing video signals and systems


Luminance


Chrominance


Chrominance magnitude = 22 VU

Total magnitude = 22 VUY

Computing the waveform of Color Bar Patterns


-0.33

1.33

Y = 0.3R’ + 0.59G’ + 0.11B’

U = B’ - YV = R’ - Y

.Actual TransformationActual Transformation

Y = 0.3R’ + 0.59G’ + 0.11B’U = 0.493(B’ - Y)V = 0.877(R’ - Y)

RGB to YUV transform

R’,G’ and B’: Gamma corrected color components

Documents

Color Television - Receive Channel 1Channel 2Channel 3 8 MHz Multi-channel Broadcast Frequency Specturm Tuner Luminance Chrominance Sound