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

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  • Color Television - Receive Channel 1Channel 2Channel 3 8 MHz Multi-channel Broadcast Frequency Specturm Tuner Luminance Chrominance Sound
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  • Color Television - Receive TUNER Video Detector Syn Sep Amplifier Y Syn Color Decoder U,V Figure 21
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  • Color Television - Decode Amplifier Y Syn Sep Syn Color Decoder U,V R G YUV TO RGB G B R Time Base R G B V scan H scan Figure 22
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  • Color 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
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  • Color Television - Receive TUNERIF 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
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  • 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 - Receive
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  • TUNERIF Stage CH33 575.25-585.25 31.5-41.5MHz 575.25+41.5 MHz = 616.75MHz (LO) Vision Carrier IF Vision Carrier
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  • Tuning and I.F. f f Tune f Figure 23a 31.5 MHz41.5 MHz
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  • Tuning and I.F. f f Tune f Figure 24b 31.5 MHz41.5 MHz
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  • Tuning and I.F. f f Tune f Figure 25c 31.5 MHz41.5 MHz
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  • I.F. filter response f db 0 Adj, vision 31.5MHz Sound 33.5MHz Chroma 35.07MHz Vision 39.5MHz Adj, sound 41.5MHz
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  • Color Television - Receive TUNERIF Stage Video Detector Syn Sep Amplifier Y Syn Color Decoder U,V Figure 21
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  • Color Television - Receive TUNERIF Stage Video Detector Syn Sep Amplifier Y Syn Color Decoder U,V Figure 21
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  • YUV Frequency Distribution freq Line frequency = 1/T = 15.6kHz Line duration = T = 64 s Color Subcarrier frequency f sc = 283.5/T = 4.43MHz Y U V f sc 284/T 1/T 1/2T Figure 26
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  • Y-C Separation Figure 27 Notch Filter f sc +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.
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  • U-V Separation freq Y U V f sc 284/T 1/T 1/2T Figure 28 Line frequency = 1/T = 15.6kHz Line duration = T = 64 s Color Subcarrier frequency f sc = 283.5/T = 4.43MHz
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  • U-V Separation freq f sc Desire Filter to Extract the V Component Figure 29 UV Line frequency = 1/T = 15.6kHz Line duration = T = 64 s Color Subcarrier frequency f sc = 283.5/T = 4.43MHz
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  • U-V Separation freq f sc Desire Filter to Extract the U Component Figure 30 UV Line frequency = 1/T = 15.6kHz Line duration = T = 64 s Color Subcarrier frequency f sc = 283.5/T = 4.43MHz
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  • U-V Separation freq f sc Desire Filter to Extract the U Component Figure 31 UV Line frequency = 1/T = 15.6kHz Line duration = T = 64 s Color Subcarrier frequency f sc = 283.5/T = 4.43MHz
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  • Comb Filter The ideal Filters are not available in practice Solution: Approximated by Comb Filters T = 283.5/f sc Delay + + + _ + _ ViVi V o1 V o2 0.5 Sum Output Diff erence Output Figure 32
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  • Response of Comb Filter f f Sum Output Difference Output 283.5f sc
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  • U-V Separation with Comb Filters f f Sum Output Difference Output f sc = 283.5/T f sc Figure 33 UV
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  • Where are We? Notch Filter f sc +100KHz-100KHz Y YUV Diff. Comb FiltersU Sum Comb Filters V 0o0o +90 o Gain Supress all frequency components around the color subcarrier.
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  • Color Television - Receive TUNERIF Stage Video Detector Syn Sep Amplifier Y Syn Color Decoder U,V
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  • Envelop Detector Figure 34 R
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  • Inverter Figure 35
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  • 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
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  • Automatic Gain Control (AGC) 300mV 150mV Transmitted signal Received signal Required Amplification = 2 Figure 37 Reference voltage obtained from syn pulse (0.7V)
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  • Color Television - Receive TUNERIF Stage Video Detector Syn Sep Amplifier Y Syn Color Decoder U,V
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  • Automatic Gain Control (AGC) Received signal Figure 38 Gate I.F Amplifier Gain Control I.F. Video Signal Output
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  • Clamping - DC Restoration DC AMP 100% brightness 50% brightness DC Figure 39
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  • VcVc R -V s 0 - + V o = V i -V c ViVi ViVi V c gradually charged to -V s Steady State: V o = V i -V c = V i +V s Figure 40
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  • Color Television - Receive TUNERIF Stage Video Detector Syn Sep AmplifierY Syn Color Decoder U,V
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  • U-V Demodulation YUV-Y cos c t (LO Inphase component) cos ( c t + 90 o ) (LO Quadrature component) U V Figure 10 LPF MultipliersLow Pass Filters UV components only
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  • 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 Demodulation
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  • Color Subcarrier Regeneration Color Burst Detector Subcarrier Regenerator Figure 41
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  • . Basic Transformation Y = 0.3R + 0.59G + 0.11B U = B - Y V = R - Y RGB to YUV transform R = V + Y G = (Y - 0.3R - 0.11B)/0.59 B = U + Y YUV to RGB transform Note: no Gamma correction or UV weighting
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  • YUV-RGB Y Figure 41 U V w1w1 w2w2 w3w3 R G B
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  • Color Bar Patterns Useful in testing video signals and systems
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  • Color Bar Patterns Luminance
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  • Color Bar Patterns Chrominance
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  • Color Bar Patterns Chrominance magnitude = Total magnitude = Computing the waveform of Color Bar Patterns
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  • Color Bar Patterns -0.33 1.33 Y = 0.3R + 0.59G + 0.11B U = B - Y V = R - Y
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  • . Actual 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