hdbase-t – structured connectivity for digital av · pdf filehdbase-t – structured...
TRANSCRIPT
Our Learning Objectives• Define digital video (DV) and set the
expectations of connectivity distance • Explore the technical challenges of
“long” point-to-point DV connections• Dissect and review the components of
DV necessary for practical system utility
• Review DV connectivity options and formats
Analog Connections Follow Simple Rules• Analog is continuous in nature
– Signal is varied continuously with respect to the information
• Analog systems have an infinite bandwidth
• Primary disadvantages of analog are noise and non-linearity– Additive noise– Generation loss– Intermodulation noise– Harmonic distortion
Advantages of Digital Signals
• Digital systems use discrete representations of information
• Digital systems exhibit a finite resolution• In a binary system, information payloads
double with each additional bit• Disturbances in a digital communication
do not result in errors unless the disturbance is so large as to result in a symbol being misinterpreted
Digital Connections Leverage Analog Signals!
• A digital signal is a representation of a series of discrete values
• Digital signals in cables leverage analog waveforms
• Clock signals used to synchronize digital circuits often act to limit connection length
The Physics Of Wire• Longer wire = greater resistance
– Cross-sectional area of the wires– Material composition– Pure resistance causes A frequency independent voltage
drop
• Capacitance and inductance are proportional to wire length/construction– Impedance is defined as the frequency domain ratio of
voltage to current– Capacitance and inductance cause a frequency dependent
voltage drop
Characteristic Impedance
• Opposition that a circuit presents to the passage of a current when an AC voltage is applied, expressed in Ohms (Ω) – Determined by the physical material composition
and geometry of the cable assembly
• A precise, constant conductor spacing, is necessary for a cable to function efficiently as a high-frequency transmission line
Skin Effect
• Alternating current in a conductor produces an alternating magnetic field.
• When the intensity of current in a conductor changes, the magnetic field also changes
• The change in the magnetic field creates an electric field which opposes the change in current intensity (counter-EMF).
• The counter-EMF is strongest at the center of the conductor and forces the conducting force to the outside of the conductor.
WHAT IS THE DIGITAL VIDEO PAYLOAD?
“For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled.” - Richard Feynman
The Elements of a Video Signal
• RGB additive color model divides a video signal into 3 ”components” RGB or YPbPr (YCbCr)
• Bandwidth is directly proportional to visual detail In analog systems, the ability to pass higher
frequencies equates to the ability to display finer detail
• Amplitude is directly proportional to color saturation
time
Chroma Subsampling4:4:4 Each R, G, and B channel, or each Y′, CB, and CR channel, is sampled at the same rate. Maximum
color detail is maintained.4:2:2 The color channels are subsampled so that the color resolution is halved. For example, the first
pixel in a line contains Y′, CB, and CR samples. The next pixel contains only a Y′ sample. This pattern repeats. Most professional video formats use 4:2:2 color subsampling.
4:1:1 The color is subsampled so that the color resolution is quartered. The first pixel in a line contains Y′, CB, and CR samples. The next three pixels only contain Y′ samples. This pattern repeats.
4:2:0 This ratio indicates that the CB and CR channels are subsampled both horizontally (as in 4:2:2) and vertically. This reduces color resolution in both the horizontal and vertical dimensions compared to 4:2:2, which only reduces horizontal chroma resolution.There are several methods for locating CB and CR samples relative to Y′ samples, yielding several different 4:2:0 formats.
Chroma Subsampling And The DV Payload
DetailD2K = 2M PixelD4K = 8M Pixel
Chroma Subsampling
Up To 16-Bits Per sRGB Component
4:2:2 YCbCr 4:4:4 “Deep Color”
DV BandwidthData rate * chrominance
decimationData rate = color depths *
vertical resolution * horizontal resolution * refresh frequency
Digital Audio
• Digital audio is not a discrete element of the DV package– Bits are “fungible”– Digital audio is
embedded into the horizontal ancillary data space (HANC) of the
– Audio travels with videoA sound wave, in red, represented digitally, in blue (after sampling and 4-bit quantization).
Digital Rights Protection - HDCP
• High Bandwidth Digital Content Protection (HDCP) is a technology designed to allow digital rights management implementation of AV content
• Converting digital video w/ HDCP is forbidden unless the output supports the HDCP protection
System Control• RS232• CEC is an HDMI feature designed to allow
the user to control enabled devices– Allows for individual CEC-enabled devices to
command and control each other without user intervention
• Infra Red• USB
– If “Interactive” is involved, so is USB!
DDC, EDID and DisplayID• Display Data Channel• Extended Display Identification
Data (EDID)– Enables the display (sink) to communicate
supported display modes to the source via a compact binary file format that describes the monitor's capabilities and supported graphics modes
– Stored in a read-only memory chip programmed by the manufacturer of the monitor
CONNECTION TYPES
“Given a choice between two theories, take the one which is funnier.” − Blore's Razor
Optical Fiber
• Multi-Mode Fiber– Supports many propagation paths
within the fiber– Used for shorter connections with
emphasis on power
• Single-Mode Fiber– Supports only a single transmission
path within the fiber– Used for the longest connections
Twisted Pair
• Differential (balanced) signaling ensures environmental noise rejection
• Differing twist rates (pitch) minimizes crosstalk between pairs
• Cable shield ensures integrity of the eye pattern of the digital signal– Next near end crosstalk– Fext far end crosstalk– AXT alien crosstalk
WHAT DOES “BASE-T” MEAN?
“It is difficult to get a man to understand something when his job depends on not understanding it.” - Upton Sinclair
Baseband
• BASE denotes a baseband transmission– A systems whose range of frequencies is
measured from close to 0 Hz to a cut-off frequency, a maximum bandwidth or highest signal frequency
• “T” denotes twisted-pair (balanced) transmission
Passband• Also known as bandpass, the
signal is sent over a limited frequency range that is a subset of the total signal range
• Passband signals are typically translated to a higher frequency, often for transmission by frequency division multiplexing
• RF and modulated systems are examples of passband technologies
TMDS Over Twisted Pair• Typically Dual UTP Connectivity
– TMDS – RGB and Clock– SCL/SCA I2C, Hot Plug, 5V Power, 5V Ground– No Fundamental Changes Are Made To The Signal
• Carriage Distance Is Inversely Proportional To Signal Bandwidth– 60 Meters For 720P Content– 25 Meters For 1080p/60– 20 Meters For 1080p With 10 Or 12 Bit Color Depth
Content
THE NEWEST IEEE STANDARD!
“The nice thing about standards is that there are so many of them to choose from.” − Andrew S. Tanenbaum
HDBaseT
• HDBaseT Alliance was established in 2010 – LG electronics, Samsung Electronics, Sony
Pictures, Valens Semiconductor
• Working to create a global standard for advanced digital media distribution
• HDBaseT 2.0 standard finalized in August 2013
• HDBaseT standard will support up to 8 “hops” of 100 meters each
Power Over HDBaseT• Powered by a 50- to 57-volt DC
power supply– All 4 pairs can support power– Defined in the latest high-power PoE
standards, four-pair powering gives PDs two power interfaces
• 1 amp per 2 pairs for up to 100 watts– Backward compatible with IEEE802.3at-
2009– POH enables the PD to identify the
cable length/resistance and draw more power, as long as the overall power consumption does not exceed 100W.
Pulse Amplitude Modulation 16
0000 : 150001 : 130011 : 110010 : 90110 : 70111 : 50101 : 30100 : 11100 : -11101 : -31111 : -51110 : -71010 : -91011 : -111001 : -131000 : -15
0 0 . 5 1 1 . 5 2 2 . 5 3 3 . 5 4-1
-0 . 5
0
0 . 5
1
PAM16 TX Eye Pattern
One Symbol Period
TX D
iff P
eak
4bits
Level
HDBaseT uses PAM16 symbols where each symbol is transmitted using one of 16 discrete, differential voltage
levels, each representing 4 bits of data
HDBaseT Lite• Operational advantages
of HDBaseT at a lower price– 60 meter maximum– Supports UltraHD 2160p
in 4:2:0
HDBaseT Over Fiber• 2nd Generation VS2311 - 5Play™ Gen
2.0 Fiber - HDBaseT over fiber for transmission over much longer distances
– Can be used for single mode (SMF) and multi-mode (MMF) solutions
– Supports MST and HDBT2.0 performance– 600m with OM3 MM fiber / 800m with
OM4 MM fiber / 1Km / 10 Km - standard HDBaseT 2.0 over fiber optics
OTHER EXTENSION METHODS
“All truths are easy to understand once they are discovered; the point is to discover them.”- Galileo Galilei
Modulated PassBand
• Digital television!• Coaxial cable systems using modulated content can
deliver dozens of HD streams simultaneously
Video Over IP• Uses video codec to reduce the program
material to a bitstream– MPEG transport stream
• Uses an Internet Protocol (IP) network to carry that bitstream encapsulated in a stream of IP packets. – Variant of the RTP protocol
• Quality of Service (QoS) places significant demands on system design and implementation
Fascinating…• In all commercial applications, HDBaseT should
be run using S/UTP Cat6• HDBaseT supports up to 8 hops of up to 100
meters (or 60 meters for HDBT Lite)• HDBaseT supports 5-Play• HDBaseT supports 2160p 4K video in a 4:2:0
color space• HDBaseT PoH is based on PoE standards • New HDBaseT “Colligo” solutions can leverage
fiber links
“Live long and prosper.”