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Color Television - Receive

Color Television - Receive. Multi-channel Broadcast Frequency Spectrum. Channel 1. Channel 2. Channel 3. 8 MHz. 8 MHz. 8 MHz. Luminance. Tuner. Chrominance. Sound. TUNER. Syn Sep. Color Television - Receive. Y. Amplifier. Video Detector. Syn. Color Decoder. U,V. Figure 21.

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Color Television - Receive

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

  2. TUNER Syn Sep Color Television - Receive Y Amplifier Video Detector Syn Color Decoder U,V Figure 21

  3. Amplifier Color Television - Decode Y R YUV TO RGB G U,V Color Decoder B V scan Syn Time Base Syn Sep H scan Figure 22

  4. 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 A Better solution Translate the viewing channel to a fix Intermediate Frequency A circuit to process a fix bandwidth of 8 MHz will suffice

  5. TUNER IF Stage Color Television - Receive LPF 31.5-41.5MHz 565.25-575.25 Low Pass Filter Vision Carrier IF Vision Carrier 565.25+41.5 MHz = 606.75MHz (LO)

  6. Color Television - Receive LPF 31.5-41.5MHz 565.25-575.25 Low Pass Filter Vision Carrier IF Vision Carrier 565.25+41.5 MHz = 606.75MHz (LO) Video Spectrum Inverted Video Spectrum Noted that the downconvert process also inverted the spectrum

  7. TUNER IF Stage Color Television - Receive 31.5-41.5MHz CH33 575.25-585.25 IF Vision Carrier Vision Carrier 575.25+41.5 MHz = 616.75MHz (LO)

  8. Tuning and I.F. Tune f f 31.5 MHz 41.5 MHz Figure 23a f

  9. Tuning and I.F. Tune f f 31.5 MHz 41.5 MHz Figure 24b f

  10. Tuning and I.F. Tune f f 31.5 MHz 41.5 MHz Figure 25c f

  11. I.F. filter response db 0 Sound 33.5MHz Vision 39.5MHz Chroma 35.07MHz Adj, vision 31.5MHz Adj, sound 41.5MHz f

  12. TUNER IF Stage Syn Sep Color Television - Receive Y Amplifier Video Detector Syn Color Decoder U,V Figure 21

  13. TUNER IF Stage Syn Sep Color Television - Receive Y Amplifier Video Detector Syn Color Decoder U,V Figure 21

  14. Y U V YUV Frequency Distribution Line duration = T = 64s Line frequency = 1/T = 15.6kHz Color Subcarrier frequency fsc = 283.5/T = 4.43MHz 1/T freq 1/2T fsc 284/T Figure 26

  15. Y-C Separation Notch Filter Supress all frequency components around the color subcarrier. Gain Y A simple method to suppress chrominance component with a notch filter. Luminance signal is suppressed as well, but it is stronger than the chrominance. fsc -100KHz +100KHz Figure 27

  16. U-V Separation Line duration = T = 64s Line frequency = 1/T = 15.6kHz Color Subcarrier frequency fsc = 283.5/T = 4.43MHz 1/T freq Y 1/2T fsc U 284/T Figure 28 V

  17. U V U-V Separation Line duration = T = 64s Line frequency = 1/T = 15.6kHz Color Subcarrier frequency fsc = 283.5/T = 4.43MHz fsc freq Desire Filter to Extract the V Component Figure 29

  18. U V U-V Separation Line duration = T = 64s Line frequency = 1/T = 15.6kHz Color Subcarrier frequency fsc = 283.5/T = 4.43MHz fsc freq Desire Filter to Extract the U Component Figure 30

  19. U V U-V Separation Line duration = T = 64s Line frequency = 1/T = 15.6kHz Color Subcarrier frequency fsc = 283.5/T = 4.43MHz fsc freq Desire Filter to Extract the U Component Figure 31

  20. Comb Filter The ideal Filters are not available in practice Solution: Approximated by ‘Comb Filters’ Difference Output Delay Vi + -1 T = 283.5/fsc Vo1 0.5 + _ Vo2 0.5 + Sum Output Figure 32

  21. Response of Comb Filter Sum Output f Difference Output f 283.5fsc

  22. U V U-V Separation with Comb Filters fsc Sum Output f Difference Output f fsc = 283.5/T Figure 33

  23. Where are We? Notch Filter Supress all frequency components around the color subcarrier. Gain Y fsc YUV -100KHz +100KHz Diff. Comb Filters U 0o Sum Comb Filters +90o V

  24. Color Television - Receive TUNER IF Stage Y Amplifier Video Detector Syn Sep Syn Color Decoder U,V

  25. Envelop Detector R Figure 34

  26. Inverter Figure 35

  27. Automatic Gain Control (AGC) Transmitted signal Amplitudes of transmitted and received signals are generally different. Automatic Gain Control (AGC) is employed to recover the original signal amplitude Received signal Figure 36

  28. Automatic Gain Control (AGC) Transmitted signal 300mV Reference voltage obtained from syn pulse (0.7V) Received signal 150mV Figure 37 Required Amplification = 2

  29. TUNER IF Stage Syn Sep Color Television - Receive Y Amplifier Video Detector Syn Color Decoder U,V

  30. Automatic Gain Control (AGC) Received signal Gate Gain Control Output I.F Amplifier I.F. Video Signal Figure 38

  31. Clamping - DC Restoration 100% brightness AMP DC 50% brightness DC Figure 39

  32. Vi 0 -Vs Vc - + R Vi Vo = Vi -Vc Vc gradually charged to -Vs Steady State: Vo = Vi -Vc = Vi +Vs Figure 40

  33. TUNER IF Stage Syn Sep Color Television - Receive Amplifier Y Video Detector Syn Color Decoder U,V

  34. ´ ´ U-V Demodulation cos c t (LO – Inphase component) LPF U YUV-Y Multipliers Low Pass Filters UV components only LPF V cos (c t + 90o)(LO – Quadrature component) Figure 10

  35. Problems in U-V Demodulation • 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

  36. Color Subcarrier Regeneration Color Burst Detector Subcarrier Regenerator Figure 41

  37. Basic Transformation . RGB to YUV transform Y = 0.3R + 0.59G + 0.11B U = B - Y V = R - Y YUV to RGB transform R = V + Y G = (Y - 0.3R - 0.11B)/0.59 B = U + Y Note: no Gamma correction or UV weighting

  38. YUV-RGB R Y w1 G U w2 B V w3 Figure 41

  39. Color Bar Patterns Useful in testing video signals and systems

  40. Color Bar Patterns Luminance

  41. Color Bar Patterns Chrominance

  42. Color Bar Patterns Computing the waveform of Color Bar Patterns Chrominance magnitude = Total magnitude =

  43. Color Bar Patterns -0.33 Y = 0.3R’ + 0.59G’ + 0.11B’ U = B’ - Y V = R’ - Y 1.33

  44. Actual Transformation RGB to YUV transform Y = 0.3R’ + 0.59G’ + 0.11B’ U = 0.493(B’ - Y) V = 0.877(R’ - Y) R’,G’ and B’: Gamma corrected color components

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