The Engineer's Guide to Standards Conversion - Snell

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High quality standards conversion implies high quality decoding and encoding. In early converters digital circuitry was expensive, consumed a great deal of power and was only used where essential. The decode and encode stages were analog, and converters were placed between the coders and the digital circuitry. Fig 1.3.1b) shows a later design of standards converter. As digital circuitry has become cheaper and power consumption has fallen, it becomes advantageous to implement more of the machine in the digital domain. The general layout is the same as at a) but the converters have now moved nearer the input and output so that digital decoding and encoding can be used. The complex processes needed in advanced decoding are more easily implemented in the digital domain. a) Composite in Analogue PAL/SECAM/NTSC decoder ADCs Luminance interpolator DACs Analogue PAL/SECAM/NTSC encoder Composite out DEMOD R-Y interpolator B-Y interpolator MOD F sc b) Digital Decoder Digital Encoder Composite in ADC Luminance interpolator DAC Composite out DEMOD MOD Component digital in DEMUX R-Y interpolator B-Y interpolator MUX Component digital out Fig 1.3.1 Block diagram of digital standards converters. Conversion can only take place on component signals. a) early design using analogue encoding and decoding. Later designs b) use digital techniques throughout. 5
A further advantage of digital circuitry is that it is more readily able to change its mode of operation than is analogue circuitry. Such programmable logic allows, for example, a wider range of input and output standards to be implemented. As digital video interfaces have become more common, standards converters increasingly included multiplexers to allow component digital inputs to be used. Component digital outputs are also available. In converters having only analogue connections, the internal sampling rate was arbitrary. With digital interfacing, the internal sampling rate must now be compatible with CCIR 601. Comprehensive controls are generally provided to allow adjustment of timing, levels and phases. In NTSC, the use of a pedestal which lifts the voltage of black level above blanking is allowed, but not always used, and a level control is needed to give consistent results in 50Hz systems which do not use pedestal. 6
Page 1 and 2: The Engineer’s Guide to Standards
Page 3 and 4: INTRODUCTION Standards conversion u
Page 5 and 6: SECTION 1 - INTRODUCTION TO STANDAR
Page 7: One solution to large area flicker
Page 11 and 12: changing. In short it is a form of
Page 13 and 14: To prevent aliasing, a band limitin
Page 15 and 16: The theoretical vertical bandwidth
Page 17 and 18: 2.4 Kell effect In conventional tub
Page 19 and 20: 2.6 Quantizing error It is possible
Page 21 and 22: unpredictable and gives the system
Page 23 and 24: clairvoyant powers. Shortening the
Page 25 and 26: 2.8 Composite video For colour tele
Page 27 and 28: Line n received with phase error
Page 29 and 30: 2.9 Composite decoding The reason f
Page 31 and 32: Vertical spatial frequency Temporal
Page 33 and 34: A single pixel has meaning over the
Page 35 and 36: 3.2 Line doubling Input samples Out
Page 37 and 38: Input samples A B C D Sample value
Page 39 and 40: a) Data in Phase select b) FILTER R
Page 41 and 42: Vertical frequency Stop band Tempor
Page 43 and 44: Vertical axis Time axis Fig 3.5.4 b
Page 45 and 46: Vertical frequency Unsuppressed = M
Page 47 and 48: a) Drama aperture +525 c/ph Vertica
Page 49 and 50: 3.7 Motion compensated standards co
Page 51 and 52: This is because relative motion res
Page 53 and 54: a) Input fields Interpolation axis
Page 55 and 56: SECTION 4 - APPLICATIONS 4.1 Up and
Page 57 and 58: It is possible to identify the 3:2
Page 59 and 60:
Published by Snell & Wilcox Ltd. Du
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The Engineer's Guide to Standards Conversion - Snell

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