A Chroma System TX example - PowerPoint PPT Presentation

Loading...

PPT – A Chroma System TX example PowerPoint presentation | free to view - id: c9f28-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

A Chroma System TX example

Description:

Samples colour burst signal from TX for FREQUENCY and PHASE. ... Colur burst is at 0 degrees reference. I is at 57 degrees and Q is at 147 degrees ... – PowerPoint PPT presentation

Number of Views:73
Avg rating:3.0/5.0
Slides: 8
Provided by: CITS7
Category:
Tags: burst | chroma | example | system

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: A Chroma System TX example


1
A Chroma System (TX) example
  • ENCODING Why encoding? RGB alone was not
    compatible with black and white receivers. Each
    of RGB contains only part of picture.
  • Remedy? Encoding- arranging colour video signals
    in specific proportions to provide all video
    information.
  • 2 separate signals 1.) C or chrominance ( I and
    Q) and 2.) Y or luminance.
  • ADDING COLOURS combining primary colours
    produces wide range of mixtures. ex. GBcyan

2
A Chroma System Example contd. (TX)
  • 3 MAIN CHARATERISTICS 1.) HUE- Tint, different
    hues for different wavelengths. Phase angle of C
    signal. 2.) SATURATION - Degree to which colour
    is saturated. Amplitude of C signal. 3.)
    LUMINANCE (Y) - amount of light intensity
    perceived by the eye. Lighter areas have more
    luminance than darker areas. Y level indicates
    how colour will appear in black and white.
  • SIGNALS 1.) Chrominance A.) I signal - B-Y from
    matrix B.) Q signal R-Y from matrix. 90 degree
    phase difference with I signal.

3
A CHROMA SYSTEM Example contd. (TX)
  • 2. Luminance - provides relative brightness for
    the C signal. Y 0.30R 0.59G 0.11B
  • Note chroma subcarrier is PHASE modulated by I
    and Q which in turn modulates the main picture
    carrier.

4
A Chroma System Example (RX)
  • How does the chroma RX synchronize to the
    transmitted signal? Samples colour burst signal
    from TX for FREQUENCY and PHASE.
  • SIGNIFICANT BLOCKS OF THE CHROMA RX
  • Comb filter - separates the video (Y) signal and
    colour signal. Older systems use narrowband
    filter. Comb filter constructed of a glass cavity
    with a transducer and speaker at opposite ends.
    SAW in nature.
  • BPA - 4 tuned narrowband I.F. stages for
    sideband amplification.

5
A Chroma System example (RX) contd.
  • Why do we require chroma subcarrier reinsertion?
  • Burst Gate - detects the presence of a colour
    burst and enables or disables BPA by way of the
    COLOUR KILLER.
  • ACC - automatic chroma control. Acts like AGC for
    R.F. and I.F.

6
An Example
  • Colur burst is at 0 degrees reference
  • I is at 57 degrees and Q is at 147 degrees
  • Where is R-Y and B-Y relative to each other?
  • Are they in quadrature in the colour phase
    diagram?
  • How is green produced? A two transistor system
    combines (R-Y) and (B-Y).
  • Demodulators include I, Q, (R-Y)(B-Y),
    (R-Y)(G-Y),(R-Y)(G-Y)(B-Y), X-Z and RGB.
  • Vectors lengths represent the magnitude of the C
    signal.

7
R-Y
I
147 degrees over from chroma burst
Q
57
3.58 MHz burst reference at 0 degrees
B-Y
About PowerShow.com