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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
Color Television - ReceiveColor Television - Receive
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
Color Television - ReceiveColor Television - Receive
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
Color Television - ReceiveColor Television - Receive
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)
Vision Carrier IF Vision Carrier
LPF
Low Pass Filter
565.25-575.25
Video Spectrum
Inverted Video Spectrum
Color Television - ReceiveColor Television - Receive
Color Television - ReceiveColor Television - Receive
TUNER IF Stage
CH33 575.25-585.25 31.5-41.5MHz
575.25+41.5 MHz
=
616.75MHz (LO)
Vision Carrier IF Vision Carrier
Tuning and I.F.Tuning and I.F.
f
f
Tune
f
Figure 23a
31.5 MHz 41.5 MHz
Tuning and I.F.Tuning and I.F.
f
f
Tune
f
Figure 24b
31.5 MHz 41.5 MHz
Tuning and I.F.Tuning and I.F.
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
Color Television - ReceiveColor Television - Receive
TUNER IF Stage
Video Detector
Syn Sep
Amplifier Y
Syn
Color Decoder
U,VFigure 21
Color Television - ReceiveColor Television - Receive
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
Line frequency = 1/T = 15.6kHz
Line duration = T = 64s
Color Subcarrier frequency fsc = 283.5/T = 4.43MHz
U-V SeparationU-V Separation
freq
fsc
Desire Filter to Extract the V Component Figure 29
U V
Line frequency = 1/T = 15.6kHz
Line duration = T = 64s
Color Subcarrier frequency fsc = 283.5/T = 4.43MHz
U-V SeparationU-V Separation
freq
fsc
Desire Filter to Extract the U Component Figure 30
U V
Line frequency = 1/T = 15.6kHz
Line duration = T = 64s
Color Subcarrier frequency fsc = 283.5/T = 4.43MHz
U-V SeparationU-V Separation
freq
fsc
Desire Filter to Extract the U Component Figure 31
U V
Line frequency = 1/T = 15.6kHz
Line duration = T = 64s
Color Subcarrier frequency fsc = 283.5/T = 4.43MHz
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.
Color Television - ReceiveColor Television - Receive
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
Automatic Gain Control (AGC)Automatic Gain Control (AGC)
300mV
150mV
Transmitted signal
Received signal
Required Amplification = 2Figure 37
Reference voltage obtained from syn pulse (0.7V)
Color Television - ReceiveColor Television - Receive
TUNER IF Stage
Video Detector
Syn Sep
Amplifier Y
Syn
Color Decoder
U,V
Automatic Gain Control (AGC)Automatic Gain Control (AGC)
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
Color Television - ReceiveColor Television - Receive
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
Color Bar PatternsColor Bar Patterns
Luminance
Color Bar PatternsColor Bar Patterns
Chrominance
Color Bar PatternsColor Bar Patterns
Chrominance magnitude = 22 VU
Total magnitude = 22 VUY
Computing the waveform of Color Bar Patterns
Color Bar PatternsColor 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